[misfire on number 1 cylinder '06 Tribeca, H6]

I have over 200 miles post ECU swap, and no problems. Hope it stays that way . I got a used ECU off ebay for $145 and it cost $115 to have the dealer program it.

 

Not as expensive as it could have been. I was glad I didn't diagnose it with a credit card, as some shops would have done...

 

Following some info on these forums, I boiled my diagnosing for a misfire down to the following steps:

1. Verify spark

2. Verify fuel and air

3. Verify compression

 

Once I saw the injector wasn't working (but all the others were), I then:

1. Checked for power at the injector

2. Checked for a pulse with a noid light

3. Gave the injector 12 V while engine was running and the misfire went away.

4. Traced the wiring harness and connections back to the ECU.

5. Tested the pulse coming out of the ECU to verify no injector pulse.

 

Hope this can be helpful to someone else...

[misfire on number 1 cylinder '06 Tribeca, H6]

In my case, the misfire started about 40 miles after the head gasket replacement.

 

I'll let you know what fails next!

[misfire on number 1 cylinder '06 Tribeca, H6]

Update: Found a used ECM on ebay. Took car, key fobs and ECM to a dealer. Dealer reprogrammed new ECM. VOILA!! Problem fixed!

 

So apparently this was that 1% probability that the ECM failed shortly after the head gasket work and the two problems were unrelated.

 

Definitely goes against reason, but hey, it's fixed now...

 

Thanks to you all for all the help!

[misfire on number 1 cylinder '06 Tribeca, H6]

I have 12 V at the ECU both with key on and with it running. No fluctuations - no grounding of the circuit to cause the injector to pulse.

[misfire on number 1 cylinder '06 Tribeca, H6]

I verified you guys are right. Gotta bring car, new ECU, and key fobs to Subaru dealer to get it all programmed. Can't plug and play with ECUs, at least not on the '06 Tribeca. Can't just grab another ECU and throw it in and expect the car to run.

 

I have checked wiring extensively but didn't check for voltage on the ground pin for injector 1 at the ECU. Just go from the ground pin to ground, correct? Won't I have some voltage drop across the injector?

[misfire on number 1 cylinder '06 Tribeca, H6]

Quick update. I took GD’s advice and back probed the injector wire at the ECU connector and hooked it up to the noid light. Nothing.

I checked another injector wire using the same method and got the noid light to flash.

 

I am pointing at a faulty ECU based on the diagnosis so far. The only other thing I can think of is possibly the ECU isn’t getting the #1 signal from the crank or cam positioning sensor, but based on other comments, it sounds like I wouldn’t have signals at the other injectors.

 

I will post an update after I get another ECU programmed and installed. Hoping the Honda or Toyota dealer can do the programming as I’m a few hours from the nearest Subaru dealer.

[misfire on number 1 cylinder '06 Tribeca, H6]

As far as a pinched harness: for my peace of mind I also unwrapped the harness from the injector back to the ECU connector and visually inspected the wire. Nothing. Wiring the noid light in at the ECU connector sounds like a good test, but I'm not sure how to physically do that, and still crank or start the car??

[misfire on number 1 cylinder '06 Tribeca, H6]

I don't have voltage on the wires going to the ECU. I did check the resistance of injectors all were the same at around 14 ohms.

[misfire on number 1 cylinder '06 Tribeca, H6]

I could be wrong, but I'm pretty sure the H6 doesn't fire pistons at the same time. The wiring diagram certainly doesn't show any injectors or coils wired together, but I suppose the ECU could send signals out to multiple cylinders at the same time. The H6 has 6 dedicated wires going out (1 per injector) to the injectors for the pulsing of the injectors.

[misfire on number 1 cylinder '06 Tribeca, H6]

Yes, I have 12V at the injector but no signal from the ECU. Last night I verified that I have continuity from the injector back to the ECU and went through the connectors, etc.

[misfire on number 1 cylinder '06 Tribeca, H6]

Good Idea. I could check compression on another cylinder. I wasn't able to tighten my compression tester, so not sure I had a perfect seal.

 

I'm with you on the problem probably being related to the recent work, although everything worked fine for a day or two.

 

I don't think the misfire is from low compression, though.

 

Main reasons for this thought are:

1. No pulsing signal at the injector.

2. When I give the injector 12 V while the engine is running, the misfire goes away, engine runs smooth, etc.

 

Will the car run if I swap out the ECM/ECU, or does the programming (done by a dealer) need to be done right away?

[misfire on number 1 cylinder '06 Tribeca, H6]

Quick update: I checked continuity from injector to the ECM. All is well. So I suppose I start diagnosing with a credit card now and try a new ECM?

 

I have no idea how to check if the cam sensor is sending a signal to the ECM for cylinders 3 and 5, but not #1. Seems like the cam and crank sensors are fine if all other 5 cylinders are working...

[misfire on number 1 cylinder '06 Tribeca, H6]

I agree something could have happened in the pulling and replacing. Not sure about older gen Subaru's but this one has two main connectors on the harness at the bell housing and the engine harness can all come out with the engine. Pulling the engine was super easy. It's almost like it was designed with engine swaps in mind!

 

One other thing that is a little befuddling...It ran fine for 40 miles or so and many starts and restarts (to burp the air out of the cooling system) before the misfire started.

 

I was hoping some of the guys you mentioned would weigh in on the discussion...Understanding how the ECU uses the cam and crank signals would be helpful in this diagnosis...

 

For now I'll trace the one wire back. As I mentioned, I have power like I should at the injector, just not getting the grounding pulse.

[misfire on number 1 cylinder '06 Tribeca, H6]

Thanks for the response! I was starting to think there was a special forum for stupid people like me that buy Tribeca's without reading the negative reviews, LOL! Not to mention the lack of love for the H6! Regardless, that's what I have and I'm sure there's help out there, somewhere...

 

I can easily swap injectors. I'm 99% sure it isn't an injector.

 

I'm thinking it must be in the wiring somewhere between the injector and the ECM. So I'll do a little more probing.

 

One thing I forgot to mention that I also checked is that I have power at the injector on the one side (just like I should).

 

If I understand right, the injector is fired by grounding the circuit. This signal somehow comes from the cam sensor or the crank sensor or both.

 

Does anyone out there actually know how this works? I was thinking that the injector was triggered off of the impulse from the coil on a cylinder a few cylinders ahead in the firing order, but I'm not confident that I understand how this takes place.

 

I couldn't follow (maybe don't know how to read) the wiring diagram enough to figure this out.

[misfire on number 1 cylinder '06 Tribeca, H6]

Update- tried the noid light and no signal or flash. Tried number 3 and had signal. So now I really need help! Is it possible to not have cam signal on just one cylinder?

 

Also, I put 12 volts to the injector while running and the miss went away, so that trick worked!

 

What now?

[misfire on number 1 cylinder '06 Tribeca, H6]

I just replaced head gaskets on daughter's '06 Tribeca with 130k. Fired up right away and no problems or leaks for 40 miles or so. Now it is missing and threw the code for "cylinder 1 misfire". I did replace the plugs when I had the engine out.

 

So I did the following in this order:

 

1. Switched #1 and #3 coils - no change. cylinder 1 still misfiring. I double checked the engine code by pulling the injector connector off #1 while it was running - no change.

 

2. Checked compression - it's around 130 psi. The spark plug was dry, expected it to be fouled if there was fuel and no spark.

 

3. Checked resistance on injectors. They were all around 14 ohms.

 

4. Did the hold-screwdriver-to-ear-and-to injector trick while vehicle is running. I can hear the injector clicks on cylinders 3 and 5, but nothing on #1.

 

What next? Noid light and see if I'm getting impulses from the injector connector while running? I don't have a noid light yet, but thought I could put 12 volts to the injector while it's running and see if the miss goes away. Would that rule out a bad injector? Or is that a bad idea?

 

I tried to search this before posting, but didn't see a comprehensive post on testing injectors.

 

Thanks in advance for the advice. I'm a first time caller, but have gotten a lot from this site just searching the old posts. You guys are great!