One injector not firing

Sat Mar 12, 2016 11:59 am

Engine is a 1998 M44 (it's in an E30 xD) which I've swapped into the car recently. The car had a running M42 in it before that.

Car starts on the turn of the key but only runs on cylinders 1,2,3 but not 4.

There is spark on all 4 cylinders and compression in all 4 cylinders..

There is no fuel getting to cylinder 4. I've swapped injectors 1 and 4 and then 3 and 4 and the problem remains. The car still runs on 3 cylinders.

There is 12 volts to each injector and when I measure the voltage across the connector it reads about 6 volts. This is the same for all 4 connectors.

I hooked up a bulb and cranked the engine. Both injector connector 4 and 1 make the bulb pulse. There maybe the tiniest difference with connector 4 being weak.

Obviously something is not right here.. I've double checked my main earthing points.. Thoughts, ideas..?

Cheers

Sat Mar 12, 2016 3:32 pm

mcspike wrote:There is no fuel getting to cylinder 4. I've swapped injectors 1 and 4 and then 3 and 4 and the problem remains. The car still runs on 3 cylinders.

does the not firing follow the injector? can you hear the suspect injector clicking?

Sat Mar 12, 2016 5:31 pm

When you get your injectors cleaned by Injectortune, they say if 1 is sticking it can be freed with a little tap from a screwdriver or something.

Sat Mar 12, 2016 7:05 pm

Its not the injector, hes swapped them around its still the same.

loose connection on inj 4 wiring, trace the injector loom, clean any plugs in goes through.

the live is permanent ignition fed from the main relay (all 4 injectors are connected together), the earth of the plug pluses from the ecu, each injector will go back to the ecu separately, if the others are firing it wont be a main earth. (ECU uses earths directly from the battery)

its deffo a loose connection or a broken/damaged cable in the loom.

Sat Mar 12, 2016 10:56 pm

he said its still the same not that its in cylinder 4 still ? did the injector from four work in 1 ? if so id say its a wiring issue or possibly ecu?

Sat Mar 12, 2016 11:23 pm

It read to me, that the problem was with cylinder 4? The OP didn't say if the misfire followed the injector when he swapped them around.

Sun Mar 13, 2016 10:25 am

Thanks for the replies. Yes the problem remained on the same cylinder after swapping injectors twice.

Is it right that there is 6 volts across the connector for the injector with ignition on but no cranking? I don't recall checking continuity with ground from the switched earth but will do..

I'm working today but free tomorrow so will double check all the switched earth's to the ECU...

I suppose I'll try the cylinder 3 injector wire on cylinder 4 and see if that fires any fuel also.

Sun Mar 13, 2016 10:32 am

Wen running you should have 12v plulses . Measure from the battery + to the - on injector plug. Should be the left prong on the injector (looking into it).

If you tester cant keep up it may look like 6v.

It may test fine , but not be enough strength.

Id be checking the wiring.

Sun Mar 13, 2016 10:37 am

Your measured voltage, if I'm reading it right, suggests an ECU fault - the driver for that injector is leaky, and will possibly overheat and damage the injector if left in that condition for long.
Your injector wire swapping idea is good, if the loom arrangements allow it. It doesn't really matter when an injector fires, as long as it fires sometime between every two turns of the crank.

Sun Mar 13, 2016 10:41 am

Brianmoooore wrote:Your measured voltage, if I'm reading it right, suggests an ECU fault - the driver for that injector is leaky, and will possibly overheat and damage the injector if left in that condition for long.
Your injector wire swapping idea is good, if the loom arrangements allow it. It doesn't really matter when an injector fires, as long as it fires sometime between every two turns of the crank.

Are they batch fired or sequential?

Sun Mar 13, 2016 7:49 pm

_Dan_ wrote: Are they batch fired or sequential?

They're individually wired on a M44 (AFAIK), so can be sequentially fired, if the ECU so decides.

Mon Mar 14, 2016 2:27 pm

Some follow-up

I swapped injector wiring #3 onto injector #4 and I get fuel spraying in cyl #4.

I also checked for continuity with the engine running between earth and the earth wire #4 injector (so checking that the ECU is switching the ground for the injector. The multimeter beeps as if it should be firing the injector.

The engine still runs on a consistent three cylinders with no difference when you pull the coil off cyl #4..

Does this leave me in the position where the fault is almost certainly with the ECU's injector driver?

Logical step would be to find another person with an M44'd car and try the ECU on that? It's had the EWS deleted so it shouldn't be a problem..

Mon Mar 14, 2016 3:10 pm

mcspike wrote:
Logical step would be to find another person with an M44'd car and try the ECU on that? It's had the EWS deleted so it shouldn't be a problem..

Probably your best bet, or buy an ecu probably a cheap one on flebay

Mon Mar 14, 2016 3:35 pm

Well... if anyone knows of an M44'd car somewhere in the mid Wales / English border area please put me in touch with them.

I can't just buy an ECU because the EWS on it will not even let me turn the engine over..

Sat Mar 26, 2016 11:15 am

Update! So I got hold of a replacement ECU, swapped that in and the problem is still there.

If you turn the engine over with no spark plug in cylinder #4 it doesn't push any fuel out. If you hook up the power for a different injector and do the same you get fuel spray pushed out of the cylinder.

Engine still runs consistently on 3 cylinders, has spark for all 4 but the engine sound does not change when you pull coil #4 off the plug.

I wired power direct from the battery to the injector and back to the ECU which didn't help anything.

I'm slightly out of my depth at this point, I think! Any further suggestions or possible points of failure for the system?

Short of stripping the intake side down again and poking around for things im not sure where to investigate next. I really don't want to hand it over to my local garage and admit defeat!

Sat Mar 26, 2016 2:30 pm

If the ECU is known good, and the injector and plumbing to it is known good, I can't see how it can be anything else than the wiring between them.
There is one other possibility - that an unknown electrical fault is damaging the ECU.
It would be useful to try one of your ECUs in another car.

Sat Mar 26, 2016 4:07 pm

Thanks, Brian. Your help is much appreciated!

I'm happy that my suspicions were correct but

for fucks sake what could it be then! I guess I'll strip down the intake side, have one more look over that and test that my makeshift injector wiring works on one of the other injectors.

Failing that I might just source another engine... likely cheaper than taking it to a garage and I'll have spares. .

Sat Mar 26, 2016 11:59 pm

yea i deffo say its the wiring between the ecu and injector, be worth doing a resistance test on the injectors to see if there's high resistance as you can always get voltage but current wont flow properly if there's high resistance in the wiring which i reckon you will find your problem.