98 K2500 losing power intermittently

My 98 K2500 seems to intermitently lose power while pulling my 5th wheel. It has a 454 with a Banks power pack. (it did this before I installed the Banks kit) When running right, it has tons of power. Seems after pulling with it for an hour or so, it tends to lose power and starts downshifting to 3rd and sometimes to 2nd. Dealer says the K&N air filter I am using got oil on the mass air flow sensor and cleaned it, among other things that didn't help. I put stock filter back in it. Still does the same thing but not as bad. Don't really want to spend more money on a MAF if it isn't going to take care of problem. Already spent around $1500 since it has been out of warranty. Any Ideas? Thanks!!

Have you checked your trouble codes?

I am having the same issues with my 97 C2500 and am looking for answers also. I had the problem with oil and my k&n filter at 100k (I now have 150k on it). I over-oiled my filter and covered the maf with oil. I cleaned it and it fixed that one. My biggest complaint isn't the power loss, it's the mileage when towing. I used to get 12-13 pulling my 18' bass boat, now I am getting 9-10. And even less when pulling a bigger load. I have not found anything yet either. I am looking at the catalytic converters, possibly getting stopped up???

I have considered replacing the maf, fuel injectors, throttle position sensor, etc. but have not wanted to start throwing money at it without knowing what is wrong.


So far, haven't found anything usefull. I do know I don't have any performance/mileage issues when running empty. Still get 13 at 70-80mph on the freeway. I will be more than happy to share info if I find anything, feel free to email me, I want my power and mileage back and I want to what has stolen it!!!

Hi, I am having similar problems with my 94 C3500. Looks like mine is narrowing down to an electrical fuel problem. Might want to check this out.

http://www.automotiveforums.com/vbulletin/showthread.php?p=2008746

Pulled the trailer last weekend, mileage dropped to 7, used to be 10. No codes, ran up some hills great in OD and others had to kick down to 2nd to keep it at 50 mph, was running 70. Problem very intermittent and doesn't to seem to relate to anything, hot, cold, etc. Don't think it's the cats, that should be a consistant problem,(?). Had fuel pump replaced, going to try fuel filter again. BTW J. C. Whitney has a code reader for OBD2 for around $40.00.

I got a wild hair this morning and pulled all of the air filter and plumbing so that I could look at the throttle body. I was completely disgusted when I pulled the trhottlebody. The back side looked like the inside of an oil pan. Completely gunked up. I have never seen so much crud on the intake side. I removed all the sensors and cleaned with alcohol and q-tip, pulled the butterfly and cleaned the throttlebody and butterfly whit come carb cleaner. When I put the plastic muffler back on the top, I noticed that the seal was not very good, it was kind of squashed. I spent some extra time getting it to seal properly. Perhaps it was leaking air into the system after the map/maf sensors???

It seems to have more power and idles a lot smoother. We'll see how it behaves in the next week... I may really get ambitious and pull the intake and look at the injectors if it doesn't act right.

Pulled the upper manifold. Found more gunk, made me sick. Also found a loose screw on the distributer cap. Went ahead and replaced the cap/rotor and gave it a good cleaning.
I ran mine through a decent OBD2 analyzer. I have dual cat's and 4 O2 sensors. It is running extremely rich out of the back O2 sensor on the #1 side (I would have to assume that would be the drivers side). To compound the problem, the #1 side is adding extra fuel at the injector (long term fuel trim). That seems to explain why my mileage had dropped off.
We are going to start swapping O2 sensors around to see if the problem follows the O2 sensor; starting with the rear ones. The bummer of the whole deal is that it is a one try per day project because of the heat under the cats.
It just doesn't get any better.
The more I read, the more of us are seeing the same thing with our big blocks!

Swapping rear O2's won't change anything as they don't affect fuel delivery they just monitor the catalytic efficiency. The O2's close to the manifold affect fuel delivery

you might need to replace the cat converters... if semi plugged the hotter the vehicle gets the more backpressure they will give you and result in extreme loss of power and terrible gas mileage.

Any way to eliminate the cats without turning on the check engine light?

I have not tried (yet) but I hear you can get some O2 sensor eliminators to plug in place of the 2 rear sensors. They are supposed to send the computer a "perfect" reading all the time so that the computer does not compensate either way.