1986 XJ6 Series III:

It is non-reliable! The following has happened a number of times, such as I can’t take my wife out!

Driving locally, all is fine until engine simply stops. I manage to pull over. Maybe a few times it has restarted normally but usually it does not.

It cranks fine but does not start. I give it a little while and try again. No start. Wait longer: same thing. More often then not, after a lot of waiting then retrying, battery gets flat.

it always starts up normally if I wait LONG ENOUGH, like an hour or two.

One time this happened and left me facing down a moderate hill. After many failed tries and waits and eventually a boost from a kindly passerby, it started but I SAW A FAIR PUDDLE OF GASOLINE on the ground under the right front of the engine. I did not take time to investigate, but it was obviously under the air intake.

That’s all I KNOW.

What I THINK is the engine occasionally wildly overfuels. And since the stopping is so sudden (no sputtering), my further GUESS is that it is a gross error by the ECM. I know zero about this realm of reality and technology, and surely cannot imagine the mind of that ECM (is it all analog, i.e., pre-digital??), and I suppose it might not be the ECM’s fault but instead some flakey input, but that seems less likely.

Is there any way to “read the mind and memory” of that thing?

Used ECMs look available and inexpensive, so if no one here can help me, probably I’ll buy one and see. If I do that do I need to be sure to get the correct version? Is there any sort of setup?

I am frightened but excited - I guess.

Has anyone either experienced what I have or any bright ideas?

Many thanks!!

Henry Lanford

 

if I were you I would check the output of the air flow meter and the temperature sensor, Those would be the main feedbacks the ecm uses to control the injector duty. I would also check for any big vacuum leaks as it also sounds to me that your car will start okay when its in cold start enrichment phase but as it leans the mixture out you have too much air going in to support combustion. And what your saying about waiting a long time your letting the car cool enough where it goes back into cold start mode, Possibly??
Where your saying there is fuel on the ground on the right front of the engine. You may also have a significant fuel leak from the fuel rail, there are rubber hoses that connect the rail to the injectors and they harden and crack over time which will cause issues with fuel pressure and running issues, its also a fire safety hazard if you have raw gas dripping anywhere inside your hot engine bay.

 

Will it happen only on the right tank not the left? If your switching valves are not in concert with each other, The return fuel will go out to the charcoal canister, Then raw fuel will enter the the engine causing it to over fuel. Your clue is the puddle of fuel at the right front under the charcoal canister. Your diagnosis has to be as follows provided that the fuel tanks are very low on fuel. Start the vehicle over a dirt driveway, While your fuel switch is on the left tank, Carefully and slowly open the fuel flap, Using a long thin screwdriver and a very bright flashlight, push down the next flap and observe a 8mm pipe that points to the outside of vehicle. Is there fuel flowing from it? Leave flap open while you go to other side and open fuel flap. Observe other pipe in below neck, Is there fuel flowing out of it? Switch fuel switch to right side and the flow of the pipes should go opposite of the other fuel switch position.
Report back what happens.

 

Fuel pressure regulator????? Just a guess...

 

I agree with Carl

fuel pressure regulator and the hoses connecting to it, hence the leak.

also the ignition amplifier gets hot and shuts everything down. I doubt it is the ECM. Ignition Amp is a GM part. Available at most autoparts.