Has a crank correlation relearn been done recently? If not, consider having it done (can be done with a Tech 2).
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S33k3r
Full Access Member
Based on the previous engine experiencing the same behavior, and replacing the MAF not fixing it, I'd say you have an electrical gremlin. Sounds like you are going to need to trace some wires. And I'd start with the circuit the MAF is on. Why? Because replacing the old MAF with a new one fixed it the first time, but not the second. That leads me to believe it is the MAF circuit, and old MAF couldn't handle the degradation, a new MAF masked it, temporarily, and the circuit has degraded sufficiently that even a new MAF can no longer mask it.
In any case, gremlins like these make me crazy. Good luck to you in your banishment attempts.
In any case, gremlins like these make me crazy. Good luck to you in your banishment attempts.
rockola1971
Full Access Member
Swap #2 & #4 ignition coils around and see if misfire moves to #2.
Stayed at 4.
Update: I took off the absolute MAP Sensor today, cleaned it off with some MAF spray and reinstalled it. It was loose feeling when I took it off, and much firmer after I reinstalled it. It felt much smoother/more power immediately. I drove, very smooth no rough idle etc., but the codes didn’t clear. I cleared the codes myself drove for ten miles and the code never came back on. Do you guys think I got it?
Hell, anything is possible. Not many threads here about MAP cleaning or replacement fixing problems. Hope it fixes yours.
MassHoe04
Full Access Member
Depending on specific codes, it can take X number of drive cycles and/or x number of miles before enough errors occur for the CEL to light up on the dash.
If you have a Tech 2, great! If not, you may still be able to dive in deeper into the computer to see what pending codes might be collecting in there.
Tech 2 will certainly get into the pending data that might be stored and can also show the misfire counts in the live data.
If you plan on keeping your Yukon a while, do yourself a favor now and invest in a Tech 2 scan tool. Clones are about $300, but the information they can give you is off the charts!
Another option, if you need something for other vehicles, a good bi-directional scan tool like an Autel tablet would be the way to go. Better ones run $800+, but can do a lot of the stuff the Tech 2 can.
However, there are specific directions with detailed steps written into the field service manuals. Those instructions in the FSM are specific guides on using the Tech 2 to do all the mechanical, electrical and functional diagnostics for the GM mechanics. (Not to mention... all the module testing and programming that the Tech 2 can do, that others can't...)
Not an official plug for Tech 2... Just wanted to mention that you might want to dive in deeper to the stored data and live data to see if there are things happening that exist, but not enough to trip the CEL on the dash just yet. You may have misfires still on 4 and just haven't been told about it.
Keep us posted. Good luck!
If you have a Tech 2, great! If not, you may still be able to dive in deeper into the computer to see what pending codes might be collecting in there.
Tech 2 will certainly get into the pending data that might be stored and can also show the misfire counts in the live data.
If you plan on keeping your Yukon a while, do yourself a favor now and invest in a Tech 2 scan tool. Clones are about $300, but the information they can give you is off the charts!
Another option, if you need something for other vehicles, a good bi-directional scan tool like an Autel tablet would be the way to go. Better ones run $800+, but can do a lot of the stuff the Tech 2 can.
However, there are specific directions with detailed steps written into the field service manuals. Those instructions in the FSM are specific guides on using the Tech 2 to do all the mechanical, electrical and functional diagnostics for the GM mechanics. (Not to mention... all the module testing and programming that the Tech 2 can do, that others can't...)
Not an official plug for Tech 2... Just wanted to mention that you might want to dive in deeper to the stored data and live data to see if there are things happening that exist, but not enough to trip the CEL on the dash just yet. You may have misfires still on 4 and just haven't been told about it.
Keep us posted. Good luck!
rockola1971
Full Access Member
If the code comes back then I would check your #4 cylinder ignition coil wiring all the way back to your PCM. Your PCM could be the culprit too. The PCM drives each ignition coil separately.
Hey Rockola, the code came back P0304, so I swapped the coils and wires (before a shop said they had done this) between 2 and 4. Now I have P0300 code being sensed, but not throwing all the way yet. I also hear a sigh when I turn the car off. Like there’s a vacuum being release.
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