Carbed 87 Comanche RENIX 4.0

[kaidenlem]

I haven't seen many write-ups on putting a carburetor on the Renix 4.0, now there is a good reason for this also.  The EFI system is decently reliable and gets good gas mileage being maintained by the computer.  It is also cheaper to maintain the EFI system than buying all the parts for the swap over.  However, when there is no computer and cut wiring (I'm old school and like hot rods and custom engine upgrades) what is the next best option?  Put a carburetor on it of course.  I know this sounds like a silly idea, but I'm determined.  This will require you to only need minimal wiring (I'm not an electrician so I enjoy this idea.) I have the HEI distributor with coil, a 2 barrel carburetor adapter (I 3D printed mine with special filament) a 2 barrel carburetor, and a small electric fuel pump.  In theory, you only need 2 toggle switches and a push button or key start switch (that is if you no longer want/need air conditioning or heat.) I plan on putting the whole system together this upcoming weekend as the weather will be about 70 and sunny as opposed to 40 and cloudy.  My only fear is that the transmission will no longer shift itself either since there is no computer to control it with RPM.  The 2 barrel carburetor is believed to have been off an 80's Ford, not sure of the CFM but it's one of the "Motorcraft Variable Venturi" models.  I paid 10 bucks for it so we will see how it'll run.  But I'll give it a shot.  This truck is put together in pieces with absolutely no interior.  The parts I acquired for my restoration on my 87 Pioneer so they'll be going on there, and I figured why not try them on this truck.  I can always buy another set of parts later down the road.  I like the idea of this barebones setup, and I'm old school so I'd enjoy the challenge.

[eaglescout526]

Look into the AMC 4.2L set up to get you a good base on what you want to achieve. Then you can also look at the 2.8L and get an idea on wiring for the chasis there as well(even though the 2.8L was ECU controlled as well). In other words take a gander down the Jeep history trail and get some good notes along the way. You might have better luck securing a 4.2L intake manifold for your carb. But if you go the hot rod route you could take it further and build a stroker using 4.2L internals with the 4.0L block and head. Just a couple ideas and thoughts.

[Eagle]

The YJ Wranglers ran the carbureted 4.2L until '91 or so. It should be easy enough to find a wiring diagram for an AMC YJ.

 

The MJ auto transmission has its own computer (TCU), so all you need is to provide a way for it to be powered up.

 

[Tex06]

Very cool idea. What filament did you use for the spacer (if you know by chance)? I have a 3D printer and have been experimenting printing in different materials specifically to be able to make my own car parts.

[kaidenlem]

On 11/1/2020 at 6:47 PM, eaglescout526 said:

Look into the AMC 4.2L set up to get you a good base on what you want to achieve. Then you can also look at the 2.8L and get an idea on wiring for the chasis there as well(even though the 2.8L was ECU controlled as well). In other words take a gander down the Jeep history trail and get some good notes along the way. You might have better luck securing a 4.2L intake manifold for your carb. But if you go the hot rod route you could take it further and build a stroker using 4.2L internals with the 4.0L block and head. Just a couple ideas and thoughts.

I also have the Haynes book on this truck, so shouldn't be too hard to piece the wiring together.  The problem comes into play is that I have to lay underneath this thing with flat tires on a gravel parking lot .  I may consider waiting a few months until I have a while off, then I can sneak it into the heated concrete garage at my grandparents house.  I like the 4.2 idea of swapping components, but I want to see how basic I can get this thing to run.

 

On 11/1/2020 at 9:02 PM, Eagle said:

The YJ Wranglers ran the carbureted 4.2L until '91 or so. It should be easy enough to find a wiring diagram for an AMC YJ.

 

The MJ auto transmission has its own computer (TCU), so all you need is to provide a way for it to be powered up.

 

Absolutely all of the interior is gutted in this truck, no interior wiring, and no computers or control boxes whatsoever.  This is what I am confused and lost about, because I don't want to end up swapping a trans into a 120 dollar truck if it won't work without the brains.

 

On 11/2/2020 at 9:36 AM, Tex06 said:

Very cool idea. What filament did you use for the spacer (if you know by chance)? I have a 3D printer and have been experimenting printing in different materials specifically to be able to make my own car parts.

I used PLA for the test piece, and then upon looking into it, PLA seems to be decent against fuel protection.  There is a better solution somewhere I saw for using nylon that should be completely resistant.  I just searched "gasoline resistant 3d printer filament" into Google, not sure the exact article though.  My 2 barrel carb adapter test piece I designed in Autodesk came out very well, took 25 hours though.  It bolts right up to a 2 barrel, and it narrows down to bolt and line up exactly with the Renix intake manifold.  I had to cut the sides for the throttle linkage, but it will be cut out in the final print after I make some changes.

[Tex06]

12 hours ago, kaidenlem said:

I used PLA for the test piece, and then upon looking into it, PLA seems to be decent against fuel protection.  There is a better solution somewhere I saw for using nylon that should be completely resistant.  I just searched "gasoline resistant 3d printer filament" into Google, not sure the exact article though.  My 2 barrel carb adapter test piece I designed in Autodesk came out very well, took 25 hours though.  It bolts right up to a 2 barrel, and it narrows down to bolt and line up exactly with the Renix intake manifold.  I had to cut the sides for the throttle linkage, but it will be cut out in the final print after I make some changes.

A warning against PLA. It doesn't like heat, or stress. You're gonna have both under the hood. Just the tension of the bolts is enough to cause deformities over time and the heat from the motor will severely accelerate this. You might get the truck running with this but I'm afraid that's not a long term solution. I've had PLA deform in the car sitting on the dash in the hot Louisiana sun....and that's only about 120F give or take.

[kaidenlem]

1 hour ago, Tex06 said:

A warning against PLA. It doesn't like heat, or stress. You're gonna have both under the hood. Just the tension of the bolts is enough to cause deformities over time and the heat from the motor will severely accelerate this. You might get the truck running with this but I'm afraid that's not a long term solution. I've had PLA deform in the car sitting on the dash in the hot Louisiana sun....and that's only about 120F give or take.

Exactly.  That's why I only used it as a mock-up piece, and to see if it'd even work on one of these manifolds.  The stronger material isn't all that much more expensive anyways, but I wanted to make a test piece before spending the extra.

[kaidenlem]

On 11/1/2020 at 9:02 PM, Eagle said:

The YJ Wranglers ran the carbureted 4.2L until '91 or so. It should be easy enough to find a wiring diagram for an AMC YJ.

 

The MJ auto transmission has its own computer (TCU), so all you need is to provide a way for it to be powered up.

 

Not sure how I'm going to get the auto trans to work   I'm considering finding a 86-92 AX-15 out of a junkyard and going that route

[omega_rugal]

10 minutes ago, kaidenlem said:

Not sure how I'm going to get the auto trans to work 

 

why? the transmission has its own electronics to do the shifting, all you have to do is hook up the tps to the carb linkage, not difficult, oh and the TV cable, which is not difficult either

[omega_rugal]

also why a plastic adapter/spacer? plastic won't last long there, or any material you can 3d print, unless is aluminum or iron...

 

with minimum fabbing skill and tools, you can take an aluminum plate and drill holes

[kaidenlem]

2 minutes ago, omega_rugal said:

 

why? the transmission has its own electronics to do the shifting, all you have to do is hook up the tps to the carb linkage, not difficult, oh and the TV cable, which is not difficult either

I mentioned above that there is absolutely NO interior wiring whatsoever.  There aren't even the computer boxes anymore inside.  There is no dash even.

[kaidenlem]

Just now, omega_rugal said:

also why a plastic adapter/spacer? plastic won't last long there, or any material you can 3d print, unless is aluminum or iron...

 

with minimum fabbing skill and tools, you can take an aluminum plate and drill holes

I do not have a metalworking shop or the necessary tools to do so.  There is a material that can be printed to withstand both heat and fuels.

[omega_rugal]

oh you mean you don't have the wiring and TCU? you can get them at a junkyard...

[omega_rugal]

1 minute ago, kaidenlem said:

I do not have a metalworking shop or the necessary tools to do so.

 

i used a drill to make my LPG mixer to Renix TB adapter out of a piece of wood, but aluminum would be the same thing

[kaidenlem]

3 minutes ago, omega_rugal said:

oh you mean you don't have the wiring and TCU? you can get them at a junkyard...

I don't plan on rewiring the whole entire truck simply because it wouldn't be worth the time.  I was going to rig it up enough to use as a trail rig/around town rig, maybe take to shows as a rusted out heap.

[omega_rugal]

the TCU doesnt need that many wires... whatever...

[ghetdjc320]

Just a thought but painless makes a nice YJ harness for the 87-90 that could be so easily adapted into your MJ. I used it in my YJ along with a Holley efi system. 

[kaidenlem]

3 hours ago, ghetdjc320 said:

Just a thought but painless makes a nice YJ harness for the 87-90 that could be so easily adapted into your MJ. I used it in my YJ along with a Holley efi system. 

I'll look into that, I thought about just making my own custom harness

[ghetdjc320]

15 minutes ago, kaidenlem said:

I'll look into that, I thought about just making my own custom harness

You could but the YJ painless harness will fit pretty well on most MJs. Even the firewall plug connector will bolt in. It’s plug and play with our steering columns and most major components. Plus it has provisions for efi or carb and tons of alternator options. 

[kaidenlem]

24 minutes ago, ghetdjc320 said:

You could but the YJ painless harness will fit pretty well on most MJs. Even the firewall plug connector will bolt in. It’s plug and play with our steering columns and most major components. Plus it has provisions for efi or carb and tons of alternator options. 

Is steering columns a requirement?      I'm liking the idea with the firewall connector, luckily mine still has the connector in the lower left by the drivers feet.

[ghetdjc320]

1 hour ago, kaidenlem said:

Is steering columns a requirement?      I'm liking the idea with the firewall connector, luckily mine still has the connector in the lower left by the drivers feet.

I’m referring to the GM connectors on the steering column for ignition ant turn signals. Nice to have those be plug and play . 

[kaidenlem]

On 11/6/2020 at 10:06 PM, ghetdjc320 said:

I’m referring to the GM connectors on the steering column for ignition ant turn signals. Nice to have those be plug and play . 

Very true, lots and lots and lots of wires lol

[Eagle]

The AX-15 wasn't used from '86 thru '92, it was only used from '89 thru '92.

 

The AW4 automatic will function just fine without the TCU. In fact, pulling the fuse to disable the TCU is part of the diagnostics described in the factory service manual. You will have to shift it manually, and it will be missing one gear -- I don't recall offhand if that's first or second. If you get a wiring diagram, you can rig a simple toggle switch for the torque converter lockup solenoid.

[Tex06]

On 11/6/2020 at 2:51 PM, omega_rugal said:

also why a plastic adapter/spacer? plastic won't last long there, or any material you can 3d print, unless is aluminum or iron...

 

with minimum fabbing skill and tools, you can take an aluminum plate and drill holes

3D printers can handle a lot of different materials now. Nylon would probably be my 1st choice, good gas and heat resistance. In fact, my cruise control cable end (the one that attaches to the throttle body and always breaks) is 3D printed nylon. Has held up great for the past 8 months so far.

[Eagle]

For less than the cost of the materials to throw at a 3-D printer you can probably get a pre-made aluminum adapter for putting a two-barrel carburetor on a one-barrel manifold. You might have to drill some new mounting holes, but that's nothing.

 

Like this:

https://www.amazon.com/Trans-Dapt-2025-Carburetor-Adapter/dp/B000N8GTL8/ref=sr_1_33?dchild=1&hvadid=77996736689548&hvbmt=be&hvdev=c&hvqmt=e&keywords=carburetor+adapter&qid=1605654219&sr=8-33