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Discussion Starter #1
here is one for you. just put a new engine in my 98 gmc 3500hd ran fine for about 500 mi. took it in to get the timing checked. and it started running bad it has a miss all the time and about every 30 sec it revs up by itsself it gains about 400 rpm. feels like you hit the throttle real fast and let off. it does it if you give it some throttle and hold it at a constant rpm
i have one person telling me it needs an ip and another telling me it is getting air in the fuel line please help
 

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Fill out your signature with the details of your truck. It will help those that know what's going on diagnose. Also go to the FAQ and go through the diagnostic checklist.
 

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do you have access to a scanner that can read the timing from the injection pump?
 

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Did it ONLY start running crappy AFTER the timing was checked/changed?? If that was the case then it is a timing issue not a pump issue.
 

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I would check all the simple overlooked crap that makes our beloved motors "miss"....vacuum lines and rubber hoses. I barely bumped a line and it shattered into little pieces. If it is "surging" while in idle I would say check your water pump and belt tension. Or could be your throttle position sensor on the pedal, those guys are a problem area as well. Known to cause rev issues, usually high rpm rev. Thats my 2 cents, could be worse but these are just some things to consider.
 

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Double check the grounds. Three on the right side rear head, battery on each head about the middle and last but not least the battery connections.
 

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Discussion Starter #7
checked all grounds all fuel lines went ahead and pulled ip and took to get checked. they found the pdm resistor was missing am in the process of putting ip back on hopefully that was the problem will let ya'll know thanks
 

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Discussion Starter #8
the dealer tech said it was running bad when he got in it but it was running fine when i pulled in the drive. setting the timing did not help any seemed kind of fishy to me. and then the resistor was missing. think i might change dealers.
 

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Welcome to the forum coke, pepsi, or rc guy..........

Unfortunately, your symptoms could be low fuel or air in the fuel lines - any SES or stored DTC's before or after you had the timing set?
 

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Discussion Starter #10
pepsi. there was one code for timing when i took it in and they cleared it out. just got the ip back in and it is running fine now i think somebody was trying to make some money at my expense. when i took the pump in they said there was no resistor in the pdm they put one in it and checked it out and everything was working fine. i think my problem is solved thanks for everybodys help
 

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Don't be a stranger, pcg............

Post back how the 'cure' works out - someone musta replaced the PMD, if it truly had no cal resistor.
 

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Discussion Starter #12
everything is working fine runs like a top thanks for all the help
 
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