Good Old Random Cylinder Misfire Mystery

[Nicolai8775]

Any idea of the brand of crank and cam sensors?

I don't know unfortunately, I was having trouble ordering the AC Delco through O'Reilly's so I'm assuming it's the generic auto parts store brand

 

[Nicolai8775]

 

[Nicolai8775]

LTFT is currently +8.59 in bank one and +14.84 in bank 2, at idle. Does this indicate a vacuum leak? I think Fless mentioned this earlier. The trims don't drop when I accelerate, they increase slightly

 

[Nicolai8775]

Also wanted to add. The fuel tank depressurization when I open the gas cap issue. Everytime I fill up on gas and it nears full, you can hear the gurgling fuel coming up the filler neck as if it's close to overflowing. That's not normal

 

[Fless]

LTFT is currently +8.59 in bank one and +14.84 in bank 2, at idle. Does this indicate a vacuum leak? I think Fless mentioned this earlier. The trims don't drop when I accelerate, they increase slightly

Great that you're getting some improvement!

Couple of thoughts... that Bank 1 S1 O2 sensor seems to be a bit lazy waking up, so as long as the heater circuit is working you might want to consider replacing it and the other upstream sensor. Best done in pairs, but not totally necessary. A sleeping or dead sensor will stay around 0.450v; weak or lazy sensors will switch slowly or not make full range under various rpms.

The somewhat high fuel trims seem to indicate a vacuum leak or unmetered air getting in past the MAF. Could be a leak in the intake tube (is everything tight and sealed; no open ports or cracks in the tube?). Less common, could also be a dead or weak fuel injector causing the cylinder to run lean; that would pump air into the exhaust and the PCM is going to add fuel to compensate. I'd expect that only on the bank that has the issue, though.

 

[Nicolai8775]

Great that you're getting some improvement!

Couple of thoughts... that Bank 1 S1 O2 sensor seems to be a bit lazy waking up, so as long as the heater circuit is working you might want to consider replacing it and the other upstream sensor. Best done in pairs, but not totally necessary. A sleeping or dead sensor will stay around 0.450v; weak or lazy sensors will switch slowly or not make full range under various rpms.

The somewhat high fuel trims seem to indicate a vacuum leak or unmetered air getting in past the MAF. Could be a leak in the intake tube (is everything tight and sealed; no open ports or cracks in the tube?). Less common, could also be a dead or weak fuel injector causing the cylinder to run lean; that would pump air into the exhaust and the PCM is going to add fuel to compensate. I'd expect that only on the bank that has the issue, though.

It's got the stupid K&N intake. I want to get a volant, heard those are good.
The tube looked worn where it hits the fan shroud, I will make sure it's not worn through. The rubber is in good condition on the intake tube. The clamps are all right.

I still really don't want to believe that I did the intake gaskets wrong lol. I don't think I did cause of the water test and even propane around the manifold. Could it be the pcv valve/hose or perhaps the EGR tube?

I'm not so sure about injectors now cause torque is showing very minimal misfires if any the last couple trips. When cylinder 5 was throwing a misfire code I listened to a few of the injectors with a stethoscope and compared to #5 and heard the same consistent clicking sound.

 

[Nicolai8775]

What's more likely to cause a long crank? A vacuum leak, or bad injectors?

If it were injectors, why isn't it misfiring? I don't see any seepage around the injectors indicating bad o-rings. I will check more thoroughly when I get home. Or is it internal failure, like a clog. Cause my fuel system did leak down a little after like 45 minutes or so

 

[Nicolai8775]

O2 sensors changed, no difference

 

[Nicolai8775]

I once again tested intake for leaks by unplugging iac and spraying the crap out of the intake with carb cleaner and any other vacuum source I could find. No change in ltft in torque. I have 6 injectors left from my 2001 Tahoe if I need to replace. How do I diagnose?

 

[Fless]

One thing you can do is an injector balance test (injector removal not required), which measures the difference between the initial fuel rail pressure and the pressure change when each injector is fired. Ultimately an injector flow test might be needed to measure the volume of each injector's contribution, but that requires removal of the fuel rail.