fuel problem and hesitation

[30csl]

Hi guys,

took the csl out last night for its first drive of the year. before that I changed the filter/screen on the tank pick up and also the in line one in the engine bay. I also cleaned the gauze going into the pump.

I then went for a drive and the car went very well but after 4500-5000 there was a noticeable stumble. It felt like fuel starvation.

The in line fuel pressure gauge now shows 26-7 psi which is too low. I will try adjusting it this evening but I thought the pressure would be increased after changing the filter if anything!

Could the vacuum advance on the distributor be a culprit? I tried checking it by sucking on tube yesterday and it moved but only with what seemed like excessive vaccum!

Regards,

Rohan

 

[dang]

Are you still running a stock ignition setup?

 

[30csl]

Hi Dan,

I have the pertronix and some fancy coil.

I found another topic that suggested the coil was a good place to check but this really feels like fuel and when revving the car at idle the pressure drops a bit on the in line gauge which I imagine shouldn't happen?

 

[Tom M]

Hi Rohan:
Have you checked the condition of the D-Jet points?
What is the Tach doing when the stumble occurs?
If you know someone with a mobile ignition analyzer, you can confirm or eliminate the ignition system.
Tom

 

[30csl]

Hi Tom,

do you mean the trigger points in the dizzy? I had them out a while back and cleaned them up.

The tach does nothing strange when it happens. It really feels like fuel and the stumble occurs later when i step on it from 3000 than when i hit it from idle.

Regards,

Rohan

 

[30csl]

Well I hooked up an in car fuel pressure gauge and took the car for a drive. It had 32 psi pressure regardless of how hard I drove it and stayed there when the hesitation occurred. Looks like fuel supply is ok.

I am not looking at ignition side. The lead from the coil to the cap looks fairly old but has two wires from the coil - one to the loom? Are these available from BMW?

Any other ideas? I swapped the ECU - no change - newish leads, plugs. Points in the bottom of the distributor are clean.

I retarded the timing and the pinging has gone but if anything the hesitation seems to occurr earlier.

Seriously annoying.

 

[MMercury]

Very random thoughts

[H]ooked up fuel pressure gauge and it [registered] 32 psi pressure regardless of how hard I drove it and stayed there when the hesitation occurred. Looks like fuel supply is ok.
I am not looking at ignition side. The lead from the coil to the cap looks fairly old but has two wires from the coil - one to the loom? Are these available from BMW?
Any other ideas? I swapped the ECU - no change - newish leads, plugs. Points in the bottom of the distributor are clean.
I retarded the timing and the pinging has gone but if anything the hesitation seems to occur earlier.
Seriously annoying.

:evil:


You describe the unwanted symptom as a stumble and hesitation. Is this really a highspeed misfire or cutcut? Or is it more like a flat spot where the engine continues to run but essentially runs out of power?

My first reaction is to agree the high speed flat spot or hesitation is typically due to a lean mixture condition. This could be due to inadequate fuel supply but this does not rule out an ignition issue as simple as a defective rev-limiting-rotor, plugs with an incorrect heat range (usually too hot), a weak or defective coil, plug gaps that are too wide, or for standard Kettering ignition, a funky condenser (they don’t last indefinitely.).

Your first post states the pressure was 26-7 psi and now it is at 32psi. Is the difference due to different gauges or did you adjust the fuel pressure regulator? (I once dealt with a slightly different regulator - from a different vehicle - and it would change pressure readings if the fuel line were deflected enough to slightly change the regulator’s position. This shouldn’t be the case, but we repeated the experiment enough times to warrant replacement.)

Fuel pressure is a good indicator of your fuel system but it does not guarantee volume. Only way to test that is measure the pump outflow. You mentioned the thimble screen in the pump inlet and the tank pickup. What about the filter (usually found under the battery tray? Can you blow through it with minimal effort? (I doubt this is your problem, but anything is possible.) Along those lines, is it possible you have some occult water in the tank? As unbelievable as this may sound, I know someone who inadvertently managed to pump diesel in his Jaguar's tank. The engine ran fine until he pushed it. Perhaps very unlikely, but fuel contamination might also account for a high speed miss/flat spot.

Next, you mention swapping the ECU. What about the other fuel-inj. related electrics? I cannot say these suggestions are high on my list of possible culprits, but a Pressure sending unit that is on its way out can cause erratic operation. Similar results could be caused by a loose connection to the temperature sensor II (under the intake manifold and to the right of the auxiliary air valve). A worn or maladjusted throttle position switch can also be responsible for hesitation and cutouts, although this generally occurs during low speed operation and acceleration. Finally, do not overlook a bad ground strap between the engine and the body. As a very brief overview of the subject, review this thread: http://www.e9coupe.com/forum/showthr...?t=2879&page=2

I touched on the ignition issue earlier and most of these issues are dealt with as part of any minor tune-up. In any event, I would carefully examine the rotor (especially if it is a rev limiting type). Regarding your distributor, if it is a typical Csi D-Jet affair, it actually retards the ignition timing at idle. However, it should hold a vacuum and if it doesn’t you may have a vacuum leak and a source of a leaner mixture.

You mentioned retarding the timing. I am not sure why you did this, but if you use a timing light, that tool could be helpful to insure that your distributor’s centrifugal advance is functioning properly (not sticking and/or reaching maximum advance within specs). The mechanism includes two moving weights (requiring lubrication), and two springs (that may loose their tension or even break).

As noted by others, if your coil gets too much voltage due to a bad ballast resistor, or if it is toward the end of its duty cycle, or if there is voltage leaking/arcing from the terminals, this may result in production of a weak spark. Some have described this symptom as like a failing fuel pump. Hint: if you have another coil hand (as you did with the ECU), try running it. Who knows, by doing so, you may discover a loose connection, corrosion etc. where you never thought to look.

End of random thoughts. . . .

HTH.

 

[30csl]

:evil:


You describe the unwanted symptom as a stumble and hesitation. Is this really a highspeed misfire or cutcut? Or is it more like a flat spot where the engine continues to run but essentially runs out of power?

Hi Mercury,

yes it is a flat spot rather than a hesitation, it still runs and revs up slowly but the power is gone.

My first reaction is to agree the high speed flat spot or hesitation is typically due to a lean mixture condition. This could be due to inadequate fuel supply but this does not rule out an ignition issue as simple as a defective rev-limiting-rotor, plugs with an incorrect heat range (usually too hot), a weak or defective coil, plug gaps that are too wide, or for standard Kettering ignition, a funky condenser (they don’t last indefinitely.).

I had a look at the rotor and it is fairly new but I will swop it out to make sure, same with the cap. I will also use the original type plugs to try and eliminate this. I have pertronix installed so no condensor but the coil is a higher performance one without a ballast resistor.

Your first post states the pressure was 26-7 psi and now it is at 32psi. Is the difference due to different gauges or did you adjust the fuel pressure regulator? (I once dealt with a slightly different regulator - from a different vehicle - and it would change pressure readings if the fuel line were deflected enough to slightly change the regulator’s position. This shouldn’t be the case, but we repeated the experiment enough times to warrant replacement.)

Yes the fuel pressure gauge was faulty so I have now changed it and it is ok, tested with two gauges.

Fuel pressure is a good indicator of your fuel system but it does not guarantee volume. Only way to test that is measure the pump outflow. You mentioned the thimble screen in the pump inlet and the tank pickup. What about the filter (usually found under the battery tray? Can you blow through it with minimal effort? (I doubt this is your problem, but anything is possible.) Along those lines, is it possible you have some occult water in the tank? As unbelievable as this may sound, I know someone who inadvertently managed to pump diesel in his Jaguar's tank. The engine ran fine until he pushed it. Perhaps very unlikely, but fuel contamination might also account for a high speed miss/flat spot.

I did also change the can type fuel filter, I am fairly sure the pump is working well now.

Next, you mention swapping the ECU. What about the other fuel-inj. related electrics? I cannot say these suggestions are high on my list of possible culprits, but a Pressure sending unit that is on its way out can cause erratic operation. Similar results could be caused by a loose connection to the temperature sensor II (under the intake manifold and to the right of the auxiliary air valve). A worn or maladjusted throttle position switch can also be responsible for hesitation and cutouts, although this generally occurs during low speed operation and acceleration. Finally, do not overlook a bad ground strap between the engine and the body. As a very brief overview of the subject, review this thread: http://www.e9coupe.com/forum/showthr...?t=2879&page=2

The temperature sensor could be worth checking alright. The TPS has been checked and is ok. I will put another MPS on it to check that this week but I checked it not long ago and it was fine.

I touched on the ignition issue earlier and most of these issues are dealt with as part of any minor tune-up. In any event, I would carefully examine the rotor (especially if it is a rev limiting type). Regarding your distributor, if it is a typical Csi D-Jet affair, it actually retards the ignition timing at idle. However, it should hold a vacuum and if it doesn’t you may have a vacuum leak and a source of a leaner mixture.

I sucked on the vacuum advance and it moved inside the distributor housing so that seems ok?

You mentioned retarding the timing. I am not sure why you did this, but if you use a timing light, that tool could be helpful to insure that your distributor’s centrifugal advance is functioning properly (not sticking and/or reaching maximum advance within specs). The mechanism includes two moving weights (requiring lubrication), and two springs (that may loose their tension or even break).

I retarded the timing as she was pinking and I thought that when the distributor was advancing at high revs it may be advancing too much causing the flat spot.

As noted by others, if your coil gets too much voltage due to a bad ballast resistor, or if it is toward the end of its duty cycle, or if there is voltage leaking/arcing from the terminals, this may result in production of a weak spark. Some have described this symptom as like a failing fuel pump. Hint: if you have another coil hand (as you did with the ECU), try running it. Who knows, by doing so, you may discover a loose connection, corrosion etc. where you never thought to look.

I will try the other coil but it is a standard type so will require a ballast resistor right?

End of random thoughts. . . .

Many thanks for the ideas MM - I fear if I don't solve it soon I will give up!

 

[MMercury]

Random Thoughts II.

yes it is a flat spot rather than a hesitation, it still runs and revs up slowly but the power is gone.

I had a look at the rotor and it is fairly new but I will swop it out to make sure, same with the cap. I will also use the original type plugs to try and eliminate this. I have pertronix installed so no condensor but the coil is a higher performance one without a ballast resistor.

Yes the fuel pressure gauge was faulty so I have now changed it and it is ok, tested with two gauges.

I did also change the can type fuel filter, I am fairly sure the pump is working well now.

The temperature sensor could be worth checking alright. The TPS has been checked and is ok. I will put another MPS on it to check that this week but I checked it not long ago and it was fine.

I sucked on the vacuum advance and it moved inside the distributor housing so that seems ok?

I retarded the timing as she was pinking and I thought that when the distributor was advancing at high revs it may be advancing too much causing the flat spot.

I will try the other coil but it is a standard type so will require a ballast resistor right?

I could be all wet and usually am, but I am convinced your issue is something simple that you have inadvertently overlooked.

Per the Blue book’s fuel injection troubleshooting advice:
"Engine misfires under part load: trigger contacts covered with oil; Distributor rotor from carburetor engine installed; Contact breaker points gap too small."
"Engine misfire between 3000 and 4500 rev/min: "[fuel pressure regulator] Control unit has reached min. tolerance limit."
"Engine misfires at speeds above 4000 rev/min: ground cable on cylinder head making poor contact; water in fuel tank; fuel filter blocked; fuel filler cap defective."

I understand the guide is hardly comprehensive nor does it specifically mention flat spotting or hesitation which might be dealt with in another section (ignition?) But maybe it will kindle some ideas.

Further considerations:

A rev limiting rotor is an round oblong affair with markings on it indicating the speed at which it shorts the distributor (presumably preventing over revving). If you have one, you should know it right away by looking at it. See no. 3 below. Although I hadn’t thought about it, given the troubleshooting guide, I guess its possible to run the smaller rotor from a carb’d distributor; however, if the car ran fine with the same distributor I doubt this is the issue.

As far as the coil is concerned, your original coil was equipped with a ballast resistor. Since I haven’t dabbled with petronix in quite a while, I am not sure exactly what is recommended as a coil to run with that unit. Nevertheless, most “high performance” coils tend to use a ballast although most bosch blue coils have the ballast incorporated into the design of the coil. I cannot say this with certainty, but others claim that calling the blue coil “high performance” is a bit of a misnomer.

If the polarity of the coil reversed (by reversing the wiring pos/neg), you will get the coil to function - but not as well as it should. There is a simple test for this with a pencil lead, but I am reluctant to describe it for fear that you may find the results shocking. Double check a manual for the correct hookup.

Another simple “rule of the wrist “ test might be to remove the distributor cap and twist the rotor to feel the action of the mechanical advance. You may find it barely moves or has little resistance. The point being that a spring may have come loose or the mechanism is sticking. If either situation exists, your ignition timing advance may be affected enough to cause your flat spotting. Lastly, you mention the vacuum pot on the distributor. Unless your distributor has been modified or is from another model, this should not affect high speed operation. To the extent I am wrong, why not eliminate it as a remote suspect by plugging the vacuum source? Golf tee in the vacuum line?

This is the best I can do at the moment. In a hurry. Good luck.

 

[30csl]

I could be all wet and usually am, but I am convinced your issue is something simple that you have inadvertently overlooked.

Per the Blue book’s fuel injection troubleshooting advice:
"Engine misfires under part load: trigger contacts covered with oil; Distributor rotor from carburetor engine installed; Contact breaker points gap too small."
"Engine misfire between 3000 and 4500 rev/min: "[fuel pressure regulator] Control unit has reached min. tolerance limit."
"Engine misfires at speeds above 4000 rev/min: ground cable on cylinder head making poor contact; water in fuel tank; fuel filter blocked; fuel filler cap defective."

I understand the guide is hardly comprehensive nor does it specifically mention flat spotting or hesitation which might be dealt with in another section (ignition?) But maybe it will kindle some ideas.

Further considerations:

A rev limiting rotor is an round oblong affair with markings on it indicating the speed at which it shorts the distributor (presumably preventing over revving). If you have one, you should know it right away by looking at it. See no. 3 below. Although I hadn’t thought about it, given the troubleshooting guide, I guess its possible to run the smaller rotor from a carb’d distributor; however, if the car ran fine with the same distributor I doubt this is the issue.

As far as the coil is concerned, your original coil was equipped with a ballast resistor. Since I haven’t dabbled with petronix in quite a while, I am not sure exactly what is recommended as a coil to run with that unit. Nevertheless, most “high performance” coils tend to use a ballast although most bosch blue coils have the ballast incorporated into the design of the coil. I cannot say this with certainty, but others claim that calling the blue coil “high performance” is a bit of a misnomer.

If the polarity of the coil reversed (by reversing the wiring pos/neg), you will get the coil to function - but not as well as it should. There is a simple test for this with a pencil lead, but I am reluctant to describe it for fear that you may find the results shocking. Double check a manual for the correct hookup.

Another simple “rule of the wrist “ test might be to remove the distributor cap and twist the rotor to feel the action of the mechanical advance. You may find it barely moves or has little resistance. The point being that a spring may have come loose or the mechanism is sticking. If either situation exists, your ignition timing advance may be affected enough to cause your flat spotting. Lastly, you mention the vacuum pot on the distributor. Unless your distributor has been modified or is from another model, this should not affect high speed operation. To the extent I am wrong, why not eliminate it as a remote suspect by plugging the vacuum source? Golf tee in the vacuum line?

This is the best I can do at the moment. In a hurry. Good luck.

Hi MM,

many thanks for your posts - very helpful.

Just a bit of background - the car had 200hp on a rolling road a few years back and recently when I took it (3k miles later) it had 180.
I am pretty certain it is not the regulator as under heavy load the pressure did not budge from 32psi.

Fuel tank is clean - no water.

It does have a cut out rotor but I would have thought this would be much more brick wall like than a flat spot?

The connection in the top of the cap - graphite?? sprring loaded thing does look very loose however so I will change the cap.

I tried twisting the cap and it felt nice and spring!

The coil worked fine and has done c. 6k miles. The poles are the right way around - I checked that a while back.

The wire from the coil to the cap seems very old however. no.9 in this diagram http://www.realoem.com/bmw/showparts.do?model=7031&mospid=47808&btnr=12_0941&hg=12&fg=05

It also has two wires coming out of the large end of it that goes onto the cap?????


I will try it with the vacuum pipe detached as you say. Would vacuum leaks cause any of these symptoms??

Thanks,

Rohan

 

[MMercury]

Originally Posted by 30csl
-car had 200hp on a rolling road a few years back and recently when I took it (3k miles later) it had 180. I am pretty certain it is not the regulator as under heavy load the pressure did not budge from 32psi.
-Fuel tank is clean - no water.
-It does have a cut out rotor but I would have thought this would be much more brick wall like than a flat spot?

The connection in the top of the cap - graphite?? sprring loaded thing does look very loose however so I will change the cap.
-I tried twisting the cap and it felt nice and spring!

-The coil worked fine and has done c. 6k miles. The poles are the right way around - I checked that a while back.

-The wire from the coil to the cap seems very old however. no.9 in this diagram http://www.realoem.com/bmw/showparts...41&hg=12&fg=05

-It also has two wires coming out of the large end of it that goes onto the cap?????
-will try it with the vacuum pipe detached as you say. Would vacuum leaks cause any of these symptoms??

Hi R.

Your drop in numbers (200 v. 180) is disturbing but explainable. Several things can account for this including different operating conditions (temperature and humidity), wear and tear = loss of compression, modifications (restrictive exhaust) and changes in engine tune. I am no expert but I have seen the same car tested on two different dyno’s produce different results.

I wonder what you have done to your car that may have changed things for the “un-better.” Reduced ignition timing can easily have that result. And if the available octane has been reduced in the fuel you normally run, you may not have much of a choice but to retard the timing and live with reduced performance. Colder plugs, reducing engine operating temps, water injection or even reprogramming the Djet to run richer is another workaround, but on an older car, sometimes things can go from bad to worse despite the best intentions.

Something you did not mention is valve adjustment. This can obviously alter valve timing. Too much lash may result in smooth idle but impaired breathing at higher revs. I am not suggesting you have anything wrong with your valve train, yet it probably would not hurt for you to measure the valve lash (COLD) as suggested in the manual. A little sewing machine ticking is normally a good sign, while no clicking can portend trouble. Conversely, loud percussion means something is out of adjustment and/or worn (rocker shafts or rocker bushings?)

Back to your response. I doubt the cap is bad and did not mean to suggest that the center carbon contact on yours is worn. I really have no idea. I mentioned it as an example of something that is easily overlooked. Another example might be spark plugs. How many times I have heard someone say they checked the plug gaps after they manhandled the plugs, only to later find a plug is misfiring because it has no gap!

You mentioned “twisting the cap”. To be clear, I did not mean to have you test the distributor cap. I was referring to the rotor, but you probably meant that.

As far as the rev limiting rotor is concerned, its value, other than authenticity, is dubious. It is supposed to cut out the ignition as the spring stretches due to centrifugal force. Unfortunately, if the spring fatigues, the rotor can cut out at a much lower rpm than intended. And, while the theory is a good one to prevent overrevving, you can still overrev the engine with the ignition off - by missing a shift and engaging a lower gear at high speed. We would never do such a thing. You know it can happened to others. If you can find the inexpensive plain vanilla rotor for your distributor, you might want to try it and save your pence.

It occurs to me that with some so-called high energy electronic ignitions the makers recommend using rotors that do not have a built in resistor. Your rev limiting rotor has a resistor as do most OEM rotors. It can serve several purposes and be essential for the proper operation of newer computer controlled vehicles. In the E9, it is most likely there to suppress radio interference. The reason for ditching the resistor is that higher voltage can allegedly melt the resistor medium and cause poor conductivity. You might want to measure the resistance in any rotor you are using just to make sure it is as advertised. I am certain your rev. limiting rotor actually has the resistance spec. printed on it. If you are a glutton for punishment or you merely want to take your mind off your current dilemma, look at these sites:

http://huelsmann.us/bugman/RotorTech.html (do it yourself rotor mods)

http://www.hotrod.com/techarticles/i...ech/index.html (select the right aftermarket coil)

http://www.tegger.com/hondafaq/badsecondary/index.html (your guess is as good as mine)

http://www.peachparts.com/shopforum/...d.php?t=257263 (Mercedes bad rotor blog)


Regarding the high tension lead from the coil to the distributor, I believe it is a vestige of ancient diagnostic design. That piece transmitted a signal to a small molex female connection/diagnostic terminal. As pictured below, there was a ring attachment that slid over the number 1 plug lead and it presumably functioned as an inductive pickup. In theory, you could plug in your expensive proprietary BMV test equipment and check the ignition timing and a few other things. If you have the factory shop manual page "11-00/3" (bottom right hand corner) describes installation of the “diagnostic socket.”

You state the condition of your coil to distributor wire is shabby. Frankly, I’ll bet the wire is original to your 30+ year old car. Unless you have access to the ancient test equipment, that wire no longer serves any useful purpose and should be retired to your private museum. That wire can be replaced by any decent solid core high tension lead. There is nothing magical about it. If you have a decent spare solid core ignition wire lying around, check its resistance with an ohmmeter and connect it in place of the subject relic cable. This may be your problem, part of your problem or part of a future problem that will hopefully never materialize!

Respecting the distributor’s vacuum feed, if you disconnect the hose and plug it, I would expect your idle speed will increase as the vacuum on most injected E9's retards the ignition timing at idle. It should not have any noticeable effect on higher speed operation. I only mentioned experimenting with the vacuum line plugged because if it resulted in an improvement, it might suggest the existence of a vacuum leak, or some mix up in your vacuum plumbing, or even something wrong with you distributor vacuum mechanism. In answer to your question, a serious vacuum leak or leaks could easily contribute to an overly lean condition. Yet, in all honesty, I doubt any leak at that manifold-ported vacuum hose - not noticed at idle - would be noticed at higher rpm.

Hope some of this makes sense. :wink:

 

[30csl]

Something you did not mention is valve adjustment. This can obviously alter valve timing. Too much lash may result in smooth idle but impaired breathing at higher revs. I am not suggesting you have anything wrong with your valve train, yet it probably would not hurt for you to measure the valve lash (COLD) as suggested in the manual. A little sewing machine ticking is normally a good sign, while no clicking can portend trouble. Conversely, loud percussion means something is out of adjustment and/or worn (rocker shafts or rocker bushings?)

Back to your response. I doubt the cap is bad and did not mean to suggest that the center carbon contact on yours is worn. I really have no idea. I mentioned it as an example of something that is easily overlooked. Another example might be spark plugs. How many times I have heard someone say they checked the plug gaps after they manhandled the plugs, only to later find a plug is misfiring because it has no gap!

You mentioned “twisting the cap”. To be clear, I did not mean to have you test the distributor cap. I was referring to the rotor, but you probably meant that.

As far as the rev limiting rotor is concerned, its value, other than authenticity, is dubious. It is supposed to cut out the ignition as the spring stretches due to centrifugal force. Unfortunately, if the spring fatigues, the rotor can cut out at a much lower rpm than intended. And, while the theory is a good one to prevent overrevving, you can still overrev the engine with the ignition off - by missing a shift and engaging a lower gear at high speed. We would never do such a thing. You know it can happened to others. If you can find the inexpensive plain vanilla rotor for your distributor, you might want to try it and save your pence.

It occurs to me that with some so-called high energy electronic ignitions the makers recommend using rotors that do not have a built in resistor. Your rev limiting rotor has a resistor as do most OEM rotors. It can serve several purposes and be essential for the proper operation of newer computer controlled vehicles. In the E9, it is most likely there to suppress radio interference. The reason for ditching the resistor is that higher voltage can allegedly melt the resistor medium and cause poor conductivity. You might want to measure the resistance in any rotor you are using just to make sure it is as advertised. I am certain your rev. limiting rotor actually has the resistance spec. printed on it. If you are a glutton for punishment or you merely want to take your mind off your current dilemma, look at these sites:

http://huelsmann.us/bugman/RotorTech.html (do it yourself rotor mods)

http://www.hotrod.com/techarticles/i...ech/index.html (select the right aftermarket coil)

http://www.tegger.com/hondafaq/badsecondary/index.html (your guess is as good as mine)

http://www.peachparts.com/shopforum/...d.php?t=257263 (Mercedes bad rotor blog)


Regarding the high tension lead from the coil to the distributor, I believe it is a vestige of ancient diagnostic design. That piece transmitted a signal to a small molex female connection/diagnostic terminal. As pictured below, there was a ring attachment that slid over the number 1 plug lead and it presumably functioned as an inductive pickup. In theory, you could plug in your expensive proprietary BMV test equipment and check the ignition timing and a few other things. If you have the factory shop manual page "11-00/3" (bottom right hand corner) describes installation of the “diagnostic socket.”

You state the condition of your coil to distributor wire is shabby. Frankly, I’ll bet the wire is original to your 30+ year old car. Unless you have access to the ancient test equipment, that wire no longer serves any useful purpose and should be retired to your private museum. That wire can be replaced by any decent solid core high tension lead. There is nothing magical about it. If you have a decent spare solid core ignition wire lying around, check its resistance with an ohmmeter and connect it in place of the subject relic cable. This may be your problem, part of your problem or part of a future problem that will hopefully never materialize!

Respecting the distributor’s vacuum feed, if you disconnect the hose and plug it, I would expect your idle speed will increase as the vacuum on most injected E9's retards the ignition timing at idle. It should not have any noticeable effect on higher speed operation. I only mentioned experimenting with the vacuum line plugged because if it resulted in an improvement, it might suggest the existence of a vacuum leak, or some mix up in your vacuum plumbing, or even something wrong with you distributor vacuum mechanism. In answer to your question, a serious vacuum leak or leaks could easily contribute to an overly lean condition. Yet, in all honesty, I doubt any leak at that manifold-ported vacuum hose - not noticed at idle - would be noticed at higher rpm.

Hope some of this makes sense. :wink:[/QUOTE]

MM - thanks for the great info and help.

The drop in power is a problem because it just dies at 4500 whereas before kept going, its a noticeable flat spot which I recognised before the rolling road session.

I didn't adjust the timing between sessions but did play around with a lot of things as in between I had a fuel supply problem with gunk in the tank that was hard to track down - the car would lose power on left hand bends only! Generally I went through checking everything rather than changing stuff per se.

Yes I meant twisting the distributor innards but I mention the cap as i noticed the centre connection is bad, the graphite piece fell out when I removed the cap - looks like the spring should hold it in but doesnt now. I have ordered a new one.

I plan to replace the coil to cap lead like you say as the diagnoss port will not be used!I will also check the resistance of the 6 plug wires.

I will try plugging the vacuum tonight and see how that goes - i suspect there is a vacuum leak somewhere though.

When I get this nailed I'm going to absolutely trash her to death!

Thanks,

Rohan

p.s. if you come over to the UK we will have to go for a spin in her if she is fixed!

 

[MMercury]

The drop in power is a problem because it just dies at 4500 whereas before kept going, it’s a noticeable flat spot which I recognised before the rolling road session.

I noticed the centre connection is bad, the graphite piece fell out when I removed the cap - looks like the spring should hold it in but doesnt now.

Since you are also describing an issue that only appears at higher speed operation, maybe you are suffering from valve float. Is it possible your valves adjusted too tight or maybe the valve springs have gotten weak with age? Ordinarily, this happens at much higher revs, but dealing with an older car is full of surprises. This is idle speculation on my part.

If the center carbon button is falling out of the cap, you may be on to something, especially when you describe a high speed issue. Still, if things are that loose, I would think you would have issues at other speeds too. On the other hand, you wouldn't be aware of a need for a more robust ignition system - until you place a higher demand on the system and it begins to fail. At higher speeds, your coil has less saturation time between discharge and, who knows, with a combination of a leaking coil-distributor high tension lead and a goofy cap that could mean ignition Waterloo.

I am no Wellington or Nelson and this may be beating a dead horse, but I still have reservations about condemning your ignition. The fact that your fuel pump pressurizes the system to 32psi seems more than adequate to satisfy your engine's high speed thirst. I am sure you are aware the manual states you should be able run your engine on less pressure 28-31 psi, so, if your gauge is accurate, you are already above the recommended pressure. Nevertheless, pressure is distinct from volume.

If you were to pressurize the small distributor vacuum hose to 32psi, it would not flow as much volume as say a 3/8" hose or a larger garden hose or a fire hose. The point being that you may have an unforseen obstruction in the fuel system that does not leak and maintains pressure but does not flow. It could be as simple as a kinked line or flex hose. Another broad analogy: if you have a spigot at the end of your hose and only crack it a bit, the hose will maintain pressure, but only a little bit of water will exit the hose. High pressure - low flow.

Again, I wonder if you do not have a volume issue related to the pump or a fuel line or filter. You could adjust the pressure regulator to increase the pressure even higher to insure greater volume or actually measure the flow either at the pump or toward the front of the car. I would try the ignition mods first, but would not rule out going back to the dirty basics.

As before, good luck!