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Discussion Starter #1
Ive got a 2005 LLY that just broke 200,000 miles, been a good truck for the six months ive owned it. Just recently, it started misfiring, bad. foot on the floor, chugging down the road going 15 mph bad. Not a single code thrown or pending. Reading up on this, ive discovered the terrible injector harnesses and went down that road, and found a thicker yellow wire with a hole worn through the insulation going to the FICM. Fixed that, and now the truck runs and revs, it is drivable, but its in the "Tractor mode", injectors are loud as hell. Now its throwing P0088, P0089, P0090, and P0653. Ive cleared them many times, they keep coming back. I also got codes for the turbocharger boost sensor and a Barometric sensor somewhere but they havent come back yet. Im stumped, I cant figure out what these have in common, and I don't want to drive the truck for fear of hurting something expensive. Here are pictures of the codes, and what I did to fix the misfire.
634473
634475
634469
634470
634471
634472
 

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Discussion Starter #2
Also, i might add, before i "fixed" it, I had about 5000 PSI to the fuel rails, today its reading 26,000 PSI. That also scares me. The trucks got a number of mods done to it, none of them by me, so i have no idea whats going on elsewhere. Kryptonite suspension, Sinister Diesel EGR delete, charge pipes, down pipe, 5 inch exhaust all the way back, overload bags in the rear, its a nice truck, and i wanna get it going again
 

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Welcome to DieselPlace
If you do a forum search on the issue you'll find a few threads on the topic to help guide you, like this one.
(y)
 

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Discussion Starter #4
Welcome to DieselPlace
If you do a forum search on the issue you'll find a few threads on the topic to help guide you, like this one.
(y)
Yeah I checked that, i havent gotten any relevant information that i havnt looked at, or tried. That particular one ended with an injector harness being at fault, which wouldnt explain the reference B circuit being pulled high. I cant figure out what those yellow and green striped wires are that i spliced, or what in that harness is a decent culprit to look for. At this point I dont think thats what solved the injector misfire, I think I just moved something or wiggled a connector just right to make the injectors fire correctly.
 

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Is it going to max rail pressure at idle? If so check that the harness to the fuel regulator on the CP3 is plugged in or damaged.

Also read up on the “ice pick procedure” for the harness plugs at the injectors. That can contribute to the tractor like sound.

And there’s also a injector harness repair/lengthening kit for our LLYs available through GM. Although a site sponsor might be a cheaper place to find that if needed.
 

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Discussion Starter #7
Is it going to max rail pressure at idle? If so check that the harness to the fuel regulator on the CP3 is plugged in or damaged.

Also read up on the “ice pick procedure” for the harness plugs at the injectors. That can contribute to the tractor like sound.

And there’s also a injector harness repair/lengthening kit for our LLYs available through GM. Although a site sponsor might be a cheaper place to find that if needed.
It is hitting max fuel pressure at idle, and ive been chasing harnesses all day trying to figure it out. It started out with one or two misfires at idle in the driveway, didnt make It 2 miles before it was full blown missing on all cylinders, no power, no cel or pending codes. It wasnt until I attempted the harness repair that I started getting codes, which is why I'm trying to figure out what the yellow wires w/green tracers do. Ive yet to put a volt meter on the 5 volt reference lines for the sensors, thats my plan tomorrow. There's just so many systems that can fail from these faulty harnesses that I'm not sure what road to go down. Tempted to build a custom harness that doesnt run across the engine and lay in the valley. Give it enough length and route it like sane people so its not constantly chafing on everything
 

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If you’ve checked the regulator harness, then try swapping out the regulator itself. Not uncommon for those to go bad. Try ice picking the injector harness plugs.

Did you or the previous owner splay out the wires from the harness running by the alternator? Looks like there’s at least one other repair besides the larger gauge yellow wire that you did. Maybe check for previous wiring repairs and clean them up/redo them?

Stock tuning or aftermarket? Prob wouldn’t help the circuit issue but might help the pressure issue if it’s got a bad tune file in it.
 

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Discussion Starter #9
If you’ve checked the regulator harness, then try swapping out the regulator itself. Not uncommon for those to go bad. Try ice picking the injector harness plugs.

Did you or the previous owner splay out the wires from the harness running by the alternator? Looks like there’s at least one other repair besides the larger gauge yellow wire that you did. Maybe check for previous wiring repairs and clean them up/redo them?

Stock tuning or aftermarket? Prob wouldn’t help the circuit issue but might help the pressure issue if it’s got a bad tune file in it.
Once payday hits I'll get a regulator, though that doesn't look much fun to do, and that one repair is all I did. Ive checked for splices elsewhere but this harness looks factory. I did icepick the connectors before I went to splicing the harness.I'm not sure about the tune, electronically controlled diesel is entirely new to me, all ive got to go on with that is the EFI live logo under the Allison badge, I dont know if that itself is a tune or a tuning program or whats going on there. Again, once i run a volt meter over the harness to check for shorts to voltage I'll try and figure something out. If one sensor is pulling the reference high could that affect the regulator circuit, and is there a way those two can short together and give me both these issues? Again, the only other diesel ive delt with beforehand is the 12 valve. This is a whole new beast and ive got no idea whats all going on there.
 

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Yes EFILive is a tuning software package. It’s very popular in the duramax game and is arguably the best tuning program. Having said that, EFI is just the tool. It all depends on how good the person is who is writing the tune file. It’s likely that your truck was at least tuned at one point, if not still tuned.

According to the post I linked the following are bused together in the ECM under the same reference circuit:
Accelerator Pedal Position Sensor,
Air Conditioning (A/C) Refrigerant Pressure Sensor (Non-HP2),
Engine Oil Level Sensor and/or Switch,
Exhaust Pressure Differential Sensor Replacement (Pickup), and
Fuel Injection Fuel Rail Fuel Pressure Sensor

So the answer to your second question is yes. It’s possible that a reference circuit fault on any of those systems could affect all others. I’m by not means an expert. But I’d assume that yes the circuit fault code and the fuel pressure codes/max rail could very well be tied together.
 

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To me it seems path of least resistance (pun intended) would be to check the other sensors on that circuit before tearing into the FPR.

Also, don’t give up. I know it’s frustrating. I just dealt with an electrical issue where the interior lights would stay on always and the cluster wouldn’t work. I thought the worst, ended up being both batteries were dead and couldn’t hold a charge. Easy fix in the end.
 

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Discussion Starter #12
To me it seems path of least resistance (pun intended) would be to check the other sensors on that circuit before tearing into the FPR.

Also, don’t give up. I know it’s frustrating. I just dealt with an electrical issue where the interior lights would stay on always and the cluster wouldn’t work. I thought the worst, ended up being both batteries were dead and couldn’t hold a charge. Easy fix in the end.
Will do, my overall plan is to check reference voltage at each plug, and chase the individual wires from it up the harness to see if theyre chaffed somewhere. Im not positive if I can get to it today, ive got a job interview and its looking like its gonna rain all day, I'll see what I can do in the breaks between the storms. I'm tempted to just sell the truck if I'm honest, but some part of me knows that's dumb and its just a wire somewhere thats shorted. I'm losing my mind here but i didnt pay $18,000 for a lawn ornament. It'll get fixed.
 

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Discussion Starter #14
Sounds solid. Good luck. If you can try to figure out if it’s tuned or not. Would suck to have a stock trans and a max effort tune. Here’s a link to a tube repository EFI Live Tune Files
Turns out, I'm stupid. Had the plugs swapped. FPR was connected to a little black module and the harnesses were connected to eachother. However, today i come out, half the dash lights dont turn on and it wont crank, so still SOL
 

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Sounds solid. Good luck. If you can try to figure out if it’s tuned or not. Would suck to have a stock trans and a max effort tune. Here’s a link to a tube repository EFI Live Tune Files
Got it to crank, fired up, idled good for about 30 seconds, stumbled really hard, picked itself up, ran good for another little bit, couple small stumbles, stumbled hard enough it almost died, picked back up and idled normally. I have no idea whats happening here cause it isnt consistent. Just whenever it feels like it. Started recording a video and it took about 4 minutes for it to stumble really hard again. Runs flawless inbetween stumbles. No codes present, one pending for the glowplugs but they havent worked since I bought it. Winter was hell. Will post a video
 

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Simple things usually are the answer. Your first post (post 14) sounds like mine when the batteries were toast.
The Duramax is very sensitive to good grounds. I would check your ground connections. No rust, metal to metal, etc.

Check out first post Runs like crap / Code PO192

Check your fuel filter. Assuming it’s new or like new, but maybe some rust in the hard lines got dislodged, or it’s just old and plugged up.

Verify you maintain prime at the filter head. Not uncommon for a filter head to need resealed and allowing air in.

Try to verify not air leaking into fuel system. Look up DIY injector cleaning. It’s a good thing to do if you suspect faulty injectors. But more importantly it shows how you can run off a jerry can hooked up at the rear of the engine. Might help eliminate issues with fuel lines from engine back to tank.
 

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Might try monitoring in real time your sensors to see if anything out of normal. Lots of wires not loomed - perhaps you could at least put them in split loom so that they don't have a way to ground. I realize you may have them out while troubleshooting. Are you able to connect with ECM TCM, etc thru DLC when running poorly??
 
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So, after a couple hours of digging through harnesses, I found a wire that had damn near rubbed through the copper, few strands barely touching. Some connector on the front of the block down near the bottom. Fixed that, improved it a bit. Checking continuity I found a single 16 guage wire in the computer on the radiator in the middle of the loom that was chafed bad, fixed it, substantially improved, still has occasional misses but not bad enough for the injectors to tractor. Now it seems the longer it runs the better it gets. I'm not sure what the slow incline in performance is about, but I think I got it. I appreciate your guys help with this, ill let you know if it did actually fix it or if this is a temporary thing. I'm still looking everything over to see, might just rebuild/relocate the harness anyway just for peace of mind.
 

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Nice work! Like Ron said make sure to get everything protected in split loom when you’re done chasing wires.
 
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