2.5L running VERY rough

Just brought an 86 with 2.5L home. It takes forever for it to start, gotta hold it full throttle to even fire, once running it cuts and pops back through the throttle body, after it warms up it clears out a little, and will idle but it has absolutely no power and if you put it ingear without holding it to the floor it dies. I pulled the plugs and they appeared burnt, replaced them and it helped a little but not much at all.

I'm pretty new to cherokee's and totaly new to 2.5L's. If it matters it has an auto with command trac 4x4.

this old girl probably has a cluster of problems, and picking out a main cause is not easy, based on descriptions alone.

But if she's backfiring, has no power, and hard starts, one plausible single cause/effect failure is an obstructed exhaust, which is usually due to a melted catalytic converter. Look for weak outflow from the tailpipe.

Another possibility is a slipped timing chain.

Timing chain doesn't go too often on these, but a weak fuel pump will give you these issues. Clogged fuel filter or bad gas too! (add some Lucas injector cleaner with octane boost) Maybe it has some diesel in it? Dist cap condition?
There is so many other issues, but these are where I start. The trans could have a bad converter issue too if it's a lockup. (mine would jam and stall the motor once I got off idle)

PS: Are you sure it's Renix TBI and not a carb? '86 was a mixed year. If carb, then the feedback system may be screwed up (do the nutter bypass!)

Its the TBI. But there is no air breather box present, I know in my 94 Mazda it owuldnt run with out it hooked up properly, could this be an issue with the 2.5L?

Today I started it u and held it at around 4500 rpm, till it cleared out, after that it would rev good if not in gear, but still idled ruff, also never popped back through the tb

If you put it in gear at an idle it dies, if you get the engine about 2500 rpm and power slam it, it'll dog/cut out but if I feather the gas it'll stay running and ocne above 2500rpm it'll run smooth again. Seems like its a low rpm issue.


I've traced all the vaccum lines and the only ones missing are running from the breather box according to the digram on the firewall. There is aslo a two prong plug laying by where the box goes, is there something electrical its supposed to control in the box?

Also, the tail pipe broke right before the flange on the downpipe so there is nothing o nit but a downpipe, no clogs or anything there.

Sounds like my daughter's 2.5 that was behaving like that. Ended up changing the timing chain. JMO

How hard is that on a 2.5?

This thing has a 130K so its possible.

First thing I would check would be the plug wires, full tune up with factory parts, wires, cap, rotor, plugs and go from there. Good throttlebody cleaning to, off the engine and on the bench. Keep the cleaner out of the sensors, the FI cleaners eat plastic. Then I woudl smell the fuel, if its been in there a while it could be bad or full of water.

The 86 2.5L is a TBI injection setup. It even has a CPS, but that isn't your problem. Just like on the 4.0L, this symptom sounds like the mixture is way off. That tells me it is one of three things. A massive vacuum leak, a bad MAP, bad TPS, or lack of fuel pressure. Burnt plugs mean it is running lean, so check for a vacuum leak to start with. The leak could be an EGR valve that is stuck open, but not necessarily the most likely. An intake manifold gasket is also a possibility. To make it run real crappy takes a pretty good leak.

It is possible that there is a lack of fuel pressure causing the lean run condition. A cheap swap is to do the fuel filter. It is a normal maintenance item anyway.

Did the problem come on suddenly, or over a period of time?

The other possibility is the seals around the fuel injector are leaking and flooding it out.

Not sure how the problem came about. Igot it in like this in a deal I made for my new cherokee, if its a relativly easy fix, it should be a good driver, if not its becomming a parts rig. I think I'm going to run out and buy me one of those testers to see what codes it throws, I have two cherokee's and my g/f has one so it cant hurt to have a tester.

Don't bother. The computer is not compatible with the current scanners.

There are none I can get for that year?

Looks like tommorrow I get to tear a buncha crap apart and spend money.....