Poor Performance check engine light

gydion · July 8, 2006

I have a 2001 GMC 2500HD Crew Cab, 4wd, long bed truck and have been having an interesting problem. I have taken it to two different established repair shops and haven't got this thing nailed down yet. So here it goes:

Symptoms:

1) P0101 error code read with OBDII scan tool at autozone. Description is a difference in the MAF value as compared to the derived MAF value based on other sensor.

2) Works good in lower ranges, but seems starved for fuel or air in upper ranges.

3) at about 50-70mph, if you keep the accelerator steady, a steady drop in rpms and speed is noticed. Sometimes, pumping the gas works to keep the speed steady.

4) the symptoms get worse the longer the drive is. Seems to get better after the engine cools down.

5) New eror code: P0106. Possible MAP or barometric sensor. nothing further.

6) Works good cold, then gets worse, especially at higway speeds. After it starts acting up, it does it at all speeds, extremely slow acceleration, 0-60 in 2 miles or so.

New parts changed out: MAF sensor, fuel pump, fuel filter, air filter, PCV valve.

Any help is appreciated.

Thanks,

Mike

Haulin' 8.1 · July 8, 2006

As long as you're throwing parts at it the most likely one is the MAP sensor. That along with the O2 readings are the MAF's check system. So you've got a code for MAF/MAP correlation and now one for MAP itself. Make sure the vacuum port is open and try cleaning the MAP sensor port out with intake cleaner first.

Another thing other than bad parts you should look for is a loose intake duct. I've seen this exact problem several times when the hose clamps on the duct were not retorqued after last reassembly. As your driving they blow or work loose. Also holes in the intake duct or a vacuum leak on the intake that seals with high vacuum.

It would help in most instances to know exactly what engine you have a question about. Such as 4.3/5-speed or 6.0/auto, etc. Sometimes certain combos have known problem areas that make it easier to diagnose from here.

Vernon

gydion · July 8, 2006

My apologies for not putting more information. My truck has the 6.0L with automatic transmission, air conditioning.

It no longer has the P0101 since I changed out the MAF sensor. Please note that I am not just "throwing parts" at it. I had the fuel pump on order anyways for a bad fuel level sending unit. It only cost me $130 for the whole unit, brand new and still sealed int he box.

Also, each part change was as a direct result after seeking advice of professional auto mechanics. I have taken this truck to two different places and nobody has any clear answers for me. Only maybe this or maybe that. Not a whole lot of help, but it at least gave me an area to check out.

One thing further, I felt that if I was going to work further with this, I decided to clean the engine compartment. After cleaning and rinsing, the check engine went away. No idea why. Maybe I'll get lucky and it will stay away, but I doubt it. Maybe I have a vaccum leak. I'll keep at it till I fix it.

Thanks for the help.

Mike

Haulin' 8.1 · July 9, 2006

Hey no offence meant, I see other mechanics throw parts all the time. It eventually works 50% of the time Also since the new gas came out fuel pumps and filters are dropping like flys. I had to replace mine already too.

Mike I know it's hard to find a really technically proficient mechanic so just in case you're in the Houston area speak up and I'll tell you where my shop is.

Vernon

gydion · July 9, 2006

Hello again,

No offence taken. I just wanted to make sure everything was clear. Also, I was a bit tired when I posted so that may have colored my postings a bit.

Well, I drove my truck last night and it worked fine. Ever since I cleaned under the hood, it has worked fine. I went to one of the quarter (well, 5 quarter) car washes where you do it yourself. I cleaned the outside of the truck till the engine cooled and then sprayed the degreaser stuff they have all throughout the engine compartment. I let that sit for five minutes and then rinced it out thouroughly.

I'm still not sure what did the trick, but I am certianly not complaining.

Thanks again for replying, I do appreciate it.

Mike

gydion · July 9, 2006

One other thing, I do know what you mean about the hard problem of finding a "technical mechanic". I spent almost $100 at the first place and they had no idea other than "clearing the memory" of the onboard computer to fix the problem. I watched and they never took it for a test drive, which is when the problem is noticable, not just sitting there idling.

The second one didn't charge me a thing. Although he did recommend changing the MAF sensor. That I changed myself because it was much cheaper that way. Also it was an easy swap, and it did help, but not completely cure the problem.

Thanks again,

Mike

Norseman · July 11, 2006

Do what Haulin' 8.1 said try cleaning the MAP sensor port out with intake cleaner.

gydion · July 11, 2006

Intake cleaner? Is that like carb cleaner? Haven't heard of that. Guess I'll look at AutoZone when I get by there later on.

Thanks,

Mike

gydion · July 14, 2006

Tried intake and carb cleaners (although I think they may be the same thing). No luck. Tried swapping out the MAP sensor. No luck. No more check engine lights, but still takes 2 miles to get it over 70mph. Can't respond to fires quickly like this. Guess I'll have to keep trying mechanics till I can find one that can fix it.

Thanks,

Mike