99 Gmc 2500 Troubles

[Forsythian]

Here's an interesting problem for you mechanics out there...

The truck has a 5.7L Vortec engine with about 100,000 miles... has always run well.

I was driving in a bit of traffic when it very suddenly began running rough, and a strong sulfur smell filled the air.

It got me home, and I've had it out since for the short trip to Oreillys.

The sulfur smell seems to be gone, but the truck acts like it's only running on 7 cylinders.

No "check engine" light has appeared. I've replaced plugs and wires so far. Any ideas? thanks a bunch

[JobyKSU]

I'm not an expert, but I did stay at a Holiday Inn last night.

It sounds to me like you have at least one cylinder that's not firing for some reason. I'd take a look at the distributer, maybe a broken rotor? The sulfur smell is from unburnt fuel making it to the cat converter so you should only have one thing to fix for now.

The good thing about that engine is that it shouldn't be that expensive to fix, and then you'll drive it for another couple of hundred thousand miles.

Good luck!

[Forsythian]

Thanks Joby, but I don't think that's it.

I drove it a bit today, it runs pretty well on the highway, it's idling horrible. It's lost some power too, but it doesn't seem to be missing (especially at about 35 mph or better).

I was hoping some bad gas (I know how that can be), but no.

Maybe an O2 sensor, but shouldn't that cause the dummy light to come on?

[Rusty]

catalytic converter

[crappiefisherman]

you have a stuck open egr valve, Carbon has prolly stuck it.Also if it was missing a check engine light would shine, and a miss code would be set.

[Forsythian]

you have a stuck open egr valve, Carbon has prolly stuck it.Also if it was missing a check engine light would shine, and a miss code would be set.

Well, I just replaced the egr valve... It seems to be idling better, but once in gear and accelerating from a stop it is still pretty rough. Looks like I might be headed for the shop.

[snagged in outlet 3]

I have a 99 Yukon and your problem sounds familiar. Mine was caused by a bad rotor. It was riding high on the points and ran rough because it was missing one occasionally.

SIO3

[crappiefisherman]

make sure you dont have another vacumn leak as hose are easy to damage, on that vehicle it prolly has hard plastic lines that can break or rub holes in them.has the smell subsided?Has it set any codes?IE check engine lite shining?Did you find any carbon in the internal workings of the old egr valve?

[gonefishin]

Is your check engine light operational? First thing I would do is a complete tune up, rotor, cap, plugs, wires ie the works. At 100, 000 miles it is probably due.

Second thing I would do is swing by Orileys and have them test the ECM, not to see if it is throwing codes but to make sure the ECM it self is good.

Finally I would put in all new O2 sensors and MAF. O2 sensors can get 'lazy' which won't kick on the CEL but can cause the car to run bad and reduce economy. Good rule of thumb is to change O2 sensors ever 100,000 miles wether they need it or not. MAF is easy to check...just unplug it and drive the truck, bring it up to 70 mph if you don't notice a big loss in power the MAF is bad.

[Forsythian]

Well, the check engine light finally came on last night... the truck is running progressively worse. Lucky for me, I work about 0.8 miles from home. It goes to the shop on Wed. Thanks for the suggestions, I'll let you all know what the deal was. sheesh, maybe I'll get 20mpg after this is all done!