1. home
  2. how to
  3. tech qa
  4. Your Jeep Tech Questions Answered

Your Jeep Tech Questions Answered

Your Jeep

Barn-Find TJ
I have a 2006 TJ with 865 miles on it. Yes, only 865 total miles. It sat in someone's garage for 10 years after being built to wheel with front and rear Dana 60s, 39-inch Krawlers, Atlas transfer case, lift, armor, and all the goodies you can think of, right off the showroom floor in 2006. I bought it last year. It has the stock engine and manual tranny. Randomly, it runs rough. It feels like an old carbureted engine; it coughs and sputters and needs throttle to stay running. I've had two shops and a Jeep dealer look at it. I've replaced every sensor in the fuel system. Still does it, all the time, but it throws NO engine codes that are at all helpful. The dealer could not find any vacuum leaks. Any ideas?
Mark M.
Via email

Wow, that's one heck of a barn find! There must have been some odd circumstances around why that built TJ just sat in a garage, but we've heard plenty of strange stories over the years.

Our biggest question would be how was the Jeep stored for a decade? Was the fuel system drained or did it sit with a full tank of fuel that slowly turned to varnish? It's highly doubtful someone would build something like your Jeep without intending to use it, so we'd be willing to bet the Jeep wasn't prepped for long-term storage. Bad fuel wreaks havoc on all kinds of things, and the more modern the engine, the worse it can be. Assuming you've drained whatever bad fuel is in the system already, we would suspect the fuel pump or the injectors. Surely one of the shops or the dealership checked the fuel pressure, but it's worth asking. Low fuel pressure can cause the exact symptoms you describe and won't necessarily cause a check engine light. If the pressure is within spec, then the next thing we'd suspect is the injectors. Even if someone had the foresight to drain the fuel system for long-term storage and deliberately run the Jeep out of fuel, there's really no way to remove all traces of fuel in the injectors. It doesn't take much varnish or debris to partially or entirely clog an injector, and the only time it will reliably throw a code is if the injector mechanism itself isn't firing the way it's supposed to. A poor spray pattern on one or more injectors can cause a rough idle and potentially codes that are seemingly unrelated (such as O2 sensor banks running lean or rich).

While it's difficult to imagine that a dealer wouldn't have found a bad injector, if they were unaware of the long-term storage of the Jeep or maybe just had a casual tech, then an injector problem could have gone undetected. A good shop should have the ability to run a power balance test, which indicates the health of individual cylinders as the engine is running and could help diagnose which cylinders might have bad injectors. There are some pretty good professional fuel system cleaning systems out there that might be able to flush and clean the system, but with your Jeep sitting as long as it has, you may want to consider just swapping them out, or sending them out to be professionally rebuilt.

There really aren't that many vacuum hoses on your TJ, so a good visual inspection should be able to eliminate any potential leaks. Beyond these ideas, it may be time to consider having an in-depth diagnostic done on the Jeep. Dealer and good aftermarket scanners have the ability to monitor all sorts of engine vitals in real time and should be able to track down the problem. You might think it's expensive, but there's a strong chance it would actually be cheaper in the long run than just guessing and continuing to throw parts at it. Plus, with such a low-mileage find, it's worth it to get the Jeep running properly so you can enjoy it.

J-Truck Frame Repair
I have a 1982 J-10. I live in Pennsylvania and of course the frame has gone bad. I can't bring myself to send this Jeep to the junkyard as it runs and drives fine but is unsafe. These Jeeps are rare around here and I want to rescue it. I would like to fix the frame myself. Can you recommend a name brand welder for a beginner that runs on household current (not 220) that's easy to use and can take on this job? I plan on using 1/8-inch plate steel.
GR Grace
Via email

It's always good to see people trying to save old iron, but battles with the tin worm can be rough. Usually when we see badly rusted J-truck frames, the body is in about the same shape, so before you dive into the project you should make sure that the rest of the Jeep is worth saving. After all, spending a bunch of time and effort fixing a frame is kind of pointless if the cab and bed are rotten as well.

You didn't indicate which parts of the frame are bad, and you should know that certain areas of a frame can be difficult to fix. We don't want to discourage you, but generally speaking, frame repair is not the easiest project to tackle for a beginner. You're often welding in places that are difficult to reach, usually on your back while getting peppered with red-hot BBs. We'd recommend taking a couple of classes so you can get the fundamentals down, and then maybe tackle a few smaller projects to get some real-world practice. But then again, we all have to start somewhere, and a Jeep project is as good as any.

We've owned a Miller 130XP (millerwelds.com) for about 15 years and have always been impressed with its performance. It's a 110V welder and can handle up to 3/16-inch steel in a single pass. The model isn't available new anymore, but they were produced for a long time and can be picked up used at a fairly affordable price. If you're looking for a new welder, the Millermatic 141 is the modern equivalent of a 130XP, and the company also offers the Millermatic 211. Both of these modern welders feature the company's Auto-Set technology, which is awesome for beginners. Some experienced welders gripe about the lack of controls, but we've found the Auto-Set technology to be pretty amazing. You tell the welder what material thickness you're using and it does the rest, allowing you to focus on actually applying the welds to your work. The larger machine runs on both 110V or 220V power, which is a really nice option for stepping up the welder's capacity as you get more experienced and tackle other projects. The 211 can weld up to 3/8-inch-thick material in a single pass when running on 220V.

Another brand we've had excellent luck with is Hobart (hobartwelders.com). Marketed more toward farms and ranching than automotive repair and fabrication, Hobart welders are produced at the same factory as Miller welders and are very similar in many ways. The Hobart Handler 125 and Handler 140 are both good choices that run on 110. Lincoln (lincolnelectric.com) and Esab (esabna.com) are also reputable manufacturers of welders.

Though all of our suggestions represent an investment, we'd recommend these brands over the many cheap imported welders that you see online. Though you might be able to pick up a 110 welder for a lot less than a Hobart or a Miller, with these brands you know service parts and consumables will always be readily available. This is not the case with most of the cheap imported stuff. As with many things, you get what you pay for, and a quality welder can serve you for decades with proper care and use.

Return to Center
I bought a 1953 CJ-3B about 3 years ago that needed a complete rebuild. It was in very sad shape, but it did have a Dauntless V-6 in it mated to a TH350 auto trans. I had a 1970 Jeepster Commando years ago and I decided to rebuild this one with good stuff just to be different. After three years of rebuilding everything from the frame up, it's about 90 percent done. It seems to handle okay up to 60 mph at 3500 rpm with 5:38 gears and 33-inch tires. I made some caster shims and bolted it to the springs with new center bolts, so it makes full contact with the axle spring pads. It has 4 degrees of caster now but the steering wheel will not return to center after a turn. The front axle has been rebuilt with all new bearings including the kingpin bearings set to about 9 lbs. of pull. All the tie rods and the drag link ends are tight. It also has Saginaw power steering.

Here is the kicker: the steering wheel will return to center with authority if I lock the front hubs in. The fact that the front axle is turning makes the steering act as it should. I've been messing with cars and Jeeps since 1966 and have never experienced what this Jeep is doing. It has 1/16-inch toe-in and it was set the right way. I tried 1/8-inch toe-in with no effect. The springs were rebuilt and I welded all new shackles also. Do you have any ideas?
Bob K.
Via email

Four degrees of caster is right about where you want to be, so our first thought is where are you measuring caster? It should be measured on a flat surface near the kingpin caps using an angle finder. We mention this because some people mistakenly think that caster is measured at the pinion, which is totally different and not a reliable indicator of true caster angle.

You didn't mention how much lift you are running, but since you mention degree shims we're assuming you have some sort of lift. While 4 degrees is acceptable, taller Jeeps with bigger tires often like a little more caster than the factory specifications. Since you mentioned that you made some degree shims, you could try making another set that would put the front end at 6 degrees and see if that improves things. If you're on the taller end of the spectrum you may find that there's going to be a delicate balancing act between caster and driveline angle; you may need to make some compromises in order to make one or the other acceptable.

Since you mentioned everything is new or rebuilt and you didn't mention any other undesirable handling characteristics, we wonder if maybe there's something else causing the steering to not return to center. It sounds like the kingpins are set up properly, but what about the steering box? An excessive amount of drag within the steering box could cause the symptoms you describe, or even the steering shaft joints if their angle is really excessive. With the drag link disconnected from the pitman arm, the steering box should feel smooth and very easy to rotate all the way through its travel cycle. If there's any resistance, then there is something wrong with the steering box.

As for the Jeep returning to center in four-wheel drive, that's normal. The engine torque going to the front tires in 4-Hi or 4-Lo tends to make everything rotate at the same speed, which can only happen when the vehicle is going straight. This is why you feel a slight tug in the steering wheel when turning in four-wheel drive on a hard surface.

Slow-Speed Overheating
I am struggling with slow-speed overheating issues on my fullsize Jeep that is equipped with a GM Performance Parts LS crate engine. On the highway the engine runs in a "normal" heat range for an LS engine (205-215 degrees F), which makes me believe that radiator is big enough to adequately cool the engine. However, as soon as I slow down for in-town traffic or on a trail, the temperatures climb, leading me to believe the 16-inch electric fan is not keeping up. How do I determine if the fan is working as it should be, or if it is at some lesser output?
Steve M.
Via email

Usually when we hear about overheating issues, it's when the engine is working hard, such as going up a steep grade or pulling a heavy load. These symptoms are normally indicative of either a problem with the cooling system (such as a clogged radiator, a failing water pump, or a bad fan clutch) or an inadequately sized radiator or fan. Since you aren't having any issues when the engine is working hard at speed, your radiator is probably big enough to handle the heat output of the engine and all of the components are working like they should. Therefore, your slow-speed overheating problem is most likely related to airflow.

The two biggest factors in electric fan performance are how it's controlled and getting proper voltage. An electric fan needs a lot of power to run at maximum performance, so be sure that the power leads for the fan have a direct line to the battery and are adequately sized—12-gauge wire is adequate, but really 10-gauge is best if it's a really high-cfm fan or a long run to the battery. Check voltage at the battery and at the fan with the fan running. The voltage should match; if it doesn't, then you have a wiring problem. You could also compare the fan's speed with how it's normally wired and with some heavy-gauge jumper wires going to the battery. A fan that noticeably speeds up with jumper wires is another indicator of a wiring problem.

We're assuming you have the fan on a relay, but what is turning the relay on and off? Many of the GM Performance Parts crate engines have the ability to control an electric fan, and that's what we would recommend doing if your engine's PCM has that capability. We've had zero luck using any aftermarket fan controller, and we have yet to hear of one lasting more than a year among our friends. If you have the computer controlling the fan, at what temperature is the fan turning on and off? Sometimes the PCMs are programmed to control an auxiliary fan that supplements an engine-driven fan, so the thresholds for fan-on and fan-off temperatures are higher than if it was controlling the main engine fan. The paperwork that came with the engine should tell you what the factory settings are, but you might double-check the settings if your engine has been tuned (the tuning shop should be able to tell you). A tuner can also adjust the settings if needed and even recommend what works best for your part of the country.

If all that checks out, then we'd look at increasing airflow through the radiator at slow speeds. A single 16-inch fan might be adequate to cool a stock V-8, but most of the GM Performance Parts offerings are well beyond stock power levels. There is quite a bit of real estate on a fullsize Jeep radiator, so you may find that you'll be able to squeeze a pair of 12-inch fans that offer more cfm than the single 16-inch one. If there's room, you could also look at installing a pusher fan on the front side of the radiator. Things like an oil cooler can also reduce stress on the cooling system. Last but not least, keep in mind that a mechanical clutch fan is going to move a lot more air than a single electric fan, and it might be worth considering if you're looking at buying hundreds of dollars of electric fans to solve your problem.

Barn-Find CJ
We have a barn-find 1965 CJ-5. It was parked in a garage in Phoenix, Arizona, in 1985 with 40,000 miles on the odometer. The Jeep being rust free and almost original we would like to replace the aftermarket bucket seats with original seats. Originally Jeep equipped these with a combination frame, coil spring with a cloth covering. After contacting several Jeep restoration-parts companies it appears that there is nothing available. We would hate so start modifying the steering or replacing the OEM steering wheel with a custom wheel just to keep incorrect seats. Any ideas?
Norm S.
Via email

Sounds like you found yourself a very nice Jeep! While we understand you wanting to keep the Jeep original, be aware that there's a reason that someone put bucket seats in the Jeep at some point. The factory ones, while adequate, are far from luxurious, and some would even go so far as to say uncomfortable. Like you, we don't care much for Jeeps with seats donated from a random car, but it's worth mentioning that your desire to return to stock might be a bit disappointing.

You are correct that the original seats in your Jeep are a tubular frame with springs and cloth, or even just foam and cloth. Finding a set of original seat frames might be a bit of a challenge, but a little digging should net you a set of frames that are serviceable. We'd start by contacting AMC 4x4 (amc4x4.com), which is located in nearby Glendale. You can also try The Jeep Farm (thejeepfarm.com), which is a local restoration place that might have a set of takeouts from one of their projects. Willys Works (willysworks.com) is a Jeep repair and salvage yard in Tucson that specializes in older Jeeps. We'd be a little surprised if one of these three places didn't have a set of seat frames and brackets for you, but if they don't, they can probably suggest some additional places to try.