Intermittent stall and no start
07-29-2012, 06:53 PM
#1
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Year: 88
Model: Cherokee
Engine: Inline 6 4liter
Intermittent stall and no start
You guys probably get this one a lot.
I've been going thousands of miles without a lot of problems with my 88 4.0l. After I changed the fuel pump and fixed the overheating problem, it was running good - until a few days ago. I had gone on a half hour drive, stopped, then restarted the car after filling with gas. The parking lot was large so I was going for a few seconds without accelerating and then it stalled. Restarted just fine. Same thing happened in the evening, I started it up in a parking lot and rolled for a bit then it stalled.
Next day I drove it 5 minutes across town. Shut it off and then came back half hour later, and it wouldn't start. I tried about 4 times, then rolled it to a curb so I could run home and call someone. I figured while it was in neutral I would try again and it started up and I drove away.
I'm quite confused by this... Of course, it could be several things. But what and how should I go about testing it? Right now it is firing up every time.
some notes:
Recently I've not been getting bad mileage (20 on the freeway and 16-17 in town).
Often times when I first start the car it will idle way high for the first 30 secs or more, and sometimes if I tap the gas it will calm down.
I have 31psi at the rail and 39 without the vacuum line attached.. But then again that reading was when it was running good after I got home.
Any pointers?
I've been going thousands of miles without a lot of problems with my 88 4.0l. After I changed the fuel pump and fixed the overheating problem, it was running good - until a few days ago. I had gone on a half hour drive, stopped, then restarted the car after filling with gas. The parking lot was large so I was going for a few seconds without accelerating and then it stalled. Restarted just fine. Same thing happened in the evening, I started it up in a parking lot and rolled for a bit then it stalled.
Next day I drove it 5 minutes across town. Shut it off and then came back half hour later, and it wouldn't start. I tried about 4 times, then rolled it to a curb so I could run home and call someone. I figured while it was in neutral I would try again and it started up and I drove away.
I'm quite confused by this... Of course, it could be several things. But what and how should I go about testing it? Right now it is firing up every time.
some notes:
Recently I've not been getting bad mileage (20 on the freeway and 16-17 in town).
Often times when I first start the car it will idle way high for the first 30 secs or more, and sometimes if I tap the gas it will calm down.
I have 31psi at the rail and 39 without the vacuum line attached.. But then again that reading was when it was running good after I got home.
Any pointers?
07-29-2012, 08:32 PM
#2
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Year: 1997
Model: Cherokee
Engine: 4.0L
I don't know the renix motors real well... does that TB have a throttle position sensor? If it does that might be the first thing I'd check.
07-29-2012, 09:36 PM
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Year: 1990
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Engine: 4.0
Welcome good sir to the renix club
It could be your NSS, have you tried (with the key on accessory power) just shifting it though the gears like 50x, then try starting it, drive around, stop. give it a bit to rest then try to start it. sometimes they get a little gunk on the connections and that can cause the issue
secondly, it could be your CPS, next time it dies, if it doesnt restart after, try getting under it and tappin the cps with a wrench or something. its located on the drivers side (ish) of the top of the bell housing, a bit hard to get to, but if its not getting a good connection, that could cause it
next, check your battery terminals!! if its a side post especially.
It could be your NSS, have you tried (with the key on accessory power) just shifting it though the gears like 50x, then try starting it, drive around, stop. give it a bit to rest then try to start it. sometimes they get a little gunk on the connections and that can cause the issue
secondly, it could be your CPS, next time it dies, if it doesnt restart after, try getting under it and tappin the cps with a wrench or something. its located on the drivers side (ish) of the top of the bell housing, a bit hard to get to, but if its not getting a good connection, that could cause it
next, check your battery terminals!! if its a side post especially.
07-30-2012, 06:03 PM
#4
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Year: 88
Model: Cherokee
Engine: Inline 6 4liter
Ok. So today it failed again in the morning. So I first tried out the shifting like mad method, no luck. Then got underneath and wiggled the cord for the CPS and tried to hit it a bit with a wrench (kinda hard to reach for a wrench)... Then it started. However, I do note that the time interval was similar to last time, as in, last time I tried it a few times, then had it pushed a few feet, took a one minute break and then it started, and this time that break was about the same. So I'm not entirely sure the cord wiggling was what did it... But its possible
If I get a meter on the other side of the sensor, what should I look for on a failing CPS? Ohms or voltage, how much, etc? And will it even give results when it is working just fine... Hmm.
If I get a meter on the other side of the sensor, what should I look for on a failing CPS? Ohms or voltage, how much, etc? And will it even give results when it is working just fine... Hmm.
07-30-2012, 06:37 PM
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Year: 1990
Model: Cherokee
Engine: 4.0l 6Cyl
Try this.....
IV had similar issues and I wiggled my cps this morning and my xj started right off the bat. But here is the testing procedure.
IV had similar issues and I wiggled my cps this morning and my xj started right off the bat. But here is the testing procedure.
Originally Posted by cruiser54
Try this:
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
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
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07-30-2012, 10:56 PM
#8
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Year: 1990
Model: Cherokee
Engine: 4.0l 6Cyl
Originally Posted by 88cherokeepyles
Did I do it wrong?
I got 3 volts DC and 6.5v AC at the plug... The one that is accessible from under the hood.
I got 3 volts DC and 6.5v AC at the plug... The one that is accessible from under the hood.
07-30-2012, 11:53 PM
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Year: 1990
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Engine: 4.0
basically, you want to stick in the 'A' socket and ground socket. on the plug you should see the letters...try it with A-ground, B-ground, if either one looks like its in the .3-.5 range, tis all good.
remember you need to be checking this while trying to start the vehicle, and dont worry-without the cps connected it wont roar to life and drive away :P
remember you need to be checking this while trying to start the vehicle, and dont worry-without the cps connected it wont roar to life and drive away :P
07-31-2012, 01:05 AM
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Year: 88
Model: Cherokee
Engine: Inline 6 4liter
I set it at the smaller of the two AC readers, 200. The only other setting for AC is 750 on mine....
07-31-2012, 01:14 AM
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Ah. You need to measure at the connector attached to the wires for the CPS, (they go from the plug down to the bellhousing) not the mating connector that runs into the main wiring harness.
Depending on your meter the 200V scale may not have enough resolution to measure a fraction of a volt accurately, and the 750V scale would be worse. If there is only one digit to the right of the decimal point, you should see 000.5 or so
Depending on your meter the 200V scale may not have enough resolution to measure a fraction of a volt accurately, and the 750V scale would be worse. If there is only one digit to the right of the decimal point, you should see 000.5 or so
07-31-2012, 01:20 AM
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DFlintstone has a picture towards the bottom of this thread showing how to connect up to test the CPS:
https://www.cherokeeforum.com/f2/cps-swap-140917/
https://www.cherokeeforum.com/f2/cps-swap-140917/
07-31-2012, 01:27 AM
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Year: 88
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Sometimes when I read things it is hard to visualize what is actually meant. 
So it is the three prong plastic connecter with only 2 wires going to it, that heads down to the sensor that I measure? Then I put the positive into the A or B, and ground to something metal or just the empty hole... Correct?
I have a DC setting 20 v, but DC and AC are different...
So it is the three prong plastic connecter with only 2 wires going to it, that heads down to the sensor that I measure? Then I put the positive into the A or B, and ground to something metal or just the empty hole... Correct?
I have a DC setting 20 v, but DC and AC are different...