Mystery Renix 4.0 Problem...help!

[4WDXPRT]

I just moved to Spokane, WA from Denver, CO and drove my 1989 Renix 4.0/AW4 Auto Cherokee 1000 miles in 18 hours. I've only been driving it a short distance to work or towing it to trail heads for the past two years so it hasn't been running at 80mph for 18 hours straight for a while.

I've owned this Jeep for 10 years and have never had this problem where the motor seems to start sputtering/missing when you start pressing the accelerator above 10mph but clears above 2000 rpms. It's very noticeable when you first start it up and begin to drive to work and goes away somewhat after the XJ has warmed up. It doesn't completely go away and is not as exaggerated. I can still feel the sputtering when I let off the throttle somewhat at highway speed and the RPM drop below 2000.

I've ran into all kinds of issues in the past with high idle, etc but can not figure this one out...without buying $500 worth of new Mopar EFI/Emission sensors. It never dies, the idle is good although a bit rough.

I just did new standard autolight plugs at .035 gap w/ a new cap and rotor and replaced the fuel filter, plus new plug wires. This made no difference. I also cleaned the throttle-body, Stepper motor but it made not difference.

It has a brand new Catalytic converter in 2005 as well.

I suspected the coil so I replaced that but it made no difference. It has a newer Mopar fuel pump that was installed in 2003 but I can't imagine it is the fuel pump because at high throttle it runs great, at idle it works ok, but anything under 2000 rpm it acts like the choke is stuck or there is too much fuel. Sputtering Gurgling sound out of the engine...sometimes backfire.

With the heat from the long drive I'm curious is the CPS has been damaged but I do not have any starting issues as far as cranking or stalling goes.

I'm down to the MAP sensor, the O2 Sensor or the MAT sensor (Which I highly suspect) as I've never replaced and I pulled it out of the intake and it looked pretty dirty. I cleaned it with throttle body cleaner and the sputtering seemed a bit worse when I took it for a test drive.

The EGR Valve is newer in 2003 but I suspect it could be bad as well. I unplug the vacuum lines to the EGR and the sputtering/Gurgling is a lot more exaggerated. I do this test before I drive home after work...but had to pull over and hook up the vacuum.

The 4.0 is a new rebuild with about 15,000 miles on it. The fuel-injection wiring harness has never been cut but I suspect some bad grounds for the combo TPS, AIS, MAT but who knows. The plastic EFI wiring loom is dried-out cracked and needs to be replaced. I would think I would have serious driveability issues across the RPM band if I had a bad ground though...

Any advice would be appreciated as I'm at a loss. I do have a brand new MOPAR fuel-pump that I've been saving as an emergency spare but I don't believe it is a fuel pressure issue...and would like to save this install as a last resort.

Please let me know what you guys think.

 

[xjtrailrider]

I've got a similar issue with my 90'. But with a low slightly rough idle, and a slight stumble from take off. It otherwise drives fine and I'm getting 18 mpg in town.

I've replaced the TPS(OEM), MAP, O2, Knock sensor. It has a new motor with only 500 miles on it. There is a bunch of other new stuff also that I can't remember right now.

My EGR is unhooked and plugged.

I'll be watching this thread to see what turns up.

 

[langer1]

I'm down to the MAP sensor, the O2 Sensor or the MAT sensor

I'd say your down to the TPS

 

[4WDXPRT]

I'd say your down to the TPS

As in maybe a ground or the whole TPS needs to be replaced...and this needs to be a OEM Mopar TPS right...no NAPA or other knock-offs?

I'll do the resistance test tonight...can I use an analog guage or does it need to be digital?

Randy

 

[langer1]

Either, your looking for a dead spot. The TPS is similar to a volume control they will get dead spots sooner or later. Some time a good cleaning is all thats needed.

 

[XJING]

If you check your TPS and its all right, the problem is a classic Renix EGR issue(rough under 2000 slight stumble) make sure you have good vacuum, and the rod goes up and down in the little bell shaped thing in the manifold and doesnt leak. good luck

 

[lawsoncl]

Since you're in Spokane, keep in mine that Pull-n-Save over by Spauldings off of Argonne usually has at least a dozen late 80's, early 90's XJs on the lot. http://www.pullandsave.com. Great place to grab spare parts. Most sensors and coils go for $2, which is really nice if you just want to try swapping something to see if the problem changes.

I think about half of my MJ came from Pull-n-Save. Lets see that would be seats, rear bumper, 1999 AW4 transmission, all the parts to do a manual->auto swap, 3-axles, front drive shafts, parts for the crown vic rear disk swap, and tons of miscellaneous stuff. I usually grab other parts that I know sell for a decent price on eBay. I think I'm actually ahead dollar-wise.

 

[4WDXPRT]

Since you're in Spokane, keep in mine that Pull-n-Save over by Spauldings off of Argonne usually has at least a dozen late 80's, early 90's XJs on the lot. http://www.pullandsave.com. Great place to grab spare parts. Most sensors and coils go for $2, which is really nice if you just want to try swapping something to see if the problem changes.

I think about half of my MJ came from Pull-n-Save. Lets see that would be seats, rear bumper, 1999 AW4 transmission, all the parts to do a manual->auto swap, 3-axles, front drive shafts, parts for the crown vic rear disk swap, and tons of miscellaneous stuff. I usually grab other parts that I know sell for a decent price on eBay. I think I'm actually ahead dollar-wise.

I'll be heading over there to harvest some widgets...thanks. I'll try the EGR first but I'll get as many sensors as I can to trouble-shoot this.

With the colder weather this morning it has been behaving a lot better...but the issue is still there.

 

[xjtrailrider]

I don't know if this will help you with your problem, but I just put a new EGR/EGR solonoid in mine today and the hesitation is gone. I still have a low idle though.

 

[jneary]

if you put a new motor in it you should make sure the distributor is indexed exactly right.

 

[RNMedic]

Egr solenoid was the cause of this in mine. Disconnect the EGR valve and got worse, apply vacuum from tester and the EGR valve was okay. took the one of the 87 and it was good.

 

[Wa Woody]

The 4.0 is a new rebuild with about 15,000 miles on it. The fuel-injection wiring harness has never been cut but I suspect some bad grounds for the combo TPS, AIS, MAT but who knows. The plastic EFI wiring loom is dried-out cracked and needs to be replaced. I would think I would have serious driveability issues across the RPM band if I had a bad ground though...

I would also upgrade the stock ground with a better one. Bad grounds can cause problems. Welcome to Spokane. Good Luck

Woody

 

[4WDXPRT]

Well I just installed a new Napa $120 EGR last night and it made no difference...It's off to Pull and Save for the EGR solenoid gizmo on the firewall, a MAT, a MAP, and and anti-knock sensor. I'll pick up a TPS or two and try those out. I'll need a knock sensor and some O2s. I think I may pick up a MOPAR TPS and O2 as these I can't imagine would be too good out of a wrecking yard of late 80s XJs.

The EGR seemed like a good guess and was easy to change out, the TPS is next but I need to be able to adjust it or have it set on a dealers/shops scope.

I'll get up to speed on the testing the multi-meter too. This is so frustrating when I keep changing out the wrong part only to find it made no difference...at least the XJ is drivable.

 

[jneary]

before ypou may waste money on things you may not need, search for posts to check and see if your distributor is indexed properly. if you replaced the engine, chences are that it could be the problem since you transfered the distributor over.

 

[4WDXPRT]

The motor was replaced two years ago and this weird issue just started about two weeks ago...In 10 years I've never had this problem.

I'll look for the post and double check but it's looking like the TPS as was mentioned earlier in this post.

I've held off on this because I do not have a way to adjust a new one if I pull off the current one but this is my next step.

 

[langer1]

4WDXPRTAs in maybe a ground or the whole TPS needs to be replaced...and this needs to be a OEM Mopar TPS right...no NAPA or other knock-offs?

I'll do the resistance test tonight...can I use an analog guage or does it need to be digital?

Randy
I try real hard to get people to test things first, even the EGR could have been tested, but hay it's your money.

 

[sjx40250]

So how old are your injectors? I have owned my 90 since new. In April one of the injectors started to leak around the metal to plastic interface. I bought Bosch Green Meenies from FiveO Motorsports on line. (sp?) Fixed a multitude of problems. Never ran so good! even new. Better milage, power, torque, throttle response. But I had to adjust the MAP and use hotter plugs to pass emissions. Best $240 I have spent on my rig with 148K miles.

 

[4WDXPRT]

New injectors from Napa in 2002...I was in a pickle in Moab and had to buy 6 injectors @ $90 a piece...

Obviously now we would just order a set of Mustang 5.0 injectors off ebay for $99.

The injectors are newer anyway.

It's the TPS...but I'll find out for sure on Monday.

 

[ltkaknm]

I had a similar problem recently when I installed Autolite plugs into my 90 XJ. THe other day I installed $1.39 Champion and the problem almost disappeared. I still think I might have a short somewhere that causes my RPMs to go down but for $9 it is running a lot better. I would check that out.

LTK

 

[4WDXPRT]

Well I've had it in a shop and they can't figure it out either...They tested the TPS, even replaced it, but still this little gremlin persist.

I'm about to install my new Mopar fuel pump as even though the pressue test ok the issue is still there.

No vacuum leaks...

I'll switch out the Autolights for Champions this weekend as that's a pretty easy thing to do and cheap.

I'm going to hit Pull and save for a bunch of parts but as said this is pretty goofy.

Randy