02 CCSB LB7 severe lack of power (like a 4cyl)

[Diesel Krazy]

I have a truck that I bought a while back with some preexisting problems. 02 2500HD LB7
The main problem is the thing can't get out of its own way. When stone cold, it barely responds to throttle input, barely comes off idle even when floored. As it warms up it gets better, but acts like it is limited to 1/4 throttle or less other than trans shifts late or kicks down on heavy throttle input.
It starts easily when cold and runs smooth with no unusual noises. No CEL ever.
No smoke and 11 psi is the most boost I have ever seen.
Almost tolerable it I load level 4 tune, but only with heavy input.
My bone stock LB7 3500 flatbed running on 7cyl has way more power. It has a valve train problem.. :-(
I have Torque Pro for logging, but it has its limits. Can't afford EFI Live yet.

New Fuel filter (Dealer tested for restriction in fuel system @ 2hg)
Tested Rail Pressure and it scales properly and Demand / Actual stay close.
Injector Balance is within spec. (Injector Age unknown) Not Making Oil!
PO did head studs 30k ago and Truck has 210k on it. (Said He couldn't afford to do the injectors then.
Checked engine harness connectors and 1 pin was pushed in a little, but no change.
Cleaned MAF and swapped with other truck, No change.
MAP Seems to scale fine ( Maybe I should swap with known good?) Cleaned, no help.
New Batteries and have tried another pair.
Currently set to stock and ECM was updated at dealer recently with no change in power.
The only think tech said was MAF not scaling to 450? I was able to get there but it took a while. Cleaned / Replaced made no difference.
Had an AFE intake on it, switched to stock and noticed a slight change, but not much.
Changed Trans Filter and topped off ATF as I heard that could affect it.
Exhaust is a 4" MBRP SS Catback system so no restriction there.
Not California model so no EGR.

I am at a loss why it refuses to give it fuel, like something is holding it back. Anyone nearby have EFI Live or a tech 2? I can only do basic checking and logging with Torque Pro and I can't afford to go back to the dealer or throw parts at it. I have spent many a night researching and testing only to come up empty handed so far. Maybe if I get a chance I will recheck or swap out MAP and even the AP? Sensor. I believe they both show the same with key on.

Any help solving this would be greatly appreciated...

[DmaxMaverick]

Brakes sticking? Check for free-turning wheels. The E-brake may be stuck. It's happened before.

Other than that, it sounds like you'll need some hands on. Other than checking for actual fuel flow (collapsed line, other restriction), looks like you covered the basics.

[Diesel Krazy]

No problems with the brakes. It is even sluggish to rev the engine with no load. I just did some more logging to look at fuel rate and it looks like the ECM is holding back on fueling. Swapped MAP with other truck and seemed to help ever so slightly and was able to get 15psi if I floored it long enough uphill. It is a fueling issue for sure, just can't figure out why. Seems like something is telling it to limit fuel??? Rail pressure was holding at 22k and even saw 24k momentarily under load up a hill, so that would eliminate and fuel restrictions, leaking injectors or weak pump.

[Diesel Krazy]

I finished more logging with Torque Pro on my other truck and now wondering if it is either bad FICM (Wouldn't it throw a code?) or maybe rust and junk plugging the injectors from when PO did the head studs? I would think if it was rust and junk in the injectors that the balance rates would be all over and in the + side due to trying to add fuel unless the restriction is not affecting it at idle? Any thoughts on this?

[Diesel Krazy]

Another thought on this is possible air ingestion in fuel. Normally this would cause hard starting and other symptoms, but dealer tech said vacuum on fuel port was 2hg which could indicate an air leak? One thing I noticed is at one stop on my way home which is on a hill and I coast quite a ways to the stop and it feels like it has a lot more power and more responsive when I take off from there. Going to try a clear hose on feed line and look for air bubbles. Seems like this or FICM going bad, but everyone says FICM rarely has problems.

Stay tunes for more results...

[rapidoxidationman]

The fuel system is under vacuum from the tank through the filter all the way to the high pressure fuel pump. If there's a leak in that vacuum system, it'll suck air in.

It's been said that a lift pump (and extra filtration)at the tank will help things live longer. It will certainly make any fuel line leaks obvious by pushing fuel out of the leaky area instead of sucking air in. Take a look at Kennedydiesel.com to see what he offers for a lift pump/filtration system. He's a member/vendor here and stands behind what he sells.

What kind of fuel filter are you using (OEM or aftermarket)? Lots of aftermarket filter cans use plastic housing instead of metal and have reportedly been prone to leak at the gasket. Even with the GM metal can, you've got to make sure the O ring gasket is properly in place or it'll leak.

A clear section of fuel line will be a good diagnostic tool. Let us know what you find!

(shamelessly stealing an image of a fuel pressure guage with and without a lift pump):
http://www.kennedydiesel.com/images/Dmax-fuel-filter-rest1.gif

How's the truck run with a loose fuel cap? If the tank isn't venting properly you could be building up vacuum in the tank, which could lead to collapsed fuel lines and fuel starvation.

I'd be looking for another dealer tech... It doesn't sound like the one you've got now quite knows how the OEM system works.

[Diesel Krazy]

Well, spent a lot of time on it again today.
Swapped FICM with known good.... No change
This was after installing a clear line between the FICM and Filter housing to check for air leaks. Was getting a ton of air for a while, but eventually that mostly stopped.
Got dark before I could try the clear hose after filter housing. That and the hose is a b!tch to get at.
Filter is from local GM dealer. Had Napa plastic on it before, but no change after new OEM filter was installed.
If I had the money, I would install a lift pump, but currently unemployed and broke.
This is incredibly frustrating since all logging indicates no fueling problems.
I am aware of Kennedy Diesel and the great products he carries and has developed, just can't afford them right now. I wish I had his LB7 tune, at least once the current problem is fixed.
I am well versed in diesels and understand the workings of a Duramax from massive amounts of research, just lack the experience.
Have had and worked on tons of VW diesels new and old as well as 5.7 olds, 6.2 and 6.5td rigs. I have gained a lot of knowledge reading the forums and wish I had time to contribute more on here.
Anyway, tomorrow is a new day...
I just don't see it being injectors or the pump and the balance rates are good and it maintains pressure under load. That kind of eliminates a lot of stuff.

BTW: I just installed a new OEM and correct fuel cap because it had a gasser cap on it. Running with cap loose did nothing as well.

One thing I might add is that even just sitting there revving the engine with no load it is noticeably sluggish compared to my other stock LB7 running on 7 cyl...

[cabletech]

Have you data logged the gas pedal to see if the ecm is seeing the full range of voltages? I would also try a known good ecm.You would have to go through the vats learn process unless you have acess to a tech2.

Jay

[Diesel Krazy]

I stated in a prior post that the pedal scales properly. Had swapped ECM with no change as well. It's handy having a truck that I can swap parts with, but so far I have been able to make very small inprovements, but overall it is far from normal.
Going to check return line for restriction and more checking for air leaks.
these things take time...


Don't mistake the "newbie" under my title as being a newbie with diesels, I'm well versed in diesels and electroncs. I do appreciate any input as sometimes it is something simple that was overlooked. :)

[DmaxMaverick]

No problems with the brakes. It is even sluggish to rev the engine with no load. I just did some more logging to look at fuel rate and it looks like the ECM is holding back on fueling. Swapped MAP with other truck and seemed to help ever so slightly and was able to get 15psi if I floored it long enough uphill. It is a fueling issue for sure, just can't figure out why. Seems like something is telling it to limit fuel??? Rail pressure was holding at 22k and even saw 24k momentarily under load up a hill, so that would eliminate and fuel restrictions, leaking injectors or weak pump.

Do you have a boost gage? Or was this reported by the PCM, read on your scanner? 15 PSI is (minimally) respectable, if read from the gage, and the engine should be making power. NOT so, if reported via the PCM. It's barely above atmospheric pressure (1 BAR), at sea level (15-14.7=0.3 PSI, with a margin of error, may equal zero).

Check the wastegate for operation. If it's stuck open, or not closing for any reason, no boost, no power.

[Diesel Krazy]

The boost is corrected for atmospheric pressure. No gauge, but logging both trucks there is a big difference in boost. The other truck hits 22psi and spends a lot of time at 20+ under load. The truck in question briefly peaks at 10 - 15 but mostly sits at 5-9 while trying to get up to speed. I don't think boost is even an issue because no load revving of the engine should produce very little boost and it is noticeably unresponsive just trying to rev while in Park. My other truck revs much quicker and it is bone stock with 1 dead hole.

I should also reiterate that if I load level 4 on the PPE (120 hp?) Have not tried level 5, 2 or 3 give lesser improvements. it wakes it up to almost tolerable except off idle and low load or hills without having to push it hard to start making some power.

Didn't get time to work on it today due to GF and having severe back pain again. Probably will get back to it in a few days. Will keep updating the thread as I feel this is a somewhat unusual problem as it has no other symptoms besides being slower than a Mercedes 240D.

I tried to log the fueling rate, but the only thing I can get data on is PID ff125d labeled "Fuel Flow Rate" in units/hr (GPH I think?) and it hits around 3/4 of the good trucks numbers IIRC. I'm thinking that may be some other measurement or calculated estimate???

Who knows, just going to keep at it til I either get fed up or figure it out. TBC - School of hard knocks...Class Dismissed!

[DmaxMaverick]

This is curious. It's defueling to the point it has little power, like limp mode, but isn't throwing a related code. That leads me to suspect the aftermarket programmer. Try removing it (completely, physically, not just deprogrammed) and start at the beginning. If it is still that bad, it should throw some codes, without the PPE running interference. Or, as I've seen many times, that may be the problem, but they've almost all been the Edge units, and I've not seen this with PPE's.

[Diesel Krazy]

Defueling is indeed what it acts like, but never any codes. Just to clarify I unloaded the PPE tune and then had the dealer update the PCM to eliminate any corruption in the ECM. At the same time I updated the PPE with the latest program from their site to make sure it was clean as well. Truck was no better after ECM update and I tried many things before ever loading PPE back on to it again. I've heard of a Duraminimizer and it sounds one possible explanation, but I see no other toys plugged in anywhere. From what I could tell, they plug into the harness by the master cylinder and there is nothing there.

Back problems are keeping me from doing much at the moment.

[rapidoxidationman]

This is curious. It's defueling to the point it has little power, like limp mode, but isn't throwing a related code. That leads me to suspect the aftermarket programmer. Try removing it (completely, physically, not just deprogrammed) and start at the beginning. If it is still that bad, it should throw some codes, without the PPE running interference. Or, as I've seen many times, that may be the problem, but they've almost all been the Edge units, and I've not seen this with PPE's.
DK:
When you say "unloaded" does it mean you actually REMOVED the programmer?

[Diesel Krazy]

Yes, there is no reason to leave it plugged in otherwise. Except maybe to view diags, but I am using Torque Pro for that mostly. As I said, I even had the ECM updated and the PPE Programmer was not connected for quite some time afterwards while I was checking things out. Therefore the PPE programmer is not a factor whatsoever in this problem.

[dually2002]

Maybe a worn turbo? Clearances to great at the impeller to create boost.

[Diesel Krazy]

I don't think boost is an issue as it should have more power that it does with no boost. My old 6.2 N/A truck has way more power. It is definitely a fueling issue. If I had a tech II or EFI Live to log the fuel rate I might be able to see something, but all I have available is Torque Pro which has very limited support on the DMax. Anybody have a list of PIDs for a LB7? I have some, but the fueling PID does not seem to work. I was able to get Fuel Rail Pressures working on it though.

[Kennedy]

I have a truck that I bought a while back with some preexisting problems. 02 2500HD LB7
The main problem is the thing can't get out of its own way. When stone cold, it barely responds to throttle input, barely comes off idle even when floored. As it warms up it gets better, but acts like it is limited to 1/4 throttle or less other than trans shifts late or kicks down on heavy throttle input.
It starts easily when cold and runs smooth with no unusual noises. No CEL ever.
No smoke and 11 psi is the most boost I have ever seen.
Almost tolerable it I load level 4 tune, but only with heavy input.
My bone stock LB7 3500 flatbed running on 7cyl has way more power. It has a valve train problem.. :-(
I have Torque Pro for logging, but it has its limits. Can't afford EFI Live yet.

New Fuel filter (Dealer tested for restriction in fuel system @ 2hg)
Tested Rail Pressure and it scales properly and Demand / Actual stay close.
Injector Balance is within spec. (Injector Age unknown) Not Making Oil!
PO did head studs 30k ago and Truck has 210k on it. (Said He couldn't afford to do the injectors then.
Checked engine harness connectors and 1 pin was pushed in a little, but no change.
Cleaned MAF and swapped with other truck, No change.
MAP Seems to scale fine ( Maybe I should swap with known good?) Cleaned, no help.
New Batteries and have tried another pair.
Currently set to stock and ECM was updated at dealer recently with no change in power.
The only think tech said was MAF not scaling to 450? I was able to get there but it took a while. Cleaned / Replaced made no difference.
Had an AFE intake on it, switched to stock and noticed a slight change, but not much.
Changed Trans Filter and topped off ATF as I heard that could affect it.
Exhaust is a 4" MBRP SS Catback system so no restriction there.
Not California model so no EGR.

I am at a loss why it refuses to give it fuel, like something is holding it back. Anyone nearby have EFI Live or a tech 2? I can only do basic checking and logging with Torque Pro and I can't afford to go back to the dealer or throw parts at it. I have spent many a night researching and testing only to come up empty handed so far. Maybe if I get a chance I will recheck or swap out MAP and even the AP? Sensor. I believe they both show the same with key on.

Any help solving this would be greatly appreciated...

I'm not sure why the previous owner would have done head studs just out of the blue? Odds are that when the injector lines were removed and reinstalled they dropped a bunch of rusty junk in the inlet bowls of the injectors and that is what is giving it fits. It just cannot deliver the volume that it needs to make HP.


Details here: http://www.kennedydiesel.com/docs/Duramax%20LB7%20Injector%20Line%20Corrosion.pdf

[Diesel Krazy]

I have thought about the injectors having crud in them from being worked on, but wouldn't balance rates be all over the board as they should not all be restricted the same? Also, why would it have significantly more power if I load a tune from the PPE? I really can't afford to do injectors right now, and don't like throwing parts at a problem unless there is a high probability of success in doing so.
I would assume if this is indeed the problem, I'm looking at new injectors and lines both?
Any real life symptoms described on one that was found to be badly plugged for comparison?

[DmaxMaverick]

The injectors and lines don't really get "plugged up", in the traditional sense. Debris from a R/R of the lines can contaminate them at the microscopic level, in the internal passages and valves.

I agree with your supposition, though. If it were caused by fuel line contamination, it would likely cause a significant balance issue.

Have you physically removed the PPE, yet?

[Diesel Krazy]

Yes, the PPE is a loader and is not physically connected except to load a tune. I had the ECM flashed at the dealer and the PPE was never reconnected after that, so that was not a factor. Currently running stock tune with nothing plugged in and it is so very slow...

[DmaxMaverick]

Was the PPE program unloaded, and returned to stock programming, BEFORE the PCM was flashed by the dealer? In any case, I suggest finding someone in your area with a similar truck that has a completely stock PCM, and swap it in.

Still, the problem points back to fueling anomalies that aren't causing the PCM to complain. A significant power loss should cause some data discrepancies, and DTC's. That is, unless the PCM does not interpret the data as being outside acceptable limits, or the limits are artificially adjusted, such as is commonly done with many programmers and power modules.

[Kennedy]

I have thought about the injectors having crud in them from being worked on, but wouldn't balance rates be all over the board as they should not all be restricted the same? Also, why would it have significantly more power if I load a tune from the PPE? I really can't afford to do injectors right now, and don't like throwing parts at a problem unless there is a high probability of success in doing so.
I would assume if this is indeed the problem, I'm looking at new injectors and lines both?
Any real life symptoms described on one that was found to be badly plugged for comparison?

Best I can say is I've seen it before. Texas truck as I recall. In for head gaskets came back a turd. Never the same. Had to use an Edge Juice on 90HP to even feel like stock. I believe the end result was dumping the truck.

Whenever I see a LB7 truck that does not perform properly, but runs otherwise fine and everything checks out fine it always comes back to injectors.

This will NOT show on balance rates.

[Diesel Krazy]

The ECM was put back to stock before reflash, I tried another stock ECM and even swapped out the FICM all with no change. Probably is plugged injectors which I considered early on, but would have thought that would have some other symptoms besides just low power. It sorta makes sense as it is totally non responsive stone cold when fuel is heavier and gets better as the fuel heats up and thins out. I may pull 1 or 2 injector lines to see if I can see any visible crud in them. I'm just afraid of opening a can of worms by doing that.

[DmaxMaverick]

I would not recommend pulling the lines, without fully intending to replace them, or give them a proper cleaning (ultrasonic). Removal alone can, and does, cause the contamination. Re-installation doubles the chance of that.

If warmer/thinner fuel seems to improve power, try going to the extreme. Run a 50/50 mix of #2 and kerosene, with about 2% 2-cycle oil (replaces lost lubrication). This will make the fuel about as thin as you'd want to run. It will have a lower BTU content, but that should not be noticeable if more fuel is allowed.

Another thing to try:
Supply the fuel from a fuel can, bypassing the OEM fuel filter assy (use a high volume inline filter). Position the can at or above engine level for minimal suction required. This will eliminate nearly all of the OEM fuel system, if there is a restriction (or collapsed fuel line) causing the issue. Keep in mind, the fuel return circuit will not return to the can, so most of the fuel from the can will be returned to the tank. Ideally, a fuel container can be placed in the bed, with a long hose to the engine compartment, suspended at the door handle(s), and over the mirror.

Have you eliminated the possibility of fuel contamination (gasoline, or other fluid)? The fuel can test will do this, if you haven't. A 50%+ mix of gasoline could easily cause this power loss.

[Diesel Krazy]

If I do pull the lines, I would likely use an ultrasonic cleaner to clean them after working out what I could manually first. I have run several tanks of fuel through it and it kind of liked B20 over the straight #2 Diesel. I had run some 2 stroke oil through it, Did injector clean with bottle feeding engine directly (that helped the injector balance greatly), Tried 1/2 bottle of ATF per tanks for 2 tanks full and it runs slightly better, but not affecting the main problem apparently. I did just pick up the test port adapter to monitor the vacuum on the fuel system. Dealer tech said it was showing 2Hg, but I think he only tested it at an idle. I want to try it while driving to see what happens. I'm hoping it's just an air leak causing the problem. I do appreciate the input...

[Kennedy]

The problem is you can't clean the lines in the hidden areas. The nut does not slide back to inspect and when you start to run the line down the nut grinds on the line well before the ball is seated.

If the injectors have debris in them you pretty much need to R&R them and then disassemble the nozzle and if you are lucky you can back flush them. Trick is not to not lose and small parts and to not get nozzle leaks and a crankcase full of diesel from removing the nozzles and reinstalling.

[Diesel Krazy]

I wish the injectors were easy to test like the old style. I have a pop tester for them. Probably cost as much to have them cleaned and tested as buying replacements too. I'm pretty much stuck at this point as I am broke and broken... Can't work on much due to back problems and broke because I got laid off and my ex-wife is forcing me to pay her off or she will force me to sell my home... :-(

Anybody wanna buy a truck...

[Jm1205]

I have the same issue with LB7. Need help. Did you ever figure out problem??
Thanks

[Kennedy]

Posts #23 and #27

[More Power]

John,
Why can't you tear it down, and if the injectors are relatively low time, take them to a certified shop to inspect/test?

In the meantime, wire-wheel and spotlessly clean the injector lines (as clean or cleaner that new) before reassembly.

What's a new set of lines add to the cost?

Thanks, Jim

[Kennedy]

The trash is all inside the line nut area up the backside of the "ball" and impossible to clean. Once you start to spin the nut the trash grinds up and gravity takes it to the inlet bowl of the injector.

See pics here: http://www.kennedydiesel.com/docs/Duramax%20LB7%20Injector%20Line%20Corrosion.pdf


I don't know that we've seen any confirmation that the lines or heads were off for either of the trucks in question, but basically this and MAF signal errors are the keys assuming fuel supply checks out.

New set of lines is $600 OE and mandatory in my experience.

[Jm1205]

Mine has done exactly same. Except everything is new, including motor. Ran great for first 2k miles. Then something took a crap. Started throwing $$ at it and has not stoped. After engine rebuild, put pensacola injectors in. Every time i would talk to anyone and say that they would tell me its those injectors without even hearing anything else. Got to the point i had to put new injectors in again just so i had peace of mind the pensacola ones were out of my truck. Put new bosch in now but still same problems. Ficm is new, ecm is new, all sensors are new including maf. To save time only things on that are not new is fuel pressure sensor, alternator and a/c. Tuner is saying mass air flow is not working like it should. Put another new oem in and still saying its not ramping up like it should. New wcfab intake and cooler pipes. New 64mm ryans diesel service turbo.
Im lost at this point. Dont know what to do next. Ive put so much money in this truck its ridiculous. Wanted to make the truck new again instead of buying a new one but cant even enjoy it yet. Motor and all related now have 2500mi. Everyone always wants to jump to injectors but i will not do injectors again. And when i say new i mean all line, all seals n gaskets and even injector harnesses.
What the hell is the fix for this problem??
I promise to post my fix when found.

[Kennedy]

Mine has done exactly same. Except everything is new, including motor. Ran great for first 2k miles. Then something took a crap. Started throwing $$ at it and has not stoped. After engine rebuild, put pensacola injectors in. Every time i would talk to anyone and say that they would tell me its those injectors without even hearing anything else. Got to the point i had to put new injectors in again just so i had peace of mind the pensacola ones were out of my truck. Put new bosch in now but still same problems. Ficm is new, ecm is new, all sensors are new including maf. To save time only things on that are not new is fuel pressure sensor, alternator and a/c. Tuner is saying mass air flow is not working like it should. Put another new oem in and still saying its not ramping up like it should. New wcfab intake and cooler pipes. New 64mm ryans diesel service turbo.
Im lost at this point. Dont know what to do next. Ive put so much money in this truck its ridiculous. Wanted to make the truck new again instead of buying a new one but cant even enjoy it yet. Motor and all related now have 2500mi. Everyone always wants to jump to injectors but i will not do injectors again. And when i say new i mean all line, all seals n gaskets and even injector harnesses.
What the hell is the fix for this problem??
I promise to post my fix when found.

Did you have the tuning adjusted for the change in intake pipes? I'm assuming this is the one that the air filter is on as well.