idahomike

I recently bought a '89 Cherokee for my daughter for $750 and of course we're having trouble with it. It will run for awhile then randomly dies. Sometimes will go for couple miles, then dies. Had been dying after 5-10 miles. She was always able to restart. Never had trouble on the way home from school - about 20 miles. Until recently would always restart within a minute or two, but today it would not restart for about an hour. It has never died when I take the car for test drives. I've replaced the CPS, ECM, and cleaned grounds at firewall and on post behind the oil dipstick. Also checked fuel pressure on the fuel rail. At idle pressure is 30 psi, if rev motor to about 2000RPM (a guess with no tach) quickly rose to 32, then dropped to about 29 psi. Let idle for hour with back end sticking out of the garage hoping it would die so could watch the pressure gauge. But it never dies, and the pressures never changed. Just for fun I kept pressure gauge hooked up, and put car in drive and revved engine while standing on brakes until tires started to spin. Fuel pressure rose to about 38 psi. Are these fuel pressures good? What should the fuel pressure be? Any ideas? I have a new 2 gauge negative cable I intend to put on tomorrow, and add a better ground to the post behind dipstick. Thanks in advance! Mike

freegdr

Does it have spark when it wont start ?

cruiser54

Fuel pressure is good.

Click on the link below and do Tips 1,3,4, and 5.

Testing CPS output would be a good idea also. Tip 7.

idahomike

Freegdr - I was only with her the last time the Cherokee died. And that time I was on my way to work, so I didn't have time to try and diagnose it. Just called the tow truck, took her to school, and came back to meet the tow truck. So I don't know if it had spark or not.

Cruiser54 - Thanks for the link to the website with the different things to work on. I've cleaned the ground at the dipstick, and at the firewall, added a new ground between the firewall and the heat shield, and added a new 2 gauge negative ground, connected to the block (before had been connected to the dipstick stud along with the other grounds), and replaced the ground cable between the dipstick stud and the frame. So now it has four ground straps. Also cleaned the small grounds under hood hinge on passenger side, and on the driver side fender. Also, cleaned every electrical connection under the hood, including the ceramic resister on driver side fender. Haven't taken it out for a drive, but it idled in the garage for an hour without dying. I'll take it out this weekend and see what happens.

Thanks for the help!!

cruiser54

Woohoo!!!!!

F1Addict

While these symptoms could be a number of things, I would focus on your CPS. I would use Cruiser's guide to test for AC voltage at the harness and I would bring along some tools to check for spark when it dies. I realize that it was recently replaced but defective replacements are not unheard of, especially if it happens to be an aftermarket CPS rather than a MOPAR part.

idahomike

Okay, my son and daughter took the Cherokee out today because I was working on my truck. They made it about 4 miles and it died. it started back up again about 30 seconds. Then made it home. They didn't check for spark because they were on a narrow road that was pretty busy, and wanted to get moving.

I checked the CPS, and low and behold, it was only registering 0.1v. Not sure how accurate the multimeter is, because should it run that low? It runs, just wont stay running. Anyway, tomorrow I'll call NAPA and the dealer to see if they have one.

I hate buying new parts that aren't good! By the way, where is the ground for the CPS? Is it's connection to the bell housing?

Thanks, Mike

cruiser54

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 the upper mounting hole to 3/8” from the stock 5/16”, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.




Revised 01-26-2013

DFlintstone

Yes! Last fall at a yard sale an elderly gent mentioned his Renix Jeep would die at every stop sign with a new CPS. In less than 3 minutes I saw his was just that, a .1. No follow up there....

idahomike

Bad news. I installed a new CPS from NAPA and it started. However, again I only read 0.1v when cranking the motor. What are chances of getting two bad CPS units? No way to get a drill in there to enlarge the hole to 3/8" - at least not a straight hole! But I might be able to take the CPS back off and clean up the bell housing to get a better ground if that would help?

Could it be an issue with the flywheel?

Also, like I said, not sure my digital INNOVA multimeter is sensitive enough to pick up 0.5v. The lowest setting is 200v. Think that could be the problem?

I took it for a drive that was about 9 miles after changing the CPS. No problems, but still worried about my daughter taking it to school tomorrow. Its about 20 miles each way. And with 0.1v detected, seems likely could have the same issue again. Thoughts? Thanks,

cruiser54

Click on the link in my signature and go to Tip 7.

Also, if you haven't done tips 1,3,4, and 5, you're leaving yourself wide open to continued problems.

DFlintstone

I might have a little guarded faith. Granted it's not my daughter heading out. Two things. Meter aside your symptoms sounded very much like a failing cps, and seem to have cleared up. Also my last new Echlin'Napa) Cps tested low at first...35? I forget exactly. Then next I checked it was closer to .5.

No, that particular hall effect transducer operates independent of the grounds. The AC we measure is just from it ind the gaps/metal going past it. Removing it, drilling the hole, and remounting it closer to the flex-plate/flywheel can increase the output. I wonder if the auto parts store would let you use another meter for a minute?

idahomike

Well, on my third CPS, finally got one that produced more than 0.1v. This one generates between 0.3 and 0.4, staying mostly at 0.4v. Prior to installing it, I took sandpaper and lightly sanded the flywheel, to make sure there was a good connection on that side. The after drilling all three new CPS's out as described in #7. Third times a charm, almost. Took it for a drive, died leaving the driveway but started right up. Then about 2 miles down the road, it backfired, then seemed like the tranny downshifted and upshifted twice in about a second (two quick bucks) then everything was fine. Drive it about 10 miles with no other problems. Have completed 1, 3, 4, 5 and 7.

Any ideas about the backfire and the transmission shifting issue? When I got back and described what it did, my daughter said, oh yeah, it had done that a few times too. Thanks, Mike

DFlintstone

A new to me 90 was randomly dieing. I was a little surprised when adjusting the TPS cured that. The TPS affects more than shifting! Btw mine still doesn't always up-shift right, after it's been sitting hot. Different issue I suppose.

cruiser54

Not gonna waste any time on the Tips, eh?