L18 8.1L swap resource thread

[Larry]

I hear ya. Its a struggle because i love mine in my 12 so far. Its a 5.3 with VVT and AFM. Its got great torque off the line, great hp in the upper end, and has gotten up to 22.2 mpg on the highway so far. Its one of those things where, when they work good, they work good.

Yeah, we have that same LMG 5.3L in our 2013 Tahoe Z71 as well. It runs well with much more noticeable power than the 2004 Tahoe we had before it. I wouldn't go as far to say it has great torque but compared to the prior Tahoe it does. The 4:09 first gear in the 6L90 trans gives it the added low end grunt that the older 4L60's couldn't provide. Like the rest of the small block Gen III engines, even the VVT engines are high reving HP engines rather than low RPM toque machines.

awesome thread larry! i saw your truck for the first time on EXPO way back in the day, ive been a fan of it since day one across all the forums lol. i always knew when i got around to my swap that you would be a great resource. appreciate the thread itll be a huge help for me in the future.

Hey biglos, good to see you around these parts

 

[Big Ray]

Awesome info Larry


this should be a sticky fo sho

 

[herkdriver007]

Hmmm, wonder how tough it would be to replace the 6.0L in my pickup with an 8.1...oh the interwebs and ideas it puts in my mind!!!

 

[Larry]

I received about 4 messages lately related to the fuel system so I guess it is time to add fuel delivery to this thread.

Fuel System:

Plumbing the L18 fuel system is not much different than doing an LS engine swap. Earlier in this thread I mentioned the L18 came with two different fuel rails over its life in service. The 2001-2003 engines had two fuel lines connecting to the fuel rail (Supply and Return). The 2004-2010 L18’s only had a supply line due to GM making changes to the fuel system across the board on all GM engine to meet the new evaporative emissions changes for 2004. While it is nice to only run a single line on the later engines, I prefer the earlier fuel rails as they have an adjustable regulator built into the fuel rail (L18’s love higher than stock fuel pressure so it is nice to be able to easily adjust it on the fuel rail). The later engines fuel pressure was regulated inside the fuel module inside the fuel tank. There are ways around plumbing returnless systems by using Corvette pieces but I do not have the experience with doing one myself to speak to it. If your plan it to use a returnless fuel rail GOOGLE is going to be your friend.

This is how I did mine.

Used an AC Delco EP381 fuel pump mounted to a 1987 truck fuel sending unit. This fuel pump is a high pressure pump (62 psi) for the early Vortec engines (1996/1997) and has the same foot print as the TBI fuel pumps. (I mentioned 62 psi, but this pump is capable of much higher pressures if you wish to adjust the regulator higher. I had one peg my fuel pressure gauge at 100 psi by accident once )

1987 Fuel TBI fuel tank. The TBI fuel tanks are different from the older carb tanks.

Fuel lines - (No pictures of these). I used supply and return fuel lines for a Workhorse RV application. These are really nice high quality steel braded lines about 4 or 5 ft. long with quick connect fittings on both ends. You will need to get creative with connecting the quick connect fittings to the lines on the frame. I used a GM fuel filter with a built in quick connect fitting (late model Silverado application) then made up something to connect the quick connect fitting on the fuel line to connect to the frame line. The Workhorse part numbers for these lines are W0000539 Supply, W0000540 Return.

This is a 2001—2003 image of an engine with the Supply and Return line

Number 8 is the nifty adjustable regulator. It should look familiar as GM has used this regulator on many different engines over the years.

Another view of the adjustable regulator

2004-2010 Returnless

Even though this looks like a fuel regulator in the fuel rail it is not. It is a pulse damper in about the same location the fuel regulator was on earlier engines. The damper and regulator are not interchangeable. This damper itself is actually missing in this illustration

Engine Oil Cooler Delete:
A question that has come up several times is related to the oil cooler and how to delete it for those that don’t want it or have room to mount a cooler. If you chose not to run an engine oil cooler it is best to remove the oil cooler bypass valve to increase oil pressure at low RPMs. The pictures below are how to remove the bypass valve. This process is no different from any other GM V6 or V8 engine that was equipped with an oil cooler.

Remove the oil filter adapter that the filter actually screws on to with a ½ Allen bit

Now you can see the Oil Cooler Bypass Valve (P/N 25013759) stuffed up in the block

Thread a bolt into the middle of the bypass valve and yank it out like Dr. Payne did to your achy tooth. An old starter bolt works perfect for this chore.

And this is how the oil passage looks without a bypass valve. Leave the other bypass valve where it is. Only remove the one in the center.

Reinstall the oil filter adapter and plug the engine oil cooler ports with ½” pipe plugs and you’re all set

Oil Pump Priming:

By looking at it, you wouldn’t think you could prime an 8.1L in the same fashion as an old school SBC or BBC but it’s no different once you peel the intake off

Remove the oil pump drive.

This drive is just like the ones in the old 6.2 and 6.5L diesels. Probably the same part number too

Oil pump shaft down there just like the old days

Use your favorite oil pump driving tool. Mine happens to be the guts out of an old HEI dizzy attached to a drill

Then start drilling for oil. You can actually see the oil flowing right next to the shaft of the homemade tool

 

[bigblock72]

You could wire the secondary pump like the 3/4 ton suburbans and let the computer take over the transfer duties. It is a little complicated because you would have to use the newer style senders to get the proper resistance for the 0-5 volt signal the pcm needs, somewhat involved in wiring but totally doable. Alernatively you could use a fuel pump balance module from a cab and chasis truck and do the same thing and not have to reflash your computer to suburban software. Wow I think that sounds like a lot of work.

Kind of thinking (typing) out loud here so FWIW, but you could use your transfer valves 3/8" ports for the return only and just T the pressure lines since you will be switching pumps anyway. Most pumps have a built in check valve that would prevent back flow so need to switch the pressure side. IDK you may have already tried it.

 

[Larry]

You could wire the secondary pump like the 3/4 ton suburbans and let the computer take over the transfer duties. It is a little complicated because you would have to use the newer style senders to get the proper resistance for the 0-5 volt signal the pcm needs, somewhat involved in wiring but totally doable. Alernatively you could use a fuel pump balance module from a cab and chasis truck and do the same thing and not have to reflash your computer to suburban software. Wow I think that sounds like a lot of work.

Kind of thinking (typing) out loud here so FWIW, but you could use your transfer valves 3/8" ports for the return only and just T the pressure lines since you will be switching pumps anyway. Most pumps have a built in check valve that would prevent back flow so need to switch the pressure side. IDK you may have already tried it.

I don’t recall Suburban’s having two tanks and using transfer pumps but I did give a thought of doing it like a Corvette or late model chassis cab truck with dual tanks where they have two tanks and use an ECM controlled transfer process. The ECM controls the levels and gauge to give it the feeling of one large tank rather than two independent tanks. It could be done but much too complex for what it is worth in my opinion.

The T suggestion sees like a decent idea in theory. I’ll have to think about that.

 

[eagle mark]

Thanks Larry for all the effort you have put into this! Excellent!

 

[y5mgisi]

The burbs do have 2 tanks. The boys that are swapping duramaxs in them had played hell getting them to work right after the swap. But I know at least duraburb has it figured out.

 

[Larry]

The burbs do have 2 tanks. The boys that are swapping duramaxs in them had played hell getting them to work right after the swap. But I know at least duraburb has it figured out.

All be damn, you’re right! The service manual shows the 2500 series Burbs get a 26 gallon tank and an optional 11.5 gallon rearward tank. Looking at the flow control module wiring confirms it would be a huge hassle to retrofit that into an old rig. Learn something new everyday

 

[Russell]

All be damn, you’re right! The service manual shows the 2500 series Burbs get a 26 gallon tank and an optional 11.5 gallon rearward tank. Looking at the flow control module wiring confirms it would be a huge hassle to retrofit that into an old rig. Learn something new everyday

The 8.1L PCM is capable of managing dual fuel tanks. Get a tune from a cab and chassis 8.1L truck equipped with dual tanks, provide a fuel level signal from each tank and the PCM will operate your existing transfer pump to maintain the level between the two tanks. The fuel tank module you speak of is old technology. The PCM just controls a fuel pump relay for the transfer pump.

 

[eagle mark]

Do you have a year and OS for the tune needed?

 

[Larry]

The 8.1L PCM is capable of managing dual fuel tanks. Get a tune from a cab and chassis 8.1L truck equipped with dual tanks, provide a fuel level signal from each tank and the PCM will operate your existing transfer pump to maintain the level between the two tanks. The fuel tank module you speak of is old technology. The PCM just controls a fuel pump relay for the transfer pump.

Yesiree it is. The P59 PCM used to run L18’s is plenty capable of turning on another relay but in my case, I simply do not want to mess with all that. I would rather just flip a switch and either transfer fuel or swap tanks to fire up the other fuel pump just like the TBI trucks did . Simple.....

Do you have a year and OS for the tune needed?

They can be tuned with any software that is used to tune an LS engine. Howell Engine Development tuned mine and it seems that there are hundreds of good tuners out there these days to choose from (guys like you that are good at tuning ). I am not one of those guys that is good with tuning one myself. I tried tuning a MEFI-4 ECM and got so friggen frustrated and decided from that point on tuning should be left up to those with experience. Either I sucked at tuning or the software I was using really sucked. The software was called TunerPro

 

[eagle mark]

Well the MEFI-4 is good, but expensive and TunerPRo is great so...



I've got EFI Live and TunerCat OBDII and seen the 2 tanks, LS1b and 8.1L, but never dealt with the transfer and thought it was interesting to look into the programming.

The old TBI trucks with dual tanks, switches and plumbing is quite complex when swapping to another truck. Wow plumbing...

 

[Larry]

How about some sound clips

This was when it was running the MEFI-4 ECM. It didn’t have much top end. Oh, yes….the fan is loud. I run a medium duty truck fan clutch. It does rob power and is loud but it NEVER overheats when in the desert in 100+ degree temps rolling a long at 5 MPH with the A/C on.

Gained a lot more top end after moving to the P59 ECM and MAF system
[youtube]BvXf-_gmC5o&list=TL8ZFGBi_tpyc[/youtube]

Just goofing off seeing if we could break through this ice wall. Ah, nope! The sound on my buddies video camera makes it sound weird. When I play in the snow I always run in 4 HI as it is too easy to overspeed the engine in 4 LO.

This is my favorite part of the 8.1L. It lugs along at 900 RPM all day without breaking a sweat. Gets great fuel mileage off-road because it isn’t working very hard. Love the sound of it lugging along cackling and blapping away. The sound of gobs of low end TORQUE! This is the lead in trail to Utah Canyonlands Maze District 2010. Still had the SM465 behind the 8.1L on this trip
[youtube]SnaGNv1yV1U&list=PLA966B54CA0B63794[/youtube]

This one sounds pretty cool from the outside. Top of the World/Kokopelli trail Utah 2011
[youtube]dMwIeDaWpJY&list=PL58161C0471F25102&index=4[/youtube]


BTW….we are not going that fast. The GoPro gives the false illusion we are going much faster than we really are. Mohave Rd 2013

 

[y5mgisi]

I just hate you Larry...

 

[Russell]

Do you have a year and OS for the tune needed?

I do have a dual tank cab and chassis OS but it is for a ZF6 manual transmission truck.

Shouldn't be too hard to find. Just track down a dual tank cab and chassis truck with an automatic transmission online and you can get tuners to grab the tune from TIS2WEB via the VIN number no problem. They just flash the OS and tune into a spare PCM and download it with EFI live or whatever tuner they use.

 

[Larry]

I do have a dual tank cab and chassis OS but it is for a ZF6 manual transmission truck.

Shouldn't be too hard to find. Just track down a dual tank cab and chassis truck with an automatic transmission online and you can get tuners to grab the tune from TIS2WEB via the VIN number no problem. They just flash the OS and tune into a spare PCM and download it with EFI live or whatever tuner they use.

Good deal. That bit of info could help someone that may be interested in setting up dual tanks with the auto transfer function

 

[pma4x4]

Just found this thread Larry, Gonna go back and read it all this weekend when I get time. See if I will be going this route or what.

 

[olive-drab]

So I am looking to do this swap since the 305D in my 1967 K2500 is a goner. Since I plan on running a SM465 for now (not much highway driving) and maybe a ZF down the road, I assume I will need an ECM from a manual truck, is there a VIN to use for the ECM?

Looking to run the howell harness, upgrading the cam sensors if it hasn't been done and the workhorse accessory kit. The motor is out of a 2002 truck, assuming it is an Allison, going to look at it tomorrow

 

[Larry]

So I am looking to do this swap since the 305D in my 1967 K2500 is a goner. Since I plan on running a SM465 for now (not much highway driving) and maybe a ZF down the road, I assume I will need an ECM from a manual truck, is there a VIN to use for the ECM?

Looking to run the howell harness, upgrading the cam sensors if it hasn't been done and the workhorse accessory kit. The motor is out of a 2002 truck, assuming it is an Allison, going to look at it tomorrow

Doesn’t really matter what you get the ECM from as long as it is a P59 ECM, as you will end up needing a custom tuner to do some tweaking to the calibrations anyway. Howell can do such tuning and provide the ECM as well if you don’t have one. My harness and ECM tune came from Howell as well. My suggestion is to have them toggle off Torque Management, Toggle off EGR (and remove it from the engine), Toggle off electronic throttle (use a L29 7.4L mechanical throttle body) then add their “Hot” tune. Electronic throttle is nothing but a pain in the rear if you ask me and the throttle just plain feels fake like a video game. I find it hard to feather the pedal when off-roading with drive-by-wire. Then when you get it running bump the fuel pressure up to about 67-68 psi and you’ll have a very strong runner that will start to find weaknesses elsewhere in your driveline .

Any GM trans will bolt behind the 8.1L from an old 2 speed powerglide to an Allison 2200. Before the NV4500, I ran a SM465 behind mine for the first 2 years as well but you will need an 8.1L specific flywheel and pilot bearing (12582964 is the flywheel, 12563485 flywheel bolts & 12557583 pilot bearing). If you want to run the Allison that brings in a whole new bag of worms dealing with the Allison TCM and calibrations and actual fitment below the floorboard. I would not recommend the ZF S6-650 6 speed. I have one in a 2001 Silverado HD with an 8.1L that I hated since the day I brought it home 13 year ago. The trans has horrible shift pattern and gates, not to mention it is huge where it requires major floorboard mods even above what an Allison would require. The ZF is very strong and will probably live longer than 2 or 3 NV4500’s but the ZF is just horrible to live with.