'06 SV6 AWD - Diagnosing intermittent hesitation/power loss

[sisson_d]

Alright, my '06 SV6 AWD has a major problem...I'm about to blow it up! But seriously, I've had an issue for a few weeks now with intermittent acceleration/hesitation problems. Basically it started as a rare occurrence and is happening more often now. Yesterday, it did it consistently for 20 minutes on one trip around town. 1 hour later, it didn't happen noticeably at all on the way home. It happens while accelerating, usually from a stop, but also sometimes when cruising at highway speeds.

The car does not stall or stumble. Everything sounds fine and smooth, but when accelerating from a stop, the car will stop accelerating and the speed slowly drops off. Pushing the accelerator down further to the floor does nothing for several seconds, then the power returns and the car responds to whatever position the pedal is in. If you haven't pushed further it continues accelerating where you left off. If you've got it to the floor, it takes off quickly. When cruising at speed, you don't notice anything until you start slowing down, and the pedal reacts the same way. NOTE: The engine does not rev up when this is happening. It's not like the tranny is slipping.

It really seems like a fuel delivery problem and not transmission. It has all the normal symptoms of a failing pump. And about 2 months ago, I had the fuse for the fuel pump melt (not blow). These problems didn't happen immediately after, but they did happen a few weeks after that.

That said, I have noticed that when cruising I occasionally hear a light clunking noise that sounds like the rear diff engaging. I assume this is just due to play in the drive train. I also had to recently do the expensive versatrack fluid flush and fill to get rid of the diff groan. But I still feel like it's probably fuel related because the engine doesn't rev up.

Here's what I've done so far:
1. Checked the wires at the problematic C305 connector. I already had to completely redo that connector several years ago as the PO had removed the connector and directly twisted all wires together covered the with tape, and filled hole with silicon. BTW, GM does sell all of those harnesses with length of wire, connectors, and heat shrink covers for reasonable $$. Anyway, found 2 wires with insulation slightly shaved off. Neither was for the fuel pump, everything else still looked good.

2. Checked voltage at the gray fuel pump wire just after the new harness (about a foot before the fuel pump). And checked the ground at the same location. Haven't checked at pump connector because I don't want to drop tank just yet. Both were fine with almost no resistance on power between that location back to the fuse box. So, it doesn't look like a bad or shorted wire unless it is in that short length up to the fuel pump that I cannot access w/o dropping the tank.

3. Checked fuel pressure at the fuel rail. The pressure when primed and idling is a consistent 60-62 psi. I know the manual states 60psi as the max. Maybe this has something to do with it?? Perhaps my cheap actron pressure guage is a bit off or perhaps the pressure regulator is bad. Could this cause the issue.

4. Checked for DTC's with code reader. No active or pending codes.

The other things I think could be the cause based on internet research:
1. Accelerator Pedal Position (APP) sensor
2. Throttle Position Sensor (TPS)
3. PCM
4. O2 sensor

The problem is that all of those things tend to set a DTC from what I've read. I still think the fuel pump us going bad and the pressure was fine because the problem is intermittent. I just don't want to spend the $$ on a new pump to find out it was something else.

Tomorrow, I will have access to a scanner that can log 10 seconds of data from the computers while driving. I think that might shed some light if I can get the problem to happen when recording. I'm not familiar with fuel trims and the lot. So, I'll probably need help translating the data into useful knowledge.

PLEASE HELP. Any advice, suggestions, questions are welcome. I just borrowed the Uncle's Explorer to go on a family trip last weekend, I don't want to borrow it again for the 4 hour drive to DE next week.

Thanks in advance,
Doug

[sisson_d]

I should probably clean the MAF too since that's easy to get at and I haven't done that for about 30k miles. And what about coil packs? I've never had a bad coil pack so I'm not sure what happens. I'll have to read up on that. BTW, the van has about 89k miles on it.

[sisson_d]

Originally Posted by sisson_d

I should probably clean the MAF too since that's easy to get at and I haven't done that for about 30k miles. And what about coil packs? I've never had a bad coil pack so I'm not sure what happens. I'll have to read up on that. BTW, the van has about 89k miles on it.

Of course if the coil packs where bad enough to misfire that bad, I'd still get a DTC.

[sisson_d]

Here's some data from a recent recording while revving in neutral ( I had my reasons). Take note of the fuel trim that goes to -11.7. I think -10 is the limit for normal. I just got the scanner and will get some data while driving later.