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1990 injector issues

F

feral badger

NAXJA Forum User
Location
Rio Rancho, NM
Just bought a non-running 1990 XJ 4.0/auto. When the key is turned to run(not start), the fuel pump(new) runs for about 3 seconds and when done, the injectors are energized. I went through all the grounds, checked sensors,etc. Anyone have any ideas on where to look? I was told the ecu was tested and was good(not that I believe the PO).
 
It will start but starts hard. Can only feather the pedal and get maybe 1700 rpm(tach doesn't work). Any more pedal and it dies. I tried 2 CPS's (both tested good) with no difference. Cleaned 90% of the connections. Tested the 4 relays. Set the TPS. One thing strange, the relays from front to back are; fuel, B+, O2 & A/C. I thought they should be O2,fuel, B+ & A/C. They're factory wired and look untouched. Also, about every other time I start it the Fuel and B+ relays are clicking rapidly.
 
do you have a fuel pressure gauge? I had a similar problem and the issue turned out to be low fuel pressure due to a hose coming off in the tank. Pretty easy thing to check just to rule it out.
 
Check the indexing on the distributor.
 
The old pump was at 37 psi and didn't sound right. Pulled it out and found that it didn't have a sock on it. I replaced it with a new pump assembly but it made no difference in the way it runs. It is now at 39/31 psi.
 
Hit a pull-n-save and grab a new ignition module and map sensor and give them a try. I wouldn't buy them new if you are going to shotgun.

What you are describing sounds like it is running too lean. Have you pulled the plugs and read them? How about a compression check. That will rule out most of the real pricey crap. Put a vacuum gauge on it and report the results. Low vacuum could signal a clogged cat.

I have 12 years experience diagnosing Renix systems and helping solve nasty problems. Give me a call and we can discuss this further.

Tom Houston
970-391-8927
 
Check your fuel pump ballast resistor on the driver's side inner fender near the air cleaner. Are the connections tight? You can jump across the 2 terminals for testing purposes and see if it runs.
 
cruiser54 said:
Check your fuel pump ballast resistor on the driver's side inner fender near the air cleaner. Are the connections tight? You can jump across the 2 terminals for testing purposes and see if it runs.
Click to expand...

X2, I would just eliminate the ballast resistor all together. Its not needed.
 
cruiser54 said:
Check your fuel pump ballast resistor on the driver's side inner fender near the air cleaner. Are the connections tight? You can jump across the 2 terminals for testing purposes and see if it runs.
Click to expand...

Connections are tight and I tried a jumper. Made no difference.
Just cleaned the large connection next to brake booster but have not tried to start it yet. I'm checking the wiring at and around the relays now.
 
feral badger said:
Connections are tight and I tried a jumper. Made no difference.
Just cleaned the large connection next to brake booster but have not tried to start it yet. I'm checking the wiring at and around the relays now.
Click to expand...

Here are a few things to do that just take a little time and no money and can bring great rewards.
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
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, and adding dielectric grease before plugging it back together. 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 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.
Revised 03/15/2012
 
I would also disconnect the knock sensor(lower drivers side of block near the motor mount bracket) Its also not needed and if its malfunctioning it will retard timing.
 
What's really got me baffled is when the key is turned to on, the fuel pump runs for 3-4 seconds(normal), but after the pump stops the injectors are energized and pump fuel for about 3 seconds then stop. This happens maybe 1 out of 3 times the key is turned to on.
 
feral badger said:
What's really got me baffled is when the key is turned to on, the fuel pump runs for 3-4 seconds(normal), but after the pump stops the injectors are energized and pump fuel for about 3 seconds then stop. This happens maybe 1 out of 3 times the key is turned to on.
Click to expand...

That is quite normal with fuel injected vehicles. My 1993 Toyota pickup does it, my wife Hyundai does that and the XJ does that.

I do not know the Renix system but I would look at the distributor timing then on to other things.
 
On my 89 MJ I ended up replacing the starter relay on the pass side near the other relays. Its a silver box and is only available at the dealer. It was the culprit on that Jeep as the symptoms stopped when the new relay was installed. I only had fuel pressure when cranking and then nothing once the key was dropped back to run. In other words the Jeep would crank, start, but as soon as I dropped the key back to run it would loose fuel pressure.

I can't explain it and I really do not know exactly what that relay controls but it was my issue.

The new relay was $60 at the dealer.
 
techno1154 said:
That is quite normal with fuel injected vehicles. My 1993 Toyota pickup does it, my wife Hyundai does that and the XJ does that.

I do not know the Renix system but I would look at the distributor timing then on to other things.
Click to expand...

None of our 4.0s have adjustable timing at the dizzy. It's all done by ECM or PCM.
 
cruiser54 said:
None of our 4.0s have adjustable timing at the dizzy. It's all done by ECM or PCM.
Click to expand...

But Cruiser, if its off a tooth either way it will run but not run "right". I was once told you could drop the dizzy in a 4.0 anywhere and it will run but I soon found out that was not true as the injectors will not be timed properly. Its waaay more touchy than I would have imagined.
 
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