LMM: 2007.5 LMM power issues

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five21racing

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Jul 7, 2013
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2007.5 Chevy 3500, 165k miles
4" down pipe back exhaust (no dpf/cat, has muffler)
S&B oil type air box
H&S mini maxx tuner
Raptor lift pump
PPE race valve in fuel rail


I tow a 26' enclosed car trailer with roughly 2500lbs inside. So basically just a lot of air drag. Pulling hills it seems to have trouble.

The last run was ~80*F outside temp and the pickup started to defuel when the water temp hit 220*F. Pulled over, idled at 1k and all was well after that. I ended up not using the cruise control (65mph) and tried being smooth with the throttle when pulling any hills afterwards. Something like 9 - 10 mpg. I've cleaned the MAF sensor a couple times now.

Called H & S on an issue with the tuner and explained what the pickup was doing while I was on the phone anyways. The tech suggested going back to the stock air filter setup.

Bought an EGR block off plate and that's going in today.

After putting the stock air box back on and cleaning the MAF sensor; I hooked on to the trailer to make a test run.

Boost: 25 - 27 psi
Fuel pressure: ~5 ksi (off the throttle slowly moving) ~26ksi @ WOT
Load: ~45% @ WOT

I'm still confused as to why the engine load will only show 45% at wide open throttle and not a full 100%.
cookoo[1].gif


What do you guys think I need to try?

Thanks for any and all help!

When you fire this thing up, after ~5 seconds or so, it sounds like a jet getting ready for takeoff. Then goes back to idling like normal. Surely this isn't normal??
 
TLyons90

TLyons90

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Apr 22, 2013
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Ditch the H&S and get some EFI! :D

When going up a hill pulling do you leave it on cruise and let the truck down shift itself and yank you up the mountain? Also what tune do you leave it in when pulling?

Last but not lease that "hiss" at idle is completely normal, most all dmaxs do this on startup. It's called vanes sweeping.
 
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five21racing

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Jul 7, 2013
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If I leave the cruise on (in 6th gear) and begin to pull a hill; it won't down shift itself. It just goes into reduced power mode. So I've been running in 5th without the cruise. The hills I'm talking about are probably only a 5% grade. Nothing like you'd see running down roads on a mountain side. I always leave the tuner in the "Tow" mode regardless of what's behind or not.

Just bought the pyrometer kit to measure EGT's. Going to need a half a day to get it all setup..
Didn't do a whole lot of research before pulling the trigger on the H&S unit. The pickup only gets used to pull a race car trailer.
 
TLyons90

TLyons90

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Apr 22, 2013
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five21racing said:
If I leave the cruise on (in 6th gear) and begin to pull a hill; it won't down shift itself. It just goes into reduced power mode. So I've been running in 5th without the cruise. The hills I'm talking about are probably only a 5% grade. Nothing like you'd see running down roads on a mountain side. I always leave the tuner in the "Tow" mode regardless of what's behind or not.

Just bought the pyrometer kit to measure EGT's. Going to need a half a day to get it all setup..
Didn't do a whole lot of research before pulling the trigger on the H&S unit. The pickup only gets used to pull a race car trailer.
Click to expand...

Hmm... I know when pulling and coming upon a hill I usually take it out of cruise and just let my foot do the work to get it up and over that way you dont overload the motor and tranny trying to keep up to the speed your maintaining. As far as the H&S goes they are a good system just EFI is alot better IMO... Shouldnt have any problem what so ever if you are leaving it in tow mode... The EGT install isnt to bad but like you said about a half day doing it slow to make sure you get it done right! EGTs are the silent killer so measuring those is key :thumb:
 
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five21racing

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Jul 7, 2013
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Is an EFI live tune going to fix my issue? Probably not. I'd like to get that sorted out first. My ol man's had 1 ton diesels since I was a kid. The load I'm putting on my pickup isn't 1/4 the weight of a tracked skid loader on a heavy duty trailer. The engine load only reading 45% at wide open throttle is making me wonder what's really going on.
 
Kappa9012

Kappa9012

MAN.... I Broke it again.
Aug 5, 2008
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when it goes into limp, what's the DIC saying? 220º isn't high enough to trip a derate. Dumb question, but have you checked the basics? when was the fuel filter last changed?
 
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five21racing

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Jul 7, 2013
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It's derating when a "big" (how it seems to the pickup) load is put on the motor. 220* is the defuel setting for hot coolant temp. Apparently that's set too low. Is the engine fan even kicking on then? I'm guessing I need to raise that.

Fuel filter is new. Changed it a couple times in the last few thousand miles. I do need to check and make sure all the turbo clamps are tight. The last run I made, the boost reading seemed to be quite low. The only thing that was changed before that trip was a new fuel filter, and EGR block off plate.

Edit: DIC is reading 210*. As it does when the mini maxx reads anywhere from 180* - 220*
 
Kappa9012

Kappa9012

MAN.... I Broke it again.
Aug 5, 2008
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is the 220 the trip point for the minimax? I though the engine coolant temp derate from GM was around 250? How does the truck run without the H&S?
 
Harbin_22

Harbin_22

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Dec 4, 2010
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The factory temp gauge lies too. It will show hotter then it actually is. Sounds like it is starving for fuel. There is a TSB for LBZ about fuel lines collapsing. Might check and see if it is for lmm's too
 
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five21racing

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220* is what the mini maxx came preset at, if I remember correctly. I'll watch the fuel pressure a little closer when I make another trip this weekend. Before I put the exhaust/tuner/lift pump on, I was having MAJOR power issues. 6-7 mpg and having trouble holding 65mph with a tiny trailer behind.

I can switch to "stock" on the tuner but, as far as removing the tune and being back to stock; I think that's out of my choices. With all the emissions equipment being removed or disabled. We've tried running in tow and stock modes with the same results.
 
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five21racing

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Jul 7, 2013
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Low fuel rail pressure. P0087X? I've tried turning the lift pump up and couldn't notice any difference. This was very small amounts (1/8th turn).
 
Harbin_22

Harbin_22

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Dec 4, 2010
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Southern Indiana
None of that stuff should matter if he is running stock or tow tune. How long are you driving before this happens? What is the fuel temperature when it happens? Injectors or pump might be on their way out. Probably be good to do a return test on each of them.
 
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