1982 MONDIAL 2 VALVE ENGINE RUNS ON...ANY SUGGESTIONS

leaking injectors? Take them out and hava them checked at a good place that has a propper test bench. Also check your fuel pressures warm control pressure inparticular.

Normaly a run-on probelm is caused by a high idle. But with C.I.S this is not a common problem. I fact I don't think I have ever seen a rn-on problem on any C.I.S equiped car. Keep us updated as to what you find.

What else has been done to car service wise before this problem occured?

 

In what country you live ??
The fuel changes here in Europe caused also this problem...
Guido

 

Angelo -- Please describe "run on" better. Do you mean that it hacks and coughs on a few cylinder for a few seconds or that it continues to just idle normally with the ignition key removed?

 

I would think that it would be a timing issue or a problem in the ignition. This isn't a common problem that I have seen. Keep us posted.

 

One thing you might do is verify that the ignition actually shuts off when you turn the key off (i.e., with a timing light on a coil wire, does it still flash during the unwanted dieseling period?).

Unfortunately, they don't include the schematics in the Mondial 8 OM so I can't really say if this is important for sure, but something easy to try would be to swap the "U - relay for ignition key controlled services" with another relay of the same PN.

One hears stories of old British sports cars with enough glowing carbon deposited on the piston tops to make shutting off difficult, but that doesn't seem consistent with a well-running injected car -- but you've got to go this direction if the ignition is truly shutting off properly yet the engine diesels.

 

Since the ignition is off, dieseling can only be caused by one of two things: 1) too low an octane; or 2) by carbon deposits. Somewhat contrary to what you would think, low octane is actually easier to ignite than high octane fuel and this is why the engine with will continue to run with low octane after the ignition is off because combustion occurs from the internal heat -- spark is not needed (this is how a diesel engine works and is why diesel fuel is very low octane). If octane is sufficient, then carbon deposits are usually the problem because they raise the internal temperatures such that heat-based combustion occurs even with high octane fuel. Even though fuel injection is very efficient, carbon deposits will still occur if the car is used for short trips because the cylinder head never reaches sufficient temperature to burn the carbon and it ends up accumulating inside the engine. The best solution is to add two bottles of Techron fuel additive and fill the tank. Then give it an Italian tune-up -- drive it at least one hour at slightly elevated RPMs to keep the cylinder head temperature elevated. The extended drive is very, very important because the fuel additives are only effective at removing carbon deposits when the cylinder head is held at sustained high temperatures. If your car is frequently used for short trips, chances are very good its carbon deposits -- you may have to run fuel additives for several tankfulls if they have really built up. Another possibility is that the valve timing is off, but this seems less likely (it should be checked if the fuel additives don't work because you don't want to break a timing belt). I'm not an expert, but I think carbon deposits are likely the cause.

 

Good info. Thanks for sharing. I would have never thought that carbon build up could cause this or low octane for that matter. Thanks Again.

 

Ibajaps guitars suck!



Just kidding, keep on rocking ...!

 

I would not think that the throttle plate is likely this given that your car idles fine -- the fuel should not ignite once you turn off the key, so something is causing it to ignite. If it is fuel-related, then it is probably caused by a lean condition rather than rich because a lean mixture is easier to burn. It seems less likely that it's caused by continued fuel delivery -- fuel injection should stop delivering fuel when you turn off the key, but even carbureted engines that don't stop the fuel supply normally don't diesel. If it isn't carbon, improper valve timing may be the cause because I think a delay in the exhaust valve opening can also cause internal temperatures to be higher than normal so that sparkless combustion occurs.

Does this ever occur when the engine is not fully warmed up? If so, it may suggest that it is valve timing. Carbon build-up or a lean mixture shouldn't cause run-on if you've only run it for a few minutes -- because, in the case of lean mixture, there won't be enough temperature to ignite and, in the case of carbon, the temperature must be high enough for it to glow like a glow/spark plug.

The EGR based cleaning sounds like an interesting technique. How long did you run it for and was the engine already very hot when you started? I read that deep carbon deposits can only be removed when the cylinder head temperature is held at very high temperatures for an hour or more.

 

Sounds like cam timing.

 

not the JEM!

 

I do think it is the cam timing -- I discounted that possibility initially only because the belt would have to slip to be off, but since you just had the belts serviced, this becomes much more likely. I am not an expert, but I think that if the timing is off, delayed valve opening can cause the effective compression ratio to be higher than normal even though the cylinder head geometry hasn't changed. The higher the compression, the higher the octane required to prevent sparkless combustion. Premium is fine for the standard timing but may not be enough when the valve timing is off. It seems even more likely to be the cause given that it happens when the engine is cold because carbon deposits would only be a factor when the engine is hot. You've already proven that it doesn't have spark and therefore I don't think it can be a fuel problem since it shouldn't ignite, so valve timing is really the only variable. The EGR cleaning technique sounds quite effective, I may give this a try.