LBZ: Losing pulse width at certain rpm

UPnGONe

UPnGONe

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Jul 23, 2008
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The shore
I have been helping a good friend of mine put a 2.5 lbz Duramax truck together and we have been fighting this issue for over an week now. I need some help truck has a built motor new 100% injectors, new stock dual cp3s ppe kit, s400 based 2.55, stock head, fingers piston and an socal alt fire can.

The issue is around 2600-3000 rpm truck pops/surges and has an horrible dead pedal has checked all wiring , firing order is right , returns are good. Logs show that the truck goes to 0 pulse width back to normal very rapidly in a constant wave on ybr graph when it does its popping/surge .

We even swapped his ecm.into my truck and it runs fine. Have undone the dual fueler to run one in valley and still acts up any help is appreciated

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UPnGONe

UPnGONe

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We moved pins in the 2 bail connectors on top of the motor we have checked and rechecked to make sure they were correct

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PACougar

PACougar

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Jun 27, 2012
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El Dorado Hills, Ca
UPnGONe said:
We moved pins in the 2 bail connectors on top of the motor we have checked and rechecked to make sure they were correct

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Click to expand...

That's what I guessed had been done. It just sounds like you might have a poor connection somewhere that's causing the problem. Have you measured the resistance for all of the connections?
 
UPnGONe

UPnGONe

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No we have not measured resistance but why would it run better with the other tune motor runs smooth as glass at idle till 2600

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JoshH

JoshH

Daggum farm truck
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Does it do it as you're slowly increasing RPM or if you just stomp the pedal?
 
UPnGONe

UPnGONe

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Both its more of a up/down surge slowly increasing rpm. If you stomp on it is when u get the pop

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DAVe3283

DAVe3283

Heavy & Slow
Sep 3, 2009
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No codes are being stored? It might have codes even with no CEL.

I would actually guess a crank or cam sensor starts to lose signal around that RPM range. Might want to check their wiring & plugs.
 
O

onebaddmaxxx

Active member
Feb 22, 2009
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Cecil County Md
JoshH said:
See if that's where the pilot is shutting off.
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Pilot Does shut off around 2700 ish. it flatlines and stays off until you let off. The tune #1 is the OP's normal tuner, and you can see where the pilot kicks on, but pulse never goes over 350 and drops to 0 the next frame as he slowly revs it up in the log. The #2 tune is something i tried its a known good tune that worked well in another truck so i know that there should be no issue here. I had them recheck the wires at the baileys already, i thought they had the wrong wires switched. I tried to attach the logs but since im on a computer that doesnt have EFI on it, it wont let me. I also looked at codes during logs and nothing out of ordinary for having s400 based charger. When i get home tonight i will attach the logs the OP sent me last night.

Also, rail pressure is right on as you rev it up. (just puting this out there to eliminate)
 
JoshH

JoshH

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I've seen pilot injection turning off cause a similar problem. What I've seen happen is the RPM will be rising steady, pilot will shut off, RPM will drop, pilot will turn back on, RPM will jump back up, this is usually accompanied with some puffs of white/gray smoke and repeats until you let out or really rev on the engine pretty hard. I've seen it pop if you push the pedal pretty hard while it is doing this also. Usually if you're giving it enough fuel, it doesn't care if the pilot shuts off, but slow steady increasing of the RPM tends to give it fits. I'm not sure that's what is going on with yours, but it sounds similar. I would try keeping pilot active and see if it doesn't change anything.
 
catman3126

catman3126

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Jul 24, 2012
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Just out of curiosity how does one change the firing order with tuning? I heard this from someone eles and would liek to know how this is done?
 
JoshH

JoshH

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onebaddmaxxx said:
It can be done with efi live only two tuners have the capability to do so.

Josh I will post logs in an hour or so for you to see.
Click to expand...

It can be flashed with EFILive, but they don't use EFILive to modify the files.
 
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