2000 XJ no start please help!!!!!
10-01-2015, 10:20 PM
#1
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Model: Cherokee
2000 XJ no start please help!!!!!
I have no idea what can be causing this please help, it's kicking my butt.
Symptoms
-Cranks but won't start (not cps)
-Backfires out of TB and exhaust sometimes when trying to start but not always.
-sometimes starts and runs very rough then stalls.
-sometimes starts and runs fine.
Parts replaced
-ECU
-coil packs
-tps
-cps
-cam position sensor
-coolant temp sensor
-fuel injectors
On the occasions that it does start or at least try to start it seems like it's misfiring or out of timing or something. I'm considering a valve issue? But when it starts it'll usually run fine so I don't know... I'm very frustrated and confused. Any help is appreciated. Sometimes, if I prime it a bunch like 15 times it'll backfire out the tb then start, could that mean fuel pump? But when I tested it it was priming to over 40 psi consistently...
Symptoms
-Cranks but won't start (not cps)
-Backfires out of TB and exhaust sometimes when trying to start but not always.
-sometimes starts and runs very rough then stalls.
-sometimes starts and runs fine.
Parts replaced
-ECU
-coil packs
-tps
-cps
-cam position sensor
-coolant temp sensor
-fuel injectors
On the occasions that it does start or at least try to start it seems like it's misfiring or out of timing or something. I'm considering a valve issue? But when it starts it'll usually run fine so I don't know... I'm very frustrated and confused. Any help is appreciated. Sometimes, if I prime it a bunch like 15 times it'll backfire out the tb then start, could that mean fuel pump? But when I tested it it was priming to over 40 psi consistently...
10-02-2015, 09:42 AM
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They started a few weeks ago and it became gradually harder to start over a few days which makes me think something was going out so waited till it went thinking that it wouldn't be so hard to diagnose.
10-02-2015, 09:44 AM
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And the codes are for tps, coil pack, can sensor, and some trans codes which I think are unrelated because they've popped up before. I can provide a list when I get home if it would help.
10-02-2015, 10:01 AM
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Year: 1999
Model: Cherokee
Engine: 4.0
I think you should check the 5 volt supply to the sensors.
All engine management sensors (not ECT or IAT) receive a 5 volt reference voltage from the PCM in order for the sensors to operate normally.
Try unplugging the MAP sensor connector (easy to get to).
Turn the ignition witch to ON/RUN (engine not running).
Using a digital voltmeter set to 20 Volts DC, touch the connector pin cavity with the Orange wire going to it with your (+) meter probe and connect the (-) probe to the battery negative post. You should read 5 volts +/- .5 volts.
Too high might be your clock spring is at fault, too low may be a high resistance in the Orange wire from the PCM. If there is a voltage fault try the TPS connector and see if the fault is there as well.
All engine management sensors (not ECT or IAT) receive a 5 volt reference voltage from the PCM in order for the sensors to operate normally.
Try unplugging the MAP sensor connector (easy to get to).
Turn the ignition witch to ON/RUN (engine not running).
Using a digital voltmeter set to 20 Volts DC, touch the connector pin cavity with the Orange wire going to it with your (+) meter probe and connect the (-) probe to the battery negative post. You should read 5 volts +/- .5 volts.
Too high might be your clock spring is at fault, too low may be a high resistance in the Orange wire from the PCM. If there is a voltage fault try the TPS connector and see if the fault is there as well.
10-02-2015, 02:54 PM
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I think you should check the 5 volt supply to the sensors.
All engine management sensors (not ECT or IAT) receive a 5 volt reference voltage from the PCM in order for the sensors to operate normally.
Try unplugging the MAP sensor connector (easy to get to).
Turn the ignition witch to ON/RUN (engine not running).
Using a digital voltmeter set to 20 Volts DC, touch the connector pin cavity with the Orange wire going to it with your (+) meter probe and connect the (-) probe to the battery negative post. You should read 5 volts +/- .5 volts.
Too high might be your clock spring is at fault, too low may be a high resistance in the Orange wire from the PCM. If there is a voltage fault try the TPS connector and see if the fault is there as well.
All engine management sensors (not ECT or IAT) receive a 5 volt reference voltage from the PCM in order for the sensors to operate normally.
Try unplugging the MAP sensor connector (easy to get to).
Turn the ignition witch to ON/RUN (engine not running).
Using a digital voltmeter set to 20 Volts DC, touch the connector pin cavity with the Orange wire going to it with your (+) meter probe and connect the (-) probe to the battery negative post. You should read 5 volts +/- .5 volts.
Too high might be your clock spring is at fault, too low may be a high resistance in the Orange wire from the PCM. If there is a voltage fault try the TPS connector and see if the fault is there as well.
10-02-2015, 05:14 PM
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I think you should check the 5 volt supply to the sensors.
All engine management sensors (not ECT or IAT) receive a 5 volt reference voltage from the PCM in order for the sensors to operate normally.
Try unplugging the MAP sensor connector (easy to get to).
Turn the ignition witch to ON/RUN (engine not running).
Using a digital voltmeter set to 20 Volts DC, touch the connector pin cavity with the Orange wire going to it with your (+) meter probe and connect the (-) probe to the battery negative post. You should read 5 volts +/- .5 volts.
Too high might be your clock spring is at fault, too low may be a high resistance in the Orange wire from the PCM. If there is a voltage fault try the TPS connector and see if the fault is there as well.
All engine management sensors (not ECT or IAT) receive a 5 volt reference voltage from the PCM in order for the sensors to operate normally.
Try unplugging the MAP sensor connector (easy to get to).
Turn the ignition witch to ON/RUN (engine not running).
Using a digital voltmeter set to 20 Volts DC, touch the connector pin cavity with the Orange wire going to it with your (+) meter probe and connect the (-) probe to the battery negative post. You should read 5 volts +/- .5 volts.
Too high might be your clock spring is at fault, too low may be a high resistance in the Orange wire from the PCM. If there is a voltage fault try the TPS connector and see if the fault is there as well.
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10-02-2015, 05:56 PM
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Oh ok. Well yea everything seemed fine then. I'm pretty positive that it's something keeping it from getting spark because after attempting to start it, I can smell gas in the TB but most times when I try to start it, it seems like it's not getting spark.
10-02-2015, 07:12 PM
#10
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Year: 1999
Model: Cherokee
Engine: 4.0
Perhaps you should turn your attention to that Cam Sensor you installed.
Did you install it per the Factory Service Manual?
It does need final adjustment using a DRBIII after install (dealer),
Did you install it per the Factory Service Manual?
It does need final adjustment using a DRBIII after install (dealer),
10-03-2015, 10:21 AM
#11
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Is that even for just the sensor cap piece or for when replacing the whole assembly? And since no symptoms changed after replacing it I'm not sure if that'd be a factor
10-03-2015, 10:26 AM
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Year: 1999
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Engine: 4.0
You're right, I guess the symptom existed before changing all those sensors and none of them made a difference.
It may be a mechanical problem, like a broken valve spring.
Or the timing chain has jumped (unlikely).
Maybe a compression check would be in order.
10-03-2015, 03:04 PM
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I performed a compression check and all were within 20 psi with the lowest at 160ish and the highest at 175 which seems high for a motor with 250,000 miles...
I looked at all the plugs and they have some carbon buildup but nothing major so I cleaned them up, gapped them to .035 (they were all close already) and put em back in. No results. I also went through all my grounds again including the braided wire from the valve cover to the firewall. I'm about to push this thing off a cliff haha