m10 troubleshooting

[Erick]

How's it going guys?

I recently purchased an M10 318i that I saw a project daily driver, however I havent had much luck finding info for it.

I purchased the car with a starting issue. The car cranks, stays on for a second and dies. Then it does not crank again for a short period of time whatsoever.

My friend has my Bentley and I have no means to pick it up so for now I have to work with this Haynes manual I have. The Haynes gave me troubleshooting tips for "Engine Starts but Stops Immediately", however it doesnt explain where can I look for these ideas, such as the fuel injector system fuel sensors or the fuel injection relays.

I am new to the whole m10 deal and I dunno what is where. I look at the fuse box and I have no idea which relay is which, and I dont know where fuel injection speed sensors are.

So any help.... pics or anything like that would be appreciated.

Thanks,
Erick

[James Crivellone]

Sounds like its only running on the cold start injector, check the fuel injectors and make sure your getting fuel.

The ECU does not control spark on that car also FYI, its managed by a little box on the firewall near the fusebox, this is what controls all spark.

The ECU just watches RPM/Fuel and Pulses the injectors.

[Erick]

Interesting.... wow. L-jetronic is really that primitive huh

[Propwash]

Sorry to drag this one up after so many months, but this is EXACTLY what my car is doing! Did you come to a resolution? Ive replaced all 3 temp related sensors, my afm is good and I have hot spark. Why would it only fire the cold start injector?
Thanks!

[Erick]

It was the fuel pump. Both my pumps went bad in a 3 month timeframe. Test for either pump to see if they are working.

They are fairly easy to replace but can get expensive. So test everything you can before you drop he dough on a pump.

1-) Check fuse #11. If it's bad replace, if not keep reading

2-) Disconnect the fuel return line from the fuel pressure regulator. Put a bottle (to avoid spills) at the FPR and try to start the car. If fuel pours out of the FPR, you are having no problems with fuel. If that's the case then:

2a-) Check for spark: Disconnect a spark plug and stick a screwdriver down the plug. Try to start the car and see if sparks come out from the plug. Since the spark plugs and the key ignition are kinda far, have a friend help you.

2b-) If no fuel came out of the FPR, it's fuel related. Turn the key to the ON position. You should hear the external pump come on. It's a humming sound coming from under the driver's door..... If not, turn key off.

3-) Locate fuel pump relay. It's in the engine bay on top of the driver's wheel well. It's inside a small plastic box cover that slides upwards. It'll be the one on the left (closest to the headlights). With the key off, remove the relay and jump the terminals 30 (I think.... if you look under the box, which slides upward, it's the one with the thick red wire) and 87b. You can jump the relay with a piece of wire or even a paper clip.

4-) Turn key in the ON position. If you hear the humming now... it's the relay. I forgot the godforsaken part number but you can look it up at realoem.com. I bought one and it cost me like $30 brand new. I should have a spare good one if anything.

5-) If all else has failed, you just have to narrow it down to which pump is it. If you heard the humming at any point (and its fairly loud, you can hear it when sitting in the car with the door open) then it should be the internal pump. If not, it's probably your external pump.

I am saying all of this off the top of my head, so I'm probably off here and there. Report back with your findings and if anything IM me. I'll be glad to give you some help.

- Erick

[Propwash]

Ok, i have hot spark, I have fuel pressure like crazy (new external pump), the relay is good, i even did the jumper wire test and it operated correctly. It seems like the cold start injector fires but then the rest of them don't pick up where it left off. Could this mean a bad ECU? I don't think the internal fp is bad b/c I have ample pressure.

[chuckybob]

check the resistance across the injector terminals, it should be around 14.7 ohms, i think its +-1ohm tolerance. then check the input voltage to the injectors, it should be around battery voltage (mine's 10.xx and it still runs fine though). if the first test fails, its the injectors, if the second test fails, its the ecu. if neither fails, it could be clogged injectors. you can listen for the injectors opening and closing with a mechanics stethoscope.

[Propwash]

It was the dme!!! Who knew!!?? lol
Thanks for the help everyone!