Gee oh Dee

1987 XJ, 4.0.

Took her out last night to grab food. On the way home I noticed the temp was indeed a tad hot, not too crazy though. (Waiting on motor mounts to put new rad in)

I left one stop light, as soon as I shifted to 3rd the Jeep started choking, misfiring, general all around poor running. The tach kept dropping to zero, bla bla bla.

I'm hoping it was just a horrid case of heat soak, but I'm going to check/clean a few things first.

I'd like to verify fuel pressure. What should it be for a Renix? 42 psi? 49? I don't remember.

I will refresh all grounds per Cruiser's write up.

I want to also check and attempt to adjust the TPS as the bucking got much worse once when I was at 2-3% throttle, but got much better the more pedal I gave it.



What I find funny is that it would only happen in 3rd, 4th or 5th gear. It seemed that the lighter on the throttle I got the worse the problem, also pushing me toward the TPS.

Anyone else with info or suggestions is welcome to share.

I appreciate all the help.

Thanks.

Jeepyjeepy

Fuel pressure should be 31 with vacuum line connected and 39 with it disconnected at the regulator. My MJ does the same thing also drops to almost zero when letting off the gas to stop as well. hope you get er fixed

DFlintstone

31...to 39 with the vac line off the regulator. Pete's TPS writeup is in my signature. Idk about the shifting correlation...coincidence? Might as well verify that fuel pressure like you said.


Mine did all sorts of rude things after sitting hot, when my (mis-routed), wiring to my lower sensors would ground. The heat shield would expand into the wires, ONLY after it had been sitting hot. Anyway you might want to take a quick look at yours.

cruiser54

Do the sensor ground test as described in the TPS write-up first. It can screw with all sorts of stuff if the connections in the harness are messed up.

Ground refreshing is mandatory as is C101 refreshing if you still have it.

dukie564

If the tach is dropping to zero, i'm betting you have a problem with your ignition coil (temperature related failure maybe?). That'd be my first stop.

And if you still have the C101 connector, get rid of it.

Gee oh Dee

Pretty sure the PO got rid of the C101 as I do not see anything resembling that assembly on the firewall. But I could be mistaken nd thinking of something else.

I will test the coil, but its been a LONG time since I've done so, and don't quite remember how.

But wouldn't the coil need to be warm for it to fail?

dukie564

it's probably experiencing temperature related symptoms, so...maybe?

cruiser54

Make sure the PO didn't eliminate the C101 using butt connectors or wirenuts.

Tach gets it's signal from the ICM. Why not refresh the plugs on the ICM and also do this while you're at it:
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

Gee oh Dee

This weekend is mostly free for me, so I will most likely tackle them starting tonight or tomorrow morning.

And thanks for posting that guide as well, Pete, that makes it real easy to have everything I'll need on hand in one place while I'm doing all this!

Gee oh Dee

Side note, this Jeep did sit for like 5 months while it waited for me to replace that trans, so it could very well just be crappy connections.

cruiser54

How about this?



I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.
ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.
Revised 07/23/2012

Gee oh Dee

Yeah, I'll do all that as well. I've got plenty of time, and plenty of beer. No reason no to do a complete refresh.

Heh, the grocery store near me has a "meal deal" going. Buy a 24 pack of miller lite, got a pound and a half of ground beef, hamburger buns, a bag of crunchers potatl chip, and a bottle of ketchup for free.

Too bad no one is really close to me. I'd buy a few of those 24 packs, and use all the free **** to feed anyone who helped!

cruiser54

So you're gonna do the coil contacts, connector refresh, and do you have the write-up for the ground refresh and upgrade?

Gee oh Dee

I don't have it saved, but I'm sure I can find it via search.

I hate it when folks don't search for simple, easily answered questions. So I'd rather not be 'that guy' if you know what I mean...

cruiser54

Oh, I'll give it to ya.....

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