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  #1  
Old January 22nd, 2012, 09:33
Crashsector Crashsector is offline
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Guess what? I have a RENIX XJ with a rough idle and misfires! SOLVED!!!

Hey everyone,

I want to start by saying this forum has already been a great help. I picked up an '89 XJ 4.0 (4WD, auto) with 189k miles for $500 last week. Get ready for this... I know you're surprised... it has a rough idle, misfires, and gets like 3MPG. I know, weird, right?!

After reading I learned about the RENIX setup and how hard this is to troubleshoot. I was hoping you guys could just help me go down the list of things to check.

SYMPTOMS:

- Cranks about 5-6 times before finally starting.
- Rough idle, almost sounds like it's cammed.
- Slight hesitation when starting from a stop.
- Accelerates up to speed (relatively) smoothly with no backfiring.
- If I slow down, then speed up again, there is major hesitation, slight bucking, and popping noises coming from the driver's side of the engine bay (backfiring?).
- Idle will eventually settle to about 350-450rpm but will go as high as 2,000rpm after turning off A/C. Sometimes stalls when finally putting it in park.
- Exhaust smells extremely rich.

Here are the things I've already checked:

- Plug wires are in the correct order, however the cap looks to be replaced and the distributor may be as well, and I have not manually re-checked the timing.
- Vacuum sits at about 5-10 inches at idle, and will go as low as 35 inches with the engine at about 3500rpm.
- Fuel pressure is 35psi.

Other observations:

- TPS looks to be new.
- Oxygen sensor looks to be new.
- No obvious vacuum leaks from up top.

I've already ordered a new MAP sensor, O2 sensor, and IACV. I hate the idea of just throwing parts at this thing, so any help is appreciated.

Thanks again!

--Andy
Annapolis, MD
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  #2  
Old January 22nd, 2012, 10:05
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Ecomike Ecomike is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

http://www.naxja.org/forum/showthread.php?t=1072534

http://www.naxja.org/forum/showthrea...ght=renx+files

http://www.naxja.org/forum/showthrea...nsor+t esting

Are great places to start.

Also, Check the vacuum line on the fuel pressure regulator for any gas while running!!
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Quote=8Mud: "Go ahead and put up the best fence you can build, I'll bet on some Mexican with a few dollars of nails and a pile of scrap lumber."
34 MPG , '85 2WD Cherokee Pioneer with custom installed, 64 hp, 2.2 L Nissan SD22 Diesel 5 spd Manual; & 4 Renix XJs, '87 Wagoneer 4.0, 4WD, 89-Cherokee, 4WD, '87 Cherokee 2WD, & '89 Cherokee Pioneer 2WD, all 4dr. #2091
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  #3  
Old January 22nd, 2012, 15:48
Crashsector Crashsector is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Quote:
Originally Posted by Ecomike View Post
http://www.naxja.org/forum/showthread.php?t=1072534

http://www.naxja.org/forum/showthrea...ght=renx+files

http://www.naxja.org/forum/showthrea...nsor+t esting

Are great places to start.

Also, Check the vacuum line on the fuel pressure regulator for any gas while running!!
Thanks for those, Mike. I had found those threads at work but lost them once I got home. I tested the TPS and got a reference voltage of 4.56 volts, and an output voltage of 4.05 volts. Obviously nowhere near the 83% specified in one of those links. I went to loosen the bolts holding the TPS on and one snapped below flush

So I may have found my problem, but created a bigger one in trying to fix it. I already have a new sensor inbound and will probably pick up a junkyard throttle body rather than trying to drill and helicoil. Not 100% convinced this was my problem, but it will cross one thing off the list.

--Andy
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  #4  
Old January 22nd, 2012, 15:53
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birchlakeXJ birchlakeXJ is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Best to get all new tuneup hardware in there. Failure to do so often results in the chasing of your tail. Besides that, it establishes a baseline for future tuneups. The importance of fresh secondary ignition (tune up parts) cannot be overstated.

Fresh Champion copper plugs gapped to .035, new wires, cap and rotor with brass contacts. New fuel filter. Check/replace your air filter; want to be sure you don't have oil in the airbox, common with a clogged ccv system on the 87-90.

Clean your throttle body and idle air control; they get carboned up over time and miles.

Here is more on the extended crank "characteristic" of the RENIX.

You have a Renix XJ (87-90) By design, the engine is not going to fire until the computer (ECU) gets a signal from the crankshaft position sensor and measures that signal to indicate that 300 rpms while cranking has been met/exceeded.

Somewhat extended crank times should be considered a “characteristic” of your engine, rather than a problem.

You can upgrade the battery and battery cables--at least 4 ga., 2 ga. better--and buy a high-torque starter.

Be sure that all grounds are good. Remove them and freshen them. You cannot tell if the grounds are electrically good by looking at them! Renix vehicles are very sensitive to ground issues.

Your CPS can be a bit weak, too. Unplug it and probe the two wires with your meter set on AC volts. You should get .5 as a reading. Anything down around .35 will cause long crank times and possible intermittent no-starts.

Last edited by birchlakeXJ; January 22nd, 2012 at 15:59.
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  #5  
Old January 25th, 2012, 15:03
Crashsector Crashsector is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Made some progress today... two steps forward, one step back. But first, PICS!









She ain't a looker, but she got it where it counts!

Next post with updates...

--Andy
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  #6  
Old January 25th, 2012, 15:09
Crashsector Crashsector is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

I replaced the hood latch cable while I waited for the new throttle body to arrive (remember this). Got my junkyard throttle body around 11AM. Went to take off the TPS and the same damn bolt snapped just like it did on my original. Drilled it out, tapped it, and used a metric hex head bolt I had laying around with a nut as a spacer on the sensor.

Adjusted the TPS to exactly 83% and started her up. The idle is the same... lopey, rough, rich, and it stalls eventually if left to its own devices. However when driving... HOLY CRAP what a difference. Smooth, torquey power all up and down the rev band. No hesitation at all, light throttle or heavy. The transmission kicks down just fine if I jab the throttle. Night and day difference.

However it now stalls randomly while driving, mostly when coming to a stop.

So that brings me back to my idle problem. I stupidly re-used the IACV of unknown providence which came on the truck, even though I had a replacement. I can unplug the IACV harness and the idle doesn't change, so I think that's my next thing on the list.

I went to open the hood with my snappy new hood cable and... nothing. Handle just pulls. Looks like the anchor end just came out of the latches. So, I'm done for tonight. Hopefully there will be enough daylight left when I get off tomorrow to take out the headlights and buckets so I can get the hood open.

I'm also thinking that running so rich for so long probably fouled the O2 sensor, so I have another one coming in which will go on Sunday.

Let the saga continue....

--Andy
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  #7  
Old January 25th, 2012, 15:47
Shorty Shorty is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

5in/hg at idle seems pretty low.

I'd look for a good sized vacuum leak-- intake gasket, injector o-rings, faulty EGR valve.

A vacuum leak will alos lean the mixture enough for the ECU to compensate with higher fuel from the injectors. If the leak causes some cylinders to run leaner than others, you can end up with an overall rich exhaust caused by a lean condition.
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  #8  
Old January 25th, 2012, 16:30
Crashsector Crashsector is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Quote:
Originally Posted by Shorty View Post
5in/hg at idle seems pretty low.

I'd look for a good sized vacuum leak-- intake gasket, injector o-rings, faulty EGR valve.

A vacuum leak will alos lean the mixture enough for the ECU to compensate with higher fuel from the injectors. If the leak causes some cylinders to run leaner than others, you can end up with an overall rich exhaust caused by a lean condition.
Oooh, thanks for the reminder about the EGR. That's one thing that DEFINITELY looks original on this thing. I'd love to test it but I can't get under the damn hood at the moment

--Andy
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  #9  
Old January 25th, 2012, 17:07
Crashsector Crashsector is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

The more I think about it, the more the EGR valve seems to make sense. The engine runs tip top until I start to come to a stop, when it stumbles (if the valve has failed it would run fine with enough backpressure, then open early and act like a vacuum leak).

ALSO, I feel the vacuum assist for the brakes drop out just before I come to a stop, at what I guess is the balance point for the failed EGR valve.

Can't wait to tear in to it and find out!

--ANdy
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  #10  
Old January 25th, 2012, 19:05
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cruiser54 cruiser54 is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Quote:
Originally Posted by Crashsector View Post
I replaced the hood latch cable while I waited for the new throttle body to arrive (remember this). Got my junkyard throttle body around 11AM. Went to take off the TPS and the same damn bolt snapped just like it did on my original. Drilled it out, tapped it, and used a metric hex head bolt I had laying around with a nut as a spacer on the sensor.

Adjusted the TPS to exactly 83% and started her up. The idle is the same... lopey, rough, rich, and it stalls eventually if left to its own devices. However when driving... HOLY CRAP what a difference. Smooth, torquey power all up and down the rev band. No hesitation at all, light throttle or heavy. The transmission kicks down just fine if I jab the throttle. Night and day difference.

However it now stalls randomly while driving, mostly when coming to a stop.

So that brings me back to my idle problem. I stupidly re-used the IACV of unknown providence which came on the truck, even though I had a replacement. I can unplug the IACV harness and the idle doesn't change, so I think that's my next thing on the list.

I went to open the hood with my snappy new hood cable and... nothing. Handle just pulls. Looks like the anchor end just came out of the latches. So, I'm done for tonight. Hopefully there will be enough daylight left when I get off tomorrow to take out the headlights and buckets so I can get the hood open.

I'm also thinking that running so rich for so long probably fouled the O2 sensor, so I have another one coming in which will go on Sunday.

Let the saga continue....

--Andy
Always adjust your TPS on the "engine side" per the following instructions when chasing a driveability problem. The trans side of the TPS (which you've been using to adjust) is separate from the "engine side" which is where the problem may very well be.
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.
If you see more than 1 ohm of resistance 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 have 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. If you have TRANSMISSION 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 11-28-2011
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  #11  
Old January 26th, 2012, 05:08
Crashsector Crashsector is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Quote:
Originally Posted by cruiser54 View Post
Always adjust your TPS on the "engine side" per the following instructions when chasing a driveability problem. ...
Thanks for pasting this... again. In one of my replies I mentioned that I performed this procedure and it solved my driveability problem. Now I just have an idle issue to deal with.

Thanks again and here's to getting my hood off!

--Andy
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Old January 26th, 2012, 05:11
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cruiser54 cruiser54 is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Quote:
Originally Posted by Crashsector View Post
Thanks for pasting this... again. In one of my replies I mentioned that I performed this procedure and it solved my driveability problem. Now I just have an idle issue to deal with.

Thanks again and here's to getting my hood off!

--Andy
The fact that you posted 4.05 volts output voltage tells me you tested the trans side...........
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  #13  
Old January 26th, 2012, 09:25
my2monkeys my2monkeys is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

I like the wood grain dash!
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  #14  
Old January 26th, 2012, 09:46
Crashsector Crashsector is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Quote:
Originally Posted by cruiser54 View Post
The fact that you posted 4.05 volts output voltage tells me you tested the trans side...........
That was with the old sensor. The new sensor calibrated right to 3.81 volts. The old sensor was obviously replaced at some point but never calibrated. The guy working on this thing really knew nothing about working on cars.

Excited to disassemble the hood and start troubleshooting the EGR valve.

The woodgrain dash was a junkyard addition by the PO... and it doesn't quite fit. I probably won't do much with it as this is strictly a beater.

--Andy
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Old January 26th, 2012, 14:09
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cruiser54 cruiser54 is offline
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Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

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.
***************
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