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Thread Title:

cat mbn

Created On Saturday December 08, 2012 14:48

ken2003

Posts: 4
Joined: Dec 2012

Saturday December 08, 2012 14:48
I have mbn cat after motor gets warm normal temp sometimes takes a few hours running the motor will skip at idle #1 cylinder cuts out changed injector still does it but if youshut motor off and restart it goes away any input wuold really help

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meanandnastycat76

Posts: 2
Joined: Dec 2012

Wednesday December 12, 2012 08:01
does it have any check engine light coming on ? ------------------------- Caterpillar dealer technician , and other diesel engine repairs , over 20 year's in truck repair

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ken2003

Posts: 4
Joined: Dec 2012

Wednesday December 12, 2012 17:20
no check engine light.Have had on cat computer and had solinoid test done and everything checks good!

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meanandnastycat76

Posts: 2
Joined: Dec 2012

Thursday December 13, 2012 21:02
Any smoke when started , if so , I've seen in the past head gasket issue , I belive a cylinder cut out test while problem is active will help out a lot ------------------------- Caterpillar dealer technician , and other diesel engine repairs , over 20 year's in truck repair

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ken2003

Posts: 4
Joined: Dec 2012

Friday December 14, 2012 12:42
No smoke when starting .Cylinder cut out test shows #1 cyl not fireing bring idle up to 900-1000 skip goes away and passes cut out test.Like i posted when it skips if you shut engine and restart it idles fine.And only does it after truck running for couple hours.

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TDcrash63

Posts: 163
Joined: Sep 2007

Sunday December 16, 2012 07:51

Some times with this kind of problems the miss is the result of problem with the suspect cylinder. Something causing lower than normal compression in that cylinder. I have seen many engines come in for repair. Tech performs auto cutout test. All cylinders ok. Then cuts them out manually at idle. Number * not firing. Simple? Pulls out suspect injector. Replaces it and reruns test. NO CHANGE O crap. Pulls injector back out. Reclean injector bore. Paying close attention to the lower area. Remove intake elbow and visually inspect intake in the area of suspect cylinder, leave intake off. Take a rubber tipped blow gun and pressurize the cylinder with shop air and carefully listen for air leaking into the intake side of the head. Also observe exhuast stack for white smoke if engine is warm or any signs of air leaking into the exhaust. You must push down straight and firm with your blow gun and achieve a tight seal blow and release, try to hold all the pressure in the cylinder and listen carefully. If you hear any air going into the intake or exhuast you will have to pull the head. If ou have an excessive amount of air going into the lower end you have a cylinder problem, rings, liner ect. If all checks out look at the tip of the injector where it seats in the head. Make sure it was seated properly Many times the lower bore where the tip seats right above the lowest oring is not properly cleaned. I use a cummins injector bore brush with the handle cut off. Put it in my drill. Take a 1 by 1 piece of scotch brite pad and stick it to the tip of the brush and run it down in the head until the lower bore is clean. You will see the carbon going away as you clean. Then clean the injector tip by hand with scotch brite as well. if the cylinder tested ok with air at this point I will swap an injector next to it as well as to see if the problem travels, or just goes away. If it travals of coarse it is the new injector. Also Beware I had a truck with improperly programmed injector codes have the same problem you are describing. They were all programed to 2200 when corrected miss went away. Program your trim codes correctly when troubleshooting.

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JoeZ

Posts: 938
Joined: Dec 2008

Sunday December 16, 2012 12:59
I wouldn't rule out "O" rings, but also check the cam and rollers, valve springs and wiring harness....run a compression test. ------------------------- One of the last 2 Stroke mechanics left. 44 years in the business and worked on everything from 53 series to 149 series. Winding it down now...time to move on.

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ken2003

Posts: 4
Joined: Dec 2012

Sunday December 16, 2012 14:54

Thanks for all the replies but what do you think about the fact that when i shut off the truck and restart imeditly the skip goes away.I had another tech tell me maybe a bad ecm with an injector drive going bad he suggested a test ecm to see if the problem goes away I just don't have a spare ecm laying around.The truck runs great exept for the skip after it gets hot no smoke no blowby does not use oil.

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TDcrash63

Posts: 163
Joined: Sep 2007

Wednesday December 19, 2012 19:13

I have never seen an Ecm cause a miss without codes. Could happen just never seen or heard of it. If you can get it to do it easily pull the front cover with it running and missing and check voltage at the solinoid with the engine running and compare it to number 2 cylinder. I have seen loose valve seats and other cylinder problems due what you are describing, I have seen harnesses cause intermittiant problems and no codes. Unplug it at the valve cover and pull it loose back to the Ecm, look it over, maybe you have a rub spot

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