So looking into an LS swap, but not the usual 4.8/5.3/6.0, but an 8.1 liter. I can get the complete motor, ECM, and harness for $500. I can get the Allison for an additional $250. Only problem with the tranny is the t-case, it's shot. Doing some research, only t-case available is one off an Allison. I want to run the 4L80, cheaper and easier to find. I think the swap itself should be fairly simple, since the 8.1 uses the same mounts as a regular big block, so wouldn't even have to change my mounts. But I'm sorta confused bout the truck wiring. I was told that the gauges work off the motor, and not always go thru the ECM. This would be going in a 99 Tahoe, so has to be a legal swap, for inspections and when they plug in the ALDL for codes and what not. I know DirtyLarry did this swap, gives the part numbers for everything, but since his is an older truck, not sure bout said gauges. Also, who has the best price and reputable service to do the ECM and harness? Since the wiring for the tranny's are different, either need to get a new one, $600 I think, or modify the stock. I'm sure I can rewire, but if not who is good place to do it? Also looked for this style swap on the net, but not finding much.
CK5
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LS swap, ECM and wiring ??
- Thread starter b454rat
- Start date
I know some vans got 8.1 and 4l80 in them .
and better check obd2 plug in test rules. last I knew the computer scanned the ecm for vin data and propor codes / settings / and if stuff was deleted . but I have been out of the game a bit . but my 1 friend said its starting to get tricky pluging in some rides with tuned out settings .
and better check obd2 plug in test rules. last I knew the computer scanned the ecm for vin data and propor codes / settings / and if stuff was deleted . but I have been out of the game a bit . but my 1 friend said its starting to get tricky pluging in some rides with tuned out settings .
I know that's the case with newer stuff, say after 2000. My brother in law has an 04 GT that doesn't have stock ECM and now can't get it inspected. But since mine being a 99, and will still have the "factory" ECM, shouldn't be an issue. But, I don't know, why Im here. I've yet to see an 8.1 liter in a yard, this one being the only one.
I saw that post before, but didn't know it's some 12 pages long!!!! I'll have to read in the morning......I just hope I can get the engine.....hate being broke....
First of all $500 is a steal. That engine is worth $2000. Same with the trans at $250. Its worth over $1500. Buy it to flip it even if you don't put it into your truck...
To answer some of your questions:
1. It is possible to put an NP241 behind the Allison. I have a ZF-650 in my Tahoe behind my Duramax. It runs the same 29 spline output as the Allison does and I have an NP241 in mine. The input gear for an NP261XHD or NP263XHD found behind a Duramax is nearly identical to the input gear on an NP241. The only modification you will need to do is either to machine down the bearing shoulder on the input shaft so the input gear sits about 3/16" deeper than it did before or you need to space the input bearing forwards by the same amount bit to allow the gear to sit deeper (I used the NP261 input bearing IIRC). I opted to space my input bearing and I haven't had any problems at all with it. I just made a spacer out of 3/16" plate steel. The NP241 is plenty strong enough to handle the 8.1L. This would save you a pile of re-wiring and you'd wind up with a far inferior transmission with a 4L85E anyways.
2. The 8.1L PCM transmits the oil pressure and water temperature via digital serial communications stock but still sends analog ground pulse signals for the speedometer and tachometer. Your 99 cluster uses the identical types of signals for both the speedo and tach so you can just hook them right up. When you have your PCM flashed you'll need to get it set to a 8 cylinder tach signal (stock is a 4 cylinder) and you'll need to adjust the speedometer output to read accurately with your gearing and tire sizes.
3. You'll need to install the sending units for the 5.7L for both the oil pressure and coolant temperature onto the 8.1L. IIRC there are ports for the oil pressure sender above the filter housing which have NPT plugs in them and there is a spare port for the coolant temperature sending unit in one of the heads. The volt meter is handled by the gauge cluster internally. You'll retain the stock sending unit for the fuel level gauge. Your gear position indicator will require you to tap into the park / neutral safety switch on the transmission to light the little LEDs up on your shift column. The newer truck uses the same wiring for that function so it'll be more or less just a matter of splicing the two harnesses together.
3. The 8.1L will communicate through the diagnostics port just as the stock 5.7L does right now. It should be possible to utilize all the emissions systems by installing a fuel tank pressure sensor into your stock sending unit and hooking the EVAP line up to your stock canister. You'll need to make sure you install cats and all 4 O2 sensors as well. I don't think the PCM cares if the fuel tank level sending unit is reading or not, you'll just need to have those DTCs disabled when you have the PCM flashed.
4. Your best bet for wiring is @Team208Motorsports. Josh is the man for that kind of stuff. He can hook you up with a killer tune done right for your swap too. He may be able to disable the emissions tests to cause them to show good regardless of if they've been completed by the PCM or not to pass your emissions testing.
Just left yard, and motor is still there. Gonna try to put a deposit on it, soon as I can get some money. I'd like to run the Allison, but finding a t-case that's not my first born is gonna be tough. But least I know I can run the 80E. Also found a local place that can reflash or program whatever it's called so I can install it in the 'hoe and have it pass inspection....
last I knew evap test for gas tank venting runs at 1/4 tank to 3/4 tank level of gas . if under 1/2 or over 3/4 it should not run the test . so this might toss a wrench in your #3 info russ.
When I talked to the guy bout the computer, he can get rid of down stream O2s, and any unnecessary BS, is the evap something that can be deleted too? I have a couple places that I can go to for an inspection, they will pass it as long as everything works; lights, good tires, etc, the obvious stuff. They do worse than what Im going and pass vehicles everyday.
Russell, do you have a pic or something of what you did? I just woke up and had couple sips of coffee, trying to understand how you did it. How much and where can I get the input? I would much rather go with the Allison than the 4L80, I could do whatever to the motor and the tranny should hold up. Plus I could use it behind the Cummins if I wanted. I can get the Allison for what I can get an 80E for.
Russell, do you have a pic or something of what you did? I just woke up and had couple sips of coffee, trying to understand how you did it. How much and where can I get the input? I would much rather go with the Allison than the 4L80, I could do whatever to the motor and the tranny should hold up. Plus I could use it behind the Cummins if I wanted. I can get the Allison for what I can get an 80E for.
Entirely possible. I'm not well versed in the emissions test requirements.
Yep, EVAP can just be disabled. I am not entirely sure if you can cheat the tests to look like they've passed or not for emissions testing purposes. It's entirely possible. If your emissions testing inspection place doesn't care, then you'll be good to go with just deleting it and mechanically hooking the evap line up.
All I did to put the NP261 input into my transfer case was to hammer the input bearing out of the case enough to slip a 3/16" plate under the snap ring that the bearing seats on then re-install the seal housing over top of it. That allows the whole input shaft to sit 3/16" deeper into the planetary ring where it is supposed to be. I ran it without the spacer for a long time but had issues with shifting it into 4lo and popping out under load (usually while hill climbing... hello suddenly in neutral!). With the spacer it sits right where it should be.
The other option would be to take the input shaft to a machine shop and have them machine the shoulder that stops against the input bearing down by 3/16" instead which would have the same effect. I'll see if I can find some pictures of what I did... I know I sent one or two via text to a local guy...
You can get the input shaft from any NP261XHD or NP263XHD (Duramax trucks or 8.1L trucks) The one in the wrecked transfer case behind the Allison right now would be a suitable donor.
Sorry, these are the only pictures I've got. First is the plate I cut out. Second is of it installed and sandwiched between the housing and seal housing / bearing retainer.
The bearing has a snap ring in it which normally seats up against the front case half. The bearing retainer plate then presses against the top of the input bearing to make sure it can't walk out the other way and it is held in place in between the two.
The plate I cut is just big enough for the bearing to pass through, but the snap ring in it doesn't. It sits up against the plate instead of the front case half, then the bearing retainer holds the bearing from walking out just like it would have if the bearing was pressed all the way in. The goal is to let the input gear stick out a bit further so the planetaries inside line up properly. When the input gear doesn't line up properly it also causes issues with the planetary shift collar for low range to become fully engaged before the shifter hits the detent that holds it into gear. The problem with that is the detent doesn't keep it in low range properly, so sometimes it pops out into neutral.
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I hope they still have the junk case!!! That would be a huge time saver....gonna check now....But this is gonna happen over night. I'm starting a new job the 1st, and money has money ridiculously tight past couple months, so gonna take some time to get money saved up. Figured tear the motor apart, see if everything is OK, maybe a rebuild to be on the safe side.
figures, I can't view the pics cause don't have paid membership...
PM me your email address and I'll send them to you.
How the F do you delete a PM????? I can only have 5, and have 4 now, but cannot find anywhere how to delete PMs!!!!! Not impressed with this new site....
Stomis
Professional Amateur
Run the allison. Seriously its the best automatic ever.
Go to your conversations inbox and click on the check box beside the conversation you want to remove. Choose "Leave Conversation" and it'll delete it.
I got it. PITA. Easier just to have a delete button. I called the yard, he said he had to look to see if he still had it. But even new wasn't crazy expensive. I'll prolly end up getting the 241 a full rebuilt anyways....
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