Fuel pressure phenom
02-24-2013, 01:29 PM
#1
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Fuel pressure phenom
OK so I have been having thermal failure upon re-start.
Today I rechecked my fuel pressure thinking I have a leak down somewhere.
Today I rechecked my fuel pressure thinking I have a leak down somewhere.
Cold start is fine but starts to run ruff after 3 to 4 minutes. Pressure is 31 at idle & 39 with vac. hose off of regulator. Upon shutdown it doesn't go down more than 15 to 20 psi. That's with a COLD engine.
If I let the engine get up to normal operating temp & test I get 31 & 39 with the vac hose off.
Replace the vac hose & it goes back to normal 31psi. When I shut the engine down & leave the tester connected the pressure goes UP.The pressure goes from 31psi hot & in less than 5 minutes it's up to 40 psi & looks like it still want to climb???
Climbing when at operating temp & falling when cold.
Input?
Replace the vac hose & it goes back to normal 31psi. When I shut the engine down & leave the tester connected the pressure goes UP.The pressure goes from 31psi hot & in less than 5 minutes it's up to 40 psi & looks like it still want to climb???
Climbing when at operating temp & falling when cold.
Input?
02-24-2013, 04:37 PM
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According to the Haynes manual when you have trouble with hot start, hook up the tester, start & idle, if it's in specs (note it) shut her off, if it drops more than 20 psi in 30 minutes do a restart let her idle, pinch of the fuel return hose & the pressure should go up to 95psi.
Shut down & note the reading on the gauge. Let sit for 30 mins. & then compare to the original shutdown reading.
They then say if the P has dropped 20 or less, replace the regulator. If the P has dropped considerably more than 20, replace the pump.
So I decided to give it a try. So at idle I was 31 & with vac hose off I'm at 39. I put the vac hose back on & goes right back to 31. Perfect.
I shutdown. So 10 mins. later I come out & she's down to about 5psi. Hot she's up to 40 plus. But this time she's at 5.
I do the above leak down test & when I pinched the return line instead of my pressure going UP to 95psi.......she goes straight down quick & almost cuts off.......
WTH ?
Shut down & note the reading on the gauge. Let sit for 30 mins. & then compare to the original shutdown reading.
They then say if the P has dropped 20 or less, replace the regulator. If the P has dropped considerably more than 20, replace the pump.
So I decided to give it a try. So at idle I was 31 & with vac hose off I'm at 39. I put the vac hose back on & goes right back to 31. Perfect.
I shutdown. So 10 mins. later I come out & she's down to about 5psi. Hot she's up to 40 plus. But this time she's at 5.
I do the above leak down test & when I pinched the return line instead of my pressure going UP to 95psi.......she goes straight down quick & almost cuts off.......
WTH ?
Last edited by randall L; 02-24-2013 at 08:22 PM.
02-24-2013, 07:20 PM
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So, hot you're building pressure in the rail?
02-24-2013, 08:19 PM
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Yes.....I did that test 3 times. Cold it goes down but stays within Haynes specs(whatever that's worth) Hot I have 31 & 39 with the vac hose on & off. Then when I switch it off it immediately starts creeping up. 40 & climbing. I disconnected the tester after the last check (engine off) & after I released fuel from the tester bleed hose........boxed it up & was about to put the port cover back on the rail & had a thought to press the valve stem on the rail port........fuel sprays out big time. I had rags around the area so there was no fire. But it had been shut down for at least 10 or more minutes & after bleeding the tester hose & removing the port hose it continued to BUILD PRESSURE???
Last edited by randall L; 02-24-2013 at 08:23 PM.
02-24-2013, 08:37 PM
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While searching for answers I discovered this article. Anybody ever seen it before?
Models:
1989 MJ & XJ Bodies
Subject:
4.0L No-Start, Hard Restart, or Engine Die-Out. Vehicles Equipped With Automatic Transmission Only.
Index:
DRIVEABILITY
Date: December 29, 1989 No.: 18-57-89 (C18-23-9) P-14
Body Code Legend:
MJ - COMANCHE (RWD, 4WD) XJ - CHEROKEE/WAGONEER (RWD, 4WD)
SYMPTOM/CONDITION:
Some 1989 vehicles equipped with the 4.0L engine and automatic transmission may experience an engine no-start, hard restart, or an engine die-out. This condition may be caused by low signal strength from the crank position sensor due to a larger than desired distance to the flywheel sensing ring.
DIAGNOSIS:
Check to see if the vehicle has a slotted crank position sensor:
1. If the vehicle is equipped with a slotted crank position sensor (see Figure 1), check to see if the CPS grommet on the top of the transmission bell housing has been updated (see Figure 2). If the CPS grommet has not been updated, replace the CPS grommet per the Repair Procedure outlined below.
If the vehicle has a slotted crank position sensor and new CPS grommet, do not install a new sensor, but reinstall the slotted sensor that was on the vehicle and verify that it is good using procedures in the 1989 Jeep Service Manual 81-370-9045 on page 14-87.
2. If the vehicle does not have a slotted crank position sensor already installed, then proceed with the Repair Procedure.
PARTS REQUIRED:
1 Crank Position Sensor (slotted) P/N 83100067
1 Crank Position Sensor Grommet P/N 83100068
REPAIR PROCEDURE:
1. Turn the ignition switch to the "OFF" position.
2. Disconnect the Crank Position Sensor (CPS) from the engine harness.
3. Raise the vehicle using a lift.
4. Remove the old CPS and grommet.
5. Install the new CPS grommet.
NOTE: THE NEW CPS GROMMET MUST BE REPLACED SO THAT THE MAXIMUM SIGNAL OUTPUT CAN BE OBTAINED FROM THE NEW CRANK POSITION SENSOR.
6. Install the new Crank Position Sensor and loosely attach the retaining bolts.
7. Firmly press down on the slotted hole side of the CPS until it bottoms on the machined lip of the bellhousing. While holding the CPS down against the bellhousing, tighten the bolt on the slotted side of the CPS to 16 ft.lbs.
8. Tighten the remaining attaching bolt to 16 ft.lbs.
NOTE: MAKE CERTAIN THAT THE CRANK POSITION SENSOR IS COMPLETELY BOTTOMED ON THE MACHINED LIP OF THE BELLHOUSING AND IS AS CLOSE AS POSSIBLE TO THE FLYWHEEL SENSING RING WITHOUT CONTACTING IT.
9. Secure the lead of the CPS to the retaining clip on the bellhousing to prevent its contact with the exhaust manifold.
10. Lower the vehicle.
11. Connect the CPS to the engine harness.
If this repair has been made, or hasn't fixed the problem, the other TSB is 18-54-89 REVISION A recommending cleaning of the throttle body assembly, DIY: Cleaning Throttle Bodies, and replacement of the PCM.
PARTS REQUIRED:
1 ECU (Automatic Transmission) P/N 53007842
1 ECU (Manual Transmission) P/N 53007843
1 Mopar Choke and Linkage Cleaner P/N 4549619
Models:
1989 MJ & XJ Bodies
Subject:
4.0L No-Start, Hard Restart, or Engine Die-Out. Vehicles Equipped With Automatic Transmission Only.
Index:
DRIVEABILITY
Date: December 29, 1989 No.: 18-57-89 (C18-23-9) P-14
Body Code Legend:
MJ - COMANCHE (RWD, 4WD) XJ - CHEROKEE/WAGONEER (RWD, 4WD)
SYMPTOM/CONDITION:
Some 1989 vehicles equipped with the 4.0L engine and automatic transmission may experience an engine no-start, hard restart, or an engine die-out. This condition may be caused by low signal strength from the crank position sensor due to a larger than desired distance to the flywheel sensing ring.
DIAGNOSIS:
Check to see if the vehicle has a slotted crank position sensor:
1. If the vehicle is equipped with a slotted crank position sensor (see Figure 1), check to see if the CPS grommet on the top of the transmission bell housing has been updated (see Figure 2). If the CPS grommet has not been updated, replace the CPS grommet per the Repair Procedure outlined below.
If the vehicle has a slotted crank position sensor and new CPS grommet, do not install a new sensor, but reinstall the slotted sensor that was on the vehicle and verify that it is good using procedures in the 1989 Jeep Service Manual 81-370-9045 on page 14-87.
2. If the vehicle does not have a slotted crank position sensor already installed, then proceed with the Repair Procedure.
PARTS REQUIRED:
1 Crank Position Sensor (slotted) P/N 83100067
1 Crank Position Sensor Grommet P/N 83100068
REPAIR PROCEDURE:
1. Turn the ignition switch to the "OFF" position.
2. Disconnect the Crank Position Sensor (CPS) from the engine harness.
3. Raise the vehicle using a lift.
4. Remove the old CPS and grommet.
5. Install the new CPS grommet.
NOTE: THE NEW CPS GROMMET MUST BE REPLACED SO THAT THE MAXIMUM SIGNAL OUTPUT CAN BE OBTAINED FROM THE NEW CRANK POSITION SENSOR.
6. Install the new Crank Position Sensor and loosely attach the retaining bolts.
7. Firmly press down on the slotted hole side of the CPS until it bottoms on the machined lip of the bellhousing. While holding the CPS down against the bellhousing, tighten the bolt on the slotted side of the CPS to 16 ft.lbs.
8. Tighten the remaining attaching bolt to 16 ft.lbs.
NOTE: MAKE CERTAIN THAT THE CRANK POSITION SENSOR IS COMPLETELY BOTTOMED ON THE MACHINED LIP OF THE BELLHOUSING AND IS AS CLOSE AS POSSIBLE TO THE FLYWHEEL SENSING RING WITHOUT CONTACTING IT.
9. Secure the lead of the CPS to the retaining clip on the bellhousing to prevent its contact with the exhaust manifold.
10. Lower the vehicle.
11. Connect the CPS to the engine harness.
If this repair has been made, or hasn't fixed the problem, the other TSB is 18-54-89 REVISION A recommending cleaning of the throttle body assembly, DIY: Cleaning Throttle Bodies, and replacement of the PCM.
PARTS REQUIRED:
1 ECU (Automatic Transmission) P/N 53007842
1 ECU (Manual Transmission) P/N 53007843
1 Mopar Choke and Linkage Cleaner P/N 4549619
02-24-2013, 08:41 PM
#7
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Yep. That's where this came from:
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
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
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02-24-2013, 08:50 PM
#8
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I have a new MOPAR CPS with less than 300 miles on it. Now I'm wondering if it's the right one & if it's installed right ?
Aside from the wackey fuel test & re-test my problem may go back to this article.
possible suicide
Aside from the wackey fuel test & re-test my problem may go back to this article.
possible suicide
02-24-2013, 08:51 PM
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02-24-2013, 08:59 PM
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Can't wait till daylight to do that test. May have nightmares tonight about my fuel pressure though.
May be a demon or something.........
May be a demon or something.........
02-24-2013, 09:52 PM
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BTW......should the CPS test be done hot or cold or both? In other words my problem is ONLY when it's warmed up. So my logic says test it warm & see if it's .5.
My logic could very well be mistaken......
My logic could very well be mistaken......
02-24-2013, 10:04 PM
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02-25-2013, 05:57 AM
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How high above 40 psi is the fuel pressure at those times? You could try starting it with the fuel pressure gauge hooked up with everything warm. Monitor the pressure.
02-25-2013, 05:23 PM
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I put the fuel pressure issue aside today.
In between these frickin rain showers EVERYDAY I managed to only test the CPS & once again the TPS. Several test on each unit.
CPS I'm getting a steady res. @ 236. That ain't good from my research. Believe it's suppose to be tween 125 & 175. On the volt side I'm only getting .2 so I've got to get this adjusted. It's a brand new MOPAR but it ain't right.
The TPS is whacko. I'm getting a steady reference of 4.86 but my output I'm not getting even close to the 17%. As a matter of fact I'm getting ZEROS on my meter.
No more parts throwing until these 2 items are resolved. If I can do that.
still on suicide watch.........
In between these frickin rain showers EVERYDAY I managed to only test the CPS & once again the TPS. Several test on each unit.
CPS I'm getting a steady res. @ 236. That ain't good from my research. Believe it's suppose to be tween 125 & 175. On the volt side I'm only getting .2 so I've got to get this adjusted. It's a brand new MOPAR but it ain't right.
The TPS is whacko. I'm getting a steady reference of 4.86 but my output I'm not getting even close to the 17%. As a matter of fact I'm getting ZEROS on my meter.
No more parts throwing until these 2 items are resolved. If I can do that.
still on suicide watch.........
02-25-2013, 05:26 PM
#15
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I put the fuel pressure issue aside today.
In between these frickin rain showers EVERYDAY I managed to only test the CPS & once again the TPS. Several test on each unit.
CPS I'm getting a steady res. @ 236. That ain't good from my research. Believe it's suppose to be tween 125 & 175. On the volt side I'm only getting .2 so I've got to get this adjusted. It's a brand new MOPAR but it ain't right.
The TPS is whacko. I'm getting a steady reference of 4.86 but my output I'm not getting even close to the 17%. As a matter of fact I'm getting ZEROS on my meter.
No more parts throwing until these 2 items are resolved. If I can do that.
still on suicide watch.........
In between these frickin rain showers EVERYDAY I managed to only test the CPS & once again the TPS. Several test on each unit.
CPS I'm getting a steady res. @ 236. That ain't good from my research. Believe it's suppose to be tween 125 & 175. On the volt side I'm only getting .2 so I've got to get this adjusted. It's a brand new MOPAR but it ain't right.
The TPS is whacko. I'm getting a steady reference of 4.86 but my output I'm not getting even close to the 17%. As a matter of fact I'm getting ZEROS on my meter.
No more parts throwing until these 2 items are resolved. If I can do that.
still on suicide watch.........