Engine has a lack of power?

Exhaust pressure is fine, no trooble codes at ell, just very sluggish acceleration, I think its either a clogged fuel filter, or a ignition problem, wires, coils, cap and rotor, I put lucas octane booster in it and it has just has a synthetic 10w30 oild change the truck has 400K on it and she's still going strong this has just recently started where she has become extremely sulggish and is lacking power

The truck aslo has a Cold Air intake on it plus a few other performance mods, I'm not really an amateur when it comes to cars I have been working on them since I was 7 years old, I'm going to replace the plugs and wires see if that's the problem as I was going to be purchacing MSD complete igniton for it anyways, also I'm going to replace the EGR valve and fuel filter as I haven't replaced those in about 3 years, it could also possibly be an bad o2 sensor as well it looks to me like I might have a bunch of replacing of small parts to get done, oh well an afternoon with some beer and music it'll get done!

Engine Performance problem
1999 GMC Sierra V8 Four Wheel Drive Automatic

Hi,

My 1999 GMC 2500 has the 6.0 liter vortec engine with an automatic transmission with tow options and 71K miles.

I am am and have been experiencing problems that occur only while towing otherwise the vehicle runs flawlessly.

While towing, I tow a fifth camper, the engine looses power and is unable to tow. Looses power meaning that with 'tow haul' disabled or enabled am only able to crawl along at 20 miles and or so with fuel pedal fully depressed.

This is what has been replaced at the GMC dealership already:
replacement of fuel pump, fuel filter, exhaust manifolds 2eac, and complete new exhaust system too include replacing two costly catalytic converters. Two sensors were replaced and the truck still has the problem.

Needless to say I am discourgaged to deal anymore with the local GMC dealership as I just paid over 5K for the above work to be performed that did not correct the problem. Is there anyone that possibly shed some light on where the problem may lay so I can take it a local mechanic?

Again without the trailer attached there are no issues whatso ever with the vehice, transmission or engine.

Thanks in advance!

Tony

My little bro had a similar problem he discovered that two of his injectors were partially clogged causing a slight misfire under a load and the computer whet into safe mode and would only let him get to about 25 or 30 mph. He removed the injectors and cleaned them and no problems since.

Hi,

Thanks for the reply - it makes sense that if the fuel injectors were fouling out under load it would cause issues with the exhaust, hence the computer code which prompted the expensive repairs which did not cure the issue.

My next question is how to does one determine
if the fuel injectors are potentially fouling under load? Would this throw a computer code?

Thanks again!

Yes and no sometimes it will throw a code but since it only does it when your haulin it may not throw a misfire code. The only way we found that the injectors were fouling was to take them out one at a time and look at the bottom and you may see some junk in them and just take some carb cleaner and spray them. There actually really easy to get out it took us about 45 min to do all 8. Now this may not be your problem but its cheap and easy and worth a try. Good luck

I'll be driving around 70mph on the freeway and the speedometer will start rapidly fluctuating. I'll slow down to around 60mph and it still continues. After a while, it feels like the engine loses power and it drops to around 45mph. I'll try to hit the gas more, but it just sounds like the engine is revving. I'll pull over to the side of the road and wait a bit to drive again. I started driving again but kept it under 55mph, and it'd be fine. If I went up to 57mph, it would act up again. I had this problem last winter, and we realized it was because I had the 4 wheel drive on while driving long distances. After we discovered that, I hadn't touched the 4 wheel drive since. However yesterday, 8 months or so later, I had the same problem. I made sure that it was in 2 wheel drive, so I have no idea what else it could be.

We scanned the codes and did a diagnostic last spring and they were fine. It showed no problems, though it was not acting up at the time. The check engine light never came on. The fuel pressure isn't the issue, because I was able to continue at the same speed while the speedometer was acting up. In brief, the speedometer fluctuates down and back up again, at first from 50-60, eventually getting worse and going down 30-60. The truck in spurts acts like its in neutral and the engine will rev up when accelerated, but the truck itself slows down to 45mph. If I keep trying to drive, it'll stay around 45mph, but I usually pull over because it doesn't feel safe to drive. After 5-10 minutes rest, often with the engine still running, I'll drive again, and it'll be fine for a bit. The tranny fluid is good, as are the other fluids.

Engine Performance problem
1998 GMC Sierra 350 Vortech Four Wheel Drive Automatic 192000 miles

When I crank up everything is fine. When I put the truck in gear my speedometer and tacometer and odometer don't work and when I take off it is really sluggish and acts like it doesn't want to take the gas. I have been told it was and oxygen sensor, or octane sensor. Not sure which is which or if there is such a thing.

I recently replaced the Idle air control valve, throttle postion sensor, MAFS, O2 Sensors, thermastat and for some reason it keep cutting out on me. What else can I check since I am a novice mechanic. Im not getting any codes and it seems difficult to start which takes about 3 times and with a little help from me pressing on the gas pedal

Called the mechanic that worked on it the other and said the vaccum were within range. He also suggested the temperature sensor I'm waiting for it to cool so I can pull out to check it. PCV valve is also brand new I forgot to mention last night. Dumb question how would the temperature sensor affect the truck? The mechanic said the sensor may not relaying back to the computer that it is operatoring at 190 degrees since I could had the wrong thermostat install which was giving them a reading of 160. I hooked up my program to the truck and I was getting a reading of 194 degrees. Wouldn't the sensor register as bad at this point? Thanks for the help sorry I'm asking a lot of questions just tired of it quitting on me it good truck and plan on keeping it for a few more years. Thanks
Gilbert

Changed out fuel filter havent been able to fuel pressure reading. The shop said it was good when I talked to them yesterday. But I have a new problem when I taking the temperature sensor I saw that the I think it the upper intake manifold was cracked where the temperature threads into. Is that the right name "upper intake manifold"; I filled it in with soem RTV I dont see any leaks and made sure to put teflon tape on it and was as careful as one could be when installing the temperature sensor to avoid cracking it anymore. Doesnt seem to be holding back anymore but the start is still a little sluggish

Truck is hard to start. Chugs really bad when idling, almost like a lope. Has a hard time accelerating from a stop, and sometimes will stall or bog really bad. Uses alot of gas for a v6. Smokes sometimes when started and reeks of a gas smell. I have a p300 multiple cylinder misfire code. Ive replaced the cap, rotor, plugs, wires, coil, and fuel filter.