So I took my truck to a mechanic because it has been idling rough as if a cylinder is missing. They ran a diagnostics and everything including vacuum, distributor, spark plugs etc were all good. They said they would have to tear into the engine to actually figure out the problem which would be $800-$900 and then fix whatever needs to be fixed.

Has anyone heard of this problem from the chevy 4.8l V8 engine? I'm basically trying to get an idea if it's worth tearing into with the possibilities of having to replace the engine etc. or just selling it. It's paid off and has 135k miles on it, but i'm not that interested in dumping 4k into an $8500 truck. Thanks for any ideas.

Take it somewhere else, that mechanic sounds stupid as sh*t. There's no need to take apart the engine unless until you know what needs to be replaced and if it's internal.

No light?

Did they specifically say they checked the distributor? I would love for them so show me the distributor on your motor

[This message has been edited by silverado_lover (edited 6/20/2013 12:26p).]

Perhaps not, maybe they said the distribution to the cylinders. I'm not certain. Would you suggest the dealership for a situation like this? Thanks.

Only time I suggest a dealer is when it is under warranty.

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They ran a diagnostics and everything including vacuum, distributor, spark plugs etc were all good. They said they would have to tear into the engine to actually figure out the problem which would be $800-$900 and then fix whatever needs to be fixed.

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GM has not ever had a distributor in a 4.8 or 5.3L Gen III V8 motor.

Get it the hell out of there.

The next thing to do would be a compression test, not "tear into the engine". F that S.

Has it thrown any codes? How "rough" is it idling?

I'd start with the easy stuff like plugs/wires and the like. Clean the MAF, too. Check the air filter. Etc.

The check engine light is on. While idling in drive it's smooth with the occasional lope. It's hard to explain but that's the best I have.

So y'all would suggest a new mechanic that is not a dealership?

if the check engine light is on, go to o'reily and have them code it.

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The check engine light is on.

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Go to O'reileys and get them to run a diagnostic test on there to see what the code/codes are. Come back and post them. I'm sure one of the gurus on here can further advise from there.

will do, thanks.

I called and got the print out of what the mechanic said and I can only assume that the receptionist or the person answering the phones didn't know what he was talking about hence the distributor comment.

The mechanic's notes are as follows, "tested ignition system. secondary and primary ignition system is good. vacuum pressure is stable and steady. fuel pressure and fuel volume are at specs. injectors are functioning properly and drop tested good. cylinder 1 found running compression is 15 psi lower than all other cylinders. suspect internal engine problem."

recommendation 1- remove and replace cylinder head gasket

They admitted that they weren't sure if that would fix the problem. Any thoughts?

So they suggested one of the most expensive repairs and then followed up with "we're not sure if that will fix it?"

Is 15psi enough to care about, 1Ags?

15 PSI lower in ONE cylinder will not cause it to run like that.

I think a leakdown test is in order before a head gasket replacement. That should at least give evidence for or against a leaky head gasket.

I assume the codes indicated misfire in cylinder #1? Any other codes?

I'd also be curious what the spark plug for that cylinder looks like in comparison to the others.

head gasket won't cause that small of a drop in compression...

then again, 15 psi, isn't complete data... lower than what? if the rest of the cylinders are running 30 psi, it's a HUGE drop. If they are running 150 psi, it's 10%.

that would likely be a leaky valve (which would ultimately involve a head gasket replacement, but be even more expensive).

Turn that cylinder to a compression stroke, put compressed air into the sparkplug hole, and see if you can hear air in the exhaust or intake...

265,000 miles on my 5.3. I must be lucky.

Ive had a rough idle and horrible gas mileage on a 2003 5.3 chevy. I dont know what exactly the problem was but it stopped and got better gas mileage after I cleaned the MAF, throttle body, replaced the alternator and seafoamed the engine and gas tank a few times.

tamu, excuse my ignorance, but what is the MAF and how did you clean it? Also, what is sea foam cleaning?

MAF = mass air flow sensor. It is needed for the computer to adjust the mixture properly. Wouldn't hurt to clean the intake and MAF with intake cleaner. Seafoam is an additive to clean out the innards...also wouldn't hurt to try before moving on to move invasive steps or parts changing.

MAF is the mass air flow sensor.
They sell a specific cleaner for them.
Seafoam is a cleaner you can either run through your gas tank or some have let it get pulled into the brake moister vacuum hose.

killer, the MAF is pretty easy to do. you don't want to touch it because it has tiny little thin wires so you spray it with MAF cleaner.

seafoam is just a motor treatment solution. I've learned that the vortec engines need about 2 ounces of seaform for each gallon of gas in the gas tanks. I add it before I fill up my tank so it mixes well. You can also put it in through the throttle body or a vacuum line. In that case, you suck it in and keep the truck from stalling, turn it off and let it sit for 30 minutes. After 30 minutes it will probably make a ton of smoke out of your exhaust from all the carbon deposits it has dissolved.

Clean the throttle body. Mas air. See how she runs. Pull the codes. Might have a bad o2 as well. No engine noises?

No engine noises yet. Ill give the cleaners a go and report back. Ill also get oreilly's to get the codes for me. Thanks guys