My 2002 Duramax - Down on power, or is it just me?

[TheAmigo]

Everyone,

The history: I've had the truck since new. No mods. I replaced the injectors myself 3 or 4 years ago. ~160,000 miles on it now. It has been a great truck other than for the injector issue. We've had four kids since purchasing it and it holds all 6 of us nicely. It's paid for, and I'd like to keep it for as long as possible.

However, over the course of the last 2 or so years(?) it seems to have lost some of its get-up-and-go at higher speeds. When starting out from a standstill it seems to do just fine up to normal highway speeds.

But:
1.) When going uphill it seems to slow down ever so gently, and then when it finally downshifts it's all show and no go. Noise, but no feeling of acceleration.
2.) At interstate speeds of 60 or 70, when downshifting, it's again all noise but very very little acceleration.
3.) At times it seems that if I >slowly< roll into the accelerator it can increase speed faster than if I put it all the way down to force a downshift.

And, really, I've had it so long and this has been such a slow deterioration (if at all) that I have a had time remembering how things should really be. I just feel that it's not normal.

It throws no codes. And it's not like what I've read here regarding the limp mode.

Any ideas?

Thanks.

[rapidoxidationman]

Any codes?
How's the air filter (can the truck breathe)?
Can you hear the turbo spool up?

When I replaced the head gaskets on my '05 at 130K, the intake manifolds and heads were getting pretty gooey with black fuzz (thanks to the EGR system?). I wonder if that might be happening to yours?

[TheAmigo]

I keep everything clean. No codes. Good air filter. I do hear the turbo. When I replaced the injectors everything inside was clean.

I think I read somewhere else that it could potentially be the transmission slipping at higher revs and just not putting the power(noise) to the wheels?



Any codes?
How's the air filter (can the truck breathe)?
Can you hear the turbo spool up?

When I replaced the head gaskets on my '05 at 130K, the intake manifolds and heads were getting pretty gooey with black fuzz (thanks to the EGR system?). I wonder if that might be happening to yours?

[rapidoxidationman]

You'd see the disconnect between the transmission and wheels on the tachometer. What does the transmission fluid look and smell like? Fresh, clean, red and sweet or brown/black/burned?

[TheAmigo]

What do you mean when you say I'd see the disconnect between transmission and wheels? The tach revs. The engine makes noise because it downshifted, but the truck just doesn't get up and go like I think it should(and used to).

I'll check on the fluid condition but every time I've checked, over time, it has been fine.



You'd see the disconnect between the transmission and wheels on the tachometer. What does the transmission fluid look and smell like? Fresh, clean, red and sweet or brown/black/burned?

[TheAmigo]

Does anyone else think this could be a transmission issue with something slipping under load?

[DmaxMaverick]

Does anyone else think this could be a transmission issue with something slipping under load?

I don't think so. As said above, if it were, you'd have a noticeable disconnect, meaning, RPM's would increase with no increase of ground speed. The TCM's monitoring threshold is less than 1%. More than that and it will set a code and Limp Mode.

What you are experiencing may be more related to (current/recent) fuel quality, and/or seasonal conditions. Try some fuel additive with cetane booster, a pint of 2-cycle oil, and during cooler weather.

[Kennedy]

You'll want to check out the obvious as in fuel system supply side restriction, and make sure that your MAF sensor is working and reading correctly.

Over the years I'd seen a fair number of inexplicable LB7 "dogs" and it tends to follow recent major service like head gasket jobs. It is pretty much always injector related. Truck runs fine, drives fine, with low power and just not "right." My take is that the reuse of corroded injector lines puts a bunch of junk in the inlet side of the injectors. Every one that I have been involved with and presented this way we fixed with 8 fresh stock injectors and new supply lines along with added safeguards like lift pump and Mega filter plus FPPF additive.

[TheAmigo]

Thanks for the responses.

Thing is, there IS an increase in RPMs due to the downshift, and like I said it just doesn't seem to move. It increases speed very, very slowly. And again, if I didn't downshift but slowly gave it the go pedal it almost seems like it would increase speed quicker than if I had downshifted. That's what makes me think transmission slippage of some sort.

And, this has been a constant annoyance over the last two years, so I don't think it's seasonal.

Finally, to the next post from Kennedy, when I replaced the injectors I also replaced the supply lines. I have also cleaned the MAF sensor.

Runs fine, just seems old... It is 12 years old, but not that many miles considering.


I don't think so. As said above, if it were, you'd have a noticeable disconnect, meaning, RPM's would increase with no increase of ground speed. The TCM's monitoring threshold is less than 1%. More than that and it will set a code and Limp Mode.

What you are experiencing may be more related to (current/recent) fuel quality, and/or seasonal conditions. Try some fuel additive with cetane booster, a pint of 2-cycle oil, and during cooler weather.

[DmaxMaverick]

Thanks for the responses.

Thing is, there IS an increase in RPMs due to the downshift, and like I said it just doesn't seem to move. It increases speed very, very slowly. And again, if I didn't downshift but slowly gave it the go pedal it almost seems like it would increase speed quicker than if I had downshifted. That's what makes me think transmission slippage of some sort........

This does not indicate transmission slippage, in any way. In fact, it may eliminate that possibility, entirely. The RPM increase I/we referred to was before a downshift, holding the same gear. What you describe (except for the loss of power), sounds like completely normal behavior.

Do this, under the same conditions you would expect to experience the problem:

Accelerate normally (T/H OFF) up to about 65 MPH and set the cruise control. You should be sitting on about 1700 RPM's (maximum available torque at low input shaft speed). Now, floor it, and watch the tach and speedo. You'll have about 4-5 seconds before a downshift, so let off before that. Repeat as necessary to provide the longest WOT condition, before a downshift is forced. The RPM's should not increase any more than necessary to increase the ground speed. If it does, these conditions will indicate any slippage. If you just accelerate, the transmission is normal. If it's slipping, you will see the tach increase at a greater rate. When you let off (zero throttle), if it's slipping, you will see an immediate drop of RPM's (before it matches ground speed). If the RPM's and ground speed remain synchronized, NO slippage.

If it downshifts immediately when you floor it (cruise control engaged), you are missing an important PCM/TCM calibration update, or something else is wrong. DTC's, even in history or pending (no SES lamp), can force performance issues and low power. If the TCM has a fault, it WILL command the MIL/SES (P0700+). If the cruise control doesn't work, it may indicate this, as well.

Another thing you can/should do is, take your VIN to your dealership and have them check for your latest calibration update, and see if there is a later update. They should do this part free. If an update is available, have them install it. This takes less than 1/2 hour, and they should charge no more than that. There is no charge for the calibration, only the labor to install it.

[TheAmigo]

Thanks very much. I understand what you're saying and I believe I agree with you. I'll do a test run tomorrow.

However, I just broke out an ODB2 connector and app for my iPhone and I found I have these stored codes:

P1093: Fuel Rail Pressure Low During Power Enrichment
P1094: Fuel Rail Pressure Low During Idle or Decel Fuel Cut-Off(DFCO)

And this pending code:
P1094: again...

So, now I'm a readin' up on those..



This does not indicate transmission slippage, in any way. In fact, it may eliminate that possibility, entirely. The RPM increase I/we referred to was before a downshift, holding the same gear. What you describe (except for the loss of power), sounds like completely normal behavior.

Do this, under the same conditions you would expect to experience the problem:

Accelerate normally (T/H OFF) up to about 65 MPH and set the cruise control. You should be sitting on about 1700 RPM's (maximum available torque at low input shaft speed). Now, floor it, and watch the tach and speedo. You'll have about 4-5 seconds before a downshift, so let off before that. Repeat as necessary to provide the longest WOT condition, before a downshift is forced. The RPM's should not increase any more than necessary to increase the ground speed. If it does, these conditions will indicate any slippage. If you just accelerate, the transmission is normal. If it's slipping, you will see the tach increase at a greater rate. When you let off (zero throttle), if it's slipping, you will see an immediate drop of RPM's (before it matches ground speed). If the RPM's and ground speed remain synchronized, NO slippage.

If it downshifts immediately when you floor it (cruise control engaged), you are missing an important PCM/TCM calibration update, or something else is wrong. DTC's, even in history or pending (no SES lamp), can force performance issues and low power. If the TCM has a fault, it WILL command the MIL/SES (P0700+). If the cruise control doesn't work, it may indicate this, as well.

Another thing you can/should do is, take your VIN to your dealership and have them check for your latest calibration update, and see if there is a later update. They should do this part free. If an update is available, have them install it. This takes less than 1/2 hour, and they should charge no more than that. There is no charge for the calibration, only the labor to install it.

[TheAmigo]

Everything's saying a new fuel pump is in my future.

[TheAmigo]

Well, a lot of things are. I'm still trying to figure out the best way for me to diagnose CP3, FPRV, or heaven forbid injectors again...

[TheAmigo]

In reading through all the potential tests and issues I have noticed that one of the fuel lines in the engine bay has collapsed... So, that needs to be fixed. Now to read more to see if that could cause these codes...?

[rapidoxidationman]

Some potentially relevant reading on your issue:

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=43158&highlight=fuel+line+collapse

That's the top result from doing a search on this site for "fuel line collapse". Here's the others:

Some potentially relevant reading on your issue...

[TheAmigo]

Thanks. I had browsed that particular post as well.

At this point I REALLY want to rule out the injectors. Is there a single thing I can check that shows that it's the pump? My ODB2 device doesn't show rail pressure, sadly.


Some potentially relevant reading on your issue:

http://www.thedieselpageforums.com/tdpforum/showthread.php?t=43158&highlight=fuel+line+collapse

That's the top result from doing a search on this site for "fuel line collapse". Here's the others:

Some potentially relevant reading on your issue...

[TheAmigo]

As a summary of what I know so far. Stock 2002 LB7

Issue: Loss of power. Gutless going up hills - maxes out about 55 on a good hill even without towing. Giving it full go pedal at 55 on flat road causes downshift and just doesn't move it much all, yet when I let off I can baby it up to 65 or so pretty well. It has been down on power for at least a year or two. Otherwise, if you take it easy things seem ok.

-I (myself) replaced injectors and feed lines in 2010 @ about 120,000 miles. There's a few pics of that on here...
-No large amount of black/white smoke on heavy acceleration.
-No diesel in oil (that I can see or smell).
-Have changed fuel filter several times since this started.
-Now has 146,000 miles.
-Shows P1093 & P1094 codes.
-One bent/constricted fuel line(closest to the front of engine/driver's side).
-No check engine lights showing, had to hook up to see the P1093 & P1094 (why is that?).
-Followed DMaxMaverick's suggestions for testing transmissions slippage and I no longer think that's an issue. Seemed to do just like you said it should.
-Hooked up my iphone & DashCommand and found the balance rates and fuel rate. Cylinders are in order from top to bottom.

http://www.thedieselpageforums.com/tdpforum/picture.php?albumid=44&pictureid=310

[rapidoxidationman]

Start with the obvious: replace the collapsed line. You might also try to find out WHY the line collapsed (restriction in the fuel pickup in the tank maybe?)

Seems like a shortage of fuel caused by a collapsed/restricted fuel supply could cause exactly the problems you describe.

Have you ever noticed the primer button on top of the fuel filter in the "in" position when you check your engine during one of its episodes (engine idling)?

[TheAmigo]

I'm going to replace the lines.

I have not noticed the primer button being "in." However, it's not really an episode. It's constant. It doesn't fail to start, or die, like a lot of the posts referencing the collapsed line. It starts and runs just fine. It's just weak.



Start with the obvious: replace the collapsed line. You might also try to find out WHY the line collapsed (restriction in the fuel pickup in the tank maybe?)

Seems like a shortage of fuel caused by a collapsed/restricted fuel supply could cause exactly the problems you describe.

Have you ever noticed the primer button on top of the fuel filter in the "in" position when you check your engine during one of its episodes (engine idling)?

[Kennedy]

OK my mistake for assuming that the fundamentals were taken care of.

Start here:

http://www.kennedydiesel.com/images/Dmax-fuel-filter-rest1.gif

[TheAmigo]

As an update... Replaced the CP3 fuel pump and the truck runs like it's brand new. Lots more power.

[More Power]

Thanks for posting an update...

Jim