2002 XL Trouble Towing

For a year my Envoy has towed my pontoon boat ok (the PCM program doesn’t seem be programmed to tow efficiently though). On my last trip, it seemed like I had a brake dragging because the truck couldn’t maintain speed and started to miss. The boat is about 3,000lbs and I tow it with the top up so there is additional wind resistance. Even though there was no message on the DIC and the engine temperature gauge wasn’t too high (110C versus 90-100 normally), it felt like it was overheating (there was also a slight smell). When I switched to neutral it seemed to coast ok (without drag).

Even though I pulled over to let it cool down, shut off the A/C, switched to 2 wheel drive and subsequently pulled a little slower, it was better but happened a second time although I made it home.

All fluids were changed in the last year but I noticed the rear diff was now down about 300ml. I didn’t detect any unusual smell there. The engine and transmission fluids were right up, clean and smelled ok.

So…


Does anyone think the problem may have been caused by the rear dif fluid level or do you have any other tips?
Should I consider getting a revised program for the PCM to help with towing performance?
Is it advisable to install an additional transmission cooler?
Thanks so much,

Dave
Ps. Otherwise love the Envoy!

You were towing in 4wd or awd drive, if so don't do this additional drag is not needed. Check for the axle seals leaking causing the diff to be low or the pinion seal also. I would suggest a trans cooler if you tow at high speeds or hilly areas. No mention of mileage, but the miss you descibe can be caused by a weak plug, injector, o2 sensor, coil, dirty injectors. Also it is not recommended that you tow in overdrive also. The forementioned issues were not covered in your post. It is unecessary to reprogram for towing a 3500 lb trailer, if all the most reent updates have been done.

Thanks for the quick response.

I generally leave the vehicle in AWD as I sometimes feel it engage when I pull out of the lake. Should I be reverting to 2WD to tow normally?

It has 134,000KM and hasn't been dealer serviced since I bought it two years ago (in other words I don't know if the PCM has ever been updated). It has new plugs and I regularly run an injector cleaner through the gas. I've not seen any indication of O2 sensor problems but that would also make sense as it seams to be loading up and mileage is really poor when I tow. It'd be pretty expensive to change them on spec though.

Thanks for the advice on overdrive - makes sense. I generally only tow on flat roads and limit the speed to 80km.

I guess I'll be making a dealer visit to at least get the PCM updated.

Thanks again...Dave

OK Max, here is what I've learned from the dealer:

He says the catalytic converter is constricted, the exhaust manifold is cracked and the O2 sensor has failed, even though there is no light or DIC message. Estimate $1800 +tx.

There was no mention about injectors, spark coils or PCM software.

Sound right to you?

Thanks...Dave

Could be, also have a clear understanding that if this does not fix the truck either you will get a refund for the work done or they will have it back to be repaired free. An aftermarket cat would be less than half of the dealer cost also.

It gets worse!

Wanting some confirmation from the technician, I learned that the O2 sensor was broken because he damaging it trying to get it out. Sur'nuf, he also admitted to stripping the manifold, which prompted the need for a replacement. It also precluded me driving the truck off their lot. Oh yeh, they only charged me $112 for the 'advice'.

Needless, to say, I've had it towed to a reputable exhaust guy where the complete job will be done for about 35% of the dealer estimate (including an after market cat).

I'm a long time GM supporter, but can see why so many people are now looking elsewhere.

I'll let you know the final outcome. Thanks again.

It gets worse!

Wanting some confirmation from the technician, I learned that the O2 sensor was broken because he damaged it trying to get it out. Sur'nuf, he also admitted to stripping the manifold, which prompted the need for a replacement. It also precluded me driving the truck off their lot. Oh yeh, they only charged me $112 for the 'advice'.

Needless, to say, I've had it towed to a reputable exhaust guy where the complete job will be done for about 35% of the dealer estimate (including an after market cat).

I'm a long time GM supporter, but can see why so many people are now looking elsewhere.

I'll let you know the final outcome. Thanks again.

Wow...a precedent has been set...a dealer technician actually admitted to screwing something up. Must've been a newbie, and was likely punished and retrained to run a vacuum cleaner. He learned quickly to keep his d**n mouth shut.

That's why I do as much of the diag & repair work as I can

Final Outcome:

The reputable muffler shop has fixed the Envoy. The cat was melted down and plugged and they replaced the manifold and O2 sensor. The total bill was exactly 40% of what the dealer estimated (including the tow job to get it threre).

I trust and hope the cause of the converter melting down was: the manifold leak, faulty O2 sensor (replaced), or bad gas which has also been replaced.

Had I not replaced the sensor and/or manifold, the problem might re-occur. Likewise, a helicoil O2 fix might have netted the same results.

Thanks again for all the tips...Dave