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Thread: Lly duramax runs good when cold but runs and idles rough when engine warmed up

  1. #11
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    Quote Originally Posted by thunderhead View Post
    OK let me know please how you make out . My Alt gauge reads minus when running .
    thanks
    One thing you might want to check if you have access to a scan tool would be your actual fuel rail pressure while idling engine warmed up, if it jumps more than 100-200 psi it is possibly your fuel pressure regulator on the back of the injection pump, example idling when warm will be around 4.2 kpsi if it jumps to 4.3 then to 4.1 then back to 4.2 it would be probably ok, but if it jumps maybe around 4.5 or a big jump while idling then there could be a problem with the regulator. I have replaced mine multiple times with no luck so that is not the problem I am having but wanted to clarify that in case it is your problem. I will still let you know the results of my alternator swap regardless thanks
    Bronson

  2. #12
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    Quote Originally Posted by bronson1376 View Post
    One thing you might want to check if you have access to a scan tool would be your actual fuel rail pressure while idling engine warmed up, if it jumps more than 100-200 psi it is possibly your fuel pressure regulator on the back of the injection pump, example idling when warm will be around 4.2 kpsi if it jumps to 4.3 then to 4.1 then back to 4.2 it would be probably ok, but if it jumps maybe around 4.5 or a big jump while idling then there could be a problem with the regulator. I have replaced mine multiple times with no luck so that is not the problem I am having but wanted to clarify that in case it is your problem. I will still let you know the results of my alternator swap regardless thanks
    Thank you . Have you ever checked the turbo sensors to see if the vanes are open when its not calling for it? I just read this on another post some where else. I started tearing mine down last night to swap out the FPR I will leet you know if this fixes mine .

  3. #13
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    Quote Originally Posted by thunderhead View Post
    Thank you . Have you ever checked the turbo sensors to see if the vanes are open when its not calling for it? I just read this on another post some where else. I started tearing mine down last night to swap out the FPR I will leet you know if this fixes mine .
    I haven't looked at the vanes, but my truck has a lot of modifications, at idle I have the tuning set for the vanes to be open anyway so it rumbles at idle not whistles, also just to let you know you don't have to remove the injection pump to swap the regulator, you can do it while in place. The bolts are a pain to get to but if you get the right size star on a socket or even a long one you can cut down to the right size and use a wrench to turn them you should be able to change it, just make sure to clean all dirt from around the regulator and maybe when it is removed before installing the new one turn the key on and just tap the starter so it blows fuel out of the hole and any dirt that would be in there. Also make sure to lube the o-rings on the new regulator and do not force it in. Gently reinstall it, if you tear the oring or cut it in any way it will cause issues as well
    Bronson

  4. #14
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    Well FPR didn't fix problem . Im leaning towards # 5 injector . when its cold the balance rate is any wheres between + 4.0 to +5.8 at idle . then it warms up and goes back down to+ 2.3 to 1.9 + and then i cant get balance rates unless i put it in gear then its still + 3.5 or 5. all other balance rates are -1.2 to -2.2. a few are +2. something but they very so much . Im ordering one injector to see if that corrects the problem . when it missis its like i turn off the injector . And if that don't fix it I'm changing the FICM. I have seen you tube on that going bad and causing a miss . Have you changed your FICM yet ?

  5. #15
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    Quote Originally Posted by thunderhead View Post
    Well FPR didn't fix problem . Im leaning towards # 5 injector . when its cold the balance rate is any wheres between + 4.0 to +5.8 at idle . then it warms up and goes back down to+ 2.3 to 1.9 + and then i cant get balance rates unless i put it in gear then its still + 3.5 or 5. all other balance rates are -1.2 to -2.2. a few are +2. something but they very so much . Im ordering one injector to see if that corrects the problem . when it missis its like i turn off the injector . And if that don't fix it I'm changing the FICM. I have seen you tube on that going bad and causing a miss . Have you changed your FICM yet ?
    I have replaced the ficm with a brand new gm unit, also I wouldn't order a injector on balance rates alone. You need to do a fuel return test on the injectors because I have seen the injector before or after on some trucks be causing the problem with the balance rate on another due to the injectors being on the same rail. The test isn't hard and you can find plenty of info on how across the internet. My opinion is stay away from Pensacola diesel, I have used them twice and the injectors tend to not be the best remanufactured and no help from them when needed on warranty. I did replace my alternator but haven't driven my truck much, but seems so far to be idling smoother, but still when it's up to temp I can't any balance rates to come up. Might just be the weather right now making the idle smoother or what not, but to early to tell until I drive it more. Also one more thing I can think of that might be both our problems is the fuel pressure plug on the back of the driver side fuel rail, I just remembered I had a issue with the race plug sealing when installed at one point so I might try to test that return as well and see if maybe I have a slight leak causing fuel pressure problems at idle and what not. If I get time to test I'll let ya know the results. I do remember the race plug I installed being a cheaper brand so maybe I'll order a ppe and see if it seals better. Also another thing to check would be the wiring to the injectors to make sure they are getting good contact, gm sells a updated injector plug kit for the front in driver side and rear on passenger that are at a 90 so the wires don't break, might check that but mine has already been done
    Bronson

  6. #16
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    Quote Originally Posted by bronson1376 View Post
    I have replaced the ficm with a brand new gm unit, also I wouldn't order a injector on balance rates alone. You need to do a fuel return test on the injectors because I have seen the injector before or after on some trucks be causing the problem with the balance rate on another due to the injectors being on the same rail. The test isn't hard and you can find plenty of info on how across the internet. My opinion is stay away from Pensacola diesel, I have used them twice and the injectors tend to not be the best remanufactured and no help from them when needed on warranty. I did replace my alternator but haven't driven my truck much, but seems so far to be idling smoother, but still when it's up to temp I can't any balance rates to come up. Might just be the weather right now making the idle smoother or what not, but to early to tell until I drive it more. Also one more thing I can think of that might be both our problems is the fuel pressure plug on the back of the driver side fuel rail, I just remembered I had a issue with the race plug sealing when installed at one point so I might try to test that return as well and see if maybe I have a slight leak causing fuel pressure problems at idle and what not. If I get time to test I'll let ya know the results. I do remember the race plug I installed being a cheaper brand so maybe I'll order a ppe and see if it seals better. Also another thing to check would be the wiring to the injectors to make sure they are getting good contact, gm sells a updated injector plug kit for the front in driver side and rear on passenger that are at a 90 so the wires don't break, might check that but mine has already been done
    Any luck?
    I read on another forum that some one replaced the nsbu switch .

  7. #17
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    Quote Originally Posted by thunderhead View Post
    Any luck?
    I read on another forum that some one replaced the nsbu switch .
    No luck yet, seemed to not idle as smooth as the other day but wasn't necessarily rough... to haven't had time to check the returns on the fuel rail plug due to getting my race car ready for the races but hopefully during this week I'll get the time to check. I haven't replaces the neutral switch but can't really see how that would cause idle issues but still have shifting and such ok
    Bronson

  8. #18
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    Quote Originally Posted by bronson1376 View Post
    No luck yet, seemed to not idle as smooth as the other day but wasn't necessarily rough... to haven't had time to check the returns on the fuel rail plug due to getting my race car ready for the races but hopefully during this week I'll get the time to check. I haven't replaces the neutral switch but can't really see how that would cause idle issues but still have shifting and such ok
    Well my Desired turbo charger vain position is 88 and my turbo charger position is 29 ? its jumping all over the place and when it really lops bad i can here it through the air cleaner like my EGR is opening up . And thats all over the place also . And i know am getting barometric pressure code . This all at idle warm .? Isn't the EGR closed at idle ?
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  9. #19
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    Quote Originally Posted by thunderhead View Post
    Well my Desired turbo charger vain position is 88 and my turbo charger position is 29 ? its jumping all over the place and when it really lops bad i can here it through the air cleaner like my EGR is opening up . And thats all over the place also . And i know am getting barometric pressure code . This all at idle warm .? Isn't the EGR closed at idle ?
    I'm not sure if the egr is supposed to be closed during idle but mine is fully deleted, but now that you mentioned it, I did have turbo vane position sensor codes awhile back before the lope started that I kept clearing and called turbo manufacturer and told them and then they kinda stopped coming up, maybe for you a bad barometric pressure sensor.... I never thought my vane control solenoid for my turbo could be bad due to my turbo only having a couple thousand miles when I was getting the codes, and I don't beat on my truck I drive it like a baby, but I guess anything is possible... tomorrow I will use the Snapon scanner and monitor the commanded versus actual vane position and let you know, my truck was idling Lopey again today so maybe that will give me something else to look into... also even with a new alternator noticed voltage at idle would randomly drop off still then come back up.... possible bad alternator from napa, will order another as well and see if that stops
    Bronson

  10. #20
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    Quote Originally Posted by thunderhead View Post
    OK let me know please how you make out . My Alt gauge reads minus when running .
    thanks
    So no luck with my issues, have you figured out what it was on the truck?
    Bronson

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