86 325es fire no start

[Landon325es]

If anyone could help that’d be great, I have a 86 325es I’m getting spark and fuel and all 6 cylinders have great compression, but when I try to start the car it fires once or twice then continues to turn over. I got the car a year ago and feel like I’m sooo close to getting it running I have a video of it trying to start just couldn’t figure out how to post lol any help would be great if you can help me get this thing running you’ll be my hero

[ZeKahr]

Check your reference sensor. There are two sensors on the driver-side transmission bell housing, one engine speed and one reference. These sensors control ignition timing. The DME needs a reference signal in order to keep the engine running after cranking. The engine should run with a working reference sensor and faulty speed sensor, albeit it will misfire

[Landon325es]

Check your reference sensor. There are two sensors on the driver-side transmission bell housing, one engine speed and one reference. These sensors control ignition timing. The DME needs a reference signal in order to keep the engine running after cranking. The engine should run with a working reference sensor and faulty speed sensor, albeit it will misfire

This would be the Crank position sensor right? From what I’ve read If that was bad wouldn’t the engine not fire at all since it wouldn’t be getting spark or fuel?

[ZeKahr]

This would be the Crank position sensor right? From what I’ve read If that was bad wouldn’t the engine not fire at all since it wouldn’t be getting spark or fuel?

On 325e (or 325) cars (i.e the M20B27 engine, which you have, unless you did an engine swap), the sensors I’m referring to are not called “crank position sensors”. That’s only the case for the 325i/is/ix cars (i.e the M20B25 engine). You have two “crank position sensors”, called the “speed” and ”reference” sensors.

[82eye]

also do you have a 13 button obc ?
they can cause all sorts of issues. i keep forgetting about that thing. there is an immobilizer in the thing that can cause issues. a lot of folk aren't aware of them. i wasn't and neither was the PO of my car.

OBC Immobilizer Bypass - R3VLimited Forums

[jbontke]

This would be the Crank position sensor right? From what I’ve read If that was bad wouldn’t the engine not fire at all since it wouldn’t be getting spark or fuel?

Correct, if you have spark, the sensors are working. Since you know you have fuel, I would check the pressure to be sure the pumps and regulators are working correctly. A quick test would be to pinch off the return fuel line while having someone crank the engine. If it runs, it's a fuel pressure issue. I had a strange one like this turn out to be a bad hose connecting the fuel pump to the fuel cradle feed line.

[82eye]

Correct, if you have spark, the sensors are working. Since you know you have fuel, I would check the pressure to be sure the pumps and regulators are working correctly. A quick test would be to pinch off the return fuel line while having someone crank the engine. If it runs, it's a fuel pressure issue. I had a strange one like this turn out to be a bad hose connecting the fuel pump to the fuel cradle feed line.

not quite

reference sensor is spark, speed sensor is fuel. you can start the car with a bad / poor speed sensor. you can't start the car with a bad reference sensor. bad reference sensor pulls spark. fuel cuts when the engine stops rotating. on an e the fuel and spark is separated, the car will have a cold start injector which requires fuel and fires independent of the main banks.

the tell is a no start with wet plugs from fuel. car will sometimes struggle and catch on the cold start injector then either fail or die immediately.


it's different on an i or late super eta.

edit : reference and speed sensors should be replaced together in pairs. you can also swap them to test. they are the same. if you suspect one, replace both, if both are faulty you'll go stupid nuts trying to figure it if you only do one. they fail about the same time.

[jbontke]

not quite

reference sensor is spark, speed sensor is fuel. you can start the car with a bad / poor speed sensor. you can't start the car with a bad reference sensor. bad reference sensor pulls spark. fuel cuts when the engine stops rotating. on an e the fuel and spark is separated, the car will have a cold start injector which requires fuel and fires independent of the main banks.

the tell is a no start with wet plugs from fuel. car will sometimes struggle and catch on the cold start injector then either fail or die immediately.

Do you have any literature on how the Motronic 1.1 uses the speed and reference sensors? I can't find anything concrete and go by only what I have found in the past (referring to step 8) like: https://hpsimotorsports.com/blogs/te...n-tech-article

I don't want to post wrong information.

[82eye]

Do you have any literature on how the Motronic 1.1 uses the speed and reference sensors? I can't find anything concrete and go by only what I have found in the past (referring to step 8) like: https://hpsimotorsports.com/blogs/te...n-tech-article

I don't want to post wrong information.

i'll see if i can find it. i got burned chasing the speed and reference sensors a few years ago getting a car going.

edit : actually it eludes to it in that article. if you dig through the e30 etm you'll see the path for the reference and speed sensors as well.

more edit : i said - fuel cuts when the engine stops rotating - which is an incorrect oversimplification. it actually cuts when the dme does not see the rotating engine signal from the reference sensor. the engine could continue to turn but the plugs aren't firing. i felt it was important to note. spark is still pulled ahead.

[Landon325es]

i'll see if i can find it. i got burned chasing the speed and reference sensors a few years ago getting a car going.

edit : actually it eludes to it in that article. if you dig through the e30 etm you'll see the path for the reference and speed sensors as well.

more edit : i said - fuel cuts when the engine stops rotating - which is an incorrect oversimplification. it actually cuts when the dme does not see the rotating engine signal from the reference sensor. the engine could continue to turn but the plugs aren't firing. i felt it was important to note. spark is still pulled ahead.

so how would I diagnose this and fix it? Seems like you had a similar problem howd you go about it? Thanks!

[Landon325es]

also do you have a 13 button obc ?
they can cause all sorts of issues. i keep forgetting about that thing. there is an immobilizer in the thing that can cause issues. a lot of folk aren't aware of them. i wasn't and neither was the PO of my car.

OBC Immobilizer Bypass - R3VLimited Forums

I do have a 13 button obc up by the Sun roof how do you go about seeing if that the issue

[82eye]

so how would I diagnose this and fix it? Seems like you had a similar problem howd you go about it? Thanks!

we got the car running after diagnosing and replacing the reference sensor, but it ran like garbage until we swapped out the speed sensor.

I do have a 13 button obc up by the Sun roof how do you go about seeing if that the issue

that's a check panel. the obc is beside the radio. you might have a clock in that spot.

[packratbimmer]

I do have a 13 button obc up by the Sun roof how do you go about seeing if that the issue

The 13 button harness can easily be bypassed behind the radio for troubleshooting purposes and yes, the 13 button module can cause a no-start. I have never known the 13 button to cause a running problem, but?

• My no-start experience was on a 1985 325e
• When I refered to a module above, I was speaking about the rectangular cuboid "relay" box that mounts above the driver's left knee

[Landon325es]

The 13 button harness can easily be bypassed behind the radio for troubleshooting purposes and yes, the 13 button module can cause a no-start. I have never known the 13 button to cause a running problem, but?

• My no-start experience was on a 1985 325e
• When I refered to a module above, I was speaking about the rectangular cuboid "relay" box that mounts above the driver's left knee

How did you fix the no start? I know some people jump that relay box not sure the best way to go

[Landon325es]

we got the car running after diagnosing and replacing the reference sensor, but it ran like garbage until we swapped out the speed sensor.




that's a check panel. the obc is beside the radio. you might have a clock in that spot.

My mistake I do have the obv beside my radio how do I know if this is the isssue?