How not to install a Duramax in a M998

loosegravel · Apr 19, 2021

Mogman said:
Man this thing is tossing allot of codes, this is going to take a while to sort out.

I forgot to mention, Brendan in Branson Missouri has the LT1swap.com website. He has also posted some material on the duramax. It looks like he's installed one into a 1967 C10. Pretty cool stuff.

Mogman · Apr 21, 2021

I worked through the codes and now the MIL light is OFF!! YAY!!

Mogman · Apr 25, 2021

Thanks to rjf189 I got the hardware for the turbo cover and got it installed today, fits a snug as a bug in a rug!

Mogman · May 1, 2021

Well things are getting closer, finished re-lamping and replacing the harness on the hood, I used plain ol GE long life truck halogen headlights and led turn signals since they seem to be just as happy on 12V as 24V and one of the original lights was toast, I did not replace the side markers as unlike the rear side markers the sockets were in good shape and I have a NOS hood that will find its way on this truck before I paint it, the wife was out at the tractor shed yesterday and spotted some 2" square tubing I can use to raise the hood, will be temporary as the front end of this one will get the same custom bumper, brush guard and hydraulic winch as did #1.

Just a few clamps to go on the engine compartment, seller shipped me the wrong T bolts clamps I need to finish.

I am still actually chasing codes, the old Autel reader I was using was not giving me all the codes that were being generated so I started using the EFILive code reader, it looks like I may have a bad TCM, waiting for one to arrive.....

EDIT, I did have a bad ECM, one of the inputs got shorted out, I have also been chasing bad wire connections at the harness plugs, seems when the truck rolled several times and the ECM/TCM came out of their mounts and the motor was on walkabout it pulled all the wires at the plugs, I should have sourced another harness, but that could be a complete crap shoot also, but all seems to have settled out in that department.

m1010plowboy · May 1, 2021

I can't wait to hear it. We'll need a comparison audio when you get a chance. Very cool.......

Mogman · May 1, 2021

Because of the variable geometry turbo, with the stock tune and no muffler the LMM sounds much more like a Bell UH-1 mixed with deuce and a half as the variable geometry pinches off the exhaust to produce more velocity over the exhaust wheel.
I tuned that out and have the turbo held at 10% closed up to 1000RPM so it sounds much more "throaty" but as soon as it reaches about 1200 it tries to boost as much as it can again, I will no doubt be spending some time tuning it with a trade off between performance and sound, it took changing over 200 entries in 10 different tables to get where I am now, sounds like a BBC with a turbo after tuning.

Mogman · May 2, 2021

It is starting to look like a Humvee!! everything fits under the hood!!!, going to bleed the brakes this evening and then install the wheels.
The govt. had drained all the fluids, I should have realized that when I saw the empty master cylinder, I had actually ran it up through the gears a couple times on he lift before checking the diffs and gear boxes but I doubt it was enough to do any damage, I have a set of 12K gear hubs and half shafts to install so the only real risk was to the rear diff.

Mogman · May 3, 2021

OK well it got to go out in the sunshine today!! It is running in "limp mode" so I was only able to get up to 30MPH in the driveway before running into the gate, don't want to take it out on the road just yet, the road in front of the ranch is a 4 lane state Hwy so I do not have the privilege of running around the "neighborhood".
This M998 is 3.5" higher than the helmet top, with a 2" body lift I am not sure if the extra weight of #1 fully accounts for the difference, makes a big difference to my short fat a$$.
This is the profile I do not really care for with a lifted body, but I have 5 brand new Baja tires on 24 bolt rims with Trailworthy bead locks to go on here so I guess I just have to get used to it, and then it may change once I get the S-788 shelter and get it fully loaded for camping.

All the damp spots on the side is sweat, it is 92 today and we had rain for three days prior so the humidity is 100%.
My new high back seat kit from Seco is at the Depot in Corpus and I may get in there on Thursday to pick it up.
SO, it ran right up to about 178deg and stayed there, the oil pressure is a little low at idle and heated up but the factory gauges cheat so much I am not sure that is actually a problem, runs right up to 60+PSI @ 1500 RPM, brought it back in the shop and do not see any runs, drips or errors!
It actually shifts better than my 08 LMM 1 ton
Now I am just waiting for a TCM (transmission control module) to get here from Canada to see if that is what is giving me the codes.

EDIT, the brand new oil pressure sending unit was bad, see actually runs over 100PSI just off of idle cold and 65PSI at 1850 RPM hot.

Action · May 3, 2021

Mogman said:
OK well it got to go out in the sunshine today!! It is running in "limp mode" so I was only able to get up to 30MPH in the driveway before running into the gate, don't want to take it out on the road just yet, the road in front of the ranch is a 4 lane state Hwy so I do not have the privilege of running around the "neighborhood".
This M998 is 3.5" higher than the helmet top, with a 2" body lift I am not sure if the extra weight of #1 fully accounts for the difference, makes a big difference to my short fat a$$.
This is the profile I do not really care for with a lifted body, but I have 5 brand new Baja tires on 24 bolt rims with Trailworthy bead locks to go on here so I guess I just have to get used to it, and then it may change once I get the S-788 shelter and get it fully loaded for camping.
View attachment 833450
All the damp spots on the side is sweat, it is 92 today and we had rain for three days prior so the humidity is 100%.
My new high back seat kit from Seco is at the Depot in Corpus and I may get in there on Thursday to pick it up.
SO, it ran right up to about 178deg and stayed there, the oil pressure is a little low at idle and heated up but the factory gauges cheat so much I am not sure that is actually a problem, runs right up to 60+PSI @ 1500 RPM, brought it back in the shop and do not see any runs, drips or errors!
It actually shifts better than my 08 LMM 1 ton
Now I am just waiting for a TCM (transmission control module) to get here from Canada to see if that is what is giving me the codes.
View attachment 833452
View attachment 833453

It shifts better than your 08 LMM 1 ton? Isn’t the transmission stuck in limp mode? It isnt shifting.

Mogman · May 3, 2021

Action said:
It shifts better than your 08 LMM 1 ton? Isn’t the transmission stuck in limp mode? It isnt shifting.

No, it is shifting, at least up to 3rd or maybe 4th, I have only been up and down the driveway (about an 1/8th of a mile) the power is way down on the engine and it is limited to 2000RPM or so, I think the engine is in limp mode

Russ Knight · May 3, 2021

Engine doesn't use DEF does it?

Mogman · May 3, 2021

Russ Knight said:
Engine doesn't use DEF does it?

No DEF, lots of deletes. It's just going to take a little time to sort out.
The DEF actually did not start until the next series Duramax, IIRC the LMM dumped raw fuel into #8 cylinder to burn out the particulate filter, tended to wash out that cylinder again IIRC

Mogman · May 5, 2021

Took it out for a quick loop on the highway today about 4 mi, even though I have transmission and engine codes (bad TCM is showing a false high trans. temp. and a bad Fuel pressure regulator, waiting for parts)
It ran up pretty dang nice to 50MPH@ 1500RPM (indicated have only done a cursory tach alignment but it's close) even while "limping" along. Hopefully the new TCM will fix the other strange codes ("U0073 communications bus off" for one) One thing I read was that a high transmission temp will not allow the TC to lock up (this actually makes NO sense because the TC makes much more heat when unlocked)
Mechanically everything is doing great, no unusual sounds or vibrations, all the gauges were working great and all the indicators were "in the black" for sure, water temp sat like a rock at 180 deg. trans temp was never over 150 deg. EGTs less than 600 deg. Oil pressure is lower than I would like to see at idle and fully warmed up but again the factory gauges are so skewed that 20 PSI at idle warm may not be abnormal, jumps right up to 80 on the road...
The motor sounds great, because of the low power I was having to back off the throttle a little bit to get it to shift but when it shifted is was very smooth.
It sounds like a UH-1 winding up before the blades start to be heard, I have tuned that out at idle but as soon as you hit the pedal those exhaust vanes in the turbo slam shut and the turbo spools up very quickly.

EDIT,,, DANG IT! it's pretty cool tooling along with no doors and no top, but this one is destined to have a shelter on it! guess I should start looking for another one!!
EDIT, tried the shelter, did not like it, I am installing a low profile helmet top and A/C winter 23/24

TOBASH · May 5, 2021

Mogman said:
Took it out for a quick loop on the highway today about 4 mi, even though I have transmission and engine codes (bad TCM is showing a false high trans. temp. and a bad Fuel pressure regulator, waiting for parts)
It ran up pretty dang nice to 50MPH@ 1500RPM (indicated have only done a cursory tach alignment but it's close) even while "limping" along. Hopefully the new TCM will fix the other strange codes ("U0073 communications bus off" for one) One thing I read was that a high transmission temp will not allow the TC to lock up (this actually makes NO sense because the TC makes much more heat when unlocked)
Mechanically everything is doing great, no unusual sounds or vibrations, all the gauges were working great and all the indicators were "in the black" for sure, water temp sat like a rock at 180 deg. trans temp was never over 150 deg. EGTs less than 600 deg. Oil pressure is lower than I would like to see at idle and fully warmed up but again the factory gauges are so skewed that 20 PSI at idle warm may not be abnormal, jumps right up to 80 on the road...
The motor sounds great, because of the low power I was having to back off the throttle a little bit to get it to shift but when it shifted is was very smooth.
It sounds like a UH-1 winding up before the blades start to be heard, I have tuned that out at idle but as soon as you hit the pedal those exhaust vanes in the turbo slam shut and the turbo spools up very quickly.

EDIT,,, DANG IT! it's pretty cool tooling along with no doors and no top, but this one is destined to have a shelter on it! guess I should start looking for another one!!

At the end of your build, it would be nice if you would comment on how much money was invested.

Mogman · May 5, 2021

TOBASH said:
At the end of your build, it would be nice if you would comment on how much money was invested.

My BIGGEST fear in life is when I die my wife will sell my stuff for what I TOLD her I paid for it!!

I would guess I have about 17-19K in it so far, the donor vehicles cost 8K total and I would think 9-11K in "parts" including the upgrade seats, NOS hood and supplemental armor doors not yet installed.
I figure the shelter system complete and axle upgrades will be another 10-15K, This would include many Items I already have, shelter, mounts, generator, axle upgrades and some I do not like the 2 door custom hard top

Mogman · May 7, 2021

Got my upgrade driver seat installed today!

Mogman · May 10, 2021

I am still waiting for the TCM to arrive but I did get some good news from Blackstone Labs on the oil sample I sent them, the oil was very black certainly was not a fresh change when the dirty side turned up, I felt bad about even starting it with the original oil but wanted to get a baseline analyses, I did however change the oil filter I just did not replenish any oil so as to not skew the results..

"Nothing in this salvage engine's first sample suggests any serious trouble within. Wear metals are
comparable to the universal averages, both in number and in their balance, which suggests that parts are
getting along like they're supposed to be. Maybe if this were a pretty short run, iron could be a bit high, but
even that could be due to factors like hard use in its previous life. If the engine runs well, we'd just suggest
checking back on a known interval to see how trends build. The universal averages for the 6.6L Duramax
are based on about 7,000 miles."

It also had a chart with the breakdown of the sample.

loosegravel · May 10, 2021

Mogman said:
I am still waiting for the TCM to arrive but I did get some good news from Blackstone Labs on the oil sample I sent them, the oil was very black certainly was not a fresh change when the dirty side turned up, I felt bad about even starting it with the original oil but wanted to get a baseline analyses, I did however change the oil filter I just did not replenish any oil so as to not skew the results..

"Nothing in this salvage engine's first sample suggests any serious trouble within. Wear metals are
comparable to the universal averages, both in number and in their balance, which suggests that parts are
getting along like they're supposed to be. Maybe if this were a pretty short run, iron could be a bit high, but
even that could be due to factors like hard use in its previous life. If the engine runs well, we'd just suggest
checking back on a known interval to see how trends build. The universal averages for the 6.6L Duramax
are based on about 7,000 miles."

It also had a chart with the breakdown of the sample.

I work for the local transit company in Seattle. We do oil samples on the Cummins engines, Allison EV drives and BAE Alternating Current Traction Motors every 12,000 miles. I used to think that it was a waste of taxpayers money. And it is...if nobody is reviewing the results and deciphering what they're reading. Thankfully we have some people who review the results and give us a heads-up when something is out of whack with one of the buses. Glad to hear that you have a good engine. It can be a crap-shoot when buying something used.
It's funny, I just borrowed a friends Chevy one ton truck with a Duramax engine tonight. It means a lot to me that he would even let me borrow it! I'm heading down to the auction yard early in the morning to pick up a tandem 10kw gen set on a trailer. My little 1/2 ton with a 5.3l and 4L60 would scream at me for trying to pull that home. These engines are so nice!

Mogman · May 17, 2021

well after several weeks chasing codes and low power it was discovered I had a bad Engine Control Module, pulled the one out of my 1 ton, dropped the tune I had built for the HMMWV into it and she damn near got away from me in the driveway!
HOORAY she is "on the road" I took it for a 45 mile jog to Beeville and got the state inspection out of the way so I can go tomorrow and get plates for it.

She runs EFFORTLESSLY at 75-80 MPH, with the 2.56 gears she is turning 1800 RPM @ 70MPH (I had the chance to look at the live data and I had calibrated the tach spot on!)
Ambient = 85, wind S @ 14MPH
The water temp modulated between 186-192 deg indicating the thermal fan clutch was doing its job
The trans temp modulated between 170-175 deg
The EGTs were 800 with tail wind, 900 with head wind
With a little more pedal she "barks" the first three gear shifts
I am ECSTATIC!!!!!

Russ Knight · May 17, 2021

Awesome! Congrats on an outstanding build!

How not to install a Duramax in a M998

Just a retired mechanic who's having fun!

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