Held diagnosing an LB7

[mrdan27611]

Sorry if this is in the wrong place. I couldn't find a section that seemed to be the appropriate one.

I have a 2003 Duramax 3500 that is new to me. We already run a 2006 and a 2015 Duramax. Compared to the other two, the 2003 is down on power and we are trying to diagnose why.

One of my first questions is that is seems the turbo isn't boosting correctly. On the other two trucks, and pretty much any diesel for that matter, there is a turbo whistle as boost is dumped through the waste gate under load. With this truck, there is no whistle. Ever. I hooked up my data logger to the ODB2 port and the reading shows 18+ psi with a quick, non-scientific check. However a visual inspection shows damage to the compressor vanes indicating some FOD has gotten in there at some point. Maybe the turbo isn't doing all it's supposed to?

My questions for you.

Does the LB7 engine have the same waste gate whistle as newer trucks?

Can I trust the ODB2 reading for boost or should I manually check the boost? (I don't currently have the setup for a manual check.)

Am I just down on power because it's a different engine? This is our only LB7. Maybe it's a bad comparison. Of course the 2015 has more power, but the 2006 shouldn't be that different, should it?

The 2006 2500 has WAY more torque at low end. I don't know the gear ratio on either truck, or how to know what it is. Probably in the VIN I guess. How would I find out the gear ratio on both trucks?

I think the 2006 may have been turned up via the computer. How would I find out if it has? If I'm comparing hopped up performance to stock, then easy answer. I'll just turn up the 2003 as well via a similar method.

Thanks for the help. You guys have helped us plenty in the past by us reading the threads online.

 

[WolfLMM]

A 2006 lbz will feel significantly more powerful than a 2003 lb7 stock for stock. Lb7 turbos do not whistle like the newer truck do. I *think* 18psi is normal for stock tuning and no wastegate modifications.

 

[Josh154]

The lb7 will not sound like any 04.5+. The lb7 uses a fixed vane turbo with a internal wastegate on it to regulate boost. Your 06 and 15 have no wastegate and are a variable vane turbo that will whistle more than any fixed vane. 18+ psi seems ok to me on a stock truck all though I've never been around a lb7 so maybe somebody else will chime in on that. I would imagine a 06 lbz would feel quite a bit stronger than a stock lb7 though.

 

[Stancedlb7]

18psi is normal for a stock lb7. Id check the bellows for exhaust leaks. And check boots for boost leaks.

 

[TheBac]

Moved into the LB7 section of Hard Parts.

Check the drivers side intercooler pipe for a hole worn into it from just behind the power steering pump. If the blades are eroding, then maybe its time to call DD member "yellowchevy" and have the turbo rebuilt.

 

[THEFERMANATOR]

Plain and simple answer, lb7's are 300HP and I believe 550 torque. Peak torque isn't until 2200 RPM's due to the fixed turbo, and not alot of torque below 1800 or so. Your 06 LBZ is 360HP and 650 torque with a peak torque reached at 1800 RPM's, but carries over 80% of peak torque from 1300 RPM's all the way up, and your 15 is 397HP and 765 torque. As said above, 04.5+ is variable geometry turbos that will have noticeable whistle, or as many call it the jet engine exhaust sound. The LB7 is a fixxed turbo, very little whistle if any with stock intake, and a deep open exhaust sound. 18-20 is normal boost if that is what you're actually getting, some scanners read actual boost which is total boost pressure minus atmospheric while others will read out total boost pressure from the sensor. They top out at 37 for the PID display, so it will only go to 22 at sea level. Sounds to me like you're just experiencing the BIG difference between the 1st gen engine and a 3rd and 5th gen engine.

 

[bristlepad]

How many miles are on the trans? Some trans problems cause low power. Hopefully just a boost leak though. Also not sure if lb7s had a TCM or not but when mine went bad on my LMM it caused it to go into limp mode.


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[mrdan27611]

Plain and simple answer, lb7's are 300HP and I believe 550 torque. Peak torque isn't until 2200 RPM's due to the fixed turbo, and not alot of torque below 1800 or so. Your 06 LBZ is 360HP and 650 torque with a peak torque reached at 1800 RPM's, but carries over 80% of peak torque from 1300 RPM's all the way up, and your 15 is 397HP and 765 torque. As said above, 04.5+ is variable geometry turbos that will have noticeable whistle, or as many call it the jet engine exhaust sound. The LB7 is a fixxed turbo, very little whistle if any with stock intake, and a deep open exhaust sound. 18-20 is normal boost if that is what you're actually getting, some scanners read actual boost which is total boost pressure minus atmospheric while others will read out total boost pressure from the sensor. They top out at 37 for the PID display, so it will only go to 22 at sea level. Sounds to me like you're just experiencing the BIG difference between the 1st gen engine and a 3rd and 5th gen engine.

Thanks for the info on the lack of turbo whistle from everyone. The lack of power seems to be a bit more than just 100 ft-lbs of torque so I'm still wondering if it isn't down on power from the specs above.

It feels like it's geared wrong, or that it's loosing boost. I'll hopefully check the gearing this afternoon if we get done in time. The boost, I'll check for leaks but other than that I'm a bit stuck on how to check actual boost delivery to the intake other than to trust the ODB2 readings. I should take a reading with a good load. I can do that tomorrow since I'll be pulling a trailer.

I'll post my results and maybe we can dive further into what is going on.

Thanks everyone for your help.

 

[Stancedlb7]

Unless its got a lift and rediculous size tires I dont see how gearing will be an issue. Even 37" tires with stock 3.73 gears is doesnt feel laggy.

 

[BlkMax]

One thing to check is fuel filter. If it has junk in it, the engine will defuel to try to save the CP3, It is a good idea to change that every 20K, regardless of engine series.

 

[mrdan27611]

So yesterday evening, we checked the rear end gear ratio. We did it via this method.

https://www.youtube.com/watch?v=ktdywT5EsiQ&t=287s

Basically, it's counting the rotations of the drive shaft vs the rotation of wheel. Easy enough. So I'm looking for a 3.73 or a 4.11 or something or other. We checked it multiple times because I thought I was crazy. We came up with roughly a 2.0. According to my Google-Fu, there has never been a 2.0 or anything close to it as a rear end put in this model truck.

I don't have the option codes for this truck. It's been painted so the door sticker is gone and there is nothing in the glove box. I have the VIN of course but nothing there decodes to my axle ratio.

The truck is a 4x4. There is nothing to indicate it's in a bind when it's engaged so I doubt the rear end gears have been changed along the way (remember, it has 300k and it's new to me).

I'm going to run the data logger today. I have a relatively heavy load to haul (maybe 15k) and I'm the driver today so I can capture some boost, HP, and torque data. I'll report back on those details when I know more.

Question for today though is, have I done something wrong on checking my rear end gearing? The check seems straight forward enough but I really don't believe the results. For one thing, the truck wouldn't run on the highway with proper gearing if it tachs where it does now with a 2.0 rear end. It's probably turning 2500 rpm at 70-75 (I don't recall exactly, we don't run on the highway often).

On another note, there is a small leak at the drive shaft entrance into the rear end. Just a dampness around the housing, not an dripping leak. Think I have something wrong in the rear end? There is no clunking, no noise, no indication of problems other than lack of torque and a very small leak.

 

[mrdan27611]

One thing to check is fuel filter. If it has junk in it, the engine will defuel to try to save the CP3, It is a good idea to change that every 20K, regardless of engine series.

Thanks. I'm going to check fuel delivery pressure when I run it today. It doesn't give any real indication of starving for fuel but like you said, it's worth changing the fuel filters anyway. I believe the one that is on it is new as the truck was fully serviced before I bought it but it's worth looking at to make sure.

 

[Hnkstang50]

When counting the driveshaft spins make sure the others rear tire isn't spinning in reverse from the diff being open.

I was completely unhappy with my 02 lb7 when I got it and was convinced something was wrong. Couldn't even spin the tires in the rain. Only thing I found was some collapsed fuel lines (theres an old bulletin in it) but after fixing them there was little change. The fix was a ppe tuner. Woke the truck up big-time. Turbo has lag. But that's normal too on the lb7.

 

[dmax_ty]

So yesterday evening, we checked the rear end gear ratio. We did it via this method.

https://www.youtube.com/watch?v=ktdywT5EsiQ&t=287s

Basically, it's counting the rotations of the drive shaft vs the rotation of wheel. Easy enough. So I'm looking for a 3.73 or a 4.11 or something or other. We checked it multiple times because I thought I was crazy. We came up with roughly a 2.0. According to my Google-Fu, there has never been a 2.0 or anything close to it as a rear end put in this model truck.

I don't have the option codes for this truck. It's been painted so the door sticker is gone and there is nothing in the glove box. I have the VIN of course but nothing there decodes to my axle ratio.

The truck is a 4x4. There is nothing to indicate it's in a bind when it's engaged so I doubt the rear end gears have been changed along the way (remember, it has 300k and it's new to me).

I'm going to run the data logger today. I have a relatively heavy load to haul (maybe 15k) and I'm the driver today so I can capture some boost, HP, and torque data. I'll report back on those details when I know more.

Question for today though is, have I done something wrong on checking my rear end gearing? The check seems straight forward enough but I really don't believe the results. For one thing, the truck wouldn't run on the highway with proper gearing if it tachs where it does now with a 2.0 rear end. It's probably turning 2500 rpm at 70-75 (I don't recall exactly, we don't run on the highway often).

On another note, there is a small leak at the drive shaft entrance into the rear end. Just a dampness around the housing, not an dripping leak. Think I have something wrong in the rear end? There is no clunking, no noise, no indication of problems other than lack of torque and a very small leak.

You don't have a 2.0 rear end. Check your methods. You have a 3.73 as 4.10s were only on trucks with the ZF-6 standard IIRC.

 

[THEFERMANATOR]

You don't have a 2.0 rear end. Check your methods. You have a 3.73 as 4.10s were only on trucks with the ZF-6 standard IIRC.

All DURAMAX trucks came from GM with 3.73 gears.

 

[mrdan27611]

You don't have a 2.0 rear end. Check your methods. You have a 3.73 as 4.10s were only on trucks with the ZF-6 standard IIRC.

I knew I had something wrong. Thanks. We'll recheck.

 

[mrdan27611]

Update from yesterday.

I pulled about 13,000 pounds yesterday, which is a decent load for us but not especially heavy. I was able to log the entire return trip. Obviously the numbers were all over the place, so I'll just reference the maximums.

I'm just typing the PID as it is in the computer. My comments are to the right in ()

Max RPM 2802
Max speed 48 mph
Max boost pressure - estimated 17.649 psi
Max boost pressure sensor 32.8 psi (No idea why the big difference)
Max air flow rate 43.60 lb/min
Max intake manifold pressure 67 in/mercury
Max fuel rail pressure 23528.02 psi
Max engine torque 240909.4 Ft/lbs (this one is off the charts??)
Max calculated load value 94.1% (this was usually much lower, the engine didn't seem to work too hard)
Max calculated engine torque 821 ft-lbs
Max calculated engine power 400hp
Manifold absolute pressure 65.9 in/mercury

The barometric pressure yesterday was 29.8

What I took away from this was, the engine seemed to be doing just fine. The boost seemed to be there and regardless of the two different boost readings, 67 in of intake manifold pressure is pretty strong so the engine is breathing ok. Seems the engine is getting the boost it needs. I usually have an employee driving this truck so this was my first trip with a decent load. I usually only drive on Sundays when we haul lighter loads. I actually think it is ok for what it is but he's been complaining since we got it that it's not able to pull a load, that it can't get up to speed, can't maintain 45 MPH, etc.

I may have been on a wild goose chase, and for that I apologize to you guys. He's usually really good at spotting problems but I don't see the problem at this point. He had a 2006, and he drives a 2012 Duramax. I think he's just used to a different torque curve.

 

[THEFERMANATOR]

The 2 different readings are because the engine has 2 pressure sensors. One reads total atmospheric pressure(barometric pressure), and the othervreads total pressure in the intake of the engine(atmospheric pressure plus boost pressure). The boost pid is total intake pressure minus atmospheric pressure, and the other is total intake pressure. The airflow sounds a little low to me, but otherwise it sounds like it's running fine. The LB7 stock isn't all that impressive, but with some minor tuning they really wake up. You can leave peak HP at stock levels, but with some tuning changes make it feel like a different engine. Since most LB7's didn't have any emission controls on them, they had to use tuning to meet enissions, and it really makes them feel sluggish.

Compared to newer trucks, a stock LB7 will feel like somethings wrong with it. If you want, a basic tune will COMPLETELY change the feel of the truck, and make it feel more like the newer trucks.

 

[mrdan27611]

The 2 different readings are because the engine has 2 pressure sensors. One reads total atmospheric pressure(barometric pressure), and the othervreads total pressure in the intake of the engine(atmospheric pressure plus boost pressure). The boost pid is total intake pressure minus atmospheric pressure, and the other is total intake pressure. The airflow sounds a little low to me, but otherwise it sounds like it's running fine. The LB7 stock isn't all that impressive, but with some minor tuning they really wake up. You can leave peak HP at stock levels, but with some tuning changes make it feel like a different engine. Since most LB7's didn't have any emission controls on them, they had to use tuning to meet enissions, and it really makes them feel sluggish.

Compared to newer trucks, a stock LB7 will feel like somethings wrong with it. If you want, a basic tune will COMPLETELY change the feel of the truck, and make it feel more like the newer trucks.

Well since I've already shown that I don't know what I'm doing, I'll go ahead and ask the question. What do I do for a basic tune? Are we talking about getting an electronic tuner. I've only used one once, on an Avalanche I had. I didn't mess with the engine, but instead changed the shift points on the transmission. Made it into a whole new truck and I was very pleased. If that's what we're talking about, do you have a suggestion on a brand/type?

Thanks.

 

[TheBac]

May I ask why you havent taken the truck to a competent diesel shop or dealer and had it gone over to see if any issues match your concerns?
I know the guys are trying to help, but its next to impossible for people on an internet forum to give any kind of accurate diagnosis from afar.