P0305 Freeze Frame Data Interpretation Help Please

[Brad Clark]

Good afternoon,
The vehicle in question is a 2008 Jeep Liberty. 3.7 Liter V-6.
I’ve been chasing this for a couple weeks now.

So far I’ve done:
New spark plugs
Swapped position of coils
Swapped position of injectors
Compression test 180 psi on cylinder 5
Visual inspection of injector wiring
The fault did not follow the coil or injector placement.

I did a live data session over the weekend. The misfire counts only increase at idle. None on acceleration. None on cruise. None on deceleration.

Three things that stand out to me:
Long term fuel trim at 7% bank 2. OK, lean on cylinder 5, add fuel…
Vehicle speed at the time of MIL, 1 MPH Huh…..?
Engine RPM at the time of MIL, 150 Huh……?
Based on the throttle position and Load Value, that can’t be right.

I suspect a bad ECU-ECM-PCM

Anyone else?

Suggestions appreciated!

Thanks Mr502

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Topic

[dave]

I’ve only done some freeze frame data analysis. I don’t see anything unusual except for the LTFT of 7%. With this in mind along with the parts swapping you have done so far, I would probably look for a vacuum leak around the #5 intake runner. Also, one item of interest that we don’t see in your list of data are plotted O2 sensor performance. Just for fun, I’d take a listen to that #5 fuel injector with a mechanic’s stethoscope.

how to find vacuum leaks
[video]http://www.youtube.com/watch?v=9CPqbaSgcok[/video]

vacuum leak repair
[video]http://www.youtube.com/watch?v=V43OTGPxYc0[/video]

listen to those injectors
[video]http://www.youtube.com/watch?v=9JDhEwMS_Us[/video]

It is possible that at idle when vacuum is at it’s highest that an intake leak could allow ‘unaccounted for’ air to enter the cylinder (making it lean). The O2 sensor finally picks up this condition and commands the ECU to start dumping fuel into the engine in efforts to correct for the lean condition, resulting in your +7% LTFT.

[Daniel]

If swapping around the coil packs didn’t change anything, have you checked the wiring for the coil packs? Also, before you conclude that the ecm is bad, you may want to contact the dealer and see if there is an update for it. I had a Honda Odyssey in the shop with a misfire. And found a service bulletin saying something about an ecm update. I found nothing wrong with the car, directed her to the dealer for an update, and presto, misfire gone.

[Bill]

If you’re sure the injector is working on that cylinder i agree that you should be looking for a vacuum leak.

The eroneous readings i’m not sure about…..yet.

[Brad Clark]

Excellent suggestions, thanks.

I emptied half a can of brake clean around the intake #5 and could not get any RPM change over the weekend. Maybe I missed it, so I’ll try again.

I have looked at the wiring to the injector, and there’s only about 3″ of it exposed, and from there it goes right into the plastic split loom covering, then disappears…

Good suggestion on the firmware update. It’ll take me probably a week to get over there, but it sounds like a good plan.

Have to stop and get a stethoscope, don’t have one. Good idea.

Thanks for the videos!

I’ll report back when I find out more.

[dave]

I emptied half a can of brake clean around the intake #5 and could not get any RPM change over the weekend. Maybe I missed it, so I’ll try again.

be sure to check other places, like the intake snorkel for example.

Now that I think about it, I think an exhaust leak could also introduce air into the system affecting O2 sensor output.

[college man]

Try a power balance test. you could have a bad or clogged
injector and or wiring issue.

[Daniel]

Ok we have checked the injector wiring but what about the wiring to the coil packs? Maybe there is a dirty connector.

[Brad Clark]

Great, thanks.

This is a coil on plug ignition system so the wiring check should be fairly easy.

I’ll add that, the power balance, and additional leak sources to my list.

Probably won’t get back to it until Thurs or Fri.

I’ll report back then.

Glad I found this board, great suggestions!

Thanks again.

Mr502

[Brad Clark]

Follow up,

I was suggested to me that a better indication of that cylinder’s health would be a leak down test. And that it was possible for it to pass a compression test, yet fail or show a substantial leak.

I did get 180 psi on that cylinder.

Opinions?

Thanks

[Mike]

Try a running compression test. I have seen burnt valves cause that exact scenario. Compression test checked out ok, but a running compression test showed signs of a burnt valve. Symptoms were missfire at idle and smooth under load.

[Brad Clark]

^^^ Interesting, never heard of such a test.

One more for the list.

Thanks

[Mike]

Technical term is dynamic compression test…make sure u remove the shrader valve for this test…here is a pdf explaining how to perform the test and how to interpret the results…pretty simple…

http://www.fme-cat.com/Docs/1524.pdf

[Brad Clark]

Got it, thanks Six

The only problem I see here… the silly car is drive by wire.

Have to see how it goes.

[Author]

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