I have a 1990 Cherokee Renix and it won't start. I've figured out that the injectors are not firing. I've replaced the CPS twice, the last one was NAPA Echlin. I have a new PCM/computer. I've checked my grounds, cleaned and they are tight. I do have spark at the plugs. Any help would be appreciated. I've read lots of old threads and none have helped me.

 

Your getting no signal from injectors when testing with noids.

 

Did you check for fuel pressure at the rail? Need to verify fuel is being delivered. Do you hear the fuel pump prime when you turn the key to run? Remove connector from one injector and check to see if 12 V is present intermittently while cranking. Spark, fuel, air and compression are the things that have to be present to fire. Also timing must be correct so that fuel is going in at the right time. Need to be systematic to rule out the obvious stuff like all fuses good etc.

 

Check fuel pressure with a gauge.

 

yes I did check pressure with gauge and I do have fuel pressure approx 40lbs. Fuel pump is newer and it does run when I turn the key on and then it turns off after maybe 5 sec. I was testing the injectors with my digital voltmeter while cranking and did not get 12V. I ordered a noid light test kit. As far as timing, I installed a rebuilt distributor and rotor and cap and it was running good with this new distributor right before this happened. I disconnected the Cam sensor connector at the distributor and it still would not start. Thanks for everyone's replys so far.

 

it seems that they are not being "told" to open up. check your wiring from the pcm. check for bad grounds or opens in the harness

 

While waiting for the noid light, try 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

 

Ok, so I got my noid light in and confirmed that the fuel injectors are NOT firing. Any help would be greatly appreciated.

 

Somebody on NAXJA had the same issue last week. Turns out the injectors weren't grounding.

Here's why:

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, failed emission tests, and wasted money replacing components unnecessarily.
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.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
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 03-04-2013

 

You checked all plugs and no light on any ? Grounds ? Ecm ?

 

Yes I have checked the oil dipstick ground, cleaned and retightened. I have also cleaned and checked ground from firewall to back of block. I have replaced the negative batt cable. (Cruiser 54 I have read all your stuff, and tried most, thanks)

I did not check every injector but I figured if one's not firing and it won't run at all, then none are firing. Plugs are sparking.

I am on my 3rd ecm. This one is remanufactured from Advance Auto.

Maybe this info will help: This all started because it was running very rough, coughing/hacking. I put on a new distributor, rotor and cap. New coil and coil wire (cleaned connections per Cruiser 54). New fuel pres regulator. Then I realized the fuel pump resistor was cracked so I jumped it and it ran perfect in the driveway for maybe 5 minutes and I shut it off. The next day it wouldn't start. I found that the CPS wires were touching the manifold and all the insulation was completely burned thru. So I replaced the CPS with one from Advance and it still wouldn't start. Then I tried NAPA Echlin and still no luck. New ECU - no luck. Now after testing I know the injectors aren't firing. Help!

 

For each fuel injector, there are two wires (+ and ground). So, if you can't get the noid to light, I would put the multimeter on the two wires to see if there is any voltage coming through. I believe 12 volts is sent to trigger the injector solenoids. See if you see any positive voltage while cranking. One of the two wires is ground so I would also check the resistance to ground (should be less than 2 ohms to ground). If you have both showing high resistance, you know there's a ground problem and the injectors aren't getting the voltage to open. The ECU triggers the solenoids on the injectors based upon the readings from the CPS. I'm thinking one of the ground crimps in the main harness is off. You've done the main grounds on dipstick and firewall to block but that doesn't mean the harness is still carrying the ground to the injectors.

I burned the CPS harness on mine too when I replaced it. That exhaust manifold is hot. I put wire-loom split conduit on my CPS cable and zipped tied it so that it can't come into contact with anything hot. Use the nylon (high temp) wire loom for this. The normal wireloom is ABS I think and just melts on anything warm.

 

Have you tested the CPSs?

 

All of the above are good suggestions! I just wanted to add my 2 cents, because I had a similar sounding issue,see my thread https://www.cherokeeforum.com/f2/198...orking-167142/

Take a few minutes and visually check all of your wiring. I found the hard way it is very easy to accidentally clip a wire, and in return cause yourself a massive headache. I had accidentally snagged a wire to my MAP sensor and it showed the same symptoms as your have now.

Good luck.

 

Just curious is your XJ a stick or auto? If it's a stick you may have a leaky clutch master leaking onto the back of the fuse panel shorting things out.