Help! Lbz won’t run under 1200 rpm
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This, and with the motor being in the bed of the truck any chance the reluctor wheel was damaged? Starting to get into the realm of "there should be a code thrown"
Could the cam be installed out of time?
What were your compression test numbers?
I haven’t scoped them but my scan tool shows there is a cam and crank signal both when cranking and running. I have also inspected the reluctor wheel and verified it has a 58 tooth count. I know the earlier duramax used a 57 tooth. To clear things up the block was complete to the pan including the front cover. Although I only inspected each cylinder and dropped the pan to inspect the bottom end. The heads were tested and machined. I have gotten it to throw a p0336 when I ran in it for 10 or 15 seconds with it knocking but I think it’s because the rpms were bouncing around so bad. I then proceeded to test the ckp circuits and all tested ok. Cleared the code and have not gotten it to return.
The cam for an lbz wouldn’t be timed differently than an lmm right?
The cam for an lbz wouldn’t be timed differently than an lmm right?
Have you bled the air out of the filter head and ensured its not sucking air through the primer? and again, what were your compression test numbers?
Pull the fuel pressure regulator and see if it will stay running under 1200 rpm. That would eliminate fuel pressure issues or injectors returning too much fuel. It will rough kinda crappy but would know if it fuel related or not. It still sounds like it is fuel to me.
Yes the air has been bled and I have ran it with clear lines in and out. No air. I’ve also unplugged the regulator. No difference.
As for compression my lowest cylinder was 380 and all are within 30 psi of each other.
As for compression my lowest cylinder was 380 and all are within 30 psi of each other.
The cam timing issue is another one of those “should throw a code” situations. I don’t like those refurbished computer sellers. I have had too many issues from the junk they sell. I would find a known good running LBZ that you can borrow an ECM from to do a test. You will have to do a VATS relearn, but it would rule it out. It’s a very odd problem for sure.
You may still have a loose reluctor if you didn't check it already, I'd check that and scope it. Overlay the signals on the screen if you can. If that checks out, and you're sure each injector connector terminal is tight (internally), then I would agree with Josh and say get a different ecm to test quick.
Well I hooked up the O scope this morning and the cam and crank signals are good. I’ll try to get my hands on another ecm. I guess a fuel map or something could cause this? As for the injectors, I can cut each one out with my scan tool and I inspected each connector but I haven’t drag tested them. I would imagine if I can cut the injector out they are making good contact right?
While you're searching for a good known ECM.... Can you get a video with clear audio of the truck trying to start / idle / run at the lowest rpm you can maintain.
Also, while you're waiting, icepick all of the injector connectors. It can't hurt.
Also, while you're waiting, icepick all of the injector connectors. It can't hurt.
No mention of engine grounds yet, did you properly ground the engine when you installed? Sometimes these ground strap bolts get left loose after lightly threading it in during install and forgetting to tighten, I have seen this a few times. Sounds like you have covered just about everything else at this point, could be something simple overlooked during install. Should be a ground cable/strap at each side of the block toward the front as well as a braided strap going to the drivers side cylinder head below the GPCM.
Sorry for the late reply, I’ve been out of town but I did manage to get my hands on a good known ecm and no change. I also replaced all 8 injector pigtails no change. I installed a FASS fuel pump. No change or leaks present. Also I have been over every ground a couple times I Just forgot to mention that part.
I did however get it to idle. But it has what sounds like a hard fuel knock and is now throwing the p0336 consistently. If I hold the rpms right above the knocking point I can get it to an idle by very very slowly lowering rpms. If I drop the rpms fast it dies.
At idle cutting out every injector individually makes it die. Injector balance rates are good. Desired and actual fuel pressure are still good.
At this point I’m not inclined to think it’s a fuel problem but everything checks out on the ckps wiring and I’ve replaced the crank sensor twice. 3 different ecm’s etc.
does anyone know if a lmm reluctor wheel would be clocked different than an lbz? I know the tooth count is correct and the sensor is sending a signal.
I did however get it to idle. But it has what sounds like a hard fuel knock and is now throwing the p0336 consistently. If I hold the rpms right above the knocking point I can get it to an idle by very very slowly lowering rpms. If I drop the rpms fast it dies.
At idle cutting out every injector individually makes it die. Injector balance rates are good. Desired and actual fuel pressure are still good.
At this point I’m not inclined to think it’s a fuel problem but everything checks out on the ckps wiring and I’ve replaced the crank sensor twice. 3 different ecm’s etc.
does anyone know if a lmm reluctor wheel would be clocked different than an lbz? I know the tooth count is correct and the sensor is sending a signal.
Where did you get the injectors from? your balance rates arent going to tell you much unless you are looking at main fuel rate as well.
this all really sounds like an injector issue to me.
Did you actually verify the reluctor wheel is not loose in there?
this all really sounds like an injector issue to me.
Did you actually verify the reluctor wheel is not loose in there?
I’m about 90% sure it’s not injectors. All 8 were replaced with gm oem injectors right from the dealer and the truck had the issue before the new injectors but hey who knows. And yes the reluctor wheel is tight.
The truck went to the dealer today... I’ll let you guys know what they find
The truck went to the dealer today... I’ll let you guys know what they find
Unfortunately, all we can do is base our answers off what we are told and I think that’s about ran its course. Probably best it went there and I’m not saying that in a bad way. Hell of an effort on it!