Seeking experts. No spark / no start S38 M5

[airkhin]

Hello!

Im pretty stumped and would like some insight if anyone has any ideas. Im sure I'm missing information as I've gone over most of the car already but will gladly recheck anything at this point.

E34 M5 No start / No spark. Car sat for over a year. "running when parked".

Starter will crank no issues. Pulled plugs are wet / Exhaust smells like fuel. all relays are clicking and all functions are same when jump the main and dme relays under the black box.
Every fuse under hood and under rear seat are in tact and give 12v with function.
Oem bmw/ alpine keyless entry / alarm functions normally
Obc functions normally, am able to set / reset lockout code as normal.
Grounds next to the ecu in the engine bay and under the rear seat have been cleaned. will be replacing the main engine mount ground hopefully in next few days.

Replaced CPS (thinking no pulse signal, but the injectors are fueling? so it must be getting signal?)
Replaced Coil
ECU does not appear to have any cracks etc to the naked eye.

Things I have noticed that I'm not sure of -
Check engine light does not turn off after key is put into acc 2. Always stays lit even if leave key in acc pos for hours.
Unable to do stomp test. tried extensive amount of times, cel never blinks or switches off. always on with the ignition.
Tried the stomp test so many times went and got a Peake 21 pin reader and it shows -- for "no error".
ECU box fan is also always on with the key in acc2, only time I've heard it go off is after an extended period of cranking the motor, and seemed to kick back on.

At this point it leads me to believe there is either something very simple / stupid that I'm missing entirely. Or an immobilizer of some sort or a bad ground / short somewhere in the wiring or ecu. The coil gets 12v with ignition as should (and it has been replaced with no change.)

Greatly appreciate any insight or points in the right direction. Would love to get this beast back on the road!

[Grim Reaper]

Question - Is the code activated/set in the Trip Computer?

You say the keyless alarm functions but what about the kill switch/code in the trip computer?

[demetk]

Jump the main relay and see if it will spark. Have you tested for spark at the coil wire?

[airkhin]

Question - Is the code activated/set in the Trip Computer?

You say the keyless alarm functions but what about the kill switch/code in the trip computer?

Yep, never had a remote for the car so got an oem replacement and programmed it. It locks / unlocks and arms the car with the other button.
The obc has all functions like normal. The code is not set when attempting to start the car.

Jump the main relay and see if it will spark. Have you tested for spark at the coil wire?

Jumping main relay was no change, Coil did not spark when put a plug into the wire and put to ground. bought a new coil and same results.

[Grim Reaper]

Coil wire continuity?

[Grim Reaper]

I'd be highly suspect of the alpine alarm....

[Jackson42]

Do you have battery voltage at the (+) terminal of the coil when the key is in the "on" position? If you connect a DVM between the (-) terminal of the coil and ground, you should see it fluctuate when you are cranking the engine if the DME is trying to make spark (this presumes you have battery voltage at the (+) terminal). Make sure that DVM will safely handle a DC voltage up to around 500V, because the flyback voltage across the primary of the coil can get that large. I second Grim Reaper's suspicion that somehow the disarm code in the trip computer is set.

[airkhin]

I'd be highly suspect of the alpine alarm....

coil replaced with new.

is there a easy way to delete/bypass the alarm that you know of? greatly appreciate you chiming in on this.

[airkhin]

Do you have battery voltage at the (+) terminal of the coil when the key is in the "on" position? If you connect a DVM between the (-) terminal of the coil and ground, you should see it fluctuate when you are cranking the engine if the DME is trying to make spark (this presumes you have battery voltage at the (+) terminal). Make sure that DVM will safely handle a DC voltage up to around 500V, because the flyback voltage across the primary of the coil can get that large. I second Grim Reaper's suspicion that somehow the disarm code in the trip computer is set.

i don't have a helper to crank it over tonight but will give it a shot. forgot to mention I tried another obc unit few days ago sorry.

[squirrelhill]

Could it be a failed coolant temp sensor (blue sensor) causing the engine to flood? The sensor is relatively inexpensive, easily accessible on the s38 and may be worth a try.

Also, when I had no-start/flooding issue on my e34 touring, it turned out to be a combo of a bad fuel pressure regulator and leaking fuel injectors. When the engine flooded, I had to clear the excess fuel by pulling the fuel pump fuse and starting the car a couple of times. I would then replace the fuel pump fuse and the car would start as normal. A new FPR and new injectors solved the problem completely.

[airkhin]

Could it be a failed coolant temp sensor (blue sensor) causing the engine to flood? The sensor is relatively inexpensive, easily accessible on the s38 and may be worth a try.

Also, when I had no-start/flooding issue on my e34 touring, it turned out to be a combo of a bad fuel pressure regulator and leaking fuel injectors. When the engine flooded, I had to clear the excess fuel by pulling the fuel pump fuse and starting the car a couple of times. I would then replace the fuel pump fuse and the car would start as normal. A new FPR and new injectors solved the problem completely.

I don't believe its a flooding issue as there is no spark coming from the plugs or the coil during cranking. Fuel is plentiful just no spark. Will order a new coolant temp sensor anyways for maint. Thank you.

[airkhin]

Well, no further than was before:

New coolant sensor
New coil
new cps
new engine ground wire
cleaned all other grounds in engine bay and under rear seat. (if there are other hidden ones know of I'm happy to go clean them. )

Everything as far as power wise seems to be functioning coil and all. Just not receiving a signal or spark at the coil or the plugs. Fuel and every function in car seems normal and functioning otherwise. Am learning more towards ecu at this point unless any one has another idea i can test?

Is it normal for the check engine light to always be on during acc 2 pos? I am unable to get stomp test to work and peake II shows no errors at the 21 pin round connector. When i cycle key to acc 2 before start the motor the cel goes on and never flashes or changes or anything, even during cranking; always light is on. the rpm needle does not bounce or imitate motor rotation.

Anybody have an ecu in norcal can test?

[demetk]

Will a 179 ecu from a b35 fit?

[airkhin]

Will a 179 ecu from a b35 fit?

Thank you but I don't think it will run the motor that I am aware of. although if it even gave a spark signal that would be already a step in narrowing it down further... 0 261 200 350 Is the number on mine. Bosch black label.

[demetk]

Looking at the wiring diagrams yours has a MAF and the b35 has an AFM so probably not.

So your coil has 12 volts at the green wire? Is there any way to disconnect the Alpine alarm?

[airkhin]

both the screw terminals at the coil and the center coil pin that goes to distributor all get battery power voltage when key is in pos 2.

unsure of the alarm, I've tried disconnecting it, removing its fuse and still no change other than no power locks with keyless (obviously). car cranks the same etc with it plugged in or removed. at least from what I can tell...

[demetk]

I would verify all of the power inputs directly at the dme. Also when you jumped the main relay did you jump 30 to both 87 pins?

[airkhin]

Main relay replaced with new. Will try to check all 12v signals at dme pinout today hopefully

[demetk]

One more question, does the new main relay have the exactly the same pin numbers and pin orientation as the old one?

[airkhin]

yep same pin orientation and numbers, oe replacement bosch relay just newer revision. will also be getting an oem unit in next few days hopefully just to rule anything out at this point... thanks

just weird as it seems everything is getting power and ecu is giving signal for fuel injectors (wet plugs), but there is no fire happening from sparks even though coil has power to it?

when you turn key to pos 2 does the check engine light normally shut off/ cycle after a few sec? or is it always on until car is started?

[demetk]

On my b35 the check engine light stays on until the engine is started.

If all else fails you can always check the output transistors in the dme (ecu).

Does the harness have two connectors side by side, one for the CPS and the other for the cylinder identification sensor?

[airkhin]

Perfect, didn't know if was something I was missing there with light always being on.

yes 2 connectors side by side just as described, and I have verified that they are plugged into correct harnesses.

I'll be researching more into the transistors in dme now thank you. Greatly appreciate the replies and help!

[jhower08]

I know it's going to sound stupid, but pull your distributor cap off and check for corrosion and/or condensation. When I first bought my m5, it had an issue if it sat for an extended period of time, it'd have a hard start and running issue until warmed up. Finally pulled the cap and found it completely wet inside from condensation. Replaced it and haven't had an issue since (nearly 3 years).

Jason

[airkhin]

Cap and rotor both look clean / recently replaced but I have no history on them; already ordered new replacements. Hopefully will have more updates for you soon as they arrive...

[Grim Reaper]

Have you pulled a plug and verified with a spark light that each plug is actually firing?