2.7L Injector Electrical Issue

First post. Hello everyone.

Just did the head gasket on my 98 2.7L.

Got everything back together and fired it up and got misfire on cyl 4 code. It was running rough similar to this before the head gasket, so I don't think it's related to that unless I hooked up something wrong.

Anyway, swapped coils, same thing. New plugs, same thing. New plug wires, same thing. Swapped injector 1&4, same thing.

Put the multimeter on injector plugs (harness side, not the injector itself) and checked voltage. 1,2,3 all read very minor voltage while pulsing, and none at all while the key is just in accessory position.

#4 reads essentially battery voltage all the time while running or while key is in accessory position.

From my understanding, the injectors are grounded and the ecu pulses the ground to inject to fuel. It's like #4 isn't grounded. The fuel injector grounds are bolted to the #1 side of the intake manifold. I cleaned them all and made sure the connection was good.

Pulled the glove box and looked at ecu connection and see the brown grounds and injector wires. All seem fine there.

I think I've narrowed it down to a broken ground somewhere in the harness, or a bad ecu. I don't know how to check either of those. If there is a broken ground in the harness, running another and connecting it before it goes into the ecu seems simple enough.

Any other ideas? Could I have hooked something up wrong? Thanks for any help.

 

See the wire colors that go to the ECM. Looks like R-L is for injector 4. I believe that is Red-Light Blue. I would start by checking continuity between pin 1 on the injector and the matching pin on the ECM.

 

Red-light blue is correct.

Checking for continuity on this will look for a broken wire (R-L) ?

Is the R-L the ground?

Sorry if the questions are dumb, but I'm not very good with electricity/wiring.

 

R-L > ECM > ground. The R-L grounds through the ECM and does not go straight to ground.

So looking at the diagram I posted, the triangle labeled EB is a ground point. Ground points are usually labeled with 3 horizontal lines. So you can see the injector wire goes into the ECM and is connected to that ground via the ECM and functions exactly as you described by pulsing connection to that ground. The B-R wire on the other injector pin is connected to the ignition circuit. This should read 12v.

 

R-L passed the continuity test, so the wire isn't broken.

I checked pin 1 on the injector connection to the Ecu plug where the wire ends.

What would be the next steps in diagnosing?

 

Check continuity between R-L and ground. I don't believe it should be grounded with the engine off.

You said you read 12v on injector 4 all the time. This makes me think that R-L is being grounded somewhere. If it is, then start tracing that wire and look for abrasions, breaks, etc.

 

I put one end of the multimeter on the end of the R-L and the other probe onto a known good ground (ground wire on rear of cyl head) and did not get continuity (multimeter did nothing).

I also tried it on the other end of the R-L (injector connection pin 1). Nothing there.

This was all done with the injector, ecu and battery unhooked.

Let me know if I did that incorrectly. If not, what's the next step?

Thanks for all of your help, nzbrock.

 

With the key on, you should be getting a constant 12v between each B-R injector pin and ground (not the other injector pin). After all, they all share the same exact power source. Recheck your other injectors to make sure this is the case.

The other pin on the injector goes to the ECM to be switched to ground. This should not read continuity to ground until the ECM tells it to, which will only happen when the engine is running.

 

That is what I'm seeing. 1-3 has voltage on B-R and a ground. 4 has voltage on B-R and R-L has a constant ground on it.

If I check injector 4 pin 1&2, I see constant battery voltage 12.xx when not running and key to accessory position and 13.xx when running.

Same check to 1-3, I get zero voltage when key is in accessory position and blips of voltage when running (pulses).

 

Assuming the ecm harness connections are clean and dry, it looks like ecm failure.

 

Is the constant ground on R-L only when the key is in ACC or On? If this is the case then the ECM is grounding this wire constantly when it shouldn’t.

 

If #4 injector is grounded constantly you run the risk of filling the cylinder up with gas and blowing up the cylinder. Be careful with that and don't run that way except for short bursts to diagnose. I saw a brand new BMW 5 series with a stuck open injector blow a softball sized hole in the block.

 

Crazy question, can I wire the R-L #4 injector ground into the #1 cylinder wire. I know they pulse independently but they are both at TDC and the plugs should fire at the same time.

Anyone got an ecu for sale?

 

http://siaelec.com/faq/

have never done business with them, it is an option though.

 

Crazy question, can I wire the R-L #4 injector ground into the #1 cylinder wire. I know they pulse independently but they are both at TDC and the plugs should fire at the same time.

Probably not a good idea. #4 cyl would be on overlap with fuel being injected.

 

Can you explain overlap?

 

Both intake and exhaust valves are open at the same time.

 

My ecm part number is :89661-04371

I've been told that 89661-04370 and 89661-04372 are the same as mine. Is that true?

 

Rip your injector driver circuit