Cherokeesun

Hi all, first post here, here goes: my mom has had an ongoing problem with her '91 jeep cherokee (completely stock, 4.0 liter inline six, approx. 150,000 miles) that is really frustrating. For the better part of a year the jeep has been "bucking" (for lack of a better word), usually at about 45 MPH or better. The motor cuts out (loses power) for a fraction of a second then regains power, cuts out again, and so on, really rapidly so that the vehicle actually lurches a little bit in a frantic herky-jerky motion. It runs perfect at idle. I believe she's taken it to several different mechanics and has replaced the fuel pump, fuel filter, oxygen sensor, replaced the rotor, cap, plugs and wires, and probably a few more things that I can't remember right now. Finally, she took it to a reputable shop that hooked it up to a diagnostic computer and was told that the ecu needed replacing and that the repair estimate was over $700, $400 for the ecu, and over $300 labor. She really can't afford this, and at this point we feel the vehicle is not worth putting that kind of money into it. The Jeep has been serviced regularly and my brother, who is a pretty good amateur mechanic, and I both feel that other than the mystery "bucking" problem the vehicle is in pretty good mechanical shape and is worth fixing, but were both stumped. We all are pretty financially strapped and can't afford to buy Mom another vehicle. I don't understand how the shop can charge over $300 labor to install an ecu. That's over 3 hours labor. Is the ecu that hard to get at, or is there another valid reason they'd charge so much for labor, such as having to program the new ecu? I just price checked a remanufactured ecu from an online company that sells them for $229 and includes programming, free phone tech support, and a one year warranty. They claim you can plug it right in and drive away. How hard is the ecu to replace? Where is it located? What about buying a used one from Pik'n'Pull? Any and all advice is greatly appreciated.

BuckB91XJ

First of all that mechanic is a crook and needs somebody to throat punch him. The ECU used in XJs is a plug and play deal. If you can find an XJ in the local scrap yard that is a 91-95 (they are all the same in that era). With the same motor and tranny combo as Mom's XJ, snag it and throw it her Jeep. All there is to swapping the ECU is a couple of connectors and mounting bolts. You could probably do this for $50 or less (if the local juinkyard dude is honest) and about a hour of your time.

Cherokeesun

Thanks Brian-I thought there was something fishy about that quote. I guess as long as it's the same motor and tranny I don't have to worry about reprogramming the ecu eh? That would be be flippin' awesome. These guys here seem to indicate that you need to reprogram the ecu specifically to the vin and the mileage of the vehicle:http://www.autocomputerexchange.com/Product/222

If I could save a few bills by getting a salvaged unit that would be great.
Thanks again for the advice!

johnnyrocket5150

Hello,

My first post here, but have been searching the forums for a while to look up good advice from all the jeepers here. I have a 1991 XJ I-6 manual and the check engine light blinked DTC 41 at me. Something regarding the charging system. Looks like I'll be replacing my ECU soon as I'm assuming you did? My only concern with junkyard parts is that they're just as old as the one in your current vehicle and might have that many miles left on them before you go through the same grief again! A side note : I agree that the mechanic needs to be severely throat punched!!!! Did you ask him what is involved in replacing the ECU? Funny how these crooks don't give me that kind of crap when I talk like I know a thing or two about mechanical issues (or at least give em enough BS lol). I'll end up getting a refurb or new unit for 2-300 $$ and forget about it. Tough to spend when the vehicle is worth only 2,000 !!! But with a new engine and tranny, why not right?? Just wanted to chime in and add my $0.02. Oh and as I'm sure you already found out, I believe the ECU is located near the drivers side, front of the engine bay, next to the Air Cleaner box. Hope everything worked out for ya ! And stay away from that PUnk mechanic!

Cheers

John from Sacramento, CA

joe bob

I got an ecu for a 91 in my garage you can have if you need it but I dont know where your at, oh yea 4.0 with auto trans.

Cherokeesun

Hey, thanks for the responses fellas. I was all set to buy a used ecu for $50 from a guy in Tahoe (I'm from Reno, about an hours drive from the lake, and my mom lives in Carson City, NV, about a 40 minute drive from me) but he flaked out on me and never returned any of my calls. Go figure. So I never got around to replacing the ecu, and amazingly enough, my mom's still driving around her Cherokee (problem comes and goes). I did locate the ecu, right where you said it is johnny rocket, pretty obvious when you know what to look for. Outrageous that that jacka$$ mechanic wanted to charge $300 labor for at most 15 minute job.

Thanks for the offer Joe Bob, but I don't know if you want to go thru the effort of shipping it for me, and the shipping costs might make it more expensive than I'd like to pay. I should probably try to find another one locally, but been real busy with my own mechanical projects lately. How much were you looking to sell it for anyway?

joe bob

Its not for sale but like I said if you need it its yours.

Cherokeesun

Wow, that's really cool of you to do that joe bob. I definitely could use it. If you're willing to ship it to Reno, I'd gladly pay the shipping fees, and even toss in a few bucks for your time. UPS allows you to bill the receiver. Let me know if you can do this and we can work out the details thru the PM.

Thanks jb.

joe bob

Its no problem I put a 360 in mine so its totaly useless to me and ive had it on craigslist for a wile now and no one wants it. Junkyard wont give me anything for it and I would hate to just throw it out. Just pm me your adress and as long as it dosnt cost me anything I can hit the ups store on monday and send it your way.

jarod93xj

I had the same problem....mines wires were all freyed,corroded
and all circuits didn't work for some reason
I pulled one from junkyard for about 10$

jarod93xj

I thought it was my ecu too.....did a lil investigating
and found my fusebox to be the culprit

jrziii05

How would you go about reprogramming your ecu? My friends ecu went bad and couldn't find the correct one to replace it and tried an ecu for an automatic instead of manual transmission. He told me it ran poorly and gave him really bad mileage. He was getting around 20 mpg before and I don't know what bad is to him. Can he reprogram it or should he keep on looking for the the right ecu?

cpnwrench

Guys.....especially Cherokeesun.....

the ECU is in the engine compartment driver side near the front with al the wires (big bundle going to it).

However.....and I have the same year so please listen.....

the black fuse/relay box in the engine compartment on the passenger side in front of the coolant reservoir has a similar wiring harness feeding it from underneath. This may sound mundane and obtuse, however, the symptoms you described led me to remove this box (yes you can, without removing any wires) and VISUALLY checking for CORROSION on the wire connectors underneath where the relays and large fuses plug in on top. I found the wire connector which goes to the "AUTO SHUT DOWN" relay in that fuse/relay box was corroded all to crap. once I removed that wire connector and several others and cleaned them. I had no problems since.

It is worth looking into.

apologies and best of luck.

cpnwrench

BuckB91XJ

Cherokeesun, I wouldn't worry about getting a bad ECU from a jinkyard. What I have found with them is they are usually either good or crap...and it is usually pretty easy to tell by looking at the Jeep and the outside of the ECU, if it has been abused. I travel to Fallon, Nv. pretty regularly for my work and I bring my Jeep down every chance I get. Is mom's Jeep pretty much a mall crawler or do you like to hit some of the local trails periodically? The infamous Rubicon trail is on my "Bucket List" of places to wheel. Last time I was there I drove my Revtal car over to Tahoe and found the trailhead. Now that i know where it is I can't wait til the next time I can bring my Jeep down there. Hey, I just thought of something else to possibly get your Jeep foxed on the cheap. Get ahold of a guy on the forum who calls himself RenoXJ. He works as a counter guy at the Summit Racing store there in Reno. He might possibly be able to hook you up.

Cherokeesun

Wow, this thread refuses to die......thanks for the advice guys, but I first posted about this issue close to 2 1/2 years ago; mom has long since moved on and bought a new car (split the cost with my sister).

I still think it was probably the ECU, and if memory serves me right, the wiring and connectors on both the engine fusebox and ECU were clean. After serving duty for a couple years as my mom's and my older sister's DD hauling around 2 messy young boys, the interior and paint was pretty roached, had a couple oil leaks, but engine and drivetrain were still basically sound (I think). Body was mostly straight and rust free though IIRC. I think she ended up selling it for $400 or $500 to a guy on craigslist who I imagine must have been pretty thrilled with the deal he got.

Last April I became the proud owner of the white '89 Limited pictured in my avatar...203,000 miles, and still looks and runs great...love these great old machines.