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Running Rough

by snelson95 on Jul 29 2017, 6:20 AM

I have a 1997 Dodge Ram 2500 4x4 5.9L V8, when its running its got a rough idle, its worse in gear and foot off the brake while the truck is creeping forward or even just trying to move, while at idle and no load, its still there just not as bad. While driving truck, cannot feel any roughness at all, no dtc's either,

Was not sure where to put this so i just chose here to start at least.

Appreciate any help.

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11 Replies

By 1986chevyman Aug 06 2018, 2:07 PM

You said cylinder #5 only had 30-40 psi compression. You need to squirt some oil in cylinder #5 and recheck compression. If compression comes up, you have a piston ring problem. If not, you have a valve issue.

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By ifixthecar Jun 15 2018, 7:55 AM

Worked for Chrysler for 13 years. I have found performing a leak down test to be the best way to diagnose these issues. Most of the time you wont find anything wrong with just a compression test. Have problems with valves not rotating, and cracked heads.

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By voltageviking Nov 10 2017, 2:33 AM

I see you found out the issue was poor valve sealing, and wanted to offer a quick test (if you don't already know of it) that can help find that issue much quicker. There are plenty of online videos about this test. Try a relative cranking compression test using an oscilloscope/lab scope. It has saved me a lot of diag time previously.

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By snelson95 Nov 10 2017, 1:56 AM

did a compression test and found number five cylinder at about 30-40 psi compared to ~130 on other cylinders, cylinder leak test found exhaust valve were leaking 100% at least on cyl 5, past compression tests were okay, which is what led me away from that, thanks for all the help

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By 1986chevyman Sep 08 2017, 6:14 PM

Check your fuel trims. If your trims get better at 2000 RPM, I would say you have a vacuum leak

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By shadetreetech Aug 03 2017, 8:41 PM

Some of Dodges have a plate on the bottom of the Intake manifold that can cause a rough idle and oil consumption. Remove the PCV and breather cover the seal the holes and see if there if a pressure build up or a vacuum. there should be some pressure . If there is vacuum be highly suspect of the intake plate gasket

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By rgerlock Aug 03 2017, 2:57 PM

Sounds like a vacuum leak for sure

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By autotechteach1 Aug 03 2017, 10:41 AM

Could be a weak spark It is most likely still misfiring at higher speeds it is just not as noticeable due to leaner fuel conditions. I believe it could be a weak coil. Also check all ground connections for the ignition system

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By jeffreyd1 Aug 02 2017, 3:03 PM

Couple of ideas. 1) put a vacuum gauge in the dipstick tube. Real common to have the lower gasket on the intake manifold leak & pull crankcase into a vacuum. Can cause roughness. 2) verify compression is even. Test both cranking & running. Uneven compression would be most noticeable at lower rpm. Sometimes we will get valves that don't seal right intermittently which would only be caught by performing a running compression test. 3) Make sure that the EGR system is not bleeding through at idle. Plug EGR ports & see if roughness goes away. Hope this helps. Keep us posted.

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By vanislewrenches Aug 01 2017, 6:04 PM

Hook up a fuel gauge and see if she's running low pressure at idle.

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