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L18 8.1L swap resource thread

I checked the fuel pressure on my 8.1l, it is sitting at 50 psi idle, remove the vac line and maxes out at 58psi. I attempted to turn the screw, it started to twist the regular cap, and I stopped. It looks to me like the screw is bottomed out. How sensitive is the regulator big swings or tiny little turns ?
I am thinking I should replace the regulator since the o rings are 21 years old. Need to make sure I get 1 that is adjustable, any suggestions?
 
Wes Harden said:
I checked the fuel pressure on my 8.1l, it is sitting at 50 psi idle, remove the vac line and maxes out at 58psi. I attempted to turn the screw, it started to twist the regular cap, and I stopped. It looks to me like the screw is bottomed out. How sensitive is the regulator big swings or tiny little turns ?
I am thinking I should replace the regulator since the o rings are 21 years old. Need to make sure I get 1 that is adjustable, any suggestions?
Click to expand...
there sticky at first . slow and steady holding the cap body . . . .
 
Wes Harden said:
I checked the fuel pressure on my 8.1l, it is sitting at 50 psi idle, remove the vac line and maxes out at 58psi. I attempted to turn the screw, it started to twist the regular cap, and I stopped. It looks to me like the screw is bottomed out. How sensitive is the regulator big swings or tiny little turns ?
I am thinking I should replace the regulator since the o rings are 21 years old. Need to make sure I get 1 that is adjustable, any suggestions?
Click to expand...
They are sensitive. Like a 1/8th of a turn will bump mine 4-5 psi at least.

I honestly have not had many pressure regulators actually fail. You may have the regulator maxed out because the pump isn't putting out enough pressure. But the regulator is much cheaper to start with first. Many you get now may not have the adjustment screw or may have a dollop of paint over the screw to hide it. The early LS truck engines used the same regulator as did 3.8 v-6's in many of the GM cars.

Spec is 55-62psi. I'm running close to 65-66psi.
 
Cool, according to the 1 receipt I found in the truck, says the pump and module were done 27k miles ago at GM agency in Orange county CA. I think the pump is good or should be.
 
Wes Harden said:
Cool, according to the 1 receipt I found in the truck, says the pump and module were done 27k miles ago at GM agency in Orange county CA. I think the pump is good or should be.
Click to expand...
50 psi is no bueno dude. If the regulator don’t perk that number up you got a pump not up to snuff.

That big dog is running lean at 50psi.
 
so the one i scored is a 2005 8.1 / 5 speed allison auto . had it delivered to my buddys shop today to suck down the A/C system so i can pull the rest and part out the truck .

since its a fixed pressure fuel rail 1 line i figure i am doing a swap anyway so i just plan to do a aftermerket vac referenced fuel pressure regulator and be done with it so i dont need a early rail . . . unless 1 happens to drop in my lap some time .
 
So testing my new to me 8.1 it popped a oil cooler line . Its a 05 truck and i dont think i plan to run a oil cooler or for now i dont .

What do i need to cap off / eliminate it on the engine side ?

Thanks fellow 8.1L masters .
 
So, I've gotten to point I need fuel hosesfor the 8.1.
I looked up the Workhorse (W) series hoses that would fit my version of the engine.
The W0000539, supply line, is $256.79, cheapest I could find it.
The W0000540, return line, is $178.95, cheapest I could find it.
Either one of those is way more money that I wanted to spend on both of them together.
Time to look aftermarket.
Check that. Rock Auto has them, both, under $100 each
 
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i used the older press fit kit from dorman . . .newer stuff now more easy to use and less work .

pics in my BUDGET BEATER build thread in my sig line on how i built my high pressure efi lines with there stuff .

i dont see the need for all this AN stuff for our mostly stock efi stuff when even stock 500+hp is feed the same way with the 3/8" nylon stuff like i used .

if i recall this was the kit used without going in my shop to double check . https://www.dormanproducts.com/p-27520-800-300.aspx . . using this kit a little HOT water to soffen the end or some lube before pressing in the end helps . but as i said there is better kit now that are less b.s. to use them .

the link build was a edelbrock pro flo 4 and i used the kit also to redo my 01 3500-hd with the factory 8.1 do to hard lines rusted out bad . both working super no problems .
 
so who is doing what for wiring harness setups for the 8.1 / allison 5 speed auto in a 05 truck doner ?

reason i ask is after @SpeedlabDan had all his troubles i dont want to go down this rabbit hole as i just need this to drop in and few mods and run .

if it helps its going in a 95 gmc 3500-HD 1.5 ton truck .
 
sweetk30 said:
so who is doing what for wiring harness setups for the 8.1 / allison 5 speed auto in a 05 truck doner ?

reason i ask is after @SpeedlabDan had all his troubles i dont want to go down this rabbit hole as i just need this to drop in and few mods and run .

if it helps its going in a 95 gmc 3500-HD 1.5 ton truck .
Click to expand...

So here’s the thing one thing that is ultra important is making everything you need match from the same year. Ecm, transmission, Tac module, throttle pedal and throttle body. There are small differences between the years and they DO NOT mix and match from different years. The harness needs to be built for that year for that reason too.

The moment you start mixing stuff you will find yourself in a mess where you will be chasing your tail on trying to re-pin connectors to make them work. Even then you’ll have issues.

I’ve sat down for a while comparing schematics from year to year and they do not match.

It’s also a big reason why every swap that has gone through Larrys shop has been a manual trans and cable throttle. Less complex and less likely to fail.

But if you need to run an Allison it’s totally possible but make sure to make it as close to factory as you can. I know Dan had issues with his Howell harness but I think a big part was the issue of changing direction mid stream. Nothing on Dan as directions change but he and I discussed a mismatch from the Tac module Or pedal (can’t remember) and I pulled multiple schematics to compare. It created more confusion than anybody needs.

A couple other thoughts that typically limit guys stacking them behind an 8.1. One they require more power than any other transmission choice. The Allison side of the controls are seriously picky. Which the Tac system freaking out will cause issues with the trans. You also are limited on tuning the 8.1 to eliminate torque management as in you can’t. That’s a big deal as it leaves power off the table down low in order to protect the transmission. We tried with Ron’s 8.1 Allison Silverado and our local tuning smart guy couldn’t crack the code. If you know somebody smarter with EFI Live or HP Tuners let them have a crack at it.

As far as the harness goes, I’d still recommend Howell. But be clear on what you are using. Larry and I have 4 between us, CaptRon has one and out buddy Andy we helped with on a L29 swap. Flawless. Works like factory.
 
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