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Unread 10-09-2012, 09:49 AM   #1
tgoad
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1990 XJ Cherokee 
 
Join Date: Sep 2012
Location: Bella Vista, Ar
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1990 Cherokee

When i sit at a stop light for a couple minutes and i start going again the jeep, for lack of a better word, hesitates. i give it gas but it takes a second or two for the power to come. I have only noticed this sitting at stop lights. any ideas?

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Unread 10-09-2012, 09:57 AM   #2
GetLifted
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Can you pull any obd1 codes?

Have you attempted to fix anything?

What do the plugs, wires, cap, rotor look like? How old are o2 sensors and the TPS?
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Unread 10-09-2012, 10:00 AM   #3
tgoad
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i havent tried, mainly because i dont know what they are and how to do it
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Unread 10-09-2012, 10:42 AM   #4
tgoad
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in reply to what i didnt see, i dont know if it was because my computer sucks or you went back and edited. As far as i know everything is original parts, except the vacuum hoses, i put new ones in last week which is when this started. im pretty sure i hooked everything up properly but im going home tonight and going to double check against the diagram i have
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Unread 10-09-2012, 11:15 AM   #5
GetLifted
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Automotive 101: if you did work on a motor and now it doesnt run/run different, retrace what you did. More then likely you caused it. Dont move on to another problem until you fix the one at hand.

I would retrace all my vac lines, and if needed run a vac gauge on the manifold and see if it is in fact leaking/mis routed.


Does your fuel pressure regulator on the rail have a rubber boot and a line attached?
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Unread 10-11-2012, 12:01 AM   #6
Reptile
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Quote:
Originally Posted by GetLifted View Post
How old are o2 sensors and the TPS?
Don't you know it's impolite to ask the age of an old O2 sensor?
---

Not knowing you worked on it recently, I'd say TPS's definitely on the list and refresh your grounds, inspect the distributor, etc. BUT you touched it you must have messed something up. So X2 on GetLifted's automotive 101.

Quote:
Originally Posted by tgoad View Post
i put new ones in last week which is when this started
See, YOU did something and oh now it's ****ed up!
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Unread 10-11-2012, 05:39 AM   #7
cruiser54
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First off, Renix throws no codes.
Has only one oxygen sensor.
If you do not know the state of the tune-up parts, replace the plugs, wires, cap and rotor along with teh fuel filter first.
Use Champion Copper or NGK plugs and get your wires, cap and rotor from somewhere like Napa. Insist on their premium line.
Clean your throttle body and IAC.
If it were mine, I would also do a ground refreshing.

--------------------------------------------------------------------
The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled



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
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Unread 10-13-2012, 01:36 PM   #8
tgoad
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I just rechecked all my vacuum lines, all of them are hook up correctly, except where the last guy bypassed the EGR Solenoid. im waiting for that part to come in because when i hook it up correctly it runs rough. i took apart the throttle and cleaned the IAC, it really wasnt all that dirty so im thinking that wasnt it. To add to my problems there is oil coming through the vacuum line on the top of my engine at the front of the crankcase into my air filter, so if you have any insight on that problem that would be great. Thank you for your help

Last edited by tgoad; 10-13-2012 at 01:48 PM..
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Unread 10-13-2012, 02:52 PM   #9
Reptile
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If your engine light is on, the first thing to do is read the code, as GetLifted suggested. It's easy, you just need to find an OBD I reader. Check with your part store to see if you can rent one. There must be a reason the last dude bypassed the EGR system. The EGR valve is controlled by the computer, mainly based on O2 sensor readings. You need to find the root cause, a failling O2 sensor can definitely cause hesitations. Don't throw parts at it, get a proper diagnosis first or you'll end up with an empty wallet. You need to clean up that oil that goes to the filter, not good.
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Unread 10-13-2012, 04:28 PM   #10
cruiser54
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Renix is not OBD and stores no codes.
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Unread 10-13-2012, 04:53 PM   #11
tgoad
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no check engine light is on, and its not the EGR Valve, it is the EGR Solenoid, two completely different parts of the system.
Cruiser, nevermind about help finding the ground on the stud, i found it so i'll report back on if that works
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Unread 10-14-2012, 06:23 AM   #12
cruiser54
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Quote:
Originally Posted by tgoad View Post
no check engine light is on, and its not the EGR Valve, it is the EGR Solenoid, two completely different parts of the system.
Cruiser, nevermind about help finding the ground on the stud, i found it so i'll report back on if that works
No CEL either.

I posted the ground refreshing info in the other post. Might be worth looking at along with the dipstick tube stud.
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Unread 12-18-2012, 09:16 AM   #13
SpokaneDmax
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Quote:
Originally Posted by tgoad View Post
I just rechecked all my vacuum lines, all of them are hook up correctly, except where the last guy bypassed the EGR Solenoid. im waiting for that part to come in because when i hook it up correctly it runs rough. i took apart the throttle and cleaned the IAC, it really wasnt all that dirty so im thinking that wasnt it. To add to my problems there is oil coming through the vacuum line on the top of my engine at the front of the crankcase into my air filter, so if you have any insight on that problem that would be great. Thank you for your help
That is the PCV you can clean it or replace it. or run it into a plastic bottle to keep the oil from runnign into your filter and off the road.
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