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L18 8.1L swap resource thread

so today was the 8.1L play day .....

stopped over at my buddys shop and used the fuel pressure guage and guess what i found the truck doing ? ........... 48psi :frown

so we lubed up the adjuster screw . held the housing and got her to move . and i did some reading in here and figured lets just go to 60psi for now and see what happens . . . . well she revs out better / climbs grade & on-ramp highway climbs better and just fells more peppy . still no :burnout: yet being a 5 speed and drw combo and my work truck playing it safe .
 
sweetk30 said:
so today was the 8.1L play day .....

stopped over at my buddys shop and used the fuel pressure guage and guess what i found the truck doing ? ........... 48psi :frown

so we lubed up the adjuster screw . held the housing and got her to move . and i did some reading in here and figured lets just go to 60psi for now and see what happens . . . . well she revs out better / climbs grade & on-ramp highway climbs better and just fells more peppy . still no :burnout: yet being a 5 speed and drw combo and my work truck playing it safe .
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Ya, 48 psi is way too low and will leave you wishing for more power. Surprised you weren’t receiving lean bank 1/bank 2 codes.

60 psi is still lower than I’d run but no two 8.1s don’t seem to want the same pressure. The GM spec is 58 to 62 psi and the pressure should go up as you snap the throttle. If it doesn’t then there is a regulator issue.

My K10 runs best around 68 psi but my Suburban smell gassy and runs to rich at 68 and likes 64 psi. After my bone stock 2001 Pewter Puff Silverado was tuned it likes 66 psi. Some tuners claim increasing fuel pressure is a scab to make up for a poor tune….well so be it, but if they run strong without ugly side affects then it is what it is
 
Yeah that’s tuners speak for self advertising. Pretty much all of the factory GM platforms respond similarly with some small pressure adjustments
 
i just played it safe for now at the 60-62 range . and i did pull the vac line running and she did jump 10psi so its good . will try it for now and se how she does .
 
sweetk30 said:
@Larry Should i bump it a bit more ? Under 90k miles and 5speed .
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I would. At least 65 at idle. Drive it and see how it runs then play with it from there. Yours may like all the way up to 68 like my K10. No two seem to be the same but 60 is on the low side.
 
jumped it to 65 yesterday and got a bit more power .

then i dawned on me the fuel filter on this thing is OLD and needs a change out . so in the next few days i will tackle this i hope . i know on a old tbi350 truck i had it wouldnt burn tires unless turning a 90* and stomp it . after i changed the filter it would fry them tires off if you let it .
 
Ok so I know this question is not really about a swap, at least not yet. :pimp:
I am looking at a 2003 chevy avalanche 2wd with the 8.1/Allison
It runs but a little rough, it has 267k miles.
Doesn't look abused, and this what codes it reads.Screenshot_20220407-110440.jpg

He already tried changing the sensors, no changes.
Any thoughts from the people that worked on them a lot?
Compression check came out good so I am assuming it is something simpler than a full rebuild.
 
imiceman44 said:
Ok so I know this question is not really about a swap, at least not yet. :pimp:
I am looking at a 2003 chevy avalanche 2wd with the 8.1/Allison
It runs but a little rough, it has 267k miles.
Doesn't look abused, and this what codes it reads.View attachment 408615

He already tried changing the sensors, no changes.
Any thoughts from the people that worked on them a lot?
Compression check came out good so I am assuming it is something simpler than a full rebuild.
Click to expand...
Avalanches didn't have Allison's, but none the less, if the didn't do a crank relearn after installing the new sensor the codes will reappear.

Oh, wait a minute...you said cam sensor. He could be using the wrong sensor as they changed a couple times over the years. Check out RayLar's tech page. They have pictures of the different sensors and cam gears used over the years. I suspect he is trying to use a later sensor with an early cam gear....or there is a wiring problem somewhere
 
Larry said:
Avalanches didn't have Allison's, but none the less, if the didn't do a crank relearn after installing the new sensor the codes will reappear.

Oh, wait a minute...you said cam sensor. He could be using the wrong sensor as they changed a couple times over the years. Check out RayLar's tech page. They have pictures of the different sensors and cam gears used over the years. I suspect he is trying to use a later sensor with an early cam gear....or there is a wiring problem somewhere
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I looked underneath and it looks like an Allison to me.
I know it's a rare combination.
It's a hd 3/4 ton
 
You can't go wrong with any 8.1 truck if the price is right, but I can guarantee you it does not have an Allison. Avalanches, Suburbans and G-vans all had the 4L80E. Only the pickups got Allisons
 
imiceman44 said:
I think I will buy it.
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Nada on the Allison. Larry is on the mark. Avs are no different than the 3/4 ton burbs or Yukon xl’s. Those all got 4L80e’s.


The utilities do not have the taller section height frame nor similar floor that the HD pickups got so the Allision does not fit.
 
ZooMad75 said:
Nada on the Allison. Larry is on the mark. Avs are no different than the 3/4 ton burbs or Yukon xl’s. Those all got 4L80e’s.


The utilities do not have the taller section height frame nor similar floor that the HD pickups got so the Allision does not fit.
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The pan didn't look like any 4L80E I have ever seen.
And does the 4L80E have an external filter?
I am picking it up tomorrow and I will check again.
I couldn't find a single picture of an Allison bottom online to confirm the shape.
But tomorrow I will look for a tag.
Either way I am fine with the 4L80E, it's eventually getting a manual when I make it 4x4
 
Larry said:
You can't go wrong with any 8.1 truck if the price is right, but I can guarantee you it does not have an Allison. Avalanches, Suburbans and G-vans all had the 4L80E. Only the pickups got Allisons
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Well it's a clean truck, and running I think the $2500 is good deal
 
imiceman44 said:
The pan didn't look like any 4L80E I have ever seen.
And does the 4L80E have an external filter?
I am picking it up tomorrow and I will check again.
I couldn't find a single picture of an Allison bottom online to confirm the shape.
But tomorrow I will look for a tag.
Either way I am fine with the 4L80E, it's eventually getting a manual when I make it 4x4
Click to expand...
GM never built an Avalanche with an Allison, I say that without a shadow of any doubt having been at GM when those first came out and had the truck order guide on my desk. I was in the Order Management group and it was part of my job to understand the option combinations. There was no option for thee Allison in the utilities. I bet you if you look at the spid label in the glove box it has the option code MT1 for the 4L80e transmission. It does not mean that somebody could have swapped one in with modifications.

But since that one is 2wd and you want to swap it to 4wd with a manual trans it doesn't matter what it has in it now.
 
ZooMad75 said:
GM never built an Avalanche with an Allison, I say that without a shadow of any doubt having been at GM when those first came out and had the truck order guide on my desk. I was in the Order Management group and it was part of my job to understand the option combinations. There was no option for thee Allison in the utilities. I bet you if you look at the spid label in the glove box it has the option code MT1 for the 4L80e transmission. It does not mean that somebody could have swapped one in with modifications.

But since that one is 2wd and you want to swap it to 4wd with a manual trans it doesn't matter what it has in it now.
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I wasn't trying to dismiss you or Larry, the reason I came here is to ask you for your advice because I know your background.
It would be interesting if it actually has a 4L80E with some kind of aftermarket pan with a recessed drain plug close to the middle.
 
Can you see the signal on the scan tool? Could be the wiring.
 
Blue85 said:
Can you see the signal on the scan tool? Could be the wiring.
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So I picked it up, haven't had the time to work on it yet but this is a video of it idling, ticking sound coming from the top of the engine, and goes away when you get to above 1000 rpm.
Not sure if it it's lifter and if it's related to the problem. View attachment 20220408_171016.mp4
 
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