325e starts and immediately dies

[wodcutr]

I am trying to diagnose a problem with an 86 325e. The car starts and runs for about 1 second and then dies. I can hear the fuel pumps running after it dies and I can feel the fuel going through the fuel lines where it goes into the rail and out through the FPR. It obviously is getting spark because it runs for that split second. If I turn off the key the fuel pumps turn off and will not come back on until the car is cranked over again. If you try to start the car again immediately after it dies it won't fire up, it just cranks. If you wait about two minutes it will catch again for that one second.

Could this be a crank sensor? I thought the e crank sensor did absolutely nothing as it goes directly to the diagnostic port.

Could this be the FPR? Maybe the rail is not getting enough pressure and all the fuel is just being pumped around back into the tank.

Would an ECU cause a problem like this?

It just seems to me to be a fuel issue, but I know both pumps are running and I can even get a whiff of gas smell when cranking so maybe too much fuel.

I thought about the AFM and disconnected it to see if the car would run without it, but it did the same thing.

I swapped relays just to be sure that wasn't the problem and like I said the pumps are running after it dies and don't turn off until the key is turned off.

Also bought a new main relay and that did not do anything either.

Could my idle computer be bogus?

Any thoughts or suggestions would be welcome. Thanks!

[wodcutr]

The Bentley says that in order for the fuel pumps to continue to run it has to have a signal from the speed sensor. My fuel pumps continue to run after the car dies and for a few seconds after the ignition is turned off. I am wondering if maybe the ignition switch is the problem because the car starts and as soon as you let the key off the starter position it dies.

[PoloRL57]

i know this is stupid but maybe your outta gas?

[bmwguy325is]

SO if the idle CPU is dead give er some gas see if it runs above idle.

[wodcutr]

i know this is stupid but maybe your outta gas?

I thought of that even though the gauge said the car had 1/4 of a tank. Added fuel and gauge went to 1/2 and car acted the same.

After doing some further thinking on this I reasoned that the ECU had to be the problem because the fuel pumps are not supposed to run unless the crank is turning. I tested this on another car to confirm by pulling the coil lead and cranking the car to see if the pumps started and then kept running after the starter was released. The pumps stopped pumping. This meant that the ECU had to be the problem as it is the only thing that controls when the pumps come on. I swapped in a different ECU and it fired right up and ran perfectly.

Now I have to figure out why the ECU failed. The owner said that he had not jump started the car and crossed the leads as I had suspected so I am wondering if maybe a bad voltage regulator could cause high enough voltage to fry a computer. What are the odds that the ECU just decided to give up the ghost?

[ScHpAnKy]

if you give it throttle does it rev up and still die? If so, sounds like you got a vaccuum leak

[russianman92]

Hmm the only time ive had my car do thwt is when I took out my idle control valve and forgot to put it back in lol started for 1 second then died. Huge vaccium hole