1990 Cherokee stalling under light acceleration

My 1990 is stalling under light acceleration from a stop, it will happen almost every time in drive, but idling in park it's a little harder to get it to stall. In park it seems to happen when the throttle closes. It seems to be lacking a lot of power unless stomping on the gas.

This just started happening this morning around the time I changed the cap and rotor, it has persisted even with the old cap and rotor back on it. I re-tested the TPS I replaced last week and it's still spot on. And a new fuel pump a month ago. The CPS was replaced at the beginning of summer.

Other recent events were the fuel pump ballast relay dieing, and I had to just bypass it because a new one isn't available here (theres not even a jeep dealer for an OEM one). I've also had an issue with intermittent long cranking (almost always when warm) and replaced the ground from the head to the firewall. The fuel pump check valve doesn't seem to be the issue with the cranking since cycling the ignition to pressurize the system didn't seem to make a difference. I just wanted to mention that in case it could be related.

Any suggestions would be more than welcome.

Could it be the IAC going bad?

First, Renix systems have to "spin up" to 300+ RPMs before the crank sensor can generate a signal to the ECU to fire the engine. Bad/inadequate battery cables, weak battery, old starter and you will get extended crank times in the Renix.

Did you adjust the TPS?

joe_peters said:

First, Renix systems have to "spin up" to 300+ RPMs before the crank sensor can generate a signal to the ECU to fire the engine. Bad/inadequate battery cables, weak battery, old starter and you will get extended crank times in the Renix.

Did you adjust the TPS?

Click to expand...

Thanks, I didn't know that about needing to be at 300 rpm's before firing. My main concern right now is the stalling, the starting I mentioned just in case it could help in diagnosing. Though what has me puzzled about the starting is how intermittent it can be.


Mine idles at about 1,000. However it's always done this, and the gauge cluster I swapped in shortly after I bought it (before I knew there was a difference) may have been from a 4cyl, causing it to read high. However its been too long to view the auction description and find out (about 3-4 years).

The battery was replaced last week when the cold killed it, and the starter last year when a bad starter relay was misdiagnosed as a bad starter, but we decided to leave the new one in and call it preventative maintenance.

Battery cables are all new within the last 2 years, no corrosion present on them. Head to firewall ground was all but dust and i replaced it 2 weeks ago to see if it helped with the starting, which it didn't.

The TPS was adjusted to .80 and was still there yesterday when I rechecked it. It made a huge difference when first replaced in overall performance.

I just had this problem with mine and I fixed it today... It was the ground wires... I would try to clean them and scruff or lightly sand the mounting spots and then tighten down all 3 grounds... Hope this helps

purkeyda said:

I just had this problem with mine and I fixed it today... It was the ground wires... I would try to clean them and scruff or lightly sand the mounting spots and then tighten down all 3 grounds... Hope this helps

Click to expand...

purkeyda is correct. Those grounds need to be removed, cleaned, scraped, polished before reinstallation. A good dielectric grease applied afterwards is recommended. Accept no substitutes for this 20 minute ground refreshing, or you could end up chasing your tail for quite a while............

Well I've found the stumbling as stalling to be a problem with the vacuum system. The EGR valve was suggested to me as a cause on another forum and while it tests good it seem sto be over-actuating? The Vacuum hoses on my jeep are quite old and patched by the previous owner. I think I reconnected the EGR valve when it's been disconnected this whole time, but some of the lines are crossed or the EGR "controller thing" (I'm too tired to look up the proper name) is bad.

I finally bought a Haynes manual and I'll probably just gut all the old lines for new ones, since a number have broken and been patched by me as well. I'll be looking into the long cranking when I can, but my wife's car is dead now and I need to get that running as soon as possible.

Having a very similar issue, stalling when easing into gas pedal...

What ground wires are you talking about that I would make sure the contacts are clean?

I hadn't written this yet, back when this thread was current. So, here ya go.

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

Wow! Thanks for the great info. I'll run through this tonight.

:cheers:

While you're under the hood, do this, too.

Renix Jeep ICU/Coil contact refreshing
　
　
The contacts between the coil and the ICU on your Renix Jeep can become corroded and loose causing a complete or intermittent no-start condition. I recommend the following procedure as a maintenance precaution to insure this is eliminated as a possible cause now and in the future.
The coil is attached to the ICU by two T20 Torx bolts. Remove these two bolts and lift the coil up off the ICU. You will see 2 pins and 2 sets of contacts. Clean both the pins and springy contact pieces with a good electronics cleaner.
Squeeze the springy contacts closer together with some needlenose pliers. Apply some dielectric grease to the contacts and bolt the coil back on to the ICU.
While you’re right there unplug the connectors from the ICU and inspect the pins in the harness connector. Make sure the pins are not retracted into the connector. Spray out the connector and the receptacle of the ICU with the same good electronics cleaner you used earlier. Apply dielectric grease to the connectors and plug them back in.
I feel this procedure should be performed at least once in the lifetime of a Renix Jeep.
　
Revised 11-29-2011

Any other tips? I just got this 1990 a couple weeks ago and I am hoping to work out the stalling issues this week...So I would love for it to be grounding issues. Stalls when light on gas during acceleration from stop, right after starting or in a slow turn if I tap the gas lightly....when the throttle is eased in lightly the rpm's drop and it dies....restarts fine though mostly just a PITA.

If it isnt grounds I'll get back to this thread (I really appreciate the info after the thread has been dead so long by the way). Might be jumping the gun but my next guesses at TPS or EGR....

I'm hoping to spend some time on it tonight or tomorrow night after I get home from the office....i'll let you know.

I'll run by the autozone on the way home tonight for cleaning supplies....what is on my list other than a wire brush, electronics degreaser and contact lube?

Thanks again!

You asked for it. All preventative procedures that can keep problems away in the future. These came from 12 years as Service Manager and Shop Foreman at a Jeep dealership. Most were influenced by, and a result of, direct contact with the service engineers at JeepTech.

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals, and adding dielectric grease before plugging it back together. Be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.
ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then dielectric grease should be added before plugging them back in. I do this on every Renix era Jeep I purchase or work on for someone else.
Revised 03/15/2012


Cruiser’s Renix Sensor Ground Test
Set your meter to measure Ohms. Be sure the key is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.
You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well.
Revised 05/03/2012


RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.
IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.
MANUAL TRANSMISSION: RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body. This manual transmission vehicle TPS provides data input to the ECU. The manual transmission TPS has three wires in the connector and they're clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Adjust the TPS until you
have achieved this percentage. If you can't achieve the correct output voltage replace the TPS and start over.
AUTOMATIC TRANSMISSION: RENIX automatic transmission equipped XJs has a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as the manual transmission equipped vehicles—
FOR ENGINE MANAGEMENT RELATED ISSUES. However, the automatic TPS also has a square four-wire connector clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.
FOR AUTOMATIC TRANSMISSION RELATED ISSUES. Check the four-wire connector side of the TPS.
If you have ENGINE issues check the three-wire connector side of the TPS. For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.
Revised 04-30-2012

cruiser54 said:

You asked for it. All preventative procedures that can keep problems away in the future. These came from 12 years as Service Manager and Shop Foreman at a Jeep dealership. Most were influenced by, and a result of, direct contact with the service engineers at JeepTech.

Click to expand...

Good thing you live in AZ or I would be hanging out at your place most weekends...

Great info here again - I just bought this jeep (Ive only owned two cars, both cherokees and they are both in the driveway) and Im looking forward to learning more about them and getting a lot of PM out of the way before I switch DDs

(also if anyone is interested in helping me figure out why my rear-end is CLUNKing here is this thread, different jeep though.

http://www.naxja.org/forum/showthread.php?p=245659826#post245659826)

Chainer said:

My 1990 is stalling under light acceleration from a stop, it will happen almost every time in drive, but idling in park it's a little harder to get it to stall. In park it seems to happen when the throttle closes. It seems to be lacking a lot of power unless stomping on the gas.

This just started happening this morning around the time I changed the cap and rotor, it has persisted even with the old cap and rotor back on it. I re-tested the TPS I replaced last week and it's still spot on. And a new fuel pump a month ago. The CPS was replaced at the beginning of summer.

Other recent events were the fuel pump ballast relay dieing, and I had to just bypass it because a new one isn't available here (theres not even a jeep dealer for an OEM one). I've also had an issue with intermittent long cranking (almost always when warm) and replaced the ground from the head to the firewall. The fuel pump check valve doesn't seem to be the issue with the cranking since cycling the ignition to pressurize the system didn't seem to make a difference. I just wanted to mention that in case it could be related.

Any suggestions would be more than welcome.

Click to expand...

Stalling and hard to start could be a leaking fuel pressure regulator, FPR, leaking gas into the vacuum line. Check for gas at the vacuum connection to the FPR.

Check the firing order on the cap, see if you crossed two spark plug wires when you replaced the cap.

Check the IAT intake air temp sensor resistance while hot and cold versus OEM specs in the manual, it can cause these problems, including high idle, hard starting hot, and dying....

Lots of other possible problems, but those are free to check, and common.