Return of the herky jerky CSL

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corsachili

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It likely never went away. I had a problem a couple years ago with stumbling upon idle which we traced to a faulty voltage regulator. I hoped that this was the cause of the other problem I'd been having with the car at constant throttle positions, such as you'd expect when you're cruising along at a steady speed, neither accelerating nor decelerating. The symptom is that the car stutters or hesitates, resulting in a slight but noticeable "bucking" sensation. This is not pleasant. I replaced the TPS and swapped ECUs, as well as the MAP sensor, all without effect.

So round 2 begins, and I'm looking for any suggestions or thoughts on a cause. I did check to make sure that I have a good solid ground at the ECU (brown wire that screws to the tab on the body) and all is well there. I will also check the ground point at the intake log to make sure that I'm good there, but those seem to be too simple a solution for a guy like me. I usually end up with you need to replace the part that they build the entire car around.

So take your best shot..................anyone have any brilliant ideas?

Injectors have been cleaned and bench flowed. Haven't done a plug chop in a while. Car idles nicely, pulls pretty smoothly, runs well otherwise.

-tj
 
It's been a while since we last left this saga, TJ. I forget, was there a chapter about the fuel supply end of things -- fuel filter, pump, in-tank pump?
 
Thanks Michael. I have installed a new fuel filter, and cleaned the filter in the pump. The symptom feels electrical to me, not fuel starvation. If it were fuel starvation you'd expect the car to not accelerate cleanly with the application of throttle, but it does. The best analogy I can use is that it feels like someone is turning the ignition off and on rapidly (like a flicker, back and forth).
 
Long shot

Try a new battery, if that helps, then check out the alternator (and/or all connections to/from). I have had more than a few vehicles with similar symptoms that were impossible to sort out until I simply replaced the alternator.
 
I have a Petri wheel that should do the trick!
 
I once had a 3.0Si with D-Jet that did everything very well except maintain a steady speed. Slight bucking all the time. Drove me nuts

I altered the ignition setting slightly (a couple of degs more or less, did it on the road by feel), and while it didn´t go away, it did linder the problem...

Then I sold the car which fixed the problem permanently (for me at least...) 8)

Now I have tripple webers which buckle under low rev acceleration. Oh well :?

Don´t know whether that helps.

But really, play with the ignition timing, not statically with a light, but brutally roadside. See what happens (you can still go home and reset the timing with a strobe afterwards)
 
A small but significant point often overlooked is the proper grounding of the ECU. This corrected similar problems for me in a CSi that I THOUGHT was sufficiently grounded. Might be worth a re-check. FWIW

RogerB

'72 Golf 3.0 CSL 2275030
 
corsachili said:
To reiterate, it's not a surging problem. It's a hesitation, a bucking, an on/off kind of symptom. I have replaced many of the items in question, as well as checked grounds. I didn't mention last time but I did replace the ignition points in the distributor and have a Pertronix installed as well.

Carl told me once a while back that the fuel pressure is really not adequate from the stock setting and advised I bump it up a bit. I don't remember the exact number but somehow 29PSI sticks in my head, which is about as good as you get from the stock pump/regulator.

Again, it feels electrical to me, not fuel related. Of course it could be that the electrical failure prevents the injectors from firing briefly, so it could be fuel related in that regard, but the root cause is still electric.-tj
Click to expand...

Your later response that you are suffering from pure hesitation - rather than surging at constant part throttle operation, caused me to rethink my earlier use of bandwidth. I am still not sure how or why a voltage regulator replacement might mask this. I also do not think reading the plugs would offer much help if what you are really describing is a “short” in the ignition/electrical system.

If, as you state, this is truly a hesitation issue, the same symptom is analogous to carbureted cars when the accelerator pump and/or ignition timing is substantially retarded or when the coil and/or condenser is/are bad or going bad. The analogous parts on the CSI are the TPS and the distributor, including its centrifugal advance mechanism and the vacuum retard setup. You did not mention the coil or ballast resistor, so I would consider looking closer at them and since you eliminated the condenser, it is a nonissue.

A simple ohmmeter can be used to test the TPS and a timing light and a keen eye might be useful to test the distributor’s proper function. Frankly, you probably can get away with out any test equipment.

No matter how smooth the CSI engine is, there is a still vibration to loosen things up. If the engine is cutting out (you don’t say this but you suggest it) I would examine the entire wiring scenario and especially the wiring to the coil, ballast resistor, distributor, (including the somewhat related fuel injection trigger points). The movement of the engine within a moving framework can result in difficult-to-locate electrical shorts. I would expect that intermittent short issues (and even a bad coil) might reveal themselves under acceleration/load than at other times - but not always.

BTW, the Pressure Sending Unit and TPS both translate mechanical movement into electrical signals. Both can develop dead spots/intermittent shorts that are not the easiest to detect. That is why, at least with TPS, it couldn’t hurt to try readjusting. A friend had a new pressure sending unit that seemed to test fine, but the engine ran erratically at a limited engine speed (lean misfire 1500 - 1800 rpm?). For grins, he tried old PSU from another car that had been modified to permit adjustments. With the modified PSU, the engine ran beautifully and all missing disappeared. Unfortunately, the engine also ran much richer than before. My point being that not all parts, including new ones, should be overlooked.

Good luck!
 
Not necessarily and ex-spurt, but here are a couple of suggestions

1) double check the brain (ECU?) connections, terminations at the plug end of the harness under the backseat, all wires for "fatness distortion" at all connector ends (signs of heat on grounds, or corrosion under the insulation of individual wires.) Also all grounds, I often eliminate gremlins by removing all chassis-ground-by-mounting electricals, using a fine dobie or scotchbrite wheel to shine up the contacting points, and doing the same for all ground straps (consider replacing all ground straps with new brown wire and new terminal lugs, they can gain a LOT of resistance just due to age. Ground straps to look for are the one by the brain under the back seat, any ground terminals coming off the harness under the dash and at the inner sides of the bulkheads, all underhood ground terminals coming off the harness, all supplemental ground straps from the engine to ancillary electricals (alternator, dizzy (?), the grounding mating surfaces at the fuel meter on top of the booster assembly) and especially the grounding from the block to the firewall

2) Staus of your fuel meter? slight surging could be lean/pulse fuel related, very slight but the nature of capacitance could make that a credible possibility, since it is harness-powered function and only apparent at balanced, "s/b stable" freeway speeds. Your symptom DOES vanish with a blip of the throttle, yes?


Hope this helps (I admit, the cumulative effect of these may be better for your needs than a Petri wheel!)
 
Thanks to everyone who has responded with input on this problem. To reiterate, it's not a surging problem. It's a hesitation, a bucking, an on/off kind of symptom. I have replaced many of the items in question, as well as checked grounds. I didn't mention last time but I did replace the ignition points in the distributor and have a Pertronix installed as well.

Carl told me once a while back that the fuel pressure is really not adequate from the stock setting and advised I bump it up a bit. I don't remember the exact number but somehow 29PSI sticks in my head, which is about as good as you get from the stock pump/regulator.

Again, it feels electrical to me, not fuel related. Of course it could be that the electrical failure prevents the injectors from firing briefly, so it could be fuel related in that regard, but the root cause is still electric.

Hard to imagine it's a vacuum leak, all new hoses, and everything has been gone through. Again, the symptoms don't say vacuum leak to me.

I am not averse to taking it to someone who knows more than me, and while I do trust Carl, he's a bit undesirable from a geographic perspective. I suppose Bavarian Professionals in Berkeley are an option.
 
Had this problem with a CSi a few years back and replaced everything including the injectors, the 'denture' in the distributor, the pressure feeler gauge--and adjusted the PSI up a bit on it to boot, as somebody else had suggested already. Also swapped the ECU for another known good one I had and still had the same miss. Finally traced it to the wiring harness for the D-Jet. Specifically the plug in the right frame rail where the front half of the loom joins the rear half. After cleaning that connection and replacing everything carefully, all was finally fixed. Didn't need any of the several thousand dollars of parts I had replaced in my search, just a clean connection.
Hope this helps.
Peter
[email protected]
 
You can stop by Harold Hurst's shop in Mountain View, Harold can be a deep troubleshooter, and if you need more eyes he has Steve Smith next door with a great reputation as well.

Last week Harold's shop was entirely 70's bimmers (two coupes and a 2002), so he doesn't have to context switch...
 
Thanks Peter and Ariel.

Regarding that connection, I know the one well. Some D-Jet harneses have a big Molex connector there, and some, such as mine, are one piece (I believe, I'll have to run downstairs to confirm this). I'm going to start checking grounds and cleaning connections today with contact cleaner.

BTW-does anyone know exactly how the TPS is suppose to be adjusted? My old one was pretty FUBAR and when I installed the brand new part, nothing really changed. Also when I move it back and forth in its range, nothing really changes either.

What is the name of Hurst's shop in MTV?

-tj
 
See above revised response

Your response rendered my original post irrelevant. See above.
 
So I just cleaned a lot of connectors with electrical cleaner, went back over all the ground points with a small grinder, including the three tabs where the ECU mounts and fiddled with the TPS a bit. A short drive did not show any of the herky/jerky symptoms but I know better than to think that I've licked the problem. Some of the technical information I have talks about how to adjust the TPS, but there's a BMW test unit that they cite for proper setup. Is there a way to get it adjusted properly with just an multimeter? Anyone have a method for doing this without the factory tool?
 
Had this same problem on my e30 m3 and it was a small hole in one of the sparkplug wires,you can get a spray bottle and mist them with water at night to tell ....good luck
 
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