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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!

Edited by Becca06
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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?

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Nice work on the diagnosis.

 

It sounds like you’ve verified it’s not the injector but would it be worth swapping injectors just in case?

 

injector not firing is unfamiliar territory, be interesting to see what others say to check next.

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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.

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The ECU fires the injector so, I'm weak at electrical, but from here I think you check wiring from injector to ECU and wherever the other side pulls 12 volts from.

 

You pulled the engine - I haven't seen this happen on newer subaru's or new gen models but make sure none of the main harness connector pins are bent, damaged, corroded.  If this engine ran 10 years with no misfires and has a misfire after the engine pull then it seems likely something happened during that work.  

 

There are accounts of H6 ECU injector driving circuits failing, so that's a definite possibility though you're headed in the right direction by diagnosing.

Used ECU for $50 - $150 and then $100-ish for the dealer to program it and all your keys/FOB's at the same time.  New ECU's i think are $500+

 

General Disorder, GLoyale, Numbchux, Fairtax are members here that would have something good to say about that.  This stuff is generally beyond by proficiency. 

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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.

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oh right you already checked power - so yep be interesting to see what you get from the ground pin to it's associated pin on the ECU.

 

i've seen rodent damage more than once - but tracing will lead you to that if that's the case. one was in an apartment complex with zillions of chipmunks and another was a vehicle with 3 kids and food particles everywhere around the car seats.

Edited by idosubaru

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Computer uses input from the cam sensor to determine when to trigger the injectors.

Similar manner, but not at all related to ignition timing.

 

I'm not sure what type of reluctor the cam sprockets have on the H6. Onthe ~02+ 4 cyl a there are only two notches on the cam wheel that signal the ECU to start the injection sequence, they're aligned roughly with TDC for number 1. It then uses the crankshaft angle to time out the rest of the firing sequence.

 

If you have voltage to the injector, the ground side somewhere between the injector and the ECU may be open, or have a poor connection. Generally if this happens it will be at the main harness connectors on the bellhousing.

Check for dirt, bent pins, and make sure they're clicked together all the way (push HARD).

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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...

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130 is pretty low compression. Don't rule that out as a cause. I would check against the other cylinders - should be up around 190. That's over 30% off from normal - way outside of acceptable 10-15% variance. Also head gaskets were just done so in all likelyhood it is related to that repair. 

 

GD

Edited by GeneralDisorder

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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?

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Yeah if you have no pulsing at the injector that's probably a priority. Do you have 12v at the injector but no control signal from the ECU? 

 

1LT has a point - check the connector carefully. That may have been touched/broken/disturbed in the HG replacement so it's on the short list of possible problems. 

 

GD

Edited by GeneralDisorder

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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.

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Don't know if this will help but on older Subarus the injectors are batched fired, 2 at a time.  Since the other 5 injectors are firing and you have 12V at the problematic injector, my guess is the problem is not the ECU.  Seems to me to be a wiring problem between the injector and the ECU.  

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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.

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You have 12v getting all the way to the ECU? Injectors are grounded at the ECU so if you have 12v getting to the ECU on the wire for injector 1, the wires/connectors are fine, ECU has a fault.

 

Something to be sure to check for is a short to power on the ground side of the circuit, that is best accomplished by unplugging the injector and checking for voltage at the ECU. If there is a short to voltage on that driver circuit it can damage the ECU.

 

Also make sure the resistance of that injector is within the same range as the others. Low resistance increases current through the circuit and current (amperage) is the killer of electronics.

Edited by Fairtax4me

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I'm fairly certain the H6 is sequential injection, not batch fire. Even going back to 1990 the EJ22's were sequential injection. 

 

Ohming the wire is not sufficient as the meter does not use sufficient current to test the wire's ampacity - you need to perform a voltage drop test, or wire the noid light directly at the ECU connector to verify that not only does the ECU ground that pin for the injector, buy also that the wire can carry a load and not drop all the voltage due to a poor connection. 

 

My money is on a pinched harness during the HG swap. 

 

GD

Edited by GeneralDisorder

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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.

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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??

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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.

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I Doubt a Honda or Toyota dealer can do it but you’ll verify that soon enough.

Edited by idosubaru

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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.

Subaru is the only one with the tools to reprogram it, and you'll likely have to get the car there.

 

Question: Did you check to see that 12v is getting to the ECU on the ground pin for injector 1? You need to verify that to rule out a bad connection or broken/damaged wiring. If you do not have voltage to that pin, there's a break in the circuit, a new ECU will do no good.

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