Well just for a quick update as it turns out my exhuast is leaking this year again so im gonna need a cat front and also put the new o2 sensor in at the same time.

I would imagine its gonna cost well over 500 bucks ill have to let you guys know how it runs after i fix it if i can somehow scrap up the money

 

Update well today i had my leaking front pipe replaced and a new o2 sensor put in the ntk one.

Still the same after it warmed up alil bit the hesistation was back. Tryed to back up and dident give it enough and it stalled just like before i just dont get it.

Could the computer be junk???

 

What did you find in the sensor ground test?

How are you setting your TPS?

 

Everything appeared normal dident appear to have bad grounds anywhere sprayed some carb cleaner around all the vaccums no leaks detected.

Could the 02 relay be bad?.

We havent changed the grounds on the sensors yet but that we might try running a new tps ground. what u and a few others have mentioned. However the original grounds dident show signs of being bad

 

You CANNOT just gander at the grounds. You MUST refresh them. Can you see electricity?

 

To clairyfy things we checked the grounds and the connectors with a volt meter

 

Not good enough. There are multiple grounds to the dipstick tube stud and the ones underneath could be bad. Need to disassemble and clean.

You checked for voltage at the stud? You sure you don't mean ohms? Just clean them.

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 11-28-2011

 

My own cherokee backfired on occasion. It was the injectors. They were not sending enough gas, consiquently the engine was running too lean. I had bought these injectors off Ebay thinking I was upgrading my jeep fuel economy. Fortunately I found my old injectors in a bucket I had saved and reinstalled them with new o-rings.

 

Hey! Precept..... I might want to buy those injectors you just removed.
Are they yellow, with four holes? Can you tell me the #'s? on them?

I put 703's in my Renix Jeep. Works Great at temp! Really nice. Just I'm a tad slow to get there.. I think the higher flow rate of the 703's makes it take longer to get to temp end trim the mix. Yea, the "open loop blues". (default pulse width in open loop, besides using more fuel, makes it take longer to go to closed loop), (02 sensor trimming the mix).

I've been posting this for months. I haven't gotten a single comment. (or support) Btw, I had Wevous Rahcheros for breakfast, then changed a ball joint in my neighbors rig, before shooting some pool. Wat's the matter? "eggs" are scrambled?

(OK Pete, you DID say renix hits 160 pretty quick). Mine certainly didn't with the 02 dead.

 

Hits 160 real fast, 195 not much later. I'm not buying your open loop theory. Crappy stat.

 

These injectors are a tan color. #280150943 FOTE-D5A Now I am told that I should have reset the computer when I installed them which I did not know until now. There is a thread on the subject although I do not fully understand the reasoning behind it. The injector numbers listed for a jeep upgrade do not include the injectors I was sold and told would work on my 91 jeep cherokee. If you want these injectors text me at 425 449-2291

 

Well ok it looks like i got a final update to this headache finally after 15-20 years of someone searching solved.

I wasnt really getting a backfire i just a small breakup a couple times out the pipe when i would rev it up and let off the gas quickly.

Anyways cruiser i appreciate all the times you have givin me info on here however anyone who works on these jeeps 87-90 renix knows that the most important tool is a voltmeter.

There arent many idiot lights so i would say you cant read much with a code scanner it would be useless.

I just thought that it was kinda funny that no matter what u suggested you seemed to be under the impression that i had no technical ability when i was acutally checking sensors and reading tsb's and dealer manuals lunghd various sites ect.

My dad was helping me check every possiable lead and he has never seen a car he couldent get running my jeep was the 2nd and only other car he couldent figure out been doing mechanic work for atleast 30 years had his own garage.

Still after hours of checking and testing replacing sensors $2,000 in work later nothing.

I needed a new inspection sticker cuz it ran out last month had my exhaust fixed the other day new o2 installed aswell.

So my dad went to go take it to get one today stopped at the bank first the thing was kinda spuddering hesitating stalled out like always so he got pissed parked popped the hood started playing with the vaccum line we normally take off half way even though the idle wasnt real low it was high like its been latly the jeep ran better in the past with it half off. Ive been saying the jeep dont run any different with the line half off anymore my dad though it would make a difference like it had in the past

I touched the pedal still a choking like sound and the tach bounced down then back up level.

So he disconnected the egr hose and magicaly the jeep ran like a brand new car perfect no hesistation or stalling in reverse???

Ive seen many posts sorta like my topic on a few jeeep forums where ppl had said the egr wouldent cause rough idle or hesitation similar problems to what i was noticing its either open or closed.

My dad is thinking the spring is bad spring on the egr causing it to be sticking not working the egr is stuck open alil all the time which was its whole problem prolly from day one??

 

At idle the EGR should not be getting a vacuum signal. That in itself is odd. Couldn't hurt to remove it and see if it's hanging up somehow.

 

When we unplugged the egr it closed and it ran better. it could only be 1of a couple of things now???

 

Maybe the solenoid that gives the EGR vacuum is stuck. Shouldn't besignaling for vacuum to EGR at idle.



TESTING THE EGR VALVE FOR 87-90 4.0 ENGINE
Valve Opening Test
1) With engine at normal operating temperature and at idle,
rapidly open and close throttle. Open throttle sufficiently to obtain
at least 1500 RPM. Movement should be noticed in EGR diaphragm.
2) If diaphragm does not move, probable causes are: faulty
vacuum signal to EGR, defective EGR diaphragm or defective
backpressure sensor diaphragm (if equipped), or leaks in vacuum lines
or connections.
Valve Closing Test
1) With engine at normal operating temperature and at idle,
manually depress EGR valve diaphragm. RPM should immediately drop,
indicating that EGR valve is not leaking and had been properly cutting
off exhaust gas flow at idle.
2) If there is no change in RPM and engine is idling
properly, exhaust gases are not reaching combustion chamber. Check for
plugged passage between EGR valve and intake manifold.
3) If engine idles poorly and RPM is not greatly affected by
manually moving diaphragm up, EGR valve is not closing off exhaust gas
flow. Check for carbon between pintle, leaking EGR valve gasket or bad
EGR valve.
***************