[The Whale]

So since it's been hot enough to run the AC in my truck, i've noticed a problem. Any time i'm sitting at a stoplight, i can feel and hear the engine dropping a cylinder. It's to the point where it shakes my truck slightly when it happens, and it's getting rather annoying. It will also sputter intermitently upon accelleration, but only through first gear. Tow/Haul seems to make it a little better, but it could just be my imagination. I changed the plugs from the Autolite Platinum plugs that were in it to a set of Delco Platinums, and it seemed better for a bit but it's back to the way it was. It's pissing me off and i'd like to figure out what is causing it. No CEL either. Any ideas? Truck is a 2k Sierra with a 5.3, with about 90k on the clock.

 

[Evan]

Maybe the AC is using too much power off the alt?

 

[nick993]

Have you unhooked your battery lately? if not, have you tried seafoam?

 

[The Whale]

Battery was unhooked while i changed theplugs, about a month ago. Haven't tried seafoam. What's the best way to do it on these trucks?

 

[Denaliano]

Whens the last time you cleaned your throttle body and MAF sensor

 

[The Whale]

that would be never. Its weird though, cause without the AC on it doesnt do it.

 

[The Whale]

ok i seafoamed and pulled out the hypertech tune... no change. In fact, it seemed to get worse. LAst night i was sitting at a red light and it was so bad i could see the tach needle jumping around and the whole truck was shaking. But turn off the AC and everything is fine. WTF?

 

[nick993]

did you do the relearn? try unhooking the battery. let it sit for 30 minutes. then hook it back up, start the truck and let it sit running for about 3 minutes without the a/c on. then after that turn the a/c on and let it run for another 3 minutes. if that doesnt work, then i dont know. maybe a weak alternator that cant keep up when the a/c clutch kicks in. take it somewhere and have it checked if the relearn doesnt help.

 

[wild_chld1]

check sparkplugs for cracks in the porcelean

 

[The Whale]

did you do the relearn? try unhooking the battery. let it sit for 30 minutes. then hook it back up, start the truck and let it sit running for about 3 minutes without the a/c on. then after that turn the a/c on and let it run for another 3 minutes. if that doesnt work, then i dont know. maybe a weak alternator that cant keep up when the a/c clutch kicks in. take it somewhere and have it checked if the relearn doesnt help.

Ill give that a try tomorrow.

check sparkplugs for cracks in the porcelean

Spark plugs are less than a month old and didnt do much to change the problem.

 

[The Whale]

Ok tried that, zero change. Still does it. Tried washing the truck too, and that didnt help either, lol. Coilpack or spark plug wire maybe? Is there an easy way to find out?

 

[nick993]

did you get your alternator checked? i doubt it would be plugs or coil cause it would sputter all the time, not just when the a/c is on. the only thing i can think of besides the alt. is the electronics on the truck, something is loosing power.

 

[The Whale]

didnt check the alternator, but it's reading 14v at idle.

One thing i notice is it won't do it unless it's in gear, AC on, and idling. Once i start moving its fine and smooth, or if i put it in park it's fine. Turn the AC off it's fine. WTF? Also, i think it idles a little low. It's normally 500rpm and about 400-450 in gear with the AC on. Is that normal?

 

[The Whale]

ok wtf... i discovered it does it without the ac on now too at idle, just not as bad.. wires? coilpacks?

 

[nick993]

cracked vacuum line?

 

[slamd91]

i am still having this same problem, i was told it could be my iac, changed it and still doing it. had a major intake leak so i just swapped to a edelbrock performer intake manifold and it got a little better but still doing it. my voltage drops to about 10-11 when it (skips) or (burps) like a misfire. im thinking the alternator myself. let me know if that helps if you change your alternator...

 

[slamd91]

?....?

 

[ah_5500]

my 94 was doing this and it was a vacuum leak. the throttle body gasket was leaking. replaced it and problem solved. check all vacuum stuff and look around the throttle body for a dark dirty spot and put a couple feet of hose up to your ear and run the other end around the tb listening for air. sounds crazy but works good. good luck bud

 

[The Whale]

did a load test on the battery today, and it looks like its junk. supposed to throw out 800cca and its only at 400. found out its a reman autozone battery too, so im gonna try switching that out and see if that helps.