What was that?!

[XJ Dreamin']

stock '93 ODB I, 4.0L, AW4, 2WD

I was driving into work this morning, doing about 55 climbing about 5% grade when there where three short, distinct breaks in power. It felt as if someone had a line attached to the hitch and gave it three quick little tugs: just, bump - bump - bump. Then everything was fine. My immediate reaction was an expectation that I would pull over right there and start cursing, but it continued on with normal power smooth as could be.

I'm not sure if it was faults in ignition, or a slipping of the transmission, or the tourque converter unlocking intermittantly. Anyway, not much I can do while it's operating normally. I'll have to wait for whatever it is to actually fail. Any ideas in the mean time would be appreciated.

wish me luck.

[jeeperjohn]

Was there any chance of ice on the road?

[Fred85]

^lol, he's in texas............i doubt the ice

did your RPM's go up at all during these power "breaks"??

[luvme88xj]

^lol, he's in texas............i doubt the ice

did your RPM's go up at all during these power "breaks"??
three armadilo's

[RichP]

Uphill, 3 quick bumps ? Thats usually low fuel and the fuel pump pickup is starving...I call it my 'terrain monitoring fuel indicator' since my dash one lies most of the time..

[Ridr]

mine has done that twice . Always going uphill but usually just one quick break. I have even tried to make it do it but no dice. Last time I had over 3/4 of a tank of fuel. It is just like the engine was off and then running in an extemely short time period. If you ever figure it out PLEASE let me know. I just came back from a 500 mile trip and it didn't do it once...go figure

[jeepinandy]

Maybe a short in the fuel pump wiring? Maybe a sensor problem?

good luck.

[XJ Dreamin']

Was there any chance of ice on the road?

See this post (http://www.naxja.org/forum/showthread.php?p=701252#post701252) :)

[XJ Dreamin']

^lol, he's in texas............i doubt the ice

did your RPM's go up at all during these power "breaks"??

We had ice back in '94. Not today, though.

I can't say about the rpm. My heep doesn't have a tach. :gonnablow

[XJ Dreamin']

three armadilo's

Well, I know it wasn't three skunks :confused1

[XJ Dreamin']

Uphill, 3 quick bumps ? Thats usually low fuel and the fuel pump pickup is starving...I call it my 'terrain monitoring fuel indicator' since my dash one lies most of the time..

Filled it yesterday. It was probably over 3/4 full when the three jinks happened. Running up a slight grade at only medium speed, I was wondering if the TCU might be trying to decide whether to unlock the tourque converter. Especially if the 216,000 miles might be wearing down the AW4 a bit. Just wondering. But, this is my first EFI vehicle so I have no idea what air in the fuel line, or at least flucuations in fuel pressure would feel like.

[XJ Dreamin']

mine has done that twice . Always going uphill but usually just one quick break. I have even tried to make it do it but no dice. Last time I had over 3/4 of a tank of fuel. It is just like the engine was off and then running in an extemely short time period. If you ever figure it out PLEASE let me know. I just came back from a 500 mile trip and it didn't do it once...go figure

I'll be sure to drop you a line :)

It's good to know that I'm not the only one, and that it does not seem to be immediately fatal.

Thanks.

[XJ Dreamin']

Maybe a short in the fuel pump wiring? Maybe a sensor problem?

good luck.

My other thought is maybe a short in the coil wiring. I just spent over $200 getting the thing past inspection and that didn't even address the leaking tranny seal, the leaking wheel cylinder, the leaking valve cover gasket, the worn out shocks, my busted seat, and the incomplete stereo install.

Thanks for the luck, anyway. I'll make good use of it :thumbup:

[8Mud]

The next time it happens. Take a look at your engine service light and see if it's on or blinks. I'm pretty sure you can get an intermittant non stored code on the O2 sensor.
The engine light comes on intermittantly, when the O2 sensor is getting flacky. Usually happens at low vacuum, like going up a hill at moderate RPM's or moderately accelarating onto the interstate from an on ramp.
Check for stored codes. The key methode works pretty good for O2 problems.
A flaky O2 sensor will also often affect your top end. The motor craps out well before the red line, with the throttle mostly open at cruising speed.

[RichP]

Filled it yesterday. It was probably over 3/4 full when the three jinks happened. Running up a slight grade at only medium speed, I was wondering if the TCU might be trying to decide whether to unlock the tourque converter. Especially if the 216,000 miles might be wearing down the AW4 a bit. Just wondering. But, this is my first EFI vehicle so I have no idea what air in the fuel line, or at least flucuations in fuel pressure would feel like.

OK, I've had my 5 speed do it when I've been too lazy to downshift but when the gas is low it literally dies for 1-2 seconds, usually uphill and going round a corner.

[Wolf]

Uphill, 3 quick bumps ? Thats usually low fuel and the fuel pump pickup is starving...I call it my 'terrain monitoring fuel indicator' since my dash one lies most of the time..
or detonation. used to get it in my old Plymouth Scamp slant-6 all the time when I'd be going over hills.

[scca28]

I have had the "bump-bump-bump" happen on several occasions, under different circumstances. The first time was on a long curved stretch of road, going about 30 mph. The next time was a few weeks later, stopped at a traffic light. It felt like the driver behind me had his foot slip off the brake and tap my bumper 3 times. Only thing was,there was no car behind me. I have felt it just driving on a straight level road. It does not seem to matter if the gas tank is full or low.
I am thinking torque converter.....

'88 Cherokee 4.0 Auto

[XJ Dreamin']

The next time it happens. Take a look at your engine service light and see if it's on or blinks. I'm pretty sure you can get an intermittant non stored code on the O2 sensor.
The engine light comes on intermittantly, when the O2 sensor is getting flacky. Usually happens at low vacuum, like going up a hill at moderate RPM's or moderately accelarating onto the interstate from an on ramp.
Check for stored codes. The key methode works pretty good for O2 problems.
A flaky O2 sensor will also often affect your top end. The motor craps out well before the red line, with the throttle mostly open at cruising speed.

I haven't noticed a service light - even intermittantly. Then, for all I know the bulb could be out and it's been trying to flash at me all along. I'll try keying for codes. I haven't yet 'cause it just seems like too good an opportunity to sit there feeling like a dope as I waggle the key back and forth. I'll have to hunt up the waggle sequence and the flash de-code tables. Give me a few days to get some results.

[XJ Dreamin']

or detonation. used to get it in my old Plymouth Scamp slant-6 all the time when I'd be going over hills.

Was that a manual tranny? I remember a lot of valve clatter from the slant-6 but not detonation - at least not with an automatic. I can get some detonation chatter out of the 4.0L if I let the oil get too low, but that feels different than this bump-bump-bump.

[XJ Dreamin']

I have had the "bump-bump-bump" happen on several occasions, under different circumstances. The first time was on a long curved stretch of road, going about 30 mph. The next time was a few weeks later, stopped at a traffic light. It felt like the driver behind me had his foot slip off the brake and tap my bumper 3 times. Only thing was,there was no car behind me. I have felt it just driving on a straight level road. It does not seem to matter if the gas tank is full or low.
I am thinking torque converter.....

'88 Cherokee 4.0 Auto

Hah. That's two votes for torque converter (or confused TCU).

[XJ Dreamin']

OK, I've had my 5 speed do it when I've been too lazy to downshift

Yeah, I've felt that often enough with a stick. This is very close to that in feel. Of course, I've only felt this bump-bump-bump once, so far. What's got tranny in my mind is that it seemed to happen right at the 'down shift now?' decision point as the Jeep loaded up with light throttle on the up-hill. Real close in feel to the 'time to down shift' bump.

but when the gas is low it literally dies for 1-2 seconds, usually uphill and going round a corner.

I've done that with an old Plymouth I had at college. The gas tank was so big and flat, trying to stretch the last penny out of the tank it would gasp like that if I tromped it too hard: cut out then catch again as the fuel settled back down on the pick up. This bump-bump-bump was not that.

[8Mud]

Could be the converter is cofused or even te TPS or TV keeping it in the wrong gear too long (both my 88 and my 96 down shift fairly early when the throttle is applied). I've seen almost exactly the same thing happen on various vehicles for various reasons.
Most times it was running lean. because of a filter, a fuel pump or the O2 sensor. Or it was timing, because of a faulty TPS or a worn distributor and/or timing chain.
It's probably running lean, but it's also possible the timing isn`t retarding enough.
Running lean usually shows up during low vacuum, with the throttle applied mostly open and the RPM's low to mid range. But also shows up again near red line. A tip off is bone white plugs after short to moderate trips, when the plugs are commonly sooted up a bit.
Bucking can also be from timing, either something mechanical or a sensor input. Even poor fuel (very low octane).
Ignition is also a possibility, the motor misses a few beats and then the left over fuel ignites on the next round. Ignition often shows up as a crappy idle and then again at higher RPM's when the spark starts to break down. You can feel the motor rythm breaking down, not like with fuel, when it just kind of dies.
My Renix was doing almost the exact same thing, it took me awhile to figure it out. But your OBD I with the stored (hopefully) codes may be a big help.

[RTicUL8]

three armadilo's

http://images.art.com/images/products/regular/10101000/10101975.jpg ??? :D

[Big Kev]

I had an 88 with a problem like that. It ended up being one of the ignition (bad speller) wires had shorted out and was not firing. Turned out to be a pretty easy fix. I would check that first.

[RTicUL8]

And now, for the official majic 8-ball diagnosis:

shakey-shakey-shakey.....BING!:confused1


The firewall ground wire is coming loose. :thumbup:

You can thank me later. - I accept paypal :D

[Ridr]

but does your magic ball say why it only comes loose going uphill ? :)

[RTicUL8]

but does your magic ball say why it only comes loose going uphill ? :)


shakey-shakey-shakey.....BING!

Uh....time for a nap.:speepin: :D

[JrTxJ]

sounds like a misfire to me...i've experienced that with other cars and it turned out to be the ignition coil.

[XJ Dreamin']

And now, for the official majic 8-ball diagnosis:

shakey-shakey-shakey.....BING!:confused1


The firewall ground wire is coming loose. :thumbup:

You can thank me later. - I accept paypal :D

I didn't see "Bottle of Shiner Bock" as a payment option at Paypal. I'm afraid I don't deal in cash - just barter. You can come by and pick it up any time :kissyou:

I had an old Plymouth with a broken right motor mount. When the engine reared up it stretched the ground strap across the heater hoses until the strap broke. When the engine fell back down the loose end of the ground strap, draped across the rubber heater hoses, fell down onto the engine block. Viola! Ignition is back. Up goes the motor (and the heater hoses) lifting the strap off the block. Back down comes the motor, dropping the strap back onto the block. It did that four times before I found the sense to take my foot out of the throttle. At idle it just sat there and purred. Touch the throttle and it's back to the PBR finals - YeeHaw!

An intermittant fault somewhere is still in the running.

[jeeperjohn]

I was in Texas last week and almost bought a guardrail because of ice on the road.

[crazyray]

the cps can do this......mine would cause it just like you cut switch then right back on....usually when hitting a bump......;unplugged and cleaned contacts and packed with dielectric no problems last six months

[Ridr]

Couldn't hurt to check that out. I replaced mine last year ,it went out in Dairy Queens drive thru (talk about a crappy place to die LOL) but I really didn't clean things up too much