gwbarm

I have been working on this 90 jeep cherokee straight 6 4Litre for a while, i have owned it since 97 until now it has been the most reliable vehicle i have ever owned.

It started about 6 months ago the fuel pump went out. I replaced the fuel pump put in new fuel filter. Drove it about 50 miles on new pump. My son was using it it dies on the interstate had it towed home. I have been working on it ever since. I got it running by replacing the fuel pump relay, but it didnt run very good like flooding or missing. I put in new plugs new wires new distributer cap checked the timing chain thats the end of round one nothing helped.

I picked back up working on it this spring replaced crankshaft position sensor, Map sensor, throttle position sensor, oxygen sensor, Iac motor, nothing seemed to fix my problem.

Round 3 i decided to go back to the basics gas and fire which i already knew that it had because it will run, but when you put a load on it it does not stall but you can tell its not right, like a miss. So i did a compression check since it had 170000 miles on it 120 across the board. Then i started pulling plug wires, pulled the #6 wire and no change. So i had the bright idea to see if the injectors are firing i thought i could unhook the coil and crank over the engine and see which plugs were dry then i would know which injectors to replace. That didnt work they were all dry. These are new plugs champion and they were black and sooty just like a rich mixture. I know something is wrong with #6 more than likely the injector but i havent been able to prove that yet.

I keep going back over this in my mind and it started with the new fuel pump something must have happened to take out the relay so soon after replacing the pump. So i dont know wheather to pull the pump even though the pressure is right on at 31 running and 39 without the vacum line on the regulator. or to pull the fuel rail or if im even looking in the right direction. Maybe the computer went out and took out the relay.

Im fairly good with engines but i am at a loss as what to do next. Any ideas from you experts would be greatly appreciated.

Jeepney

Does your model have a check engine light?..you might want to scan it for codes if it does.

gwbarm

No mine does not! but someone posted that you could pull codes with a obdII reader but the plugs wernt the same and i could not figure it out.

askingxforxit

Thats because you need an OBDI scanner. OBDII is for '96 and above

jakbob

if it is a 90, i believe that is renix. not obd 1. you need a DRB II computer.

NWhunter

I would go through all six injectors to confirm there tight, and hooked up. Try running some lucas fuel injector cleaner through it. Check the ground on the fuel pump. Make sure your wires are all in the right firing order. Beyond that, I'm stumped.

akita8

I would check the vacuum line from the MAP sensor to the throttle body and take the grounds off by the oil dip stick bolt and clean them up.

cruiser54

Wiggle #6 injector connector with the engine running and see what happens.

gwbarm

I didn't get to work on it much this evening. I appreciate all the good suggestions.I will check all the plug wires cause i did pull them on and off a few times. I put a cleaner called chem-tool in very little gas less than 1/4 of a tank cause i thought trash may have got in the fuel line after changing the pump. One sensor i haven't replaced is the coolant temp sensor, i think it can cause flooding. I also haven't adjusted the new throttle position sensor with a meter but i did move it around and it didnt seem to make any difference where it was maybe if it was running right i would notice the difference. I do need a new vacum line to the map sensor the connector to the throttle body has some issues but i think its working because it did run differently when i put the new one on. I tried to unplug #6 injector i think thats where my problem is but it was getting dark and i couldn't remember the procedure. I did try one other think that surprized me normally when its running and i unplug the fuel pump ballast resistor the engine dies. I unplugged it this afternoon and it didnt kill the engine so something has changed. I think i will replace that.

There are a few other things i was thinking of. The crank position sensor air gap i couldnt really see how to set it and it ran no better with the new one in.
There is also a sensor on the manifold i havent changed it is similar to the coolant temp sensor i cant remember what it was called. I was even thinking of the main computer and the camshaft position sensor i haven't replaced.

Again Thanks everyone for the help.

cruiser54

CPS testing instructions but I doubt it's your problem:

Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
　
Revised 11-29-2011

DFlintstone

Wow GW, you're really goen at it! First thing I did after installing my new cps a few months ago was to check it's function. Literally only seconds, to know it's working right. Of course you are just chasing your tail if it isn't.

Black sooty plugs? Some issue with the map tube? Definitely something there you want to resolve. I actually used a small extractor, (but a screw would work), to extract the busted stub out of the rubber plug in my TB. If the map doesn't see good manifold vacuum it will think you have your foot in it and tell your ECU to dump extra fuel.

Your dizzy just needs to distribute the spark, It will run OK with it unplugged.

It stores no codes. The DRBII scanner is so rare you may as well forget it.

Allot of guys can the stock one hole injectors and up-grade to the 4 hole design, even when everything is fine. I'm glad I did.

That resistor is unnecessary, the pump would just be louder without it. I'd clean all the relay sockets with ele. cleaner, assemble with dielectric grease. 5 minutes well spent.

You have two temp sensors that might make it rich, one down on the left side, and one on the intake.

In the "20 links", link here there is stuff on those, then I'm posting Cruisers Ground writeup. There is great logic in cleaning up wiring connections. Often that's the problem, and if it's not now it's something good to anyway.

https://www.cherokeeforum.com/f51/he...ix-links-1397/
Revised 11-29-2011




Renix Ground Refreshin
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.

gwbarm

I went back after it this afternoon. Pulled all the plugs they are all sooty except #6 which is the cylinder that i can pull the plug wire off and no change, so i think this injector is not firing. Then i took the grounds loose and cleaned them up.

You are right it seems like im chasing my tail but would 1 injector not firing cause all the other plugs to be sooty, im not sure but i dont think so, so that may not be the root of my problem.I did think about the relay connector, a new relay is how i got it back running, but my fuel pressure is fine.

There is one thing thats been bothering me, all this happened within days of replacing the fuel pump. My thoughts are that maybe the sock fell off the pump as i was putting it back in the hole. I have no way of knowing that and trash and sludge from the bottom of the tank got into the fuel system, the filter should get it but maybe small particles got through the filter. Does this seem possible even though my fuel pressure is good.

One other thing i haven't mentioned is the starting. It is hard to start. I turn the key on for 10 seconds to pressure up the system because it does loose pressure down to 0 in 15 minutes. I crank the engine for 5 seconds it hits. I stop and crank for 5 more seconds it pops again i do this about 3 more times and it finally starts. It does stay running until i kill it.

I do want to replace the injectors any one know of good ones to get for my 90 model.


Thanks for all the input.

cruiser54

Replacing the original injectors on a Renix is never a bad idea. Some members of this forum supply cleaned, 4 hole injectors. Perhaps they will chime in. Have you wiggled the wires to #6 or checked it with a noid light?

gwbarm

I have wiggled the connector, to #6 fuel injector and checked the spark plug wire . What is a noid light

gwbarm

Sorry for my inexpierience with fuel injection i just googled noid light and no i havent checked the wiring thats 1 tool i havent bought yet.