Duramax Diesels Forum Truck of the Week
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Old 04-15-2019, 04:52 AM
hhh217 hhh217 is offline
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Default LLY swap fuel knock. Need help

I just finished a lly swap in my 02 Chevy. I put the lly top end on lb7 bottom and used a converted harness with lly ecm. The truck runs great but has a fuel knock about mid range rpm medium throttle. Light cruising it doesnít knock and itís hard to hear or gone at wide open throttle. I have diagnosed and fixed many duramaxs with fuel issues but this one is kicking my ass. Balance rates are in range. While driving and hearing the fuel knock I used my V2 and cancelled #3 cylinder and knock goes away so I replaced #3 injector (second one back passenger side). Same results. I swapped 3 and 5 injectors to try and rule out the new injector but the knock stayed with the number 3 cylinder. I have read on another forum that only on LLY engines the v2 isnít acurate with balance rates or cylinder cut outs. He claimed it can shut down a different cylinder than what was selected. Any thoughts, or ideas? Can a Ficm cause an issue like this?
I never heard the lly engine run before I bought it and only heard the lb7 idle.
I also had 2 different ecm ls in truck with stock lly tunes and I it didnít change.
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Old 04-15-2019, 07:48 AM
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Are you sure it is not pilot injection shutting off at ~2500 rpm?

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Old 04-15-2019, 10:39 AM
hhh217 hhh217 is offline
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It will knock under 2500 rpm and it’s only one cylinder making the noise. I have driven many lly trucks and this stands out loud enough for the wife to ask what the noise was.
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Old 04-15-2019, 11:42 AM
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Quote:
Originally Posted by hhh217 View Post
I have read on another forum that only on LLY engines the v2 isnít acurate with balance rates or cylinder cut outs. He claimed it can shut down a different cylinder than what was selected.
I've experienced this same thing on an LB7. I've read a few threads on the efilive forums about this issue and it doesn't seem to be limited to just the LLYs. Efilive clames to use the exact same protocols as GM for numbering cylinders but it seems that it is actually the firing order and not cylinder number.

Try swapping out #7 injector and see if that helps
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Old 04-15-2019, 12:12 PM
hhh217 hhh217 is offline
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Thanks for the advice. Maybe I’ll grab the tech 2 from the local dealer that treats me really good and see how it acts with cancelling out cylinders. I don’t like swapping parts unless it’s last resort.
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Old 04-15-2019, 01:16 PM
hhh217 hhh217 is offline
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Default F*ck efi live and their cylinder cut out.

Quote:
Originally Posted by 2004LB7 View Post
I've experienced this same thing on an LB7. I've read a few threads on the efilive forums about this issue and it doesn't seem to be limited to just the LLYs. Efilive clames to use the exact same protocols as GM for numbering cylinders but it seems that it is actually the firing order and not cylinder number.

Try swapping out #7 injector and see if that helps

I wish you lived closer so I could buy you a beer. I took a look a decided it would be just as quick to swap out the injector as it would be to drive to town and use a tech 2. I swapped out #7 injector and the fuel knock is gone. I knew I wasnít crazy and it was a fuel knock. Thanks again.
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Old 04-15-2019, 01:26 PM
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No problem, thanks for the update

As long as you know it is firing order that is being turned off then the tool works great. Otherwise it can cause some headaches
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Old 06-13-2019, 01:37 PM
hhh217 hhh217 is offline
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I got a little ahead of myself when I made me last post. When I test drive the truck after replacing the #7 injector it was a short test drive and it sounded much better. Later that week I drove the truck again and found i still had a fuel knock but about 1/2-3/4 power level about 1500rpm. After efi live cylinder cut out it still showed cylinder #3 which I thought was actually #7 on the engine. I swapped 5&7 and it didn’t move. So long story short I had 2 injectors screwed up. I got lucky when I swapped out 7 but it wasn’t the main fuel knock. I bought a tech 2 bc the dealership was a dick about helping me out. Turns out #3 cylinder cutout on efi live if somehow #8 on the engine. Swapped #8 injector and it runs like a dream. If we can map all of them out efi live cut out will be handy. Until then don’t trust it on a LLY.
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