Vapor Lock?

T

Tyler

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Here is the situation:
- An unseasonably hot day for London (mid-80's F).
- Cruising at 80mph+ for at least 20 minutes with no traffic.
- Stock temp gauge shows about 85C, which is higher than usual for this type of driving. Typically, I'd be at or below 80C.
- Stock D-jet engine running great all day suddenly enters a lose-power / surge cycle as if it is starved of fuel, and a strong smell of fuel enters the cabin.
- I pull off to the side of the highway, engine dies, and my wife gives me the evil eye.
- I confirm no visible fuel leaks beneath the car or around the engine.
- 15 minutes later, I restart and have no problems for the remaining 20 miles home, even with city traffic. Temp gauge stays around 80s C.

Sounds like vapor lock to me, but I've never experienced it in an injection car, and never when cruising at highway speed. What do you guys think?

Regards,
 
Hello Tyler
I would be tempted to check the ignition side of things.
1.. A strong smell of petrol suggests injection was occuring without ignition.
2.. Higher than normal temperature could suggest a sticky thermostat, but I doubt it, more like the ignition was slightly retarded.
3.. Advance weights sticking? Have you put a drop of oil on the felt pad under the rotor arm recently?
4.. Check the points, change the condensor, if fitted. it could be the coil is on the way out. How old are your plug leads?
5.. What is the colour of your plugs? Black too rich, sandy brown ok, white glazed weak mixture.
6..Another possibility is that the coolant temp sensor for the injection wasn't reading correctly, check the connection etc.
7.. How old are your injection points in the base of the distributor, check them out.
8.. Check the distributor cap for tracking
9.. Check the rotor arm, there have been some very poor quality items on the market recently and even new ones are cr*p. Same applies to distributor caps.

As to the "look of death" from the wife... I couldn't possibly comment.
HTH
Malc
 
Thanks Malc.

Thermostat checks out, as does the temp sensor - so it sounds like the ignition as you suggest. I plan to replace the condenser, coil, cap and rotor to be safe, and lubricate the advance weights.

However, I'm not sure what you mean in #7 below (injection points in the base of the distributor). Can you please elaborate?

Regards,
 
Hi Tyler
As your running D-jet injection (I assume) the "triggering" information for the ECU is provided by a secondary set of "points" in your distributor.
These are located in the base of your distributor behind a small cover place in the side of the distributor housing. They do last a very long time but eventually wear out and get dirty causing poor triggering of the injection.
Changing them is easy and they are relatively cheap so worth the effort if your doing all the other stuff too.
Malc
 
Hi Tyler
I reckon Malc is fairly close to the money.

However..after you have checked /replaced electricals etc as he suggested...if the problem still exists..don't forget to check out the fuel pump/pump pressure/flow.

I also own a 1974 Citroen DS Pallas EFI with D-jet and some years ago had all the symptoms of "vapour-lock". There is no room for air-flow under a Citroen bonnet.
The problem turned out to be an operating but faulty/worn fuel pump. (Bosch roller type- same as on BMWs)

Let us all know how you get on
Cheers
Bob
 
Reminds me of a problem I had many years ago with a 3.0csi...

When you open the fuel tank cap is there vacuum inside, I mean does it make a suction noise ?

My vented cap was not vented anymore, causing fuel starvation.
 
Many thanks for all the suggestions.

I spent the afternoon replacing various ignition components to hopefully solve the very occasional power loss problem discussed above.

- disassembled the top parts of the distributor.
- cleaned out the gunk around and under the vacuum advance mechanism.
- lightly re-greased the obvious places.
- installed a new points assembly.
- got baffled by the term "dwell angle" but gapped the pivot arm to 0.38mm per the manuel.
- checked the injection points assembly, and couldn't see any obvious problems or wear.
- put 2 drops of oil on the felt under the rotor arm.
- installed a new rotor arm, cap and coil from W&N.

I also put a small drop or two of oil on each advance weight pivot, but read later in the manuel that this is verboten so hopefully it won't be an issue.

Car started with no problem, power is good, but now the idle speed is way too high. It was perfect before I tinkered with the distributor, and I didn't adjust the timing or loosen the distributor body at all. Could the timing have gotten out of whack during my tinkering? I can't think of anything else I did that would mess up the idle speed and now fear that I turned a small problem into a bigger one.

What do you guys think?
 
Dwell angle is a measurement of how long the points are open in terms of degrees. You need a dwell meter to check this and the engine has to be running. You can buy a reasonable one from places like partco, Halfords and alike. It is a much more accurate way of setting the points gap than by using feeler gauges.

As to the higher idle speed, well you have put on all the nice new shiny bits and cleaned everything up so I suspect that now the dizzy is working properly the timing could of changed slightly, its running "cleaner" and more efficiently, the weights etc are now moving as they should!

I would check the timing to see if that is still ok then reset the idle speed
as required
Malc
 
Hi idle, better firing for sure. It is best to check and reset the timing.

Once you have set/changed the point gap, the rpms will be different. It is very hard to set them accurately with just feeler gauges. If you recheck them you will probably find that their slightly out! My point is that if you adjust the gap again, you will probably have a different idle speed again.

Also, there is usually a set screw in the throttle linkage to adjust idle as well. Perhaps you can screw it out a bit to let the throttle close a bit and lower the rpm. This is usually just to help set the timing since it is supposed to be set at different rpm's that are usually higher than idle speed. I know mine was set to increase the idle speed a bit for quite some time though.

Neil
 
re: point gap

I concur with the advice previously offered.

As a supplement, a feeler gauge remains a good starting point to setting the points and it appears that the manual suggests a gap in the neighborhood of .25 - .30 mm/.012-.016". This figures appear to vary (not by much) by year. In any event, I have found that 9 times out of 10, setting the points to a tight .016 translates to the correct dwell angle. Likewise, as others have noted, changing the gap/dwell also changes the ignition timing.

To be sure, the dwell gauge is clearly more accurate than a feeler gauge, but I mention this since, in my opinion, a dwell gauge is not an absolute necessity. To a lesser degree, the same can be said for other equipment, including a timing light.

No doubt the timing light is useful for factory settings and diagnostics- especially when you can program the light with advance settings. However, the vagaries of time, maintenance and octane may give cause for deviating from factory settings.

One of my cars, with unknown mileage and guesstimated compression, clearly benefits from timing advanced approx 4-5 degrees from the stock setting (smoother operation plus improved fuel economy). It even ran cleaner last time we hooked the car to an exhaust gas analyzer. Another car, with 10.25:1 compression, pings far too much at the stock settings (even with the highest pump gas available) warranting a slight retardation of overall timing. (No problem with addition of octane booster or using aviation fuel - except inconvenience of additional cost and limited supply.)

Without knowing more about your particular situation, the stock settings are probably the best bench mark, with the well-worn caveat: "Your mileage may vary."

:wink:
 
another possibility

Another possible cause for high idle, given that you have been messing around a good deal, is that the idle air bypass is leaking, or another vacuum leak has developed or resulted from your work.

Mechanic's rule - when something goes wrong, look where you last worked.

As I am not particularly Djet familiar/knowledgeable, someone else will have to elaborate. Anyway, unmetered air entering the engine is one of the causes of high idle.
 
Yes Honolulu makes a good point - I have had problems with vacuum leaks over the years - good way to find them is to spray wd-40 or the like on suspect leak areas and when this is sucked in the idle will change.
 
fuel smell

I reread the original post and wondered whether the petrol smell didn't indicate something other than what has been suggested.

As you should know, the fuel lines including rubber hose, are under quite a bit of pressure (3 bar). Hoses and filters do not last indefinitely.

I recall trying to determine the cause of an intermittent fuel smell. I could not see anything wrong so I started wiggling things. When I got to the hose near the fuel pump, I received a head full of fuel from a cracked hose. The car was driven a few hundred feet to look at things closer and surprisingly, the hose did not seem to squirt fuel, but everything was "damp". Needless to say, disaster was averted.

The car in question did not exhibit the vapor-lock symptoms described, and the fuel smell you noticed may have been just as Malc opined, unburned fuel due to an ignition malady. Nevertheless I would think it wise to look at your fuel lines.

I also wonder if you might not have a plugged fuel filter. I pulled one (from under the battery support) and for grins, cut the filter apart. I was amazed at all the flecks of metal and crud found. I am sure the crap in the filter weighed more than the filter. While it is hard to believe this stuff might impede the fuel flow enough to cause stalling, anything is possible. Unfortunately, with these mature cars, fixing one thing often reveals something else that needs attention.

Good luck. :wink:
 
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