4.0L Power Loss

[mopar_man]

I've been noticing lately that when I get into the higher RPMs (3500-4000) when I use 3rd gear to pass on the highway (or any gear at that RPM range for that matter), when it shifts into the next gear, it loses power for about a second then it's back again. What might the problem be? My only guesses are O2 sensor or fuel filter.

[ELK]

My guess would be the O2 sensor. I had a similar problem, but my power loss was not so consistent.

[satan]

Think of dirty injectors or a slow filter... but you may actually be getting some spark-scatter (cap/rotor condition?)

That's also a good place for the ignition to advance, and you could be getting detonation (or something that your engine thinks is detonation) which is causing the knock sensor to signal the ECU (and retard your timing) ...

if the power returns, and your loss is only in transistion, it'd be safe to not look at the Exhaust system for restrictions (unless it's loose or rattles)...

The o2 sensor cold be an issue, forcing the ECU to run from stored maps, but... I'd lean in different directions unless the sensor is covered (in mud or grease) or has more than 50K miles (80km)...

[mopar_man]

I just bought the Jeep in May so I don't know how good the O2 sensor or the fuel filter are. I DO know the whole exhaust is new from just before the cat, back. I just changed the cap and rotor after I bought it using the cap and rotor with the bronze tips (not the steel or whatever they're usually made out of). Plugs were also changed at the same time. The thing that's keeping me from experimenting with the O2 sensor is the $75 price tag. I'd like to know if thats what I need for sure before getting it.

[cherokeefever]

Things must be WAY more expensive up there than down here, friend. I just replaced the O2 sensor in my 88 Chief 4.0 and it only cost me around $35 for the part and 15 minutes of my time to get it put in. But she runs much more gooder now :P

If you have a manual for your Jeep, look in it for the chapter which covers sensors and computer codes and the like. In the Haynes manual, I believe it is chapter 6. There might be a test procedure in it to determine if you have a bad O2 sensor or not.

Also, have you considered a dirty air filter as the culprit as well?

HTH and GL fixing the problem...

Bob

[wizbang]

How big is the sensor? If it is mailable, maybe one of us Southerners could send you one.:bigsmile:

[TOOLman]

The sensor is a little larger than a spark plug. You could also e-mail "Kolak" (kolak@aol.com). He sold me a Bosch O2 sensor for a lot less than $75. He also said that the O2 sensor should be replaced every other year or so.

For info about how to check the computer error codes and what they mean, you could take a look at this page on my web site (http://hem.passagen.se/suntool/en/jeep/errcodes.html), if you don't have the Haynes manual.

[mopar_man]

I'll have to check the manual for those codes. I just replaced the air filter with the plugs and cap/rotor.

$75 for the sensor changes to $48 US so by the time one of you buys it and ships it to me, it'd be pretty close to even. Thanks for the offer though :)

[satan]

mopar_man -

don't hassle with looking for codes - the ECU in that '87 won't have any (the RenixII system doesn't store/display codes)

During the time that you're "losing power", is your tachometer stable?

Have you checked the condition and level of your automatic Transmission Fluid?

You mention cap/rotoe and plugs -- did you change the wires as well?

Any clues/thoughts about when this started happening?

How long (months weeks, kilometers, tanks of fuel, etc) has this condition persisted?

Is your 4.0 currently using any oil?

[mopar_man]

Answering satan from the top:

Yeah the tach is stable. I've noticed now that it seems to be anything above 3000 rpm, not just 3500. Maybe the engine is getting to much gas after getting out of the previous gear?

Tranny fluid is good. Checked just last week.

I didn't change the plug wires. They LOOKED in good shape.

I think it probably started about a month ago.

Uses very little oil (add 0.5L between changes).