95 GMC 6.5L Turbo Diesel idling rough


Old 01-20-09, 04:47 PM
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Join Date: Mar 2005
Location: West Virginia
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95 GMC 6.5L Turbo Diesel idling rough

Alright, a buddy of mine has a 95 GMC 3500 dually with a 6.5L turbo diesel and manual tranny and it is idling rough. What can you do to maybe fix that problem? I know that the fuel injectors were replaced on it. 134k miles on the motor.
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Old 01-20-09, 05:02 PM
Join Date: Jan 2009
Location: Tennessee
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Im not sure on that 1 ,I know on fords they are bad for the IAC motor sticking which would cause rough idle not even sure if diesels have one.
Old 01-20-09, 09:11 PM
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Join Date: Apr 2008
Location: Oklahoma
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the idle and injectors are electronicly controled. if it is idling rough the first thing to start with is unfortunatly a compression test to make sure that the mechanical parts of the engine are not the problem. not sure about gm diesels but i know on cats if they have low oil pressure it will cause running problems.

are you going to cowboy up or just lay there and bleed?
Old 01-23-09, 05:43 AM
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It's because it isn't a Cummins.....JK. What is your fuel pressure? On older model (2001) Cummins, we have to install fuel pressure gauges to ensure the lift pump is constantly doing it's job. If your lift pump isn't working properly, the engine will falter and eventually fail. Consider, too the lack of lubrication in current diesel fuel. The government has reduced the sulphur content in the fuel to accommodate 2007 and up engines. Although the sticker on the side of the fuel filler tank says it is ok for "all diesel engines", don't believe it. You have to replace the sulphur somehow in order to lubricate your injector pump. The best way to do this is pour in 1 ounce of 2 cycle oil for every gallon of fuel at each fill up. No more. You will see a definite smoothout of the engine.
Old 01-28-09, 08:46 PM
Join Date: Feb 2001
Location: United States
Posts: 138
Like chandler said, check your lift pump.
We replaced these on our city buses every 6-8 months.
90 percent cause of rough idle, chugging down road and smokeing.
Also could be a injector pump

Last edited by rajung; 01-28-09 at 09:05 PM.
Old 02-08-09, 11:00 AM
Join Date: Feb 2009
Location: New Mexico
Posts: 1
Rough idle or REALLY rough idle? Remove the clutch inspection plate to make sure that your flywhell is in one piece. My 94 6.5 had a 2-part flywheel that seperated and caused a terribly rough vibration at idle and beyond. I was chasing motor problems when it turned out to be the flywheel.

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