nize

hi guys, i have an issue where the car will run fine for a day or so, the engine will suddenly and abruptly die, regardless if the gas pedal is depressed or not.. when it dies it will not start, not even after the engine has cooled overnight.

after it dies, the car will crank but not start. when i checked for spark there is no spark. the DME engine fault code shows no fault.

after about 2 or 3 days (or sometimes longer), it will suddenly start right up and run perfectly fine for another day or so like nothing happened, and then die again.

when it dies, the rpm does not seem to matter as it has died while idling and also died while driving down the freeway at 4000rpm. there is plenty of oil pressure so that is not an issue.

in chasing this issue, the distributor, rotor, wires, plugs, coil, and o2 sensor have all been recently replaced with new components.

i've also recently replaced the coolant thermostat because i had heard it plays a role in determining a/f mixture. no change in behavior and the engine still dies seemingly randomly.

i have since replaced with new components;
1. fuel pump relay
2. fuel filter

i've removed the dme and opened it up to inspect it and could not find any obvious signs of damage, no burnt resistors or leaking capacitors. i haven't thoroughly checked for cold solder joints, but could this be an issue?

any suggestions would be greatly appreciated!

RallyCV

Crank positon sensor could be on it way out. The ecu needs to see the crank and cam position before it will fire the coil. Is the plastic shield in place on the distributor between the rotor and trigger wheel?

nize

can you tell me where the crank position sensor is located? can it be accessed from the top or do you have to get to it from the bottom?

the plastic shield is in place between the rotor and trigger wheel.

thanks for your response and suggestions!

audiqv8

Is your 5000s quattro, turbo or non turbo? Crank and speed sensors were only used on the turbo model. A bad speed sensor will cause an engine to die while running; but a bad crank sensor will only cause an engine to not start, but once started a bad crank sensor will not cause it to die.

Both crank and speed sensors are magnetic sensors and as we all know from high school physics, a magnet loses its magnetic properties one it becomes hot.

nize

1988 audi 5000s quattro is a non-turbo. does this mean there is no crank sensor on my car? if it's not the crank sensor, what else could it be?

RallyCV

I think I meant to say the cam sensor in my post before. The cam sensor is in the distributor, the crank sensor would be on the top of the bellhousing if its there.

Start with the testing laid out here:

http://www.sjmautotechnik.com/troubl...g/nostart.html

audiqv8

Your engine code is designated as NF as opposed to MC for the turbo model. You have both an ignition control module and also a fuel control module. Check ground wire to the ignition module. Also clean up the connector to the ignition module. You will need an electrical schematic to determine all the ground(s) used by both ignition and fuel control module to verify that they are good. After all this car is well over 20 years old.

for more help go to the following link for NF engine.

http://www.sjmautotechnik.com/troubl...g/100ecuf.html

nize

audiqv8; thanks for the link to the ecu fault code testing. i've already checked the fault codes and it shows 4-4-4-4 which means it does not detect any fault.

do you know if the ignition module is connected to the same bracket as the distributor coil? i recently replaced the coil with a brand-new bosch unit and it seems the bracket where it connects to the engine/ecu is the ignition module. if it is, and it's connected to the same bracket, it replaces with the coil so it's a new unit as well.

i'll verify all the connections and ground are clean. thanks.

audiqv8

I don't know what you opened (DME) perhaps the TCM (Transmission control module or if you have anti-lock brakes the ABS module), but the ignition module looks like the following link. See RockAuto.com for more info.

http://www.rockauto.com/catalog/moreinfo.php?pk=480483

audiqv8

The ignition module is located underneath the windshield rain shield. Raise the hood and at the bottom of the windshield you will see a black plastic shield used to keep the water from entering the car. Remove the plastic rain shield and you will see the ignition module.