M20 Injectors Not Firing

[lennon325]

M20B27 injectors not firing.

Sparks fine so I assume the DME has good reference input (2 bellhousing sensors).

Cold start valve works great and car runs off that for a second.

Fuel pressure is good.

No vacuum leaks (smoke tester).

I have 12v at both terminals of each injector. Injectors 1,2,3 have continuity to pin 14 of the DME, injectors 4,5,6 have continuity to pin 15 of the DME (as they should).

This engine/DME/harness was all working fine before pulled from the car it came out of.

What could it be? I opened the DME, and I see no damage. I know it could still be damaged.

I've tried jumping the fuel relay and main relay, no difference. The fuel pump is running as it should with the relay anyway.

I've tested all the ground pins in the DME plug, they're good. Tested the power inputs, they're good.

[D. Hitchcock]

I'm stumped!

Had a similar situation just after installation of a rebuilt short block in my e30. 1,3,5 were not firing like yours. The others were firing and the car was trying to run. But we weren't getting electricity to the dead injectors.

Turned out the big connector under the intake manifold had gotten pulled on and loosened to the extent that there was only a marginal connection. Cleaned and reinstalled everything and vroom vroom.

Good luck,
d.hitchcock

[lennon325]

Yeah, the early model engines like this one don't have that connector. The fuel injector harness is part of the main harness. Connection to the DME seems good. DME isn't firing 'em though.

[thejlevie]

I'd try a different DME at this point as a diagnostic. If you have a known good spare on hand that is the fastest check of the DME. Lacking that I'd check the rail fuel pressure when cranking and check for an injector firing pulse with a noid light.

[lennon325]

I just don't have a spare eta DME available right now. Buying one from the junkyard is iffy, especially when I'm not sure it'll fix my problem.

[spdracrm3]

haha dont assume, i suggest checking both reference sensors (inductive pulse senders) in bellhousing as these are the signals the ECU needs for spark and injection control. you can ohm test them initially (spec is 540 ohms plus/minus 10%) also check connector integrity ,after that you will need a scope of some form to watch patterns and output strength @ ECU if you have good inputs from sensors (both) and good grounds/powers and you already check wiring integrity to injectors you have an ECU problem.

also did you remove the senders and re-install them in the wrong positions? also is flywheel correct?

do you have spark at all plugs or just at coil?

[lennon325]

I have spark at all plugs. I will test the reference sensors ohm reading, but i don't have a scope to watch their output.

[lennon325]

reference and speed sensors ohm out to spec in bentley. sensors are hooked up to the proper plugs. flywheel never changed. sparks everytime.

[spdracrm3]

sure is starting to seem like a ECU problem ,other than scoping those sensors only other thing i can think of that might stop injector fire is if it had the 13 button OBC that had a code set in it and might disable inj if ECU does not receive input from OBC(not sure how that security featured worked inside the ECU ,if it cut fuel or spark or both) on the E30M3 the code relay controlled power to coil and main relay (which supplies power to ECU)

how are you checking inj pulse ? do you have a noid light? does the check engine light come on koeo?

you will have power +12v to both sides of injector until grounded by ECU, this is normal as the voltage flows thru the inj windings ,but you need to be able to see that millisec grounding with a noid light or scope

your sure you have all the 12v power inputs to ECU?

[lennon325]

yes, i am checking the injectors with a noid light. the noid light is known working as i have tried it on other vehicles.

no check engine light on this 1986. no 13 button OBC/security.

12v to both sides of the injector.

the ECU only has two power inputs that i know of and i have power at both. also have good ground at all the ECU ground pins.

[thejlevie]

If you have spark and a noid light isn't indicating firing of the injectors, the cause has to be the wiring harness or the DME. Personally, I'd try a a different DME before I changed the harness.

[lennon325]

Yeah, I'll be picking up a DME or 2 at the junkyard tomorrow. It's just a little hard for me to accept that it went bad out of nowhere while sitting in my house. Even though all tests point to that. Hopefully it fires up tomorrow with a different DME!

[jaysee]

hey sorry to bring up a old thread but did you ever fuigure out your problem with this?
i has the same year same car and mine is doing the exact same thing, even ordered a new ecu and it didnt fix my problem

[Bimmerman4ever]

hey sorry to bring up a old thread but did you ever fuigure out your problem with this?
i has the same year same car and mine is doing the exact same thing, even ordered a new ecu and it didnt fix my problem

I'm wondering too. I've run across many threads started on different forums. Yet no one had come up with a solution or even a follow up.

[christopherq398]

Did anyone find a solution to this????