Lacking Power 2001 LB7

Lb7x2

Diesel power ... it’s an expensive addiction!
Jul 27, 2020
7
1
3
Maine
First post on this forum just looking for some help to describe my lack of power on my 2002 LB7.

So I’ve got two LB7’s 2001 and 2002. The 2002 seems to have more power and boost than the 2001. Seems like the 2001 really works a lot harder to get itself moving along, although it does have bigger tires/rims. Still something seems off to me.

I just recently replaced the passengers side manifold due to a manifold leak thinking that would fix my problem, before that you could not hear the turbo spool at all. Now you can and it does seem to have a bit more power. Still nothing like my other LB7 though.

I’ve also noticed a line on top of the fuel filter housing that has a slight leak, if it sits for a week or so you need to prime the filter for it to start right up. Besides that and the manifold I haven’t noticed much else that may be causing it to lack power. Truck does not smoke either or push out any kind of “suit” as my 2002 LB7 will pull you back and slightly put out a little bit of suit.
 

RMJ_LB7

I have a screw loose
Feb 25, 2020
155
7
18
California
I am willing to bet that your MAF sensor is dirty or not reading correctly. Mine was doing he same and did not throw a code but I datalogged the truck and noticed the MAF reading was way off. Went and got MAF cleaner and bam works like a charm.
 
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Bdsankey

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I'm wondering if your 2002 is tuned. Is the wastegate line from the outlet of the turbo to the wastegate a solid/uninterrupted hose or is there something in the line? OEM calibration LB7s aren't exactly quick.


Also like said above, is the MAF/air filter dirty?
 
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KyleC4

Tech
Dec 30, 2016
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You can also check what your rail pressure is when under WOT. Unless it falls under 145 mpa I don't think it'll set a code. I've driven them that could only make 148 when commanded is 160, and you can feel a power difference for sure. But check all else as stated above too.
 
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Lb7x2

Diesel power ... it’s an expensive addiction!
Jul 27, 2020
7
1
3
Maine
Thanks for the reply’s guys, Tomorrow I’ll dig into it and check those out! Also the other one may have a tune but I’m unsure. You say the line off the turbo is a way to tell if it has been? Any other sure tell ways to see if it has been tuned?

Thanks
 

slowlml

Undercover Epa agent
Feb 6, 2015
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You can't tell if its been tuned from the line running from turbo to wastegate. I think brad was talking about the possibility of there being a boost increase valve spliced into the line.
 

Bdsankey

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Thanks for the reply’s guys, Tomorrow I’ll dig into it and check those out! Also the other one may have a tune but I’m unsure. You say the line off the turbo is a way to tell if it has been? Any other sure tell ways to see if it has been tuned?

Thanks
If there is something in the line then the boost has been increased via a boost increase valve. Tons of companies make them. It’s very common for guys to tune them as well as add the boost increase valve to get the largest gains they can.
 

Lb7x2

Diesel power ... it’s an expensive addiction!
Jul 27, 2020
7
1
3
Maine
You guys were right. The 02 has that ppe inline boost valve. Could that be all the difference???
 

Bdsankey

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You guys were right. The 02 has that ppe inline boost valve. Could that be all the difference???
It's possible, it's also possible that the 02 has a tune as well but the only way to tell there would be to try and read the ECM. If it's locked 99.999% its got a tune, if it's unlocked (you can read the tune out) then you'd have to compare to an OEM calibration but I personally haven't seen a tuner who doesn't lock their tunes from being read.

It's crazy what just a little bit of added boost will do! Message me your address and I'll mail you my PPE valve out of my LB7 since I won't be needing it with the S300/S400 compound kit.
 

Lb7x2

Diesel power ... it’s an expensive addiction!
Jul 27, 2020
7
1
3
Maine
So what do I need to plug into the ecm to read the tune, a code scanner or a tuner?
 

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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You can also check what your rail pressure is when under WOT. Unless it falls under 145 mpa I don't think it'll set a code. I've driven them that could only make 148 when commanded is 160, and you can feel a power difference for sure. But check all else as stated above too.
Mine with a 6006 02 OS would not code even when rail was dropping down to 90 mpa, and sometimes lower. I was smoking like crazy but could tell it was down on power, data logged it, and seen rail pressure was only holding about 12,600 psi on my daily tune. Pissed me off because I found it the 1 time I took it to the track, and it only ran a 9.10 in the 1/8th.
 
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RMJ_LB7

I have a screw loose
Feb 25, 2020
155
7
18
California
I still don't see that being your issue since the boost valve would only help for a matter of seconds. When I put my boost valve on the only difference I noticed was more boost from a stop if throttle was past like 60%. Like Brad said your other LB7 could possibly have a tune on it. I know mine was a dog before I put the tune on it as well. I would still double check your MAF sensor...
 

Lb7x2

Diesel power ... it’s an expensive addiction!
Jul 27, 2020
7
1
3
Maine
I still don't see that being your issue since the boost valve would only help for a matter of seconds. When I put my boost valve on the only difference I noticed was more boost from a stop if throttle was past like 60%. Like Brad said your other LB7 could possibly have a tune on it. I know mine was a dog before I put the tune on it as well. I would still double check your MAF sensor...
I have come to find out my other LB7 is tuned. I put a boost valve on the line going to the waste gate and it might have made a bit of difference but not much.
 

Lb7x2

Diesel power ... it’s an expensive addiction!
Jul 27, 2020
7
1
3
Maine
On another note...I don’t want obnoxious clouds of suit coming from my exhaust by any means. But is it unusual for my LB7 to not produce any suit at all?? Seems like all diesels tend to I just find that unusual that mine doesn’t.
 

Bdsankey

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Feb 1, 2018
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On another note...I don’t want obnoxious clouds of suit coming from my exhaust by any means. But is it unusual for my LB7 to not produce any suit at all?? Seems like all diesels tend to I just find that unusual that mine doesn’t.
its pretty normal. OEM calibrations are usually pretty darn clean if not 100% clean. In 2001 the duramax was really a game changer compared to the VP44 cummins trucks or the HEUI 7.3 powerstrokes in terms of data available to the modules as well as the speed they could process/react.
 
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Lb7x2

Diesel power ... it’s an expensive addiction!
Jul 27, 2020
7
1
3
Maine
its pretty normal. OEM calibrations are usually pretty darn clean if not 100% clean. In 2001 the duramax was really a game changer compared to the VP44 cummins trucks or the HEUI 7.3 powerstrokes in terms of data available to the modules as well as the speed they could process/react.
Thank you for the information! You’ve been a big help!!
 

bigboybuilder

New member
Nov 3, 2019
8
1
1
First post on this forum just looking for some help to describe my lack of power on my 2002 LB7.

So I’ve got two LB7’s 2001 and 2002. The 2002 seems to have more power and boost than the 2001. Seems like the 2001 really works a lot harder to get itself moving along, although it does have bigger tires/rims. Still something seems off to me.

I just recently replaced the passengers side manifold due to a manifold leak thinking that would fix my problem, before that you could not hear the turbo spool at all. Now you can and it does seem to have a bit more power. Still nothing like my other LB7 though.

I’ve also noticed a line on top of the fuel filter housing that has a slight leak, if it sits for a week or so you need to prime the filter for it to start right up. Besides that and the manifold I haven’t noticed much else that may be causing it to lack power. Truck does not smoke either or push out any kind of “suit” as my 2002 LB7 will pull you back and slightly put out a little bit of suit.
if your fuel filter leaks your getting air also. from what i have gathered sucking a bit of air (love's drive was steep) can take a while to get the air out it took about a week for balance rates to come back to normal that time. when you think about it, that tiny air bubble will collapse at these pressures but I haven't a clue as to the physics behind that, i.e. how they would move about the system
 
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