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Old 12-08-2011, 01:26 PM   #1 (permalink)
mpanowicz123
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Rough Idle

First things first...i just had headgaskets done 5,000 miles ago with studs. With a new FPR also. Injector rates are perfectly in specs....and no smoke. It occasionally has rough idle the last 4 tanks of fuel. It will go for a little bit..then stop for a min or so. When im sitting in the cab it just kinda bounces during the rough idle...very annoying. If im in neutral or drive it wont do it and as i said...the injector rates are all good, power is good and runs smooth. I have the CTS monitor is there any type of gauge i could monitor that could give a better idea on whats going on? As far as codes...nothing except a TCM code about memory loss or somthing P1621??cant exactly remember. THanks for any suggestions!!
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Old 12-08-2011, 01:40 PM   #2 (permalink)
briano
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motor mounts?
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Old 12-08-2011, 07:22 PM   #3 (permalink)
mpanowicz123
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hmm interesting...never thought of that...Do they often get warn out? I only have 129,000
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2005 Duramax LLY, 4in Exhaust turb /back with 5in tip, Stage 2 AFE Air intake system with pro Guard 7 filter , CTS Monitor
, PPE Economy , 170,000 miles currently, EGR Blocker plate, Cooper 285 S/T MAXX tires

2013 LML
-H&S DPF/DEF Delete
-Cooper S/T MAXX 275's
-9,000 miles
-Diamond Eye Down Pipe
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Old 12-08-2011, 07:35 PM   #4 (permalink)
mpanowicz123
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actually now that i think about it...when it shakes you can hear it fluctuate in the exhaust tone too.
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2005 Duramax LLY, 4in Exhaust turb /back with 5in tip, Stage 2 AFE Air intake system with pro Guard 7 filter , CTS Monitor
, PPE Economy , 170,000 miles currently, EGR Blocker plate, Cooper 285 S/T MAXX tires

2013 LML
-H&S DPF/DEF Delete
-Cooper S/T MAXX 275's
-9,000 miles
-Diamond Eye Down Pipe
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Old 12-08-2011, 08:07 PM   #5 (permalink)
briano
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just a thought..you can check them, but you said in gear or neutral it doesn't do it so it's just in park I'm assuming? might get a TechII to do some monitoring and see what it is.
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Old 12-08-2011, 09:57 PM   #6 (permalink)
TuckerTerra
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What about the FPR? I would think it would bother in all gears, but I know mine is starting to go and sometimes sitting at a stoplight it will idle rough and shake the truck like you are describing. On your CTS, take two PIDs and have one show Desire Fuel Rail Pressure, and the other be the Actual fuel rail pressure. Those numbers should match up. When mine is running rough, I can see desired FRP stays the same, and the actual FRP fluctuates up and down.... making the truck idle rough
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Old 12-09-2011, 01:28 AM   #7 (permalink)
mpanowicz123
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sweet...ill pull that up on the cts...good idea...FYI the FPR was replace 5,000 miles ago. But ya never know know about new parts
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2005 Duramax LLY, 4in Exhaust turb /back with 5in tip, Stage 2 AFE Air intake system with pro Guard 7 filter , CTS Monitor
, PPE Economy , 170,000 miles currently, EGR Blocker plate, Cooper 285 S/T MAXX tires

2013 LML
-H&S DPF/DEF Delete
-Cooper S/T MAXX 275's
-9,000 miles
-Diamond Eye Down Pipe
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Old 12-09-2011, 09:54 AM   #8 (permalink)
pman
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I have pretty much the exact same problem along with a slight idle surge. The entire injection system was replaced by dealer about 20K ago but never seamed to be the same. If you do as above with the CTS just remember a 200 psi fluctuation is normal. When mine is acting up it my desired FP will be 4.3 but the actual FP will go from 4.0 to 4.7. I just brought mine to the dealer but of course it was running ok except for injector 8 running in the upper 7's to low 8's I've run all sorts of additive and 2 stroke oil to try a help but nothing yet, so the search continues. I'll let ya know if I find a remedy.
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Old 12-09-2011, 06:33 PM   #9 (permalink)
dmax3500
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your #8 inj is bad [.7-.8],gm says .4 in netrual and .6 in gear ,both at idle,,my 08' has this miss/lope at idle sometimes dealer says nothing wrong
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Old 12-09-2011, 09:47 PM   #10 (permalink)
pman
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That is what I would think, but for no real reason sometimes it will be at like 2.7
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Leveled with air bags in the rear
18x9 XD monster wheels
285/65/18 Toyo Open country AT II extremes
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Edge CTS
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Dana 60 locked front
14 Bolt locked rear
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