Hello,

I've got an 86 4000 Quattro CS and every now and then it dies. Like today on the way to work. Then, after sitting a few minutes, it started right back up! When I say dies, I mean the engine quits, but I still have electrics/power and my volts read 13. I try to start it after it dies and it cranks, but won't start unless it sits a few minutes. Any ideas? Could it be the fuel pump or voltage regulator? I have around 13 volts when driving and my headlights don't flicker. Recently, I've had it tuned with a new rotor, cap, wires, plugs, coil and have had the injectors flushed. Do fuel pumps quit and then come alive again? Or could it be something else?

Thanks,

Todd
Annapolis, MD

 

what are the revs running at?? clean the throttle body out and the idle air bypass valve and pipes, check for breaks in any vacuum pipes, ensure the clips on the main breather hose are tight ( check the condition of that rubber air feed pipe )

 

Thanks. It is running around 900 rpms, but I have the sport cam installed. I just had the top end apart for the cam work and a nice used throttle body from a 5000 put on. Also, all my lines and hoses were checked. I'll check them again, but I'm thinking it might be electrical. Also, my front differential green light is on sometimes and off at other times which is probably not related...or is it? And...my horn works sometimes and sometimes does not. So, do I have some bad grounds somewhere do you think? Where would I look?

Thanks,

Todd

 

as its a classic you should be able to alter the timing to advance it a little, your problem seems to be air fuel mix due to the larger 5000 throttle body it might be a good idea to increase the idle to 1000rpm because of this then it wont stumble

 

pity you didn't change the ECU as well this would have sorted the idle problem, im sure they are the same count pin outs but ill check

 

Sorry, I forgot to mention that my timing was advanced 12.5 degrees when I switched to the larger throttle body. The car has run fine since then...about 2 months. But now, it does not stumble from low revs, it dies while driving...while the accelerator is pressed and then after sitting a few minutes, will start again. But first attempts just after it dies are futile. Something is not right. I don't want to have to have it hooked to a diagnostics machine for big bucks only to have them find nothing because it's something else. It will probably die, I'll have it towed and it will start for them and they'll think I'm nuts or say they fixed it and charge me. I just thought someone might have an idea. It's something that causes the entire engine to conk out when on, prevents it from restarting for a while and then changes its mind and lets it start. What else could it be? My idle is fine. My engine runs strong.

Thanks,

Todd

 

I would say fuel air mix due to larger throttle body, when in idle not enough fuel there your ECU cant identify the problem because its set up to the 4000 T/B, you need to do some remapping of the ECU, the 5000 has a larger psi fuel pump feed which has to be taken into account basically you cant just stick the 5000 throttle body on there without the upgrades required

 

Thanks Dave! You know, that could be it. I've been meaning to replace my fuel pump anyway since its age is unknown and I'll just get a beefier one and cross my fingers. Remapping sounds like a dealer only thing, so I'd rather not go there, HA!

 

good luck but if you need any help on the old babies I have the data and knowledge because im an old fart lol