6.5 studders at acceleration - Diesel Bombers



6.2L & 6.5L Performance Discussion of Chevy and GMC Trucks with 6.2L and 6.5L Diesel Engines Related to Performance and Longevity

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Old 03-07-2015, 09:10 PM
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Default 6.5 studders at acceleration

I have replaced pmd my lift pump & ops. Nothing has helped at all. My mechanic reset the ecm replaced the crank sensor & nothing has improved what so ever. Im beginning to think that it cant be fixed & its something I will just need to deal with. Please there has to be someone out there that has had this problem & was able to figure this out.
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Old 03-09-2015, 03:05 PM
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There is still a lot more troubleshooting you can do, don't give up hope yet. Have you checked or replaced fuel filter? Also, what about vacuum pump? Do you have a boost guage and if so what numbers are you seeing? and SES light? are you seeing a lot of black smoke accelerating? Possible air in fuel lines, clogged fuel filter, start cheap and easy and work your way up.
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Old 03-09-2015, 05:23 PM
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No black smoke whatsoever. What would be easy way to see if air is getting in to fuel system? Also have been running with fuel cap loose. Runs great other than when it needs more fuel. Even taking off from dead stop it wount do it. But if u need to try & pass someone ha! I dont even try anymore.
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Old 03-09-2015, 07:25 PM
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If your only able to make it run with the fuel cap loose then replace it first. I also suggest bleeding the fuel filter/ replacing it depending on how many miles are on the filter. I go overboard and replace mine every 10,000 miles just to be safe.

Do you have a boost gauge? fuel pressure gauge? Whats been done to the truck? ECM reflash? If you can fill out your sig that would help, more info about whats been done to your truck would help greatly. Can you get a video of the truck accelerating/stuttering?
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Old 03-09-2015, 08:19 PM
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It makes no difference if cap is loose or tight. I cant send vidieo because its not at my house its at a friends we been trying figure this out together. Has a new fuel filter and has done this even after filter was replaced. No black or white smoke. I havent checked fuel pressure. It would be hard to check cuz only does it when going down road & getting in it. New lift pump ops crank sensor. I dont think its IP cuz it runs great other than that. Ill fill out the sig sorry. New to this
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Old 03-12-2015, 06:12 AM
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[QUOTE=koolbusdriver;1088382]No black smoke whatsoever. What would be easy way to see if air is getting in to fuel system? Also have been running with fuel cap loose. Runs great other than when it needs more fuel. Even taking off from dead stop it wount do it. But if u need to try & pass someone ha! I dont even try anymore.[/QUOTE

You want to get a piece of clear fuel rated hose and run it to the inlet of the IP this makes trouble shooting a whole lot easier.
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Old 03-12-2015, 09:39 AM
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Thanks ill try that this weekend weather permitting. I have to work on it outside cuz all the so called pros around here cant fix it. Taken it to 3 different mechanics. Oh well hopefully with some help here ill figure it out myself. Cant be any worse just cheaper! Thanks alot
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Old 06-21-2015, 12:54 AM
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Could be in the throttle peddle, could be in the PMD could be in the optical sensor could be bad lift pump could be bad injector pump could be computer to trans issue or even trans issue. BTW is the turbo spooling up? If the turbo is not spooling you may have snapped off the drive impellor which leads to the exhaust getting plugged leading to that stuttering on accel cause the engine is choking out.
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Old 06-22-2015, 07:12 PM
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Default Repacked all the above

I have replaced everything but turbo & really dont think that is what it is. Could it be lift pump is showing right psi but hasn't got enough fuel flow under heavy acceleration? Would a heavy duty lift pump be worth a shot?
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Old 06-24-2015, 11:09 PM
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That did not answer the question of if the turbo was spooling or not. If the turbo is not spooling then you will have issues. An you said you just replaced the lift pump you could pull the line and see if its giving a good steady stream but they really only need to supply 15psi max its the IP doing all the heavy pressure. You could try shooting the electronics under the throttle peddle with a can of electronics cleaner as well let it dry and see if that helps. Is the computer throwing any codes?
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