The stft for both is around 0. The ltft around -18%. O2 sensors are new and genuine gm with all reading good voltages. As to oil I did just do a change about 600 miles ago. Not sure about tank pressure voltage but will hook up scanner when I’m home and check. The Fuel Cell Trim isn’t the ltft or stft but has its own pid on scanner. Not sure what it is tbh
Misfires on one bank
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mikez71
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According to google, fuel cell trim is LTFT and STFT combined...
But as usual, the source they link mentions nothing about it!
Might check the fuel pressure and air filter too if you haven't already..
Make sure trims are fairly even bank to bank..
But as usual, the source they link mentions nothing about it!
Might check the fuel pressure and air filter too if you haven't already..
Make sure trims are fairly even bank to bank..
Do you mean "Fuel Trim Cell?"
Yea sorry
Can’t see tank pressure voltage on scanner or anything similar. Steady felt misfires still on cylinder 4 and now 3 only at idle and no CEL. Got curious today and unplugged MAF and restarted the truck and there was no misfires at all. Could it be as simple as the MAF which I’ve been hesitant to change?
Could be a bad MAF, I have seen them cause a whole host of seemingly unrelated codes and problems, shifting problems, misfires, lean codes, 02 codes.
even though they "seem" unrelated bad maf data can cause the whole thing to go goofy.
my experience in general has been if it has 160k on the maf it's end of life and should be replaced.
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I sure that is a tall tell sign the MAF is bad if it runs better with it unplugged. 
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Don't go cheap either. Do ur research.
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Was thinking too, about one bank misfire. Coil pack housing ground or grounds?
Isn't the MAF also the Intake Air Temp Sensor? Has the IAT value been verified with a scanner?
What does the MAF report in grams/sec at hot idle? State the idle speed, too, or show it on the scanner along with the MAF reading.
What does the MAF report in grams/sec at hot idle? State the idle speed, too, or show it on the scanner along with the MAF reading.
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delphi if those are your choices, delphi is what might be in the oem box anyway
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If I remember, Delphi is what you want.
Temporarily change your scanner to display metric units. No conversion necessary and the value is more accurate in g/sec.
Ok so changed scanner to read g/s and went on a 100 mile trip. My maf seems to be sending some data and it does rise proportionally to the rpms when I’m not driving. When I’m driving mostly they are good. At idle reads 5ish/g/s when I double rpms the g/s double also to about 10. I still misfire on cylinders 3&4 when idling under no load but all misfires go away when over 1200rpms according to graph and scanner. Also fuel trims at idle when misfiring are bad bank 1 -13% and bank 2 -22% but fuel trims almost even out completely while driving to around 0’s. Now for strange part last night when I was going uphill the Tahoe started losing power and rpms dropped to about 1500 and Tahoe was “pulsing/bucking” a hill. Also dash lights dimmed. Happened a few times so looked at scanner during on uphill pass and when it was doing it uphill I noticed each time the Air Flow Calculated PID would always go red when it happened. I’ve attached a pic
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Side note I made sure to check O2 sensors and they are new and reading good and went with genuine gm. After all this I’m starting to think it’s time for a leak down test to see if I got a leaking valve. Course that wouldn’t explain the misfire on 3 AND 4 cause there on opposite banks….in just don’t know lol
To me, it sounds like a vacuum leak. (Intake manifold, vacuum brake booster, etc) Mainly because it runs fine at higher RPM, when the extra air brought in is minor compared to the overall intake flow. At idle it's going to be a larger impact.
Good idea to do a leak down test. It could be a valve issue, but seems unlikely at two separate cylinders at the same time.
Throttle body comes to mind as well....
Good idea to do a leak down test. It could be a valve issue, but seems unlikely at two separate cylinders at the same time.
Throttle body comes to mind as well....
...you might not see any, if it's the purge valve solenoid, or internal in the brake booster....you can temporarily plug off the line to the brake booster and find that out easily. Purge valve solenoid easy to test if it's stuck open....you'll be able to blow air through it. But that would give you starting issues, with overly rich mixture. Throttle plate not closing all the way is worth checking....
