cruiser54

Scanner should show the O2 sensor switching rapidly from rich to lean constatly. If not, a faulty O2 sensor will stay "lean" and ECU will default to a richer fuel map. If you had things get worse after cleaning/touching the C101 and you've got 3 ohms of resistance in your sensor grounds, the sensors can be fine but the ECU isn't seeing proper values. Does the idle change if you wiggle the harness along the valve cover, between the MAP and C101? Here's a sensor ground test for you: Cruiser’s Renix Sensor Ground Test Set your meter to measure Ohms. Be sure the key is in the OFF position. 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. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too. You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud. On 87 and 88 models, you could have a poor connection at the C101 connector as well. Revised 05/03/2012

Re TPS so your reference voltage is 5.33v? it's to be set at 15% of reference Voltage.. I doubt it has anything to do with the crappy idle.... I too am having some idle issues, but almost the reverse of yours. I've replaced every sensor with new, and cleaned every ground. what happens on mine is the idle will not come down unless i strain the motor at a stop. Your gear switch may have issues. (you said you had an auto) there's a switch or sensor that tells it it'sin gear maybe that's why you were having issues. Is your IAC stepper motor known to be good? It's possible it has a dead spot, but that would usually just cause a very high or low idle not erratic or horrible sounding. have you gone back to basics.... Pulled plugs and examined them. checked spark wire resistance. rotor, cap, stator (i think that's what it's called located under the rotor has three wires that go to it.. tells the truck whats firing) , fuel filter, compression. Skidoo, did you ever check to see if someone "screwed" with the Throttle Body blade adjustment?

Good motors. Basically a Datsun Z motor stroked and de-bored at 2.8 liters and made into a diesel. I'll bet it would bolt right up to a Datsun pickup tranny.

After a thorough throttle body cleaning and reinstallation with a new gasket, check your TPS as suggested. Also make sure your intake manifold bolts aren't loosened up along with checking your EGR operation. Write-ups on TPS and EGR are below. 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. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, 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. FOR AUTOMATIC TRANSMISSION RELATED 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 05-20-2012 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. ***************

Never saw a Renix Police Package. I think the Package started in 1991 or 1992.

86 to 90 four cylinders and 4.0s are Renix. In 1989 and 1990 the C101 connector was eliminated.

No voltage to any sockets? According to my wiring diagram, the things in common to both front and rear signals are: 15 amp Haz/Stop fuse. Is it good? Flashers themselves. Maybe replace them Turn signal/Hazard switch. At the base of the steering column is the turn signal/flasher connector. It's long and flat. Check to see if it's plugged in all the way. Probably best to unplug it and plug it back in.

Do the hazard flashers work?

And the column shift so they had a place to put their radios and other equipment. Neat rigs. When I was at the dealership, our County bought quite a few police XJs. Shoulda grabbed the alternator, too.

At a bare minimum, you need to service the battery connections and refresh your grounds. for under $20 you can add some grounds easily. 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

Acts like a weak battery. How old is it? When is the last time you serviced the battery and cleaned the cables? Ever refresh all your grounds?

They take a "set" so replace it since you're gonna pull it down.

How much of the interior are you gonna change? The dash and everything?

Sometimes you have to make sure of what it ISN'T before you find out what it IS.

Clean your throttle body and IAC before proceeding any further. Also, do the following: 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

Did you see my post above regarding the instrument panel ground? That's a stone I wouldn't leave unturned considering the issues you've got.

Eagle is on the mark here about closed vs open loop. OP's high idle is more than likely caused by the bad TPS or bad grounds in the sensor circuit. How was it determined the TPS is bad? What tests were done?

Actually what it does is CLOSE when you select AC or vent. You can eliminate it with no problems. Factory did it in later years on the Cherokee.

Running a jumper from the battery to the starter solenoid helped because it bypassed the entire ignition system. My battery posts are clean, and both the ground and positive wires have been replaced recently. Not true. It bypassed the battery to starter wire.

ECU does not affect cranking. You're losing power or ground somehere and it's probably major. How are your battery cables between the battery and starter and battery to block? Oil soaked and corroded inside? Remember what that jumper wire did for you? It helped.

Lifter tick/valve train related. What happens if you shut it off, wait a minute and restart?

You could have someone turn the steering wheel while you watch from underneath. But something you rarely SEE but makes a popping noise is the track bar bracket to frame bolts need to be tightened up. I'd start there.

Take it all out and block off the vacuum source.

Might want to try this just for fun. Can't hurt and might help. Improving the Instrument Panel Ground The ground point for the complete instrument cluster on your XJ or MJ is located up under the driver’s side dash. If you lay on your back and look up under there with a flashlight, without wearing a hat, you will see a black wire attached to a shiny piece of metal almost directly above the hood release knob. The screw will have either a ¼” or 5/16” head on it. This ground point is responsible for handling the ground circuit for the following items: Dome lamps, Seatbelt and key warning, trans comfort switch, wiper switch, headlamp switch and delay module, fog lamp switch, cargo lamp switch, all instrument panel grounds and illumination, power windows and door locks, cruise control dump valve, and a few more things. The problem is that where the ground point is located does not have a good contact with the chassis where the ground should be. The solution is simple. Make up a jumper wire with #10 gauge wire about 10” long. On one end, crimp on a ¼” round wire terminal. On the other end, crimp on a 3/8” round wire terminal. Remove the screw from the existing ground wire and attach the small terminal of your jumper so that the original wire and your new jumper share the same attaching point, one over the other. Look above the driver’s side plastic kick panel just forward of the top of the hood release knob. You will see an 8mm stud there. Attach the large terminal end there with a washer and nut over it tightened securely. **Special note for Comanche owners: Make your jumper wire 12” long and attach it on the driver’s side kick panel close to the fusebox on the 8mm stud.** Revised 11-29-2011

Actually, you can find 28mm swaybars on XJs. Ususally 87 to 90 Limiteds and Laredos with the factory tow hitch.