Envoy Acceleration Issue

[Lasasj]

I've been trying to diagnose an issue with my Envoy for several months now. Any insight would be greatly appreciated.

2002 GMC Envoy 4x4 w/150k is lacking acceleration... very sluggish in park and when driving. Computer showed that it was trimming fuel but no codes. Replaced the fuel filter, oil filter, air filter, spark plugs... no improvement. Replaced the pressure sensor (had a code); still sluggish. Removed the CAT; not the CAT. Replaced the throttle body (w/sensor); no improvement. Recently changed the O2 sensor and checked fuel pressure... Any suggestions? I'm running out of ideas. Any thoughts would be appreciated.

Also the envoy runs perfectly fine at idle... can punch the pedal and it will sluggishly rise from there.

 

[The_Roadie]

Welcome! You've certainly done a lot. Anybody ever looked at it with a Tech II tool? What were the LT and ST fuel trim numbers? Have you checked the vacuum? You might suspect an intake manifold vacuum leak, which can be caused by manifold bolts that love to come loose. Or the brake vacuum booster diaphragm can leak.

The CPAS is another huge suspect. They can get clogged with oil sludge or lose their screens, then the valve timing advance won't work. That's another item a mechanic with a Tech II tool (doesn't have to be a dealer to own a good scan tool) can exercise.

Compression?

 

[Lasasj]

First of all: I'd like to compliment your past work. Since I bought my envoy, I've done a ton of research on a previous forum site, and I found your thread posts to be insightful and helpful countless times. When I finally got stumped and couldn't find my issue on the last site, I was sad to see The Roadie as "no longer with us" after posting my issue. I thought I'd be screwed for sure, but someone just referred me to this site from that one. Glad to see you're here.

I borrowed the computer tool from a co-worker a few months ago, so I don't remember the actual trim values. From what I remember, the trim would correlate with how ever far the pedal was pushed and the ST values were very significant. I've tried to check the vacuum in a couple locations, but to be honest, I don't know much about troubleshooting vacuums. I pulled the hose from the throttle body and there was definitely a vacuum there, but nothing from the very small hose that goes into the top black cover (resonator?). Any direction on how to troubleshoot the vacuum would be great.

I'll see if I can borrow the computer tool again.

 

[Envoy_04]

Hey, welcome to the Nation! Glad to see you found us over here.

 

[Lasasj]

In the midst of cleaning the cpas. Noticed oil in the harness... does this mean it needs to be replaced?

 

[The_Roadie]

If it's working, you can defer the replacement. But most folks start looking for a good on-line price when oil starts getting past the internal o-ring. It can end up harassing the wiring harness.

 

[Lasasj]

Cleaning the cpas helped the problem a little. I'm still looking for another culprit.

I noticed driving that the transmission seemed to be acting up when I floored it... The rpms revved up very high and shifted hard.

Separate question: I bought a replacement o2 sensor that is now giving me a code... I need to put one in to pass inspection, anyone know where to get a compatible sensor?

Thanks

 

[HARDTRAILZ]

is lacking acceleration... very sluggish in park

Acceleration is typically hampered by that darn park selection....

 

[The_Roadie]

AC Delco O2 sensor FTW. What brand did you get and what specific code?

 

[Lasasj]

O2 sensor was a "replacement" ... and yes that's the name of the company. Was about the same price as a Bosch or AC Delco. I should have known better than to buy a knock-off, but if I remember correctly I had a hard time finding a sensor with the upstream harness connection (opposite of the downstream). Now that I've used up my store credit, I'll look elsewhere and find a legit AC Delco sensor. I'll check the code again, but I think it was sensor heater readiness or something. Need to get the code reader back from a friend.

And yes... putting a vehicle in Park will 'typically' hamper the acceleration...

But in all seriousness, is there a rev limiter in Park/Neutral ? I didn't make it a habit to test the limits of my Envoy before troubleshooting this issue. As of right now I can't rev past 3k - 3.5k in Park. And it takes a few seconds to get there.

 

[HARDTRAILZ]

There is a limiter.

 

[The_Roadie]

And the classic fault from off-brand sensors is indeed the heater current not being within the too-tight specs set by GM in the PCM to try to sell more Delco sensors. The sensor part of most sensors is just fine functionally, and will control the PCM in closed-loop mode perfectly, but the heater current throwing a code will cause you to fail emissions if that's the goal.