New guy from Bama with problems!

Bought my first XJ last week from a guy. Its been setting for 2 years. Threw a hot battery on it and it turned over but no fire so I bought it. Got it home put a tune up on it and a CPS and she started up. Idle rough but would run down the road just fine.


Tonight I got to jump in a friends mudhole and it acts like its running out of gas now. It will crank but idles around 400 rpms now. Nothing is wet under the hood, checked dist cap and air intake. It will idle up if you feather the throttle but not over 2250 rpms. Thought at first maybe it was the old gas or out of gas. I put in 2 gallons of fresh fuel and nothing is better.

Thanks to Aaron Thompson to referring me here.

Let me also add this:

88 XJ Automatic bone stock 4.0 4wd

1 other minor change I made a day ago was idling rough noticed the EGR looked to be smoking, figured it was due to old grime on it. Pulled the vac hose of it started idling fine. Next day back to crap idle EGR still unplugged. Also can anyone tell me are these things always hard to start, seems worse than a carbureted vehicle when its cold.

UJSLOST said:

Bought my first XJ last week from a guy. Its been setting for 2 years. Threw a hot battery on it and it turned over but no fire so I bought it. Got it home put a tune up on it and a CPS and she started up. Idle rough but would run down the road just fine.


Tonight I got to jump in a friends mudhole and it acts like its running out of gas now. It will crank but idles around 400 rpms now. Nothing is wet under the hood, checked dist cap and air intake. It will idle up if you feather the throttle but not over 2250 rpms. Thought at first maybe it was the old gas or out of gas. I put in 2 gallons of fresh fuel and nothing is better.

Thanks to Aaron Thompson to referring me here.

Click to expand...

Welcome, You oughta find plenty of info here. This is Aaron BTW! :cheers: I'd check the throttle position sensor.

UJSLOST said:

Let me also add this:

88 XJ Automatic bone stock 4.0 4wd

1 other minor change I made a day ago was idling rough noticed the EGR looked to be smoking, figured it was due to old grime on it. Pulled the vac hose of it started idling fine. Next day back to crap idle EGR still unplugged. Also can anyone tell me are these things always hard to start, seems worse than a carbureted vehicle when its cold.

Click to expand...

Mine isn't a fan of cold weather either!

ok I think I have an article I found online that tells what the voltage on it should be.

Maybe a bad ground? Check the groud on the dipstick tube it gave me weird problems with my renix XJ

if it will start tomorrow gonna spray it with some starting fluid to see if it runs better, if so. Gonna look towards fuel problem.

Here's some homework for ya if you just bought a "new to you" Renix Jeep:

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 11-28-2001
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

Note from DJ
Try changing the fuel filter this is a cheap preventive maintains.
Probable location is in the hump and very near the top over the rear axle on the driver’s side.

If it is plugging up you are starving the engine of fuel at higher RPM’s

Also do what cruiser54 is posting he has grate knowledge of Renix era Jeeps.

I would suspect that if that XJ was setting for 2 years there is condensate water in the gas tank. Adding 2 gal of fresh gas won't eliminate the water. I'd suggest adding some Dry Gas.

Best regards,

CJR

Definately dry gas at the very least or, better still, drop the tank and properly drain it. All of the grounds... We can not say this enough about any vintage Heep but the Renix Era Heeps are particularly prone to problems with marginal grounds.

To make the point, I had my 98 for all of two days before I replaced all of the cabling both positive and negative. Had them made by a local battery supply shop out of welding cable. As this XJ is not my first by a long shot, I have learned that there are just some things that need to be done.

Verify your charging rate. Needs to be 14.2+/- as the injectors will not function properly under low voltage. Keep in mind that the Heep is a 14VDC system, not a 12VDC system. The battery is just for starting and as a ballast for the alternator. Truth be told, a large enough capacitor could be in place of the battery. Too bad it is not practical. All though, I will admit to doing just that on my Triumph MCs...

Anyway, welcome to the insanity! There are benefits to paying the dues beyond the nifty red lettered name... Pay no attention to the man behind the curtain... This is a subliminal hint to join... Just have fun with it and keep us in the loop on what you find as the root cause of the problem so we all can learn something from your experience.

I didn't even think about the old gas in it. I bet that has something to do with it.

Replaced fuel filter it was rusty inside! Added some lucas injector treatment to the tank and seafoamed the valves and intake via vac hose. Gonna check those ground connections today.

She ran fine once I picked her up from where I left her in the field. AInt sure what happened exactly but did ok on a shake down run around the block. But that doesnt prove much.

Probably don't want to mix treatments but a lot of XJ owners run Seafoam as a gas additive as routine maintenance. If you are not going to drain the tank I would fill it up with fresh gas. If that gas is more than a year old it probably don't even smell like gas anymore.

It's always a good idea to replace the fuel filter after it's sat. If it's been idle a long time you may need to do it a second time.

The "Renix era" XJ's generally take about 4 or 5 engine revolutions before they fire. That's the way the system is designed, to get a good crank position reading before allowing a spark. If it starts reliably about the same every time, don't worry. If it takes longer cold, it could be leakdown of the pressure in the fuel system. A common problem. If that happens, wait a few seconds between turning ignition on and cranking, or cycle the key on and off a couple of times before cranking. It will often start faster then.

As far as the EGR valve is concerned, when the valve wears, it can hang open sometimes and when that happens, it will wreck your idle. This is a separate issue from crud and carbon in the valve itself. If it happens again, you can sometimes reach into the diaphragm of the EGR, open it up a bit and let it snap shut, and it will work again. If that solves it, you can block the vacuum to the valve until you get it replaced.

And of course you should read Cruiser54's stuff. XJ wiring is minimal in places, and the Renix system, especially, is pretty sensitive to poor connections and voltage drops.

When I had an 87, I found it helped a lot simply to go out every once in a while, and unplug and replug every connector I could find under the hood. Do each one a couple of times, and if you have some plastic-safe non-sparking contact cleaner, squirt a little into each one as well. On my old 87 this made a lot more difference than you'd think it ought to.

Matthew Currie said:

When I had an 87, I found it helped a lot simply to go out every once in a while, and unplug and replug every connector I could find under the hood. Do each one a couple of times, and if you have some plastic-safe non-sparking contact cleaner, squirt a little into each one as well. On my old 87 this made a lot more difference than you'd think it ought to.

Click to expand...

I suggest unplugging every connection in the engine bay you can find, spraying it out with a good electronics cleaner, visually inspecting the terminals, and adding dielectric grease before plugging it back together.
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.

This can cause numerous issues also and should be addressed on your 88.

Renix Jeep C101 Connector Refreshing
　
The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of almost 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before.

Almost every critical signal between the engine sensors, injectors, and the ECU travel the path through the C101.
The C101 is located on the driver’s side firewall above and behind the brake booster. It is held together with a single bolt in it’s center. To get the connectors apart, simply remove the bolt and pull the halves apart. You will find the connector is packed with a black tar like substance which has hardened over time.
Take a pocket screwdriver or the like and scrape out all the tar crap you can. Follow up by spraying out both connector halves with brake cleaner and then swabbing out the remainder of the tar. Repeat this procedure until the tar is totally removed. This may require 3 or more repetitions. Wipe out the connectors after spraying with a soft cloth.
If you have a small pick or dental tool tweak the female connectors on the one side so they grab the pins on the opposite side a bit tighter. Apply a true dielectric grease, not the stuff that came with your brake pads, to the connection and bolt it back together.
　
　
Revised 11-29-2011