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Discussion Starter #1
Hi All,

I've been chasing a low power issue on my 2007 LBZ / 6 Speed Allison truck for about a month now.
It starts, runs, drives, shifts through all gears, stops, but is very low on power.
It wont spin the tires on wet grass and it wont go more than ~95km/hr.
The only DTC light is for an Air conditioning alarm as its been mechanically deleted.
I have replaced MAP, MAF, IAT, sensors, and the ECM.
Fuel rail pressure holds steady at WOT.
"Bottle test", not a drop of fuel.
Accelerator pedal clean sweeps 0-100%
Stock tuning, EGR disabled.

I did some data logging this weekend, and noticed a parameter under transmission.
"Requested Torque"
I data logged some brake torques, (not that the tires would spin), and
"requested torque" reads zero under all conditions, and for a split second, jumps to 56.00 N-m after letting OFF the pedal.

Truck in drive
Brake pedal pressed
Throttle to the floor
Accelerator at 100%,
RPM goes to about 1600 RPM
"Calc ruel rate" (MM^3) goes to 70mm^3 at WOT, No higher.
Requested torque remains at ZERO (0)
"Engine torque" maxes out at 565 N-m at WOT.

Could this "requested torque" be limiting the fuel rate to 70mm^3?

I do not have another truck to compare values to...

All suggestions welcome, if i can provide any more info, just ask.
635686
 

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Still struggling with the new format. Where do you subscribe to a thread so you don't have to post a useless "subscribed" . . . ?
 

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Still struggling with the new format. Where do you subscribe to a thread so you don't have to post a useless "subscribed" . . . ?
If you look at the top,right side of the thread you will see a blue follow tab. Click on that to subscribe or "Follow" the thread
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I'm not sure. Try in drive.
 

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Thanks Dullay and sorry Hozy for the thread diversion.

What you describe is classic trans-limp-mode without the 3rd gear lockup. It restricts mph, power, and locks in 3rd gear. Even though your 3rd gear is normal I believe your trans is the source of the ECU taking control of the other parameters. I don't know where the trans sensor(s) is but it needs to be tested. Look like the TPS (and everything along that path) is OK since it returned 100%.
 
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Discussion Starter #6
Thanks for the feedback Saltfever,
Is there any solid way of knowing that the transmission is in "LIMP MODE" ... ?
I have NO DTC lamp, and no indication on the DIC that its limping.
On other trucks ive worked on, "Range Shift inhibited" is the indication.
The truck also shifts through all gears, i've counted up to five on its way to top speed (95 km/hr)....
Its also just as sluggish in reverse...
So i'm not convinced that its stuck in 3rd...
I will post some more photos from the scanner of you guys to browse though.
Another "odd" parameter i see is "GEAR RATIO = 8:1
Anyone know what that's all about?

I'm still a rookie at this forum, is there a way to share a short video of the data log?

Thanks for the help guys.
-Alex
 

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Discussion Starter #7
635707

GEAR RATIO: 8:1 Whats this all about...?

-Alex
 

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Discussion Starter #8
635708
635709

BALANCE RATES
 

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I'm still a rookie at this forum, is there a way to share a short video of the data log?
The best way to share a video here is to first upload the video to youtube and then copy the video link located in the address bar.
Then paste the video link here in the forum post.
 

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When my truck was new (less than 500 miles) I was starting my first long trip and about 125 miles into it the truck just “limped” for no reason at all. I got a CEL plus the exact symptoms you mention. I was lucky as there was a Chevy dealer 2 off-ramps up the freeway. Their scanner showed “a trans censor was bad” but they didn’t have that part. They cleared the CEL for me and sent me on my way warning the problem would return. Everything was normal until about 75 miles from home when it limped again. Local dealer fixed it and no issues since. Sorry, I don’t know what was replaced.

You have done some serious repairs and a new ECU is interesting. However, if a sensor is sending bad (or no) data to the ECU then, whether it is old or new, it will react the same way. I wish I could help but it seems like you need a dealer’s tech scanner to dig deep into the code. All the best.
 

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Discussion Starter #11
Thanks for sharing Saltfever, I will go over the transmission harness again to make sure i don't have broken wires.
I wish i had a CEL / DTC lamp and a code to go by,
Is anyone able to verify whether or not the TRANSMISSION REQUESTED TORQUE is or is not supposed to read ZERO?
Thank you all,
-Alex
 

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What screen are you seeing the transmission requested torque on? I can plug my launch scanner in when I get home and see what my 2007 LBZ reads.
 

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Discussion Starter #13
That would be excellent if you could do that for me Ricky,
I do not have a "Launch" scanner, but on the scanners i have been using, the "Requested Torque was listed under the transmission section which also displays Input shaft speed, turbine speed, trans temp, slip % etc.
Thanks a ton!
-Alex
 

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Discussion Starter #14
Some additional information.
I did some more scanning with a MAC scanner this afternoon.
With the truck on, warm, at idle (680 RPM), in park, "ENGINE LOAD" reads 29 % (Doesn't this seem excessively high?)
Then,
With foot on the brake, still at idle, shift transmission into drive, "ENGINE LOAD" increases to 38-40 % ....
I scanned my car and a few other gas trucks and they idle around 11-14% Engine load.
The engine does not sound labored.
I even removed the serp. belt to eliminate P/S pump, alternator, fan, and no difference.
Just the slightest touch to the pedal, ENGINE LOAD spikes to 100%

If i can find out how the ECM is calculating the engine load, perhaps it will lead me in the right direction... ?
How doesn't the ECM see this load as a problem and trigger the DTC lamp?
-Alex
 

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Some additional information.
I did some more scanning with a MAC scanner this afternoon.
With the truck on, warm, at idle (680 RPM), in park, "ENGINE LOAD" reads 29 % (Doesn't this seem excessively high?)
Then,
With foot on the brake, still at idle, shift transmission into drive, "ENGINE LOAD" increases to 38-40 % ....
I scanned my car and a few other gas trucks and they idle around 11-14% Engine load.
The engine does not sound labored.
I even removed the serp. belt to eliminate P/S pump, alternator, fan, and no difference.
Just the slightest touch to the pedal, ENGINE LOAD spikes to 100%

If i can find out how the ECM is calculating the engine load, perhaps it will lead me in the right direction... ?
How doesn't the ECM see this load as a problem and trigger the DTC lamp?
-Alex
A diesel is different from a gasoline engine. Gasoline burning engines utilize a spark to combust the gas.
Whereas the diesel engine uses engine compression to ignite and burn the fuel thus more load.
 

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Discussion Starter #16
OkDually,
Are you suggesting that 40% engine load is an acceptable engine load with said parameters?

I understand, in-depth, the stoichiometric and mechanical differences between gasoline and diesel fuel burning engines.....

What i am suggesting is that the engine is NOT seeing any more LOAD then a good / normal running engine at idle, but the AVAILABLE power has been majorly decreased.
I am seeking why....
My logic:
%LOAD=CURRENT POWER BEING CONSUMED / AVAILABLE POWER

-Alex
 

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OkDually,
Are you suggesting that 40% engine load is an acceptable engine load with said parameters?

I understand, in-depth, the stoichiometric and mechanical differences between gasoline and diesel fuel burning engines.....

What i am suggesting is that the engine is NOT seeing any more LOAD then a good / normal running engine at idle, but the AVAILABLE power has been majorly decreased.
I am seeking why....
My logic:
%LOAD=CURRENT POWER BEING CONSUMED / AVAILABLE POWER

-Alex
For your comparisons, you will have to wait till member rickykjr gets his scanner log info and posts it or any other member chimes in.
 

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Okay I just went out and plugged my launch in. I am seeing basically the same thing on the requested torque on the transmission page. When I put the truck in gear it jumps up to .74 then back to zero. I drove it and it never moves from zero. The driver requested torque which I also chose to view does go up the more I mash on the accelerator. Let me know if I can check anything else for you to try to get to the bottom of your problem.
 

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Just the slightest touch to the pedal, ENGINE LOAD spikes to 100%
So your fly-by-wire is reporting "pedal to the metal" even though you isn't! :)
You have replaced everything but the TPS. Have you checked it (or the wiring) for any kind (or quality) of signal?
 

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Discussion Starter #20
Thanks a ton for checking that for me Ricky,
Not exactly what i wanted to hear though.... I really thought your truck was going to read something other than zero.
I will take a video of the graph this weekend and post that to try and spark some ideas.

Saltfever - The pedal is responding correctly. I report a clean pedal sweep, 0-100%. I have full control over the sweep.
Its the Engine load that is very sensitive.
But to eliminate the pedal as a problem, I am on the search for a donor / one to try out.

Here in southern Ontario, LBZ trucks are very rare to find compared to all other Dmax's.
Everyone has a clapped out LB7 though.....

Tonight i am going to try the following test and see how it effects the engine load:
Start the truck, unplug the transmission plug at the trans, then read engine load.

-Alex
 
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