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Guess what? I have a RENIX XJ with a rough idle and misfires! SOLVED!!!

Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

OK. I got the new FPR on and it made a definite improvement. Still doesn't like to hold a steady idle... up and down about 500rpm, but it doesn't stall when coming to a stop or idling any more.

Pulled a plug and it looks OK, a bit of grey ash. They're crappy Autolites, so I think the next step is to throw some Champion coppers in and see if that helps. I also have this new O2 sensor I might as well throw on.

Either way, I'm happy enough with the engine (it's driveable) now, so I'm moving on to the bumper and hitch and then calling it quits for a while. Gotta let the wallet recover a bit.

Thanks for the help guys!

--Andy

PS: bails85: the Rock Auto part numbers for my vacuum harnesses were DORMAN 46004 and 46003.
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

How do the wires look? If in doubt, replace them with some good quality ones.
Make sure your intake manifold bolts are snugged up while you're at it.
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Just for the heck of it. You mentioned the I.A.C. But no mention of the relay controlling it. It's in the row of 4 on the passenger side. It's called the +B latch relay and is what gives the power to the I.A.C. My rig will accasionally idle real high and I will wiggle that relay and it will idle right. Turns out my relay had connection issues at the relay socket and inside the relay do it would stick. Just a thought.
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Honestly at 2 bucks a pop Id change out the sparkplugs if your in doubt. My sparkplugs looked visually fine like perfect burn pattern and everything and it turned out to be my misfire/idle problem.
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

magimerlin said:
Just for the heck of it. You mentioned the I.A.C. But no mention of the relay controlling it. It's in the row of 4 on the passenger side. It's called the +B latch relay and is what gives the power to the I.A.C. My rig will accasionally idle real high and I will wiggle that relay and it will idle right. Turns out my relay had connection issues at the relay socket and inside the relay do it would stick. Just a thought.
Click to expand...

I think it's always a good idea on a Renix to remove all the relays on the passenger inner fender, clean their tabs with a wire brush, spray out the receptacles they plug into with a good electrical cleaner, and plug them back in.
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

magimerlin said:
Just for the heck of it. You mentioned the I.A.C. But no mention of the relay controlling it. It's in the row of 4 on the passenger side. It's called the +B latch relay and is what gives the power to the I.A.C. My rig will accasionally idle real high and I will wiggle that relay and it will idle right. Turns out my relay had connection issues at the relay socket and inside the relay do it would stick. Just a thought.
Click to expand...


HMMmmmm, I have a little problem with that. From what I have read the B+ latch relay keeps power to the ECU on a timed cycle at shutdown, and ECU powers the IAC with DC pulses to the motor. The B+ latch stays on (timer) after the motor is powered down (not sure how, ECU timer?), so that the ECU can reposition the IAC for proper air flow on the next restart. Then it and the ECU power down.

I just checked the Renix FSM manual. It does not say what the B+ latch relay actually does. Interesting. Now I wonder just what all it does do??? It does stay on while ignition is ON, and then the manual mentions the delay off timer and B+ latch relay that allows the ECU stay hot and reposition the IAC after the engine is turned off, then the ECU and B+ latch relay turn off.
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Had some more time to work on the Jeep today.

A tech at work had an ancient Snap-On scanner which allowed me to read the ECU data real-time. It wasn't telling me anything I didn't know. It is staying in Open Loop all the time and is constantly running rich.

All other sensor info looked good. I did replace the O2 sensor and the spark plugs today.

The old plugs looked to be gapped a bit too wide.

The new plugs uncovered a previously undiscovered problem... a pretty significant miss. So bad that it shakes the entire truck. I don't know if it was missing all the time or it just started after the plug change. I checked the plug seating and wire connections 3 times.

I started unplugging injectors and it seems like none of them made it run any worse! Same thing with spark plug wires. It still ran, just not well, with any of the 6 unplugged.

Don't really know where to go from here aside from a compression test. I'm starting to get really bummed about this project. The budget is pretty much gone. Wondering what I could get for it at a junkyard.

I hate letting machines get the best of me, but this thing is really starting to get frustrating.

--Andy
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Are you sure the EGR valve is seating completely?

No vacuum leaks in the hose/piping from the TB to MAP?
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

cruiser54 said:
Are you sure the EGR valve is seating completely?

No vacuum leaks in the hose/piping from the TB to MAP?
Click to expand...

EGR tested fine. Seals completely at idle, and the computer isn't triggering it to open.

MAP vacuum line is new.

--Andy
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

A few things to add...

Fuel pressure is great... 35psi, 40psi with the vacuum line off. Also has a new FPR. Pressure falls less than 0.5psi per minute after turning the engine off.

Vacuum at idle is low since it's stumbling, around 5 inches. Vacuum under load is a solid 30 inches.

It starts in open loop, tries to switch over to closed, stumbles, then goes back to open. It does this maybe 2-3 times in two minutes after it starts, then it goes back to open for the rest of the trip.

Unplugging random injectors and/or spark plug leads while it's (barely) idling doesn't seem to make it run any worse.

Unplugging the IAC valve at idle doesn't make it any worse (or better).

TPS calibrated to exactly 83% of reference voltage. The computer is saying the throttle is at 15% at idle and is registering that the switch is closed. Intake air charge is reading around 106 degrees C. Coolant temperature is reading around 95 degrees C.

New O2 sensor, TPS, IAC valve, tires, cap, rotor, plugs, vacuum harnesses. O2 sensor reads lean when the engine isn't running, and rich when it is.

EGR is sealed fine. Pressing the diaphragm stem in (towards the block) smooths it out a bit (since it adds air) but doesn't completely fix it.

It's tough justifying putting any more money into this thing. For the price I paid for it plus all the parts I put on it I could get a 93 XJ on Craigslist with 30k less miles which runs fine.

Any reason a bad coil would act like this?

--Andy
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Try this:

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
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

And this:
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
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Sounds like the O2 sensor is not getting 12 volts at the O2 sensor to run the internal electric heater in the O2 sensor.

Also, "Intake air charge is reading around 106 degrees C"

Is too HIGH!

IAT may be bad, or you have an exhaust leak blowing into the intake manifold, or onto the intake manifold, or both!!!!

IAT should be reading about 160 to 170 F max (Or 77 C max)

OR you may have a POOR sensor ground screwing up the data the ECU gets?!!!!!!!!!!!!!!!!!!!!!!! A variable ground, that changes with engine vibration is the worst!!
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Ecomike said:
Sounds like the O2 sensor is not getting 12 volts at the O2 sensor to run the internal electric heater in the O2 sensor.

Also, "Intake air charge is reading around 106 degrees C"

Is too HIGH!

IAT may be bad, or you have an exhaust leak blowing into the intake manifold, or onto the intake manifold, or both!!!!

IAT should be reading about 160 to 170 F max (Or 77 C max)

OR you may have a POOR sensor ground screwing up the data the ECU gets?!!!!!!!!!!!!!!!!!!!!!!! A variable ground, that changes with engine vibration is the worst!!
Click to expand...

So you've got me thinking.

Intake manifold is too hot to touch.

I'm looking at this replacement EGR valve I never put on. Moving the stem "in" (towards the block) is actually the closed position.

If the EGR valve was open, it would definitely make sense that the intake temp would be too hot, and it would be running too rich to compensate.

I think I know what I'm going to change out on Sunday...

--Andy
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

cruiser54 said:
Re-read Post # 32. I think you're on to something.
Click to expand...

I know the exhaust manifold weaved through the intake manifold raises intake temps a bit... but any idea what a normal intake temp reading should be?

Can you touch your intake manifold while running?

--Andy
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

No. I mis-read Post # 32 initially. Your EGR sounds like it's not seating and causing a huge vacuum leak. Address that first.
 
Re: Guess what? I have a RENIX XJ with a rough idle and misfires!

Crashsector said:
I know the exhaust manifold weaved through the intake manifold raises intake temps a bit... but any idea what a normal intake temp reading should be?

Can you touch your intake manifold while running?

--Andy
Click to expand...

My intake manifolds run at about 160-170 F surface temp, using 180 F T-stats, in the peak summer temps, so the air moving through the intake is running less than 160 F, on both of mine, and I use IR testers to measure it.
 
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