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

[4WDXPRT]

I just got a call and it looks like the CTS bad...of coarse there is no part available until Tuesday so I'll be heading out to Pull and Save.

I'll let everyone know for sure.

Randy

Coolant Temperature Sensor (CTS) -

Located in engine coolant jacket on the driver's side of the block. To test, use a high impedance volt-ohmmeter. Resistance should be less than 1000 ohms with a WARM engine (examples = 212* would be about 185 ohms, 160* would be about 450 ohms, 100* (not warm enough) would be 1,600 ohms).

> What does it do? Adjusts the injector pulse widths (Colder coolant temperatures result in longer injector pulse widths and richer air-fuel mixtures). Compensates for fuel condensation in intake manifold. Controls engine warm-up idle speed. Increases ignition advance when engine is cold. Energizes the EGR valve solenoid to prevent flow of vacuum to the EGR valve.

[iheartmyheep]

i have a xj manufactured in 91 but has the sticker stating that it meets 92 emission standards and im having the same problem as the rest of these owners. i have long starts, when i rev it theres hesitation then when i put it in gear and go it sputters and bucks and dosent go very well. to go i have to floor it and when the revs pick up above 3000 it finally takes off. i fixed the exhaust leak, replaced the fuel filter, cleaned the throttle body and the small sensor that threads into the intake (dont know what it is but was grimy) and it still didnt fix it. I NEED HELP!!

[Eagle]

I vote for the O2 sensor

[jneary]

have you even checked to see if the distributor is indexed right yet?

[4WDXPRT]

It looks like the CTS was acutally missing...There is a plug in the block where it was suppost to be above the driver's side motor mount.

The Jeep has been running fine for almost two years without this CTS "coolant Tempature sensor" but it started acting up when I drove it 18 hours straight from Denver to Spokane, WA.

It has never cleared up and I've been here for almost a month. I would think the CTS is an important part of the how the fuel injection decides how much air/fuel to send to the motor.

I went to pull and save on Sunday and harvested numerous sensors and checked an 87, 88, 89 and 90 XJ they had there and the three that still had engines all had this CTS sensor. I took one from an 88 and will have it installed today.

The only differenece is the elevation from Denver to Spokane but I'm not sure how the CTS could start playing a big roll now except there is simply more oxygen available here in Spokane.

I have it at a shop since I gave up last week and I'm already into them for $230 in troubleshooting.

I asked them to install the CTS and then if it still acts the same install my NEW Mopar fuel pump I've been saving for a rainy day. The current pump is about 5 years old and it gets my vote for the root issue.

The indexing is correct on the distributor and I've swapped every sensor at this point...although the fact that it's been missing the CTS since the motor switch is a little frustrating.

Just how important do you guys think this CTS sensor is?

[langer1]

It was probably a newer 91+ block. Is there one in the T-Stat housing they could be using it.

It would make sense that at lower altitudes the MAP and o2 senors could make up the difference but at High altitude they could not.
While your looking make sure the Knock sensor is installed a rebuilt block would have plugs in all the holes.

[langer1]

Just how important do you guys think this CTS sensor is?

It's the single most over looked sensor causing poor gas mileage and performance.

[4WDXPRT]

The new motor was a 1988 Engine out of Jon Jacobs "Mad Cow" from Fort Collins, CO which was an 88 w/ 5-speed.

If anyone was at the 20th Anniversary NAXJA event in Moab you may of seen Jon's white 1988 with the chopped top, black spots and 40" Super Swampers on Dana 60 front and 14-Bolt Rear.

Mine was a 1989 w/ AW4 Auto so the guy in Gilpin, CO forgot to move the CTS over. The Knock Sensor was there and I did notice that something was not plugged in where the O2/Knock-Sensor/CTS wiring junction is but I couldn't find anything to plug into...I thought it was something for the 5-Speed. Now of-coarse the CTS was not even installed or some reason and it makes sense.

The motor was and has been running great in Denver and I haven't thought about that CTS connection for almost two years.

I just don't understand why all the sudden the lack of a CTS could be the cause of my hesitation/stumbling issue.

I would be very surprised if the CTS is the issue; while it makes sense that it is a nessasary EFI gizmo I think in the end it will be the fuel pump.

I'll know tonight...

[4WDXPRT]

Well I had the CTS installed in the block and even though it was missing for almost two year has made no difference.

I broke down and replaced my fuel pump last night in my garage with my new $200 Mopar fuel pump...and of coarse no change.

I've had a slight engine vibration for a few months and I think it's getting worse so now I'm thinking that possibly the Flex Plate on the AW4 has cracked and I'm getting some messed up timing because of this.

The harmonic balancer looks ok so after talking with some mechanics this could be the problem.

I told you guys this was a totally weird issue. I had the AW4 overhauled with a new flexplate and ring gear in 2002 several years before the new engine was installed. The crank may have weakened the flexplate since it moves a lot being so old and worn out.

When I put the new tight engine in the stress of the fixed crank probably caused the flex plate to crack.

This all theory right now but I'll keep you posted as I'll pull the flex plate cover to see if I can notice any visual issues with it.

I'm going to replace the fuel pressure regulator tonight since I have a spare from pull and save.

I hadn't thought that there could be an issue with the AW4 flex plate and that could be messing up the timing and causing the hessitation.

This has got to be one of worst problems I've ever experienced with any of my four XJs...Very frustrating but I'll eventually get this figured out.

[xjtrailrider]

I fixed my hesitation and low idle problem by advancing the dist. one tooth. I had installed it incorrectly by lining the rotor up slightly before #1 TDC. I read somewhere that the trailing edge of the rotor should be lined up with #1. I tried it and it works, drives and idles much better with no hesitation(when warm).

But..... now.... I have a slight miss/stumble on cold mornings untill the engine temp gets to around 150, then it goes away. On warm days it is O.K. I'm working through this problem now.

Not trying to hijack I just thought you may wan't to check yours.

[iheartmyheep]

in response to what i was told before i replaced the o2 sensor, cts, and treated the engine with seafoam (fuel additive) with no results. Still sputtering bucking and backfiring with 3 ideas left, injectors, champion plugs, or tps. still lost and troubled. also is there any tranny sensors? i have auto tranny not sure which one though. still need help







91 green cherokee laredo. stock with custom convex rear leafs(hahaha) and factory chrysler 8 1/4 rear

[JJacobs]

Randy, if the harness convolutes are in need of replacement, I'd get going on that and check all the wires closely while you're in there.
And I'd hate to think anything happened with the motor, but have you checked base compression? Solid power and ground readings at the PCM connector pins?

[ltkaknm]

Hey guys,

I was having similar problems with my 90 XJ and I changed out (with junkyard parts) the TPS, IAS, Fuel Pump resistor, MAP sensor, ignition coil, and finally I pulled a REnix computer from the same XJ as mine. Changing the TPS and the IAS did not seem to help the problem, neither did replacing the ignition coi...or the MAP sensor. It was when I switched out the Renix that it began to run much better.

Oh I also didn't mention that I put in Champion spark plugs.....which made a huge difference!

No bucking or stalling.

The place where I got the Renix has a number of Jeeps with the REnix still in them, let me know if someone needs a late 80's early 90's REnix.

Thanks,

LTK

[iheartmyheep]

champion plugs no good didnt work absolutley no difference none at all
going to get the sensor on intake manifold tps and junkyard computer
still lost and need help

[ltkaknm]

iheartmyjeep,

Sorry to hear you are still having problems. Is your XJ a manual or automatic. As i mentioned before there are a number of renix computers at a local pick and pull here and I could get one for you if you would like. They are relatively inexpensive and as I mentioned it really helped mine, but I have been a little leary to take off the map sensor and coil I put on to see if that was the problem. You might also want to look at your battery, while I was searching for a solution to my problem I ran across a few people that had changed their battery and the stalling and bucking problem went away. It was stated that the alternator does not kick in until after 1200 rpm and if a battery is not up to par it will cause the bad idle you speak of.. hope this helps..

LTK

[iheartmyheep]

thanks friends for the xj help but i no longer need assistance for i totaled the green xj but i will say i took out a chain link fence dropped off a 5ft embankment bouced the front axle off a huge boulder then hit a tree i started it shifed it into full time for the last time and drove it out thank you jeep vehicles





R.I.P 91/92 green xj

[kg4bet]

My 91 was doing the same thing after replaceing the 02 it ran good for about a week.
I don't know why but one day when it was acting up real bad and I grabbed the plug at the distributor and it died.
After getting it to start again I did it again and it died.
I pulled the plug apart and hit it with some PB Blaster (it's all I had with me at the time).
Put it back together and problem gone.
When I got back home I cleaned the plug with contact cleaner that was about 8mo. ago still running great.

Good luck and 73's KG4BET

[Nevada City Sparky]

thanks friends for the xj help but i no longer need assistance for i totaled the green xj .

R.I.P 91/92 green xj

Well, that's one way to fix it I guess!

[iheartmyheep]

im back in the club cause i found a 90 xj for 400$ with blown head gasket so im fixin this weekend and i could be cool with the rest of you guys post if you need 92 aj parts!!!

[jeepfreak84]

Sounds like a bad egr or an ambient air temp sensor. Thats just my .02
The reason im thinking the ambient air temp sensor is that you said it gets a little better in the cold weather, The sensor tells the ecu to adjust the timing accordingly to the air temp to prevent pinging. maybe its sending a bad signal and the computer's retarding the timing. Well maybe this will help ya.

Alex

Henderson Nevada