258 engine hesitation--Help wanted!

[Petej8]

I've been chasing a nasty hesitation problem with my '82 Cherokee's I-6. It will idle fine, and 80% of the time runs great, but it will drop off just above idle and will not accelerate under normal loads, then it surges and runs normal again, and sometimes it hesitates at 40-55 mph. First I thought it was the Carter BBD finally giving up the ghost, but after upgrading to the Weber the problem came back. Next I thought it was vacuum advance going out on the distributor, so I swapped in a new one, and it still does it. I advanced the timing a little thinking that maybe that would help, but so far nothing helps.
I did the TFI conversion last year with no problems. Could it be the ignition control box is dying slowly?
Any help would be great. Thanks

[brielly]

Does your engine have the computer? If its not working properly it can really screw with your timing. You might start by replacing th ignition module since its cheap and easy to do and see what happens from there.

[Mondo Bat.]

Pete, I can almost guaranty you that the problem is your ICm, Those are exactly the kind of problems mine was having before I replaced mine, they are around 60-90 Bucks at NAPA or Autozone. Its mounted on the Drivers side wheel well in the engine compartment. The silver thingy that mesures about 5X5. Easy to replace.

[Petej8]

Mondo,
Thanks for the heads up on the ICM. The last owner left the key on too long and the black sealant on the module started to run down the fender. I'll have to see if the local NAPA carries the right part.

Breilly,
Checked out your site, and it looks like we have almost carbon copy rigs. I picked mine up for $150 with a spun bearing and hashed interior. I rebuilt the bottom end of the motor and put in new carpet and a set of seats. You just can't beat old Jeeps.

[The Anti-Chrysler]

Don't replace your ignition module in this case, before you check that ICM. You can always try to find it at a junkyard as well, I'm not sure what those would cost new.

[sloop]

ignition box should be $20-30 at advance auto parts or autozone

[mtn goat]

Before you do anything, you may want to consider bypassing the ECM(computer) all together. The so called "Nutter bypass" does just this...allows you to throw the computer and the stepper moter into a very deep trash can.

Nutter Bypass (http://home.sprynet.com/~dale02/ignmods.htm)

I am running without the computer right now, seems to be doing fine.

[Petej8]

Isn't the MCU in the Bypass the one on the driver's fender on my Cherokee? I know it was behind the dash on my CJ, but everything runs through the box in the engine compartment on the FSJ.

[Tahnka]

I just started seeing the same thing yesterday on mine. I'm running an 83 Wag with the 360 V8; does anyone know if that also has an ECM that I could I could go "Nutter" on?

Could one purchase one of these after market ECM's that could actually improve things more than bypassing the ECM does?

Would this "do I have an ECM" question be answered by a service manual for my Jeep? I haven't yet purchased a manual and am starting to think it should be my next priority purchase.

[ November 07, 2003, 02:37 PM: Message edited by: Tahnka ]

[brielly]

I just installed the msd 6a ignition which bypasses the ignition module and the computer and the difference is incredible! My idle used to be rough and I had lots of hesitation when accelerating. Now it idles real smooth and revs smoothly during acceleration as well. Best $150 Ive ever spent. The weber carb and blaster coil both were noticeable improvements but the msd ignition has made the biggest difference by far. I would highly reccomend it over the stock ignition.

[mtn goat]

Yep, on the big jeeps the computer(ECM) was on the drivers side fender. its a about 5x5x1 inches and has a whole mess of wires going into the middle of it by a bolt on connection. Little jeeps had it on the inside of the cab.

Tahnka...the 360 engine is not computer controlled and hence you do not have an ECM. The only FSJ's that had computer controlled engine (timing and fuel mixture) was '82 and later models with a 258 engine and carter bbd carb.

[Petej8]

Mtn. Goat, Thanks for all your help. I'll be bypassing the computer tomorrow.

This forum is by far the best on the web for 'real' solutions for Jeep issues.

Keep the shiny side up, and at least one wheel in the dirt.

[Petej8]

Okay, maybe I'm losing it, but when I chased the orange and violet wires from the ignition box to the distributor, they didn't go thru the computer. According to the schematic for the Nutter bypass, my '82 already bypasses the computer. The only wire that went from the ignition to the computer is the third connector with a black/blue and a white wire that goes to a green wire that runs to the computer. I disconnected that, and it didn't seem to make a difference. The wiring diagrams in my Haynes and Chiltons stink, and don't give a clear read on the engine wiring.

So the only other option I can think of is to replace the ignition module and hope the problem goes away after that. I pulled the whole wiring harness out of the loom, and traced the wires to origin, and none of the ignition wiring goes to the computer. I'm not complaining, if it would run without the computer at all, I'd pull the whole thing, but I get the feeling that won't work. I already gutted the vacuum mess, because its an Iowa tagged rig, and it runs cleaner now than with the mile of vacuum hose.

I'm running out of possibilities, and I don't think the problem is mechanical. It just seems like spark chasing.

Does anyone know if the '82 ran different wiring depending on the model? That is the only thing I can think of, because the wiring is factory, not splice-o-matic.

[Mondo Bat.]

Replace the Ignition Box

I'm telling you this is a known issue with post 80 chero 6s... I promise, promise, promise, that the problem will go away... don't do a ME and spend 200 bucks before you try the simplest course of action.

If its not that. Then its your carb, I have a year old one I'll sell you for 10 bucks..

But it IS that.

'specially if its partly melted.

[Petej8]

Mondo, you were right. I changed the ignition box and it runs much better. There is still a little drag off idle, but nothing like before. I may just need to adjust the Weber a little. I haven't changed any of the factory mixture settings yet.

Thanks a ton for getting it thru my thick skull that it could be that simple. Keep It Simple Stupid is the best way to trouble shoot.

[mtn goat]

Mondo, I'll give you ten bucks for your old carb...I have to keep the bbd to be legal