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May 2013 Your Jeep - Tech Questions

Throttle Body Comparison
Verne Simons
| Senior Editor, Jp
Posted May 1, 2013
Photographers: Jp Archives

Your Jeep Questions Answered

Idle Issue
Your article about changing the 2.5L throttle body to a 4.0L (“Dethrottled,” Jan.’13) has me asking a few questions. I have a throttle body from a ’91 4.0L Cherokee with automatic transmission that is in good shape. First of all, will it work on a ’95 2.5L Wrangler with manual transmission? And second, is there a way to change the idle after swapping out the 2.5L IAC and TPS to the 4.0L body? My engine in stock form idles at approximately 800 rpm but when I put the larger throttle body on it the idle jumps to approx 1,100 rpm and does not settle down any lower. I’ve driven the Jeep for several minutes to get the engine completely warmed up, but that doesn’t help lower the idle. I like the additional power it seems to have at the lower end. Drivability would be great if the engine would go back to a normal idle. Any suggestions you might have would be greatly appreciated.
Jim Poindexter
Via email

First off, we advised Jim to make sure that he had swapped not only the idle air control (IAC) motor but also the IAC housing from his 2.5L throttle body to the 4.0L throttle body. As stated in the original article, the 2.5L IAC is specific to the 2.5L IAC housing. We also told Jim to check for vacuum leaks which can cause an elevated idle. This could be from a bad gasket or an open port. Unfortunately for the simple solutions gods, neither of these things was causing the problem. Jim got back to us and confirmed that he had swapped both parts of the IAC and that there were no vacuum leaks on the Jeep. Honestly, at this point we were a bit stumped, but Jim kept at it and finally found that a grub screw under the throttle lever (pictured) was screwed in a little too far, and that was causing the elevated idle. Thanks, Jim, for helping us help you and solving your own problem. Here’s to hoping this helps someone else out there in Jp reader land.

Fordjeep or Jeephord?
I was thinking of putting a 4.0L Jeep engine in my Ford pickup. My Ford has a 300ci I-6 now. The Ford is an ’81 model, and the addition of horsepower and torque would be greatly enjoyed. Will the Jeep engine marry to the Ford C4 tranny. Or should I use a Jeep auto transmission.
David Boedeker
Summerville, SC

Believe it or not, I once had visions of building an old ’60s Mustang with a Jeep 4.0L in place of the old Ford 200 I-6. At the time it seemed like a great way to get a more modern engine in an older car, and it would look like (to the untrained eye) someone had modernized the Pony’s old-school engine. Plus, the 4.0L would make more power and torque than the smaller V-8s that these cars came with from the factory. Looking back, I am not sure it would be worth doing this swap in a Mustang when you could get an H.O. 5.0L V-8 pretty cheaply that would easily make more than enough power. Having said that, I guess it could be a good option for you depending, on what you want from your truck. I don’t think there is an adapter for mating a 4.0L to a C4; I could not find one. You could probably have a custom one made, but I doubt it’s worth the cash. Now if you were to do this, I’d use an AW4 transmission from a Cherokee. It has a lower First gear than your C4 and it has an overdrive. I would also look for an H.O. 4.0L from a ’91 or newer Cherokee. You’ll also want the computer and you’ll have to get the engine wiring harness and have it modified to run outside the XJ. You could send the XJ harness to Hotwire Auto (hotwireauto.com) to be pared down if you’re not comfortable doing it yourself.

Now back to if you should do this swap. If your truck is a 2WD work truck or parts runner and you want to keep your it running down the road for a long time and wouldn’t mind a little more horsepower you could swap in a Jeep 4.0L. If your Ford is a 4x4 and you want to modify it for wheeling I’d stick to a V-8 swap and there the path of least resistance is gonna be adding a 302ci or 351ci Windsor engine. In this case, the 4.0L ain’t gonna have enough grunt to move all that truck around off-road especially when you start adding bigger tires and heavyduty parts. Your time and energy would be better spent on a V-8 swap.

Dodgeep?
I have a ’93 Dodge Club Cab 4x4 and was wondering if I could put a four-door Jeep body on it—any info would help. Keep up the great work and I love your magazine!
William Roberson
Cleveland, TN

So depending on how good you are at fabrication, this is probably doable, but it ain’t gonna be easy or cheap. You are gonna need to locate a JK body or a custom built YJ or CJ four-door Jeep body like the aluminum tubs offered by Aqualu (aqualu.com). Or, try getting in touch with a Jeep specialty junkyard like Collins Brothers (collinsbrosjeep.com) or Davey’s Jeeps (daveysjeeps.com) for a pair of clean, usable tubs or parts of tubs you can merge together. Either way is costly, though.

Then you can start pulling the Dodge body and carefully removing all the wiring and other components that you’ll want to re-use. You might be able to re-use things like the steering column, the brake system, the parking brake system, the pedals, and so on from the Dodge. You will probably also want a factory service manual for the Dodge so you can figure out the wiring. Once you get the Jeep body in hand, you can start adjusting the Dodge’s wheelbase to fit the wheelbase of the Jeep body. The easiest way to do this is to move the rear axle and all its hangers and mounts. You’ll also have to remove all the Dodge body mounts and build or modify stock Jeep body mounts to make the new body fit on the Dodge frame. You’ll almost certainly need a new radiator that will fit behind the Jeep grille and still keep the Dodge engine cool. I am sure I have missed some details of what you’ll need to do. It’s gonna be hard and will take a while, so be ready to devote lots of time and a good chunk of change to this project if you have to do it. If you still want to do this swap, we’d also recommend looking at the ’07 Ultimate Adventure Jeep that 4-Wheel & Off-Road magazine built a few years back. They combined a JK body and a 1-ton Dodge diesel chassis. They modified the frame to fit the wheelbase by shortening it in the center and lopping off the extra frame front and rear. I think that’s his easiest route other than trying to move the suspension mounts/axles around on the Dodge frame. It’s not exactly the same as what you want to do, but it’s gonna give you an idea of just how much fabrication is going to be necessary. Good luck! If I were you, I’d sell or part out the Dodge and save my lunch money for an ’07 JK.

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