Hi all. I've read all the threads I can find on this but I don't seem to be able to find the right solution. Here's the puzzle:

1982 German-market base-spec auto 928

Starts and runs great almost all the time, but about a year ago and again now I have an undiagnosed running and starting issue:

It will always fire and usually run, especially when cold, but then it may cut out regardless of engine speed, load, or road speed.

Not on a bump, nor just idling at a stoplight.

Sometimes, when I go to restart, it'll restart fine. Sometimes it will fire and after a few revs or a few hundred, just quit again. Sometimes it will run for days or months.

14-pin in good shape, cleaned to no effect, recent green wire, recent pug wires (the old ones were arcing and causing rough running, but new wires completely solved that). I think the grounds are OK but haven't checked all. Basically the car is tidy.

There's no fuel injection relay (82 Euro doesn't use one I believe) and I have the cover off the fuel pump relay and as soon as the car cranks it makes contact and stays on until after the stall ie. when it should release, I think. I can manually override it but to no effect.

Battery super-strong, and starter too (incidentally, I did have a long-term battery-draining small short and an occasional no-start and replacing the starter fixed both).

The vacuum lines are a bit old and gnarly-looking, to be honest, and I should replace them.

What does the team this this could be? The baffling thing is the randomness of the cut-out - you can be idling or holding at 4000rpm, not moving, and it will completely quit. Also when it's acting up it will basically always fire and then immediately quit. No stumbling, no shocks, no fuel pump cut, just goodbye. Then it might just restart no problem.

I'm thinking a sensor or - call me crazy - some kind of intermittent vacuum thing with the injection that just lets the pressure go then reseals. I know I should check the grounds but this just doesn't seem quite right for that, what with the fire and quit.

One more thing: On a recent bad episode of fire-and-stall, fire-and-stall, fire-and stall, the catalyzer (recent OEM replacement, got car through CA smog), was glowing orange and smoking, which I thought odd. Might have been just the super-rich startups??

Thoughts?

Thanks,
ACP

 

Hello , from your report I would be looking at an interruption of power to the fuel pump or the fuel injection computer
SO this will mean use deoxit on the CE panel,
make sure the fuel pump fuse is replaced and that the contacts are tight.

Clean the battery terminals and replace the battery ground strap with a fresh strap.
Roger sells them cheap.

Clean the engine ground at the right side pf the oil pan to chassis.

Clean the Hot post and 14 pin connector and fit a hot post cover.

Clean the grounds at the top of the CE panel.

Clean the grounds on the right hand cam tower there are two of them they both must be cleaned.

Clean the grounds in the RR cargo hatch area they are either on the floor or wall behind the liner.

Clean the grounds in the spare tire well.

Replace any running relays.

 

O.K. this is a CIS car and doesn't have a fuel injection computer. So don't drive yourself crazy trying to find one. Second Stan is right about cleaning all your grounds first, always a safe bet anyway. I would almost bet that the WUR inlet screen is clogged. Clogged screen means that it will go lean. I would almost bet that someone in the past has turned the FD adjustment screw towards rich to get it to run, hence the very hot cat. Why it runs sometimes, and not others? I would look into getting some gauges so you can see what was going on with the fuel system first.
just my .02
Mike

 

The ignition resistors near the radiator driver side may be failing that would cut power to the coil BUT when you crank on the starter motor it energizes the coil but only through one resistor...normal run position and power must flow through both resisters in series to drop down the voltage for normal operation.