IAC, TPS, CPK, MAP: Failure symptoms of each
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Year: 1998
Model: Cherokee
Engine: 4.0L i6
IAC, TPS, CPK, MAP: Failure symptoms of each
These are 4 parts that seem to be often be culprits of poorly running XJ's:
For each one, what are the major symptoms when each of these fails?
Bad idle, rough idle, no start, cuts off, etc.
In other words, can we make a quick cheat sheet of symptoms each will exhibit when they fail?
- IAC motor (Idle Air Control)
- TPS (Throttle Position Sensor)
- CPK (Crank Position Sensor)
- MAP sensor (Manifold Air Pressure)
For each one, what are the major symptoms when each of these fails?
Bad idle, rough idle, no start, cuts off, etc.
In other words, can we make a quick cheat sheet of symptoms each will exhibit when they fail?
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texaca (05-22-2020)
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2) All sorts of drivability problems, bad trans shifts, cutting out on acceleration, slow idle return, no idle, unstable idle...
3) No spark, intermittent spark
4) Mixture too rich or lean
Problem with a troubleshooting list is these sensors all connect to a fairly rudimentary computer. Failure of any one sensor can mimic failure of other sensors as the computer chases the bad data around. Ex: TPS might cause unstable idle as the PCM chases it making you think the IAC is bad. Don't depend on a symptom list without doing other troubleshooting.
Last edited by Radi; 02-05-2013 at 12:22 AM.
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texaca (05-22-2020)
#4
would this cause bikfiring as well sometimes? feeling like my map and tps is bad.
Would the bad tps and map cause backfiring n bad feul mileage. Long times operating temp.every part feul system and ignition system is replaced only have like 4 sensors left I havnt replaced any help would be appreciated
1) Unstable idle, idle too low, too high
2) All sorts of drivability problems, bad trans shifts, cutting out on acceleration, slow idle return, no idle, unstable idle...
3) No spark, intermittent spark
4) Mixture too rich or lean
Problem with a troubleshooting list is these sensors all connect to a fairly rudimentary computer. Failure of any one sensor can mimic failure of other sensors as the computer chases the bad data around. Ex: TPS might cause unstable idle as the PCM chases it making you think the IAC is bad. Don't depend on a symptom list without doing other troubleshooting.
2) All sorts of drivability problems, bad trans shifts, cutting out on acceleration, slow idle return, no idle, unstable idle...
3) No spark, intermittent spark
4) Mixture too rich or lean
Problem with a troubleshooting list is these sensors all connect to a fairly rudimentary computer. Failure of any one sensor can mimic failure of other sensors as the computer chases the bad data around. Ex: TPS might cause unstable idle as the PCM chases it making you think the IAC is bad. Don't depend on a symptom list without doing other troubleshooting.
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With the CPK, Crank Positioning Sensor, I would like to add random stalling when reaching operating temperature while driving. Will start right back up most times and stall again. Will not be any CEL's or any pending CEL's.
Last edited by Ralph77; 03-27-2018 at 05:20 AM.
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BloNdeChiNeEz (06-07-2021)
#7
First thing I check when troubleshooting driveability issues is codes, that will point you in the general direction of the issue.
Unless it's poor idle and drives fine, then it's almost always an IAC.
Easy steps to verify a sensor is bad.
1. Verify reference voltage at the sensor in question, the reference wire is looped in with other sensors, obd2 is 5v, I believe obd is 8v.
2. after confirming reference voltage, verify a good ground, this can be done with a cheap circuit tester.
3. If neither of these are bad, verify contunity of the signal wire by using a ohm meter, look up the pinout on the pcm.
Depending on the sensor you can backprobe the signal wire and check voltage, it should be in range, this doesn't work with cam/crank sensors because you need a scope to see the squarewave.
Diag isn't really that hard. Just take your time.
Unless it's poor idle and drives fine, then it's almost always an IAC.
Easy steps to verify a sensor is bad.
1. Verify reference voltage at the sensor in question, the reference wire is looped in with other sensors, obd2 is 5v, I believe obd is 8v.
2. after confirming reference voltage, verify a good ground, this can be done with a cheap circuit tester.
3. If neither of these are bad, verify contunity of the signal wire by using a ohm meter, look up the pinout on the pcm.
Depending on the sensor you can backprobe the signal wire and check voltage, it should be in range, this doesn't work with cam/crank sensors because you need a scope to see the squarewave.
Diag isn't really that hard. Just take your time.
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#8
First thing I check when troubleshooting driveability issues is codes, that will point you in the general direction of the issue.
Unless it's poor idle and drives fine, then it's almost always an IAC.
Easy steps to verify a sensor is bad.
1. Verify reference voltage at the sensor in question, the reference wire is looped in with other sensors, obd2 is 5v, I believe obd is 8v.
2. after confirming reference voltage, verify a good ground, this can be done with a cheap circuit tester.
3. If neither of these are bad, verify contunity of the signal wire by using a ohm meter, look up the pinout on the pcm.
Depending on the sensor you can backprobe the signal wire and check voltage, it should be in range, this doesn't work with cam/crank sensors because you need a scope to see the squarewave.
Diag isn't really that hard. Just take your time.
Unless it's poor idle and drives fine, then it's almost always an IAC.
Easy steps to verify a sensor is bad.
1. Verify reference voltage at the sensor in question, the reference wire is looped in with other sensors, obd2 is 5v, I believe obd is 8v.
2. after confirming reference voltage, verify a good ground, this can be done with a cheap circuit tester.
3. If neither of these are bad, verify contunity of the signal wire by using a ohm meter, look up the pinout on the pcm.
Depending on the sensor you can backprobe the signal wire and check voltage, it should be in range, this doesn't work with cam/crank sensors because you need a scope to see the squarewave.
Diag isn't really that hard. Just take your time.
#9
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Year: 1990
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RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS, there are a few things that need to be done.
- Be sure the throttle body has been recently cleaned. It’s especially important that the edges of the throttle butterfly are free of any carbon build-up.
- With the KEY OFF, and using the positive (red) lead of your ohmmeter, set on the lowest scale, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself.
- Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall.
TPS ADJUSTMENT FOR ENGINE ISSUES
Both Renix manual and automatic transmission equipped XJs and MJs have a flat three-wire connector to the TPS which provides data input to the ECU. The three wires in the connector are clearly embossed with the letters A, B, and C. Wire “A” is positive. Wire “B” is ground. DO NOT UNPLUG THE CONNECTORS!
- KEY ON, measure voltage from “A” positive to “B” ground by back-probing the connectors. Note the voltage reading–this is your REFERENCE voltage.
- KEY ON, back-probe the connector at wires “B” and “C”. Measure the voltage. This is your OUTPUT voltage.
- Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts.
- Loosen both T-20 Torx screws attaching the TPS to the throttle body and rotate the TPS until you have achieved your desired output voltage.
- Tighten the screws carefully while watching to see that your output voltage remains where it is supposed to be. If you can’t achieve the correct output voltage, replace the TPS and start over.
TPS ADJUSTMENT FOR AUTOMATIC TRANSMISSION ISSUES
Renix automatic transmission-equipped XJs and MJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as outlined above—FOR ALL ENGINE MANAGEMENT RELATED ISSUES.
However, the automatic TPS also has a square four-wire connector, clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. THIS SQUARE FOUR WIRE CONNECTOR IS USED FOR TRANSMISSION/SHIFTING RELATED ISSUES ONLY.
First off, DO NOT UNPLUG THE CONNECTORS!
- KEY ON, measure voltage between “A” positive and “D” ground by back-probing the connector. Note the voltage. This is your REFERENCE voltage.
- Back-probe the connector at wires “B” and “D”. Measure the voltage. This is your OUTPUT voltage.
- Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts.
- Adjust the TPS until you have achieved this percentage. If you can’t, replace the TPS and start over.
For those with a MANUAL TRANSMISSION–the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced. The square 4 wire connector is just not used.
Revised 7/08/17
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