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April 2013 Techline - Tech Questions

Jeep Ecu
Ali Mansour
| Brand Manager, 4WD & Sport Utility
Posted April 1, 2013
Photographers: Four Wheeler Staff

Your Tech Questions Answered

Alternator Seal
Q I have a ’89 Jeep Cherokee that I took it out mudding and fried my alternator. Why Jeep would put the alternator way down low is beyond me. I love mudding and need to find a way to protect it. I simply can’t keep buying a new alternator every time I want to go have some fun!

(Editor John Cappa responds)
A You can’t really seal the alternator. It creates heat so it needs vents and the fan on the front of it. However, you can build a standoff mud/water shield for it using something as simple as a plastic milk jug and a few zip ties. Just make sure there is an air gap around where the vents are. You don’t want to cover those vents.

YJ Conversion
Q I have a ’93 Jeep Wrangler and an ’89 Chevy truck with a newly rebuilt engine, transmission, and transfer case. Do you know how much work is involved and what it would cost to install the powertrain from the Chevy into my Jeep?

A If you have the time, tools, know-how, and already own the majority of the powertrain parts, it’s not unreasonable to think that you can do the swap for under $5,000. Understand that there is much more to the swap than simply dropping in the new powerplant. Items like motor mounts, exhaust, drivelines, power steering lines, radiator, wiring, and so on can add up quickly. In terms of work, engine swaps are generally very labor intensive, especially when you are doing it yourself without the aid of a “kit”. If you live in an emissions state this can be another large problem. If you plan to drive the Jeep on the highway you will need to check with your state laws to ensure it will be legal and pass all state mandated inspections.

Power Wagon Hubs
Q My uncle’s ’72 Dodge W200 plow truck has a broken lockout hub. It is split halfway around where the locking ring is set. He doesn’t want to spend a fortune for a new hub and used ones are nowhere to be found around here (near Twin Cities, Minnesota). I am a fairly competent welder, but I know next to nothing about lockout hubs and such. Is there a way to permanently lock the front hubs so he can plow his driveway this winter? That is all this truck is used for, so drivability isn’t an issue. Thanks for any help!

(Editor John Cappa responds)
A Unfortunately, there generally isn’t a way to weld a broken hub. They are typically made of dissimilar metals like aluminum and steel. The other bummer is that it is not a very common locking hub. However, Warn ( offers new hubs for that application under part number 9072...but they aren’t cheap.

Auto Computer
Q I fried my computer (ECM) on my Jeep Grand Cherokee and need a new one. I was told that I could get one out of a junkyard, so long as it’s the same year. Are there any other places that you would suggest looking? I would rather not go to the dealer.
Harrison King

A So long as the ECM (engine control module) is from the same make, model, powertrain configuration, and year Jeep, a junkyard ECM should work fine. That will probably be your cheapest route. Since most pick-and-pull yards offer a limited warranty, you should be able to get one that works. Keep in mind that your Jeep’s VIN (vehicle identification number) is stored onto the computer. Grabbing one from your local salvage yard will give you a different number.

A different VIN could be an issue depending on your state inspections. Another option worth considering is Auto Computer Exchange ( Auto Computer Exchange allows you to option your ECM for your specific application. The company will also program your vehicles VIN so it matches as well. A core return is required.

I am currently building a custom suspension for my Jeep Wrangler and just got my coilover shocks in. I was told that the shocks need to be charged with nitrogen, but they did not specify how much. I’ve read that the shocks must be fully extended to fill them. Is this true? I have 12-inch-travel Fox coilovers.
Bill Lawrence

A Coilovers are often shipped without a nitrogen charge. How much nitrogen you feed into the shocks will depend on the application and intended use. There is usually a minimal amount of nitrogen needed to prevent the fluid from cavitation. For the 12-inch-travel Bilstein coilovers on the front of my ’97 Jeep Wrangler TJ, I run 180 psi. This pressure setting works well with the valving and spring rate. I would contact Fox and discuss your intended use of the Jeep with one of the company’s shock techs. The great part about running coilovers is that you have the ability to finely tune the shock to fit your needs. As far the nitrogen charging process is concerned, yes, the shocks must be fully extended.

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