Low Compression? Rough Idle

dthompson · Dec 17, 2015

Ok, truck was brought by for a rough idle. To me it's hardly noticeable. Had new injectors less than say 10k ago. Its a 97 with 190k, but it's a feed truck. Contribution was fine, ICP is 500ish at idle. At idle it burns your eyes with the fuel smell. Little smoke but once warm no real smoke. Starts and runs fine. Did a compression test. Not so good. Ranging from 250-280. If I'm not mistaking this is low right? Is this the problem with the slightly irregular idle? Like I said I hardly notice, but the guy says it's driving him crazy. LOL

Powerstroke1098 · Dec 17, 2015

That is pretty low, have you tested other trucks with the same tester and received good #'s?

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Arisley · Dec 17, 2015

Put a teaspoon of oil down a glow plug hole. Retest compression. If it improves, you have bad rings.

79jasper · Dec 17, 2015

Look at the airbox, if it's factory I bet it's been eating dust.

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Powerstroke1098 · Dec 17, 2015

You said it starts fine? I can't imagine it would start well with only 250-280psi.

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dthompson · Dec 17, 2015

Starts pretty good at 40 ish anyway. It's only a 300 psi gauge, but I've had it pegged before . It does have the good Ole stock obs filter box. And like I said it has a strong raw fuel smell at idle. Personally think he's just worried about nothing. It's just slightly off. I have to really pay attention to notice. But thought I'd try to make him happy.

79jasper · Dec 17, 2015

A 205° tstat got rid of the burn your eyes exhaust on mine.

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dthompson · Dec 17, 2015

^That's good to know. Any suggestions on the idle? That's what he's wanting fixed

mandkole · Dec 17, 2015

even but low compression is one thing, but uneven compression is what will give a noticeable, unmanageable idle. Agree, 250 seems pretty low for good starts.

dthompson · Dec 17, 2015

Maybe I'll try to locate another gauge. Anything else that could be giving it a off idle

79jasper · Dec 17, 2015

Some obs's just seem shakey.
Ask what brand oil he's running.

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Powerstroke1098 · Dec 17, 2015

Make sure when your cranking all eight glow plugs are out, also there's a million things other than compression or injectors that can cause an off idle.

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