Out with the Diesel LB7 in with the 6.0/ 4L80E

[ls1mike]

Well we put a lot of work in the boys diesel, more than I care to talk about. It developed a weird surge cold that would get better when warm. Then over 2100 rpm it would cut power than come back on. Like over boost cutout. Scanner showed nothing. Starts and idles perfect. Good compression. 4, yes 4 diesel shops no answer. Last one said don't put more money into it. We think, not sure it might be the reluctor ring for the crank sensor or a timing issue. At any rate we parked it until we can pull the cab and pull the front of the engine apart.
The boy has a bunch of money saved and picked up a 2004 3/4 ton GMC 6.0 4L80E (best truck made IMO) 110000 original miles. 1 owner all receipts, new tires, super clean. 9,000.
Everything works. Drove it home 4 hours. Truck is perfect.

The poor LB7. We will get to it this fall. We put a lot of love in it. Not ready to cut our loses

 

[redhat]

Wow, super nice truck. Congrats.

 

[clinebarger]

That's why automotive Oscilloscopes exist, How can one diagnose vehicles professionally without one?

 

[Timmastertech]

That's why automotive Oscilloscopes exist, How can one diagnose vehicles professionally without one?

By using the parts howitzer of course. A frequency math channel laid over the crank sensor pattern would prove beyond a shadow of a doubt whether the reluctor was moving easy peasy without ripping the timing cover off. I just watched a daves auto center video about a nissan not firing on one side of the engine and they sold the guy a teardown to inspect the timing components because one side has no compression. Give me a half hour and I will tell you where the problem lies without taking a timing or valve cover off. If I pull a cover its because I already know what I am going to find. Heck, A month ago I taught a 2 day hands on lab scope class in salt lake that we advertised the hell out of in the area, even went as far as having some of our friends in the area deliver flyers to shops. Had they sent someone to that class they would have made their money back on that truck.

 

[ls1mike]

That's why automotive Oscilloscopes exist, How can one diagnose vehicles professionally without one?

I can tell you that was done too. The list of things is pretty long. These were reputable shops who do LOTS of work to include Semis.
Last place the guy has been doing it 30 years. He had it three weeks. Was driving it to and from work. Said he has never seen anything like it. Part of the problem is it is intermittent as well. Some days won't do it all. I thought we had found the problem in the harness. Someone had been in there messing with the wiring to the fuel rail pressure sensor. Looked like they had added a ground. Was really hard to tell what they had going on. Was not the issue. Every cylinder has compression above 400PSI. New S&S sac injectors. We did replace the TCM which cured the hard starting issue, loss of communication with it and the only code it had. Also replaced the ECM as the stock one did have a tune and wanted to verify that wasn't the issue (it was cheapest route as we don't have the tuner that was used). We were unaware it had a tune, but the last two places that looked at it asked as they were sure it did. I have not driven enough LB7s to know the difference. However, you can certainly tell the original ECM had a tune. It has a lift pump and sump. Not one code, not one pressure out of spec. No over boost condition. When it does what it supposed to do it runs awesome.

 

[clinebarger]

I can tell you that was done too.

How are they not SURE the timing is off?

 

[ls1mike]

How are they not SURE the timing is off?

I probably should have said, not that timing is off but one of the gears has an issue. I didn't want to pay for someone to go in there and find out that was not problem.

 

[JavierH19]

Man that truck is nice.

 

[cptbarkey]

Nice forever truck there with the 6.0, looks very well kept.

 

[Hohn]

Well we put a lot of work in the boys diesel, more than I care to talk about. It developed a weird surge cold that would get better when warm. Then over 2100 rpm it would cut power than come back on. Like over boost cutout. Scanner showed nothing. Starts and idles perfect. Good compression. 4, yes 4 diesel shops no answer. Last one said don't put more money into it. We think, not sure it might be the reluctor ring for the crank sensor or a timing issue. At any rate we parked it until we can pull the cab and pull the front of the engine apart.
The boy has a bunch of money saved and picked up a 2004 3/4 ton GMC 6.0 4L80E (best truck made IMO) 110000 original miles. 1 owner all receipts, new tires, super clean. 9,000.
Everything works. Drove it home 4 hours. Truck is perfect.
View attachment 288730
View attachment 288731
View attachment 288732
The poor LB7. We will get to it this fall. We put a lot of love in it. Not ready to cut our loses
View attachment 288733

never sell that.

 

[supton]

Nice find!

 

[fantastic]

Nice truck and a good value at $9,000. Can't beat the one owner with receipts.

 

[CarlB]

The GMT800 with the LQ4/LQ9 is definitely amazingly reliable and well suited to high duty cycles. Maintenance and repairs are easy and not too expensive.

Mine has about 133k miles, so should be long lived.

 

[panthermike]

Sorry to hear your woes with the LB7, really like those motors. But that 6.0 he picked up is mint! Always a good sign when the P.O. springs for Michelin tires. Really like the stance more than the LB7 as well. Plus of course; much easier to work on/maintain. Best of luck with the new one and crossing fingers that the Diesel issue can be resolved.

 

[ls1mike]

Figured out the Duramax. Bad valve body. Fixed. Runs perfect. Well part of the valve body anyway. Put known good used one in. Strangest problem I've ever dealt with. I think his lift helped to cause it. Problem started around that time.

I had a day changed the fluid, filters and it almost went away. You could now tell it was a shifting issue. It wasn't a constant surge or bucking. Just some random gear hunting now. Very random. like only above 2500 RPM in a shift. Drove it around 2 hours. The kid and I actually did a really nice job putting it all back together. No leaks. All new fuel lines. QUIET and SMOOTH. I still don't want one.

Local place had a warrantied used valve body. Old valve body had some stuck items. Replaced it. BOOM!! 30 over S&S sac injectors, lift pump, sump, Gale Banks waste gate, new Y Bridge all new charge piping, different compressor wheel. It runs awesome!! We are still going to sell it. (Maybe) We are out of the Diesel business; well, I am out of the diesel business. Just glad to be out of it.

 

[panthermike]

Figured out the Duramax. Bad valve body. Fixed. Runs perfect. Well part of the valve body anyway. Put known good used one in. Strangest problem I've ever dealt with. I think his lift helped to cause it. Problem started around that time.

I had a day changed the fluid, filters and it almost went away. You could now tell it was a shifting issue. It wasn't a constant surge or bucking. Just some random gear hunting now. Very random. like only above 2500 RPM in a shift. Drove it around 2 hours. The kid and I actually did a really nice job putting it all back together. No leaks. All new fuel lines. QUIET and SMOOTH. I still don't want one.

Local place had a warrantied used valve body. Old valve body had some stuck items. Replaced it. BOOM!! 30 over S&S sac injectors, lift pump, sump, Gale Banks waste gate, new Y Bridge all new charge pipping, different compressor wheel. It runs awesome!! We are still going to sell it. (Maybe) We are out of the Diesel business; well, I am out of the diesel business. Just glad to be out of it.

Good for you guys, has to feel good! I don't blame you on selling it, especially with that beauty that he picked up.

 

[ls1mike]

Good for you guys, has to feel good! I don't blame you on selling it, especially with that beauty that he picked up.

Dude you have no idea. No scanner picked it and it surged/bucked so bad no one thought it was transmission related.

 

[supton]

Pretty wild--but goes to show, the ankle bone is connected to the leg bone, and the leg bone is connected to the knee bone, and... a vehicle is a collection of systems, and while there isn't a nasty feedback loop here, it still did a good job of having you look in the wrong place.

 

[clinebarger]

Figured out the Duramax. Bad valve body. Fixed. Runs perfect. Well part of the valve body anyway. Put known good used one in. Strangest problem I've ever dealt with. I think his lift helped to cause it. Problem started around that time.

I had a day changed the fluid, filters and it almost went away. You could now tell it was a shifting issue. It wasn't a constant surge or bucking. Just some random gear hunting now. Very random. like only above 2500 RPM in a shift. Drove it around 2 hours. The kid and I actually did a really nice job putting it all back together. No leaks. All new fuel lines. QUIET and SMOOTH. I still don't want one.

Local place had a warrantied used valve body. Old valve body had some stuck items. Replaced it. BOOM!! 30 over S&S sac injectors, lift pump, sump, Gale Banks waste gate, new Y Bridge all new charge pipping, different compressor wheel. It runs awesome!! We are still going to sell it. (Maybe) We are out of the Diesel business; well, I am out of the diesel business. Just glad to be out of it.

Glad it got fixed, Had my doubts with the Timing Gear/Reluctor prognosis without proving it out. The later 6 speeds got a lot of updates & is a all around better unit. Not that I've seen a lot of 5 speed valve body issues.

The Duramax isn't the easiest/cheapest engine to work on & the Allison 1000 can turn expensive...... So I understand your position.

 

[ls1mike]

Glad it got fixed, Had my doubts with the Timing Gear/Reluctor prognosis without proving it out. The later 6 speeds got a lot of updates & is a all around better unit. Not that I've seen a lot of 5 speed valve body issues.

The Duramax isn't the easiest/cheapest engine to work on & the Allison 1000 can turn expensive...... So I understand your position.

Nope it isn't and man it gets pricey...fast, but it is the boy's if he wants to keep it that is fine. Now he has two GMT800s. What I can say is all the other stuff that was done, well the injectors and CP3 needed to be done. The other stuff are things he wanted to do. I would not be afraid to work on another one at this point as I learned WAY more about how that thing works then I ever wanted or needed to and what to look for when working on one.