95cherokee89

Hey guys, I was hoping that someone here could help me out a bit...

A little while ago I got an 89 Cherokee (with all 95 drive-train including engine)I had to do some repairs on it because it had been sitting for 4 years, and have been driving it ever since ( 4-5 months) and its always had this problem
- it goes through an entire tank of gas in under 290kilometers
- it has very little power (I cant even make it to 120k on the highway)
- it idles horribly, changing in rpm by almost 500 every few seconds (up and down)
- if I started it when it was WARM it would rev to about 3-4k rpm for up to 5 minutes
Yet for some reason the CEL isnt on (I honestly think its broken)

So I have been tinkering around replacing and testing different things to try and fix this problem, I replaced the distributor cap and rotor and replaced the 02 sensor.
although these things did help a little bit, as it no longer revs really high at start-up. but it still idles all over the place, and gets horrible gas mileage. I suspected that the MAP might be bad so I tried replacing it with a spare one I had, but either its bad as well or not the problem as nothing changed.

I don't think its the IAC or the TPS, I tested the TPS and it got the correct readings. One other thing I forgot to mention, apparently 3 of the injectors were replaced, and the other 3 were not, I tested all of them because the spark-plugins had a lot of soot built up on them, the old 3 had an OHM reading of 17-18, and the new ones were about 15.4-15.7 OHM.
The throttle body is also strangely quite clean, so I don't that's the problem either

So what do you guys think I should do?

(engine: 4.0L straight 6)

salad

Vacuum leak
Coolant temp sensor
MAP line

Now the fun part: did it EVER run right? Are the electronics Renix or Chrysler OBD-1?

Ever seen this? https://www.cherokeeforum.com/f51/cruiser54s-mostly-renix-tips-153657/

cruiser54

Clogged converter?

CRUISER’S VACUUM TEST FOR EXHAUST RESTRICTION
Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

95cherokee89

Its definitely not the cat, I removed it (temporarily) to see if that was the problem, and it wasnt. Its not renix, I think its the obd-1.
Yes it did run properly, I have known the guy for some time and the jeep ran fine before he gave it to me.

mr white

Plug it in to a code reader. It could have a code but no cel if the dash wasn't changed.

jeepscab

check your timing, i recently rebuilt my girlfriends 4.0 in her grand and the distributor was a tooth off and it would rev up then down then up then down. also had an issue with my pick up coil or cam sensor inside the distributor on my YJ.

95cherokee89

Interesting, I will try check these things. While I'm at it, I will also swap out the three old injectors and see if that fixes anything, I will also see if theres a vacuum leak, I'm pretty sure that I heard a slight hissing sound near the map sensor last time I had the hood up.

jeepscab

get some brake cleaner and spray it on your hoses you think might be leaking. if your motor sounds like it wants to die you got a vacuum leak on that hose. Worked for me.

cruiser54

Probably best to use oxygen sensor safe carb or throttle body cleaner.

And do it with the engine running, just to clarify.

95cherokee89

UPDATE


I found that a lot of the problems were caused by the exhaust manifold, I fixed that and it no longer idles all over the place but I can feel a miss fire in one of the cylinders, it seems to idle normally then want to die then idle normally then want to die in a pattern alongside the missfire. I ran seafoam through it and everything seems nice and clean, all the spark plugs are really clean, but it still has a missfire (only audible at idle) and excessive fuel consumption. it also takes about 4-5 cranks to actually start so I replaced the fuel pressure regulator, but that didnt change anything, I really just don't know what else to do, nothing I have done has lowered the fuel consumption even a little, I'm out of ideas here, any help with this?

95cherokee89

I had the fuel pump out a little while back, I know for a fact that it is working fine.

cruiser54

That acts like a faulty oxygen sensor.

95cherokee89

interesting, because I suspected that and replaced it, so it should be working. I will check the wiring and make sure its all connected propperly

cruiser54

The Relay for the O2 sensor heater has to work.

95cherokee89

I swapped the ac clutch relay with the oxygen sensor heater relay just to test. I will see if it changes anything later tonight when I get a new spark plug ( cracked on when I pulled it out yesterday)