Intermittent Drivability Issues

[drdave81]

01 Yukon Denali. I've started noticing a random buck or surge. It would only happen once and not again. Then, the other morning it started surging, bucking and no throttle response for a second. It would come and go, no rhyme or reason to it. I've gotten it to act up a few more times, but can't seem to pin it down. There are no DTCs associated with throttle (random MAF code I've been chasing and EVAP), fuel pressure holds steady it the high 40s to low 50s while driving, no leak down with key off. No wiring damage that I can see anywhere. Idles fine, but light to mid throttle it will randomly do this. All data I'm reading on Tech2 looks good, misfire monitor didn't show anything driving around at all, but I wasn't on that screen when it was acting up, so I can't 100% confirm it's not a misfire. Anyone experienced this before? It's definitely not trans related, it is engine for sure.

 

[Fless]

Monitor what the MAF is reporting with your Tech 2; at hot idle it should be very close - in g/sec - to the engine displacement in liters (e.g., 4.8, 5.3, or 6.0). The higher the rpms, the more air (grams) it should report. It could be mis-reporting. Clean the MAF with MAF cleaner, or replace it with OE.

 

[drdave81]

Monitor what the MAF is reporting with your Tech 2; at hot idle it should be very close - in g/sec - to the engine displacement in liters (e.g., 4.8, 5.3, or 6.0). The higher the rpms, the more air (grams) it should report. It could be mis-reporting. Clean the MAF with MAF cleaner, or replace it with OE.

I replaced it a little while ago after not finding any obvious wiring issues. I replaced it with OE. The code is P0102, circuit low. Hot idle is reading a bit higher, closer to 8g/s but does go up as RPMs go up. The code isn't constant either, it will come and go, check engine light was off for about a week straight, then popped back up with that code and the 2 EVAP codes. Connector looks good, clean, no corrosion, no signs of damage to wiring. Without opening up the harness further back, there is no obvious signs of problems.

 

[Fless]

When the code pops up, look at the freeze frame data to see if you can determine what specific item caused it.

 

[drdave81]

I felt a bit more of the hesitation/bucking on the way in to work this morning. So I hooked up the scan tool when I got there. P0102 was pending, the only thing I noticed that could potentially be (or maybe not) would be that MAF g/s was at 1.59g/s. But the engine had JUST started, there was 0.0.0 engine run time in freeze frame, so it may not have been drawing much air yet when the code was triggered. It was back up around 8g/s when it was idling and I checked the DTCs. Got home from work, cleared the code and then swapped the AFE cold air intake with the stock air box, left on the intake tube. MAF g/s slowly dropped down more to mid/high 6g/s. So maybe I'll run the stock box for a bit, see if that takes care of the issue. I wonder if I'll need the tune adjusted if I stick with a stock box or not though.

 

[drdave81]

Turns out, running the stock air box was a bad idea when it's tuned for the cold air intake already on it. Massive drivability issues the next day. Once I swapped back, it was back to running alright, but intermittently. I was messing with it earlier today and swapped the old MAF back on, just because. Initally, everything was fine, no codes, reading around 7g/s. Then suddenly went flat to 1.58g/s and set the P0102. I wiggled the wire harness, tapped on the sensor, etc, nothing. Driving around and it was at 1.58g/s, then suddenly it comes back and is reading properly again. So there is a wiring issue somewhere, but no clue where or what's causing it, since messing with the harness, fuse box, etc doesn't seem to have any effect on it.
I'm still not positive this is my only issue either. The surging/bucking/lack of throttle response almost seems to be a separate problem, but I guess could be related???? Everything is so intermittent, it's next to impossible to try and diagnose.

 

[Fless]

I'd pull the connectors at the engine computer, and check for pin fitment, cleanliness, etc. If you see any evidence of water migration, clean the contacts and replace the connector gaskets.

Look at the DTC freeze frame data to see if it shows anything else out of place (other than the MAF reading). Maybe the 5v reference signal dropped out?

Electrical diagram here but verify your vehicle info:

IAC Valve, MAP, TP, MAF, ECT Sensor — 2001 GMC K 1500 Yukon Denali AWD V8-6.0L VIN U Service Manual | Operation CHARM

Detailed repair manual for the 2001 GMC K 1500 Yukon Denali AWD V8-6.0L VIN U.

charm.li

 

[SmileB44Death]

Turns out, running the stock air box was a bad idea when it's tuned for the cold air intake already on it. Massive drivability issues the next day. Once I swapped back, it was back to running alright, but intermittently. I was messing with it earlier today and swapped the old MAF back on, just because. Initally, everything was fine, no codes, reading around 7g/s. Then suddenly went flat to 1.58g/s and set the P0102. I wiggled the wire harness, tapped on the sensor, etc, nothing. Driving around and it was at 1.58g/s, then suddenly it comes back and is reading properly again. So there is a wiring issue somewhere, but no clue where or what's causing it, since messing with the harness, fuse box, etc doesn't seem to have any effect on it.
I'm still not positive this is my only issue either. The surging/bucking/lack of throttle response almost seems to be a separate problem, but I guess could be related???? Everything is so intermittent, it's next to impossible to try and diagnose.

What was the issue?

 

[drdave81]

Never figured it out. I don't drive it in the winter, so I haven't had it out much really yet. Been driving company test vehicles, and at almost $5/gal, I'm fine with someone else's dime filling the tank lol.