[Noahbleek]

I recently pulled and resealed my entire engine(m104) and transmission, and afterwards it idled great. However, it would not rev beyond 4000 rpms. I believe this is a throttle body gasket issue, as I did not properly remove the old gasket due to it being stuck on. After a few weeks of driving the car occasionally in this state, it died on the road while going around 35mph. It cut off as though it was a fuel issue, so I tested my pumps. They did not seem to turn on when jumped with a battery, so I replaced both. Now, when I attempt to start the car it cranks and fires/runs for just a moment, then dies in about 1/3 of a second. I know it has fuel, spark, and air so I think it might be a sensor of some kind. While I have replaced the upper/"main" harness, I have not yet replaced the lower (starter) harness. I don't know anyone with expertise on these cars, so I would appreciate any help on getting the car running again.

 

[plinker17722]

Noahbleek Welcome i can see you have found your cars section W124 to post in ⭐ .Thats good .
Next step is for you to fill in your profile ..this is the section under your name on the left hand side .
Use this link to take you there -> Complete your Profile to give you some idea what is needed ,you can take a look at other members profiles .
There is a lot of W124 owners ready to help you sort out you car .

.

 

[tuttebenne]

There can be a difference between having fuel present and having fuel misting out of the injectors. One condition will not be too very good, the other is a quality of a good running engine. Have you confirmed that fuel is squirting out of the injectors when this problem occurs? Let's start there.

An easy way to do this is to see how long the engine will run if you are spraying starting fluid into the intake. If it runs for more than five or ten seconds with you spraying intermittently, you have a fuel issue.

 

[Floobydust]

^ Yes (you beat me to it ).

A question: Does your tach show RPM during the short time the engine is running? The fuel pump relay is controlled by the ECU. At key turn on, the ECU closes the relay for a few seconds to "prime" the fuel rail for faster starts. After the engine starts, the ECU needs to see an RPM signal from the CPS to keep the relay energized. Something may be wrong with this so I think your engine is running off the priming fuel pressure which should last just about that long. If you tach does not move, then there is a problem there (unfortunately that points to a damaged ECU).

You posted that you had jumpered the pumps to battery previously. Do that again and try to start the car. If the car runs, your issue is somewhere as described above.

You can try replacing the fuel pump relay, but that is a long shot. Unlike earlier cars in which fuel pump relay detected the RPM signal, the relay in the later cars is just a heavy duty dumb relay controlled by the ECU.

Another long shot is to remove the Klima relay (behind the battery). This module also gets the tach signal so a failure internally could "short out" the whole tach signal line.