LBZ: "New" Truck - Multiple Possible Issues

[nubuilder]

Hi,

I literally just bought this truck and drove it all the way home 950 miles. Truck has a U0101 code for TCM communication failure. It drove fine and shifted fine, tow/haul mode works fine, but the manual tap shift wasn't working.

I did some data logging on it quick Saturday just for the heck of it (mostly to check injectors, which look great) and I've found some very strange stuff. (Forgive me if I logged the wrong/incorrect PIDs.)

- Engine RPM stays at 1024
- Fuel Rail Pressure stays at 22 (not sure if this is normal)
- Boost stays at 15psi
- Throttle Position/Relative Throttle Position stay at 100%
- Accelerator Pedal Position - Sensor Voltage stays at 0.00v

In the attached log, I start out from a stop, come to two/three stop signs very close together, accelerate to 45, stop light, ease my way onto an on-ramp, then punch it to 70/75, maintain 70 for a bit, then the rest really isn't worth looking at. I apologize for the poor log file, having things so drawn out and taking time.

The truck obviously moves and runs, but I don't think it does so properly.

I have had the truck act up 3 times (in the past 2 days of having it) when starting. I'll hit the key, it'll start, then die out. The first two times, I had to feather the throttle to keep it running for a second or two, then it was fine and idled. The third time (and this was today), I tried starting it without using the pedal and on the third attempt it idled.

Initially I thought I had an issue with the TCM (and still could be), but now I'm wondering if there's a bigger issue somewhere.

The previous owner said the check engine light came on after washing the engine bay.

Any thoughts or ideas? Any help would be much appreciated!

Thanks,
Matt

PS - if I put this in the wrong section, please feel free to move it

 

[Burn Down]

First off, welcome.

Before we get in to your logging, lets here all the specs on the truck, it can help us help you diagnose it better.

I would also start checking all the connections for the trans. make sure the connector is dry going into the trans. (round one on the right rear)

 

[nubuilder]

Thank you Burn Down. Not exactly the most fun way to join a forum (like doing a mod or something), but it is what it is.

2006
LBZ
Allison
260k

What else would you like to know? (just didn't want to bore you with too many useless details)

I did unplug the TCM twice when I initially test drove it to no avail.
I'll have to check the connection tomorrow as it's raining here today.
Does the Allison use similar connections as the 4L60/4L80? (2 on the PRNDL, 1 round for controlling the trans)

 

[Burn Down]

Yes similar.

Just curious what mods it had done, they can drastically affect how the truck operates.

 

[nubuilder]

To my knowledge, the truck has no mods at all. Exhaust is stock. It was a one-company owned truck it's entire life.

The only "mod" it has is airbags in the rear and 265 tires.

 

[zakkb787]

What gets me is that you say the previous owner washed the engine bay and the issue started. Here’s multiple parts inside the engine bay that you shouldn’t really wash. In fact, the FICM says do not pressure wash right on it. Sounds to me like he may have sprayed something and it’s shorted somewhere.

 

[nubuilder]

That's what I'm afraid of, but I don't know where the water could have gotten....and there's slim hopes of clearing this issue up by unplugging everything, cleaning connectors, drying them, and putting them back, but this may be where I have to start.

I don't understand how the truck drives fine, but there's loss of TCM communication along with the log showing my throttle at 100%.


Forgive me if I'm incorrect, but does the LBZ have the FICM? I thought that was a LB7 thing.

 

[zakkb787]

Honestly to me (amatuer thought) but sounds like an ecm issue.

 

[DAVe3283]

I pressure wash the FICM (and everything else) without issue. The key is avoid spraying the connectors themselves. That is what gets water in and causes problems.

Get a couple cans of electrical contact cleaner. Take apart every connector in the engine bay, and spray them out thoroughly. The goal is to remove any residue that might have been causing a short or poor connection. Let them dry completely. You can use clean dry air (not regular compressed air which has oil) or a can of wire dryer or just let them air out.

See if that helps things out. I like to put a small amount of dielectric grease in the connectors when I put them back together to keep them dry in the future. But don't use much! There isn't much air inside a closed connector, and if you put too much grease, it will actually prevent the connector from working.

 

[nubuilder]

Alright. When I get a chance (probably this weekend), I'll start unplugging stuff (1-by-1), use contact cleaner, unplug/plug a few times, and a bit of dielectric grease (for peace of mind).

Would it be a safe move to disconnect the batteries while doing this? Or will leaving them connected not hurt anything?

 

[2004LB7]

Best to disconnect the batteries before starting

Also, yes the LBZ does not have a FCIM but there are still things to stay away from when cleaning the engine especially when it is a higher milage vehicle where some of the insulation and seals may be dryed out and cracked

 

[gmduramax]

The no start or hard start sounds like you’re losing prime. Try pumping the primer before you start it see if that helps

 

[nubuilder]

Best to disconnect the batteries before starting

Also, yes the LBZ does not have a FCIM but there are still things to stay away from when cleaning the engine especially when it is a higher milage vehicle where some of the insulation and seals may be dryed out and cracked

Will do then.

This is why I never wash my engine bay....

The no start or hard start sounds like you’re losing prime. Try pumping the primer before you start it see if that helps

This has only happened 3 times that I've tried starting the truck. Each time was random. It has not yet happened again. I think I'm going to order a fuel filter head rebuild anyways. That along with the Nictane adapter that I already have.

 

[zakkb787]

The rebuilds are hit and miss. Some have luck with them others leak worse than before. You can get a new filter head for between 100-200 I believe.

 

[Dozerboy]

Ya I rebuild my filter head twice with a quality kit and still couldn’t get tit to stop leaking.

My engine on my 06 is clean enough you can eat off it and I’ve never had a issue. I’m not even very careful on what or how I wash it.


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[nubuilder]

Small update....

After some more searching, I found someone describing my exact transmission issue/symptoms.
https://www.dieselplace.com/forum/6...01-no-manual-shift.html#/topics/625001?page=1
(Sorry for cross-forum linking, but this has what I'm experiencing in post 3. I just dont have any limp mode.)

Indeed my IGN 0 fuse was blown. I replaced it, cleared my code, started the truck and the SES light stayed off. I shut it off, started it again, and the light was back....fuse was blown.

I replaced it again, but this time watched the fuse as I started the truck. It did not blow until I moved the shifter, then it immediately blew.

Any thoughts or ideas on this one?


Moderators, please move this thread as you see fit. I guess we'll start with this issue and go from there. Who knows, maybe this has something to do with my odd log file, maybe not.

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[nubuilder]

I'd also like to note that the dash says "service brake system" upon turning the key on. No lights on for it though or codes.

Just found another post stating to check for worn wiring by the power steering pump. Will try to investigate more.

And another one to tear the steering column apart and check for broken wires for the tap shifter. Apparently this is a common occurrence.

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