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Did you perform a handover after changing the MAF?
Again, everything references CLT, until you work that issue out, and have a stable reading thats accurate, you'll be wasting a lot of time. CLT impacts everything with these engines as it dictates which MAPS the engine is referencing constantly.
Very nice plots. A few observations:
1) You have misfires on almost all cylinders during cold start. Looks like #5 is the worst. That means you need to trace things that are common to both banks
2) Not clear when close loop happens but it looks like the engine runs smoothly once it enters close loop a/f control. To confirm, log the 4 O2 sensor voltage readings during cold start. Precat sensor voltage will start to swing once the system enters close loop
3) It does not appear your cyl #1 has mechanical problem since all cylinders smooth out
4) Appears to me that the a/f is wrong during cold start and before close loop. That points to air leak (e.g., intake or SAI) or extra fuel vapor (e.g., evap purge valve). The O2 reading should give us more clues. From the O2, you could also see the SAI system in action.
I think a simple CEL erase will also reset the DME (so reset all the fuel trim adaptations). That can be done by Durametric or a generic OBDII scanner.
Those are good tests, BUT there are times when a MAF will test perfectly, but still have an issue during certain ranges of operation can give an issue. It takes very little enrichment differential to create a misfire.
The operation voltage is also a good test, but I have had them test perfectly and still be the culprit.
I have hundreds of good cool packs.. I should give some to you guys so you can ship them to one another for evaluation purposes. That keeps people from having to buy new stuff just to test a theory.
If you are giving them away, I'll take 6 of them for a 2004 3.2
I can PM you with shipping address
Very nice plots. A few observations:
1) You have misfires on almost all cylinders during cold start. Looks like #5 is the worst. That means you need to trace things that are common to both banks
Ahsai, that was a good call earlier to look at misfires with the Durametric. That led me to look at rough running on all of the cylinders. i agree that it's not just cylinder 1, but all cylinders, which completely changes my thinking to look not just a cylinder 1, but all six cylinders. That's why I went ahead with the MAF sensor swap.
Very nice plots. A few observations:
2) Not clear when close loop happens but it looks like the engine runs smoothly once it enters close loop a/f control. To confirm, log the 4 O2 sensor voltage readings during cold start. Precat sensor voltage will start to swing once the system enters close loop
Here are the same plots of air flow, temperature, and rough running, plus the four catalytic converter oxygen voltages. The left and right banks are very different when cold. I don't know which side is working properly.
It looks like the ECU goes into closed-loop control at 149 seconds, while the engine smooths out at 99 s. At 99 s, all of the voltages have fallen to 0.03 V.
The last plot zooms in on the closed-loop control time from 150 to 200 s. The pre-cat voltages are swinging back and forth, while the post-cat voltages are more steady. They do change when I rev the engine.
Last edited by DrMEMS; 02-18-2016 at 07:21 PM.
Reason: I had described the wrong thing when looking at the close-up of the cat voltages.
Your O2 sensor plots look normal to me. Something happened/stopped at 99s to make the engine run smooth.
The postcat O2 sensors read 0v after 99s because being behind the cats, it takes them longer to get up to full operating temp. That's probably just a coincidence that when the engine also smooths out around the same time.
Attached is a cold start from my engine, which is very similar (diff ambient and 200 cell cats). BTW, have you reset the DME like Jake asked?
Did you perform a handover after changing the MAF?
I had not reset the ECU for my earlier posts. I just did by telling the Durametric to clear the error codes (of which there were none). I retook the same data, which is below. The engine had not fully cooled down during the 5+ hours it was off. This shows up in the coolant temperature ("engine temperature") being a little warmer than the oil temperature.
I frequently cannot get the Durametric software to connect to the ECU right away, so the engine was running for about 40 seconds before I could start logging data.
Again, everything references CLT, until you work that issue out, and have a stable reading thats accurate, you'll be wasting a lot of time. CLT impacts everything with these engines as it dictates which MAPS the engine is referencing constantly.
I think that the coolant temperature reading is OK now. It matches the oil temperature when the engine is cold, which you can see on the earlier temperature vs. time plots that I posted. It seems to be stable when I'm logging data and when I'm driving. It just repeatably had a bad connection when I unplugged and replugged the X59 connectors.
Very nice plots. A few observations:
4) Appears to me that the a/f is wrong during cold start and before close loop. That points to air leak (e.g., intake or SAI) or extra fuel vapor (e.g., evap purge valve). The O2 reading should give us more clues. From the O2, you could also see the SAI system in action.
And finally to your 4th points.
* Is there an easy way to check for air leaks? When I was installing a new fuel injector, my oil filler tube broke and I put it back together with a bike inner tube and hose clamps for easy disassembly in the future. That could be leaking.
* How can I diagnose the evap purge valve? And what is it supposed to do?
* Is there an easy way to check for air leaks? When I was installing a new fuel injector, my oil filler tube broke and I put it back together with a bike inner tube and hose clamps for easy disassembly in the future. That could be leaking.
* How can I diagnose the evap purge valve? And what is it supposed to do?
You're telling us this now after 56 posts?!
To test air leaks, you can use a smoke machine, or just carefully spray carb cleaner onto the areas in question to see if the idle changes.
The evap purge valve allows the fuel vapor captured in the carbon canister to be sucked into the throttle to burn as fuel and it's controlled by a PWM signal from the DME. The DME takes this into account when computing the correct injection pulse. If the valve is sticky/leaking, it will upset the a/f ratio. You can remove the valve and vacuum test it. You should able to blow through it if you apply 9v power to it.
I remember one case like yours but the misfires only happen at cold start. It was because one of the injectors is leaking so extra fuel after engine shut off causes the engine to stumble upon cold start. However, I think you said before your rough idle could also happen at warm start (i.e., restart not long after shut down)?
The oil filler tube was fine when the misfires started. I broke it in the process of replacing one fuel injector. It's not a great design, as the filler tube is in the way when the air-filter box is removed.
02-18-2016 | 03:05 PM
