kidkodiak

Ok, this time I'm stumped, so I'm hoping y'all can help me figure this one out.

My 1990 Renix. She runs great for the most part, even though I'm Frankenstein-ing her part by part all the time.

But now I'm lost. Randomly, while running just fine yesterday, it died. No warning, no provocation. Here are the symptoms as I know it (my mom was driving it at the time):

There are no problems turning the engine over. It turns over immediately and catches, but immediately dies. Manually holding down the throttle has no effect, it just rev's higher when it catches, then still dies. It ignores the throttle after that... doesnt' even try to rev after the initial when it catches.

I'm getting fuel...at least, I tested the release on the injectors and it sprayed gas out. Nothing impeding air flow. No fouled plugs, nothing sounding like it's missing w/ the timing. Fuel filter was replaced 2 years ago.

I was always taught that all you needed was fuel, air, and combustion to have it run, and I'm getting all 3.

Suggestions for where to start? The IAC and TPS were replaced last year, and the TPS adjusted correctly when I put it in, in terms of voltages...nothing has recently changed, either.

I'm wondering... sensor failure somewhere? I ruled out CPS only because it starts, and usually if the CPS goes, it won't start at all. I read to check the fuel pump resistor, but the wires and resistor look clean and wires are well seated.

That's the most I know, but I'm stumped for sure. Any help or suggestions would be greatly appreciated. I was able to tow it back to my sister's house, and my brother-in-law and I will be working on it this weekend, but I was hoping for advice pre-emptively.

Thanks muchly.

DFlintstone

I've been told, but don't remember. Looked a minute and didn't find it. Something about the ASD relay being grounded (to provide power), while starting, then something else grounding it when it starts. All I have now is check your fuses. Somebody should be along.......

Also you can always by-bass that ceramic fuel pump resistor on the fender by the air cleaner to see if that helps, but that doesn't sound like it.

kidkodiak

I thought of trying to bypass that resistor... will probably do it just to rule it out. I was also told to check the ground at the base of the dipstick... apparently a ton of things are grounded there and a bad ground is, em, bad...

But yeah, a couple ideas so far... hoping for as much as I can get to make my troubleshooting a bit better targeted tomorrow. Thank you for the reply

hankthetank

Collapsed map? Dunno...I would hook up a timing light while cranking, just to see of I could tell if the coil was still sending current as soon as it caught and died...maybe right on the coil wire...

cruiser54

Jump the resistor to rule it out. Here's what to do with the grounds:

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

kidkodiak

Thanks Cruiser, that's good stuff there.

Well, the story ends well.

I wanted to close the thread out with the solution, for anyone else who might be in this situation in the future:

Turns out that the problem WAS the resistor. I couldn't believe it... it didn't look bad on casual glance, but looking more closely, one of the leads was badly corroded. I guess it just reached a point where it wasn't able to pass the right voltage to the fuel pump, so I wasn't fully pressurizing the injectors... at least that's what seems to be the case.

It got enough fuel to start, but w/o the right pressure in the lines, immediately died. At least, that's what seemed to be happening.

A quick run to O'Reilly's to the tune of $4.00 for new female 1/4" 16 gauge electrical connectors and some steel wool to clean the resistor posts and VOILA! The XJ started right up with no problems whatsoever.

I couldn't believe it. 3 days of troubleshooting and I was ready to replace the whole fuel system practically... and it was corrosion on one stupid resistor wire.

I'd never have known to look there other than from posts I'd read here... man I love this place. I've saved so much money from reading the advice of so many here who know these trucks well. Always makes me appreciative.

So thanks muchly

cruiser54

Congratulations. Having seen the result of old and faulty connections, you should now more than ever be motivated to do the ground refreshing.

DFlintstone

""Also you can always by-bass that ceramic fuel pump resistor on the fender by the air cleaner to see if that helps, but that doesn't sound like it.""

Well...Oops/Bingo! .......And, yea^ 2X, things work allot better with the wires connected.
Yea, forums rock! Well-done.

cruiser54

Flintstone, have you done your grounds yet?

DFlintstone

LOL! Yea..a normal day usually involves more than a few. I have an "extra" 1,100 W inverter here, just pulls the saw, (sort of), is fine with the angle grinder/drill/saws-all ect...When the Aux battery and that go in the JEEP I'll show you a pic of some clean dip-stick grounds, deal? (when I work out at Rock Creek, I can put solar panels on the roof-rack, no grid power there ether).

kidkodiak

haha, yep, add it to the list of upcoming maintenance projects on the old truck.

Thanks again, y'all

DFlintstone

Is this how it's suppose to look?

freegdr

NO!

cruiser54

On yours, yes. On mine, NO!

ck88jeep

had the same thing happen to me on my 88. ended up being the asd relay connections. i tightened them up and all is good now.