Hey guys, overdue update and more questions.
Head gasket isnt blown, and i did an oil change and filter change. Replaced the oil pressure sending unit and it reads great oil pressure. Cleaned out the valve cover gaskets and pcv hose. I havent been able to check the cat because its all seized together, havent had enough time lately to sort that out. But now i'm sometimes hearing/feeling a thunk coming from the engine when at a standstill after driving a while. Its not consistent, and when it happens it's not very frequently occurring.

It still starts, idles, never stalls. But when accelerating you can feel it miss and lose power. I've heard i can pull out the o2 sensor before the cat to create an exhaust leak, i may try that instead of disconnecting the cat.

 

I'd take a sawzall to it...

 

Take it to an exhaust shop. They can check to see if it's the cat or not. I still think that will be your problem.

 

I am having very similar issues with my 86 2.5L. Drives ok till it gets warmed up. Would that be the cat issue also? The exhaust bolts are loose after the manifold. (previous owner said flange was bad)

I checked the oil, radiator, vacuum lines. This is my first cherokee, really like it!!!!

 

Whoops! I edited out stuff on the non existing exhaust leak. Plugs, cap rotor, wires? If I was having trouble with power I might change the fuel filter, or at least ask the PO if he did.

I'm learning that a Renix CPS can do about anything, and you can check it easy in just a couple minutes. You just need a $5 cheapo digital meter. If it's pulling it's tricks, you are just wasitin' your time trying to find a problem. Literally only seconds to rule it out.


AC voltage CPS test; Small clips on the meter leads really helps.

Unplug the connector at the back of the manifold with wires going down to the bell-housing/cps.
Probe the two wires to the cps with the meter set on AC volts. (a 200 scale on mine).
Crank the engine and note the voltage. (jump it if your battery is low)

Mine somehow works with only .3 my wiring/grounds must be pretty spiffy. .5 seems to be a good mark. One article talked of .5 to .8. **Update, it soon failed. I installed Napa #css980 in my 90.**

If it's low you can modify the cps. With the next largest bit that won't fit in the hole, enlarge the hole's in the bracket just a tad. Now when mounting it's crucial to maintain firm downward pressure on it while tightening the bolts. An assistant could help with that from above.


Also, if it's low and you have a manual trans, junk can stick on the sensor cause it's a magnet. You might just clean it. So there's that!

This link here has links with more sensor testing, but I'd do the above and check for vac leaks, (as well as tune up), before testing sensors.
https://www.cherokeeforum.com/f51/he...ix-links-1397/

Also...I'd take a minute..you have a little tube from the inside if your TB back, up to the MAP sensor mounted on the firewall. If that is plugged, off or even cracked that can really cause trouble. Not necessarily your trouble, but still a good thing to check.

 

I checked the CPS today and I was only getting a .2 reading. I guess I need to change that. Hahaha

 

There's a few tricks. tie a long string on the old to haul the new up. On your back with your feet out to the right you can reach up past the front driveline with your left arm. Your right ends up by the cross member with long extensions to a swivel, then a short 3" to the 7/16, (11mm) socket. Toss the plastic, and don't drop the bolts inside.

Cruiser has suggested that with a clutch there is a chance it might just be dirty...it IS a magnet.

I didn't try the drilling trick because my wires were dissolving anyway. $40 something for the napa #css980 is one way to go...

 

I replaced the CPS and it seemed to give it a smoother run, but I still have the power loss after it heats up. I also still have smoke in the valve cover. Could this just be worn rings? Bad engine?

 

So....those symptoms are gone, and you just feel like it has more power while it's cold?

I got my 84 W/2.5 long before the 90W/4.0. I gotta say, first driving the 2.5 I liked it allot better than after I loaded the tools in there. Yea, it's great there is a 5th gear up there, just wish I could see it more often!

Fuel filter been changed?

Course that matters. I suppose if it was hitten on all 4 and runnen smooth and there was good fuel pressure I'm mot sure what to say.

The cat can make it dog, maybe after checking fuel pressure, and/or a filter and checking that cat, the MAP or temp sensors could be off, starving it for fuel....I don't know, haven't been there other than to switch to the 4.0.

Hey, just a thought...if something was rattling or thumping enough the knock sensor would retard the timing resulting in some of the symptoms you mention. Soes the 2.5 even have one? Maybe someone here knows, can he just try unpluging it?

As far as blow by..unless you blew smoke in there, it's coming from past the rings! Older engines do that, it's not a good sign of course. That little 2.5 IS a tough little engine though!

 

It has the same issues, like it's missing, or starved. It just doesnt do it untill I drive for a bit and warm it up. 5 minute drives are fine.

How do I check the fuel rail pressure? It has a new fuel filter.
Could it have anything to do with the oil pressure?
Can I test the sensors or should I just replace them? (map and temp)

I already took the cat off and replaced, thinking that might be part of the problem.

Thanks so much for helping so far

 

There on the rail is a Schrader valve. (on the 4.0), it's like a tire valve. IIRC you want to see 31 lbs, then 39 when you unplug the vacuum line to the regulator there on the rail. O"Rielies there doesn't loan or rent the gauge..I think. I'm not sure of the best way to go about it. I've been known to offer lunch money for a favor from a shop! Anyway with a lack of power I'd want to eliminate that.

Renix will run in "open loop" while it's under 150* or 160*, somewhere there.
There it uses the MAP, and the two temp sensors, but not the 02 sensor or the knock sensor.

Then in "closed loop", that knock sensor will retard the spark if it senses knocking. I saw a post...a guy said you could rap near it with something and you should hear the sound of the engine change. I haven't tried it. I'd bet you could just unplug it and see if that helps to diagnose if it's an issue, but I'm not sure there.

On the 02, I guess they normally fail going rich...probably not your problem, but maybe..anything is possible I'm sure! In this link there is some tasty info. I would at least want to verify the 12V heater feed. (engine running).

http://www.naxja.org/forum/showthrea...ht=sensor+test
If you don't know how old the 02 sensor is, you might just want to change it. Since they generally fail rich and gas is so spendy, shelling out that dough might actually save some.

When my 4.0 had issues warmed up if was the wires to those lower sensors chafing and grounding, check them! It took me forever to find where one was grounding on the bottom where I couldn't see it.

So here's that link again with the sensor testing with the resistance values for the temp sensors. https://www.cherokeeforum.com/f51/he...ix-links-1397/

Also take a look at the info in the link in my signature. You got a crisp blue spark? ICU Coil contacts, then the grounds....always a good thing to not need to worry about.