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cps or fuel pump? 99xj.

J

justins99xj

NAXJA Forum User
Location
Oklahoma City, OK
Okay, so the other day I noticed my rpms drop off while driving city streets. It wasn't a slow drop, just an imediate drop off that lasted for about a second. The check engine light only popped up for a second then went off. So the next day I checked the codes... nothing, no codes.
So I thought maybe just a small glitch, no big deal, proly won't happen again. Well the problem only got worse. My XJ died in the middle of an intersection last night and wouldn't start for a minute, crank but no start. Got it to start but then died again a half mile down the road.
Anyway, even though the check engine light isn't on I went and had the codes pulled again and no codes, and died again on the way home. Did a search here and came up with cps or fuel pump, but past issues with other cars makes me think it's not the fuel pump because it dies immediately, not a slow die off of rpm's. anyone have any ideas? or is there a way to test the cps?
thanks in advance.
 
if the CPS was bad there wouldn't even be a crank. If i remember corecctly there won't be a crank. The fuel pump....not to sure about that either. I doesn't help that you don't have an codes. I now there is a vacuum line for the rpms, but to sure after that. sry if you get some codes that will help out a lot. how many miles on your xj??? maybe it is time to replace the cps. my 99 has almost 125,000 miles on it so it's time to do mine.
 
VTEK1 said:
if the CPS was bad there wouldn't even be a crank. If i remember corecctly there won't be a crank. The fuel pump....not to sure about that either. I doesn't help that you don't have an codes. I now there is a vacuum line for the rpms, but to sure after that. sry if you get some codes that will help out a lot. how many miles on your xj??? maybe it is time to replace the cps. my 99 has almost 125,000 miles on it so it's time to do mine.
Click to expand...
It's about to hit 170,000. I've only had it for a month or so and don't know what has recently been done to it, as far as sensors that have been replaced. It is in really good shape so it makes me belive it was well taken care of.
No codes make me think it might be a fuel issue but then again I'm new to Jeep's. I have also briefly looked for vac leaks. I'll take another look right now.
 
Crank Position Sensor is a pretty likely candidate here. You tried listening to the tank when you turn the ignition on? Either way, I'd borrow a fuel pressure guage from Autozone and check your fuel pressure before you go to the effort of pulling the tank.
 
lawsoncl said:
Crank Position Sensor is a pretty likely candidate here. You tried listening to the tank when you turn the ignition on? Either way, I'd borrow a fuel pressure guage from Autozone and check your fuel pressure before you go to the effort of pulling the tank.
Click to expand...
Yeah I have, nothing out of the ordinary, I hear it when I turn on the ignition, but sinse it only happens while driving (so far) I don't know for sure if it's cutting out.
Where exactly is the cps? I'd like to take a look at it, see if it has a loose/ bad connection.
thanks.
 
justins99xj said:
Yeah I have, nothing out of the ordinary, I hear it when I turn on the ignition, but sinse it only happens while driving (so far) I don't know for sure if it's cutting out.
Where exactly is the cps? I'd like to take a look at it, see if it has a loose/ bad connection.
thanks.
Click to expand...
Okay I searched and now know where it's located and am going to take a look. anyone feel free to chime in if they think it may be something else.
 
Not my info, but somebody else's that I copied because it seemed good.

CPS will cause it to crank and crank and crank, but never fire up. CPS is located on the drivers side, at about 11:00 on the bellhousing.
Diagnostic steps to confirm the CPS is the cause of your no-start

You might be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.

CPS Testing


Crankshaft Position Sensor Connector

With connector tab at top ABC is right to left.

TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines
1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (SEE Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.


That is how to check the CranK Position sensor. You inquired. I don't understand your title though. It seems like you should be asking what could be wrong and how to check it out instead of ass-u-mi-ng that it has to be the fuel pump or the CKP. You may want to start a new thread asking a better question.
 
Last edited:
VTEK1 said:
if the CPS was bad there wouldn't even be a crank. ....
Click to expand...
Simply not true. If the Crankshaft Position Sensor (CPS/CKP) has failed, one of the main symptoms is cranking a cranking but not starting up and running.


VTEK1 said:
.... I now there is a vacuum line for the rpms
Click to expand...


What ?






The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP) CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again (and will test as “good”) when it cools back down.


Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU will behave oddly until you remedy this.



Symptoms –
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauges may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump will usually run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBDII code reader cannot make a connection to the ECU/computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed. Disconnect the code reader, disconnect the CPS/CKP wire connector, and reconnect the code reader. If the code reader establishes contact with the ECU and scans, your CPS/CKP is failed and needs to be replaced.


Diagnostic steps to confirm the CPS is the cause of your no-start


You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly, replace the CPS.


Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication.


CPS Testing


Crankshaft Position Sensor Connector (CPS/CKP)


standard.jpg



TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines
1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 – 275 Ohms. . If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.


The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector may be on the passenger side, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.

.
standard.jpg
 
[/QUOTE]That is how to check the CranK Position sensor. You inquired. I don't understand your title though. It seems like you should be asking what could be wrong and how to check it out instead of ass-u-mi-ng that it has to be the fuel pump or the CKP. You may want to start a new thread asking a better question.[/QUOTE]

After searching I found that the most common problem seemed to be fuel pump or cps, seems to fit my symptoms, right?
Anyway thanks for the link.:worship:
 
Symptoms –
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauges may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump will usually run and prime for 3-5 seconds.
fuel and voltage gauge work fine.
odometer normal no "no bus"
no codes.
can't test the spark right now cause it only happens sometimes.

I also don't have an ohm meter at my disposal at the moment. I have one at work so I guess I'll test it tomorrow. I did find what may have been a small vac leak between, the valve cover and intake manifold, it was a little loose but I don't think it was anything big becaus no check engine light. I'll post again after testing tomorrow. Thanks to everyone who chimed in.:thumbup:
 
Tim_MN said:
The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again (and will test as “good”) when it cools back down.
Click to expand...
 
Tim_MN said:
Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when engine gets hot, but works again (and will test as “good”) when it cools back down.
Click to expand...
I had a thermal failure on a defective replacement CPS. I could keep the engine running by pouring cool water on it. Stop the water, engine stopped. I confirmed it failure by heating the CPS to 200 in the oven and checking the resistance.
 
Well after changing the ckps no luck, the problem only seemed to get worse. I guess I should start looking elsewhere. I'm thinking I may try heating and cooling the ckps with a hair drier and water, idk? Maybe I got a bad part. I think I may start looking at the fuel pump. So did chrysler really design these without an access panel to the fuel pump?
 
Test the fuel pressure at the fuel rail. With the engine running, you should have 49psi +/- 3psi.

Test the (CMP) Camshaft Position Sensor

standard.jpg


standard.jpg


For this test, an analog (non-digital) voltmeter
is needed. Do not remove the distributor connector
from the distributor. Using small paper clips,
insert them into the backside of the distributor wire
harness connector to make contact with the terminals.
Be sure that the connector is not damaged
when inserting the paper clips. Attach voltmeter
leads to these paper clips.
(1) Connect the positive (+) voltmeter lead into the
sensor output wire. This is at done the distributor
wire harness connector. For wire identification, refer
to Group 8W, Wiring Diagrams.
(2) Connect the negative (-) voltmeter lead into the
ground wire. For wire identification, refer to Group
8W, Wiring Diagrams.
(3) Set the voltmeter to the 15 Volt DC scale.
(4) Remove distributor cap from distributor (two
screws). Rotate (crank) the engine until the distributor
rotor is approximately in the 11 o’clock position.
The movable pulse ring should now be within the
sensor pickup.
(5) Turn ignition key to ON position. Voltmeter
should read approximately 5.0 volts.
(6) If voltage is not present, check the voltmeter
leads for a good connection.
(7) If voltage is still not present, check for voltage
at the supply wire. For wire identification, refer to
Group 8W, Wiring Diagrams.
(8) If 5 volts is not present at supply wire, check
for voltage at PCM 32-way connector (cavity A-17).
Refer to Group 8W, Wiring for location of connector/
terminal. Leave the PCM connector connected for
this test.
(9) If voltage is still not present, perform vehicle
test using the DRB scan tool.
(10) If voltage is present at cavity A-17, but not at
the supply wire:
(a) Check continuity between the supply wire.
This is checked between the distributor connector
and cavity A-17 at the PCM. If continuity is not
present, repair the harness as necessary.
(b) Check for continuity between the camshaft
position sensor output wire and cavity A-18 at the
PCM. If continuity is not present, repair the harness
as necessary.
(c) Check for continuity between the ground circuit
wire at the distributor connector and ground.
If continuity is not present, repair the harness as
necessary.
(11) While observing the voltmeter, crank the
engine with ignition switch. The voltmeter needle
should fluctuate between 0 and 5 volts while the
engine is cranking. This verifies that the camshaft
position sensor in the distributor is operating properly
and a sync pulse signal is being generated.
If sync pulse signal is not present, replacement of
the camshaft position sensor is necessary
 
Tim_MN said:
Test the fuel pressure at the fuel rail. With the engine running, you should have 49psi +/- 3psi.

Test the (CMP) Camshaft Position Sensor

standard.jpg


standard.jpg


For this test, an analog (non-digital) voltmeter
is needed. Do not remove the distributor connector
from the distributor. Using small paper clips,
insert them into the backside of the distributor wire
harness connector to make contact with the terminals.
Be sure that the connector is not damaged
when inserting the paper clips. Attach voltmeter
leads to these paper clips.
(1) Connect the positive (+) voltmeter lead into the
sensor output wire. This is at done the distributor
wire harness connector. For wire identification, refer
to Group 8W, Wiring Diagrams.
(2) Connect the negative (-) voltmeter lead into the
ground wire. For wire identification, refer to Group
8W, Wiring Diagrams.
(3) Set the voltmeter to the 15 Volt DC scale.
(4) Remove distributor cap from distributor (two
screws). Rotate (crank) the engine until the distributor
rotor is approximately in the 11 o’clock position.
The movable pulse ring should now be within the
sensor pickup.
(5) Turn ignition key to ON position. Voltmeter
should read approximately 5.0 volts.
(6) If voltage is not present, check the voltmeter
leads for a good connection.
(7) If voltage is still not present, check for voltage
at the supply wire. For wire identification, refer to
Group 8W, Wiring Diagrams.
(8) If 5 volts is not present at supply wire, check
for voltage at PCM 32-way connector (cavity A-17).
Refer to Group 8W, Wiring for location of connector/
terminal. Leave the PCM connector connected for
this test.
(9) If voltage is still not present, perform vehicle
test using the DRB scan tool.
(10) If voltage is present at cavity A-17, but not at
the supply wire:
(a) Check continuity between the supply wire.
This is checked between the distributor connector
and cavity A-17 at the PCM. If continuity is not
present, repair the harness as necessary.
(b) Check for continuity between the camshaft
position sensor output wire and cavity A-18 at the
PCM. If continuity is not present, repair the harness
as necessary.
(c) Check for continuity between the ground circuit
wire at the distributor connector and ground.
If continuity is not present, repair the harness as
necessary.
(11) While observing the voltmeter, crank the
engine with ignition switch. The voltmeter needle
should fluctuate between 0 and 5 volts while the
engine is cranking. This verifies that the camshaft
position sensor in the distributor is operating properly
and a sync pulse signal is being generated.
If sync pulse signal is not present, replacement of
the camshaft position sensor is necessary
Click to expand...

Tim,

Thanks for posting this diagnostic information......

About 18 months ago... I had this same problem although my problem was caused by the distributor shaft bushings going bad allowing the CPS to ground out on the pulse ring....
This problem required that I replace the distributor which came with a new CPS.
 
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