Cranks, turns over. NO START!!? Fuel good.
09-30-2016, 12:11 AM
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Year: 1995
Model: Cherokee
Engine: 4.0l
Cranks, turns over. NO START!!? Fuel good.
Hi. I am new this forum. This seems like a good place to post my current situation on my jeep, I have tried to get it to start for over 3 weeks now and I am out of funds and on borrowed time. My new job starts early next week and I need this thing to run or I am in deep doodoo...
My experience as a mechanic is probably a 4/10. I have basic tools and have done basic things the last few years to keep my cherokee going (8th owner) like the water pump, alternator, valve cover, filters ect. I haven't any money to pay a mechanic of course and have spent the last few hundred bucks on things that should have fixed my issues-or so I thought. 230,000+ miles
I have tested the coil direst to the battery - nice blue/purple spark
I have tested fuel pressure at the rail - good 34psi
brand new fuel filter
brand new starter
brand new alternator
brand new battery
brand new jeep cam sensor
brand new jeep cps sensor
brand new asd relay
Aggravating because it was a strong dependable vehicle. I took the jeep on a road trip and later had a hard time starting it. It ran fine but had a loud screech sound to it. When I drive it back home it would not start back up. Eventually with starting fluid I got it to start and stay on for a few seconds at a time while pulsing the gas pedal before it[computer/ASD I guess] would lower RPMS and just die. I discovered that the Alternator was making the noise. I could see it turn 'engine-on', but the belt looked odd the way it was moving.
During one of these starting fluid - "starts" I kept the engine going under the hood via the throttle cable and the belt broke and flew off. I tried turning the alternator pulley with my hand but could not. I guess it was seized. But I know this: the alternator got me home from the road trip, over 90 minutes of a drive. Therefore it must have been charging and doing it's job at some extent.
I bench tested the Alternator at the Advance Auto and it it said it was "internally shorted." I replaced the Alternator with a new one and also the Starter because it was getting kind of weak. (later the old starter failed the bench test when I could see the Gear barely push out). Cranking became easy at this point and the Engine ran rough for about 25 seconds (During one of these starting fluid - "starts.")
Cranks, turns over. NO START!!? Fuel good.
After confirming I had spark 3-4 times (not very strong spark- sorta orange) I replaced the coil. Then I got REALLY WEAK SPARK. So I put the old coil back on. NO SPARK. Put the new coil back on. REALLY REALLY WEAK SPARK. losing my mind at this point
Took my father's advice and hooked up the new coil to the battery direct.
NICE BLUE SPARK. I went to go unplug the old coil to 'battery direct' test it and the plug wire was BROKEN and corroded. I tested it with a voltmeter and found that the wire is the primary negative wire. The other primary (positive wire) was ok, but spotty. From this, I concluded my ignition system is suspect. No power to Coil = No Spark. I thought it was simple: provide "primary positive power" to coil via the ASD relay, and provide "primary negative power" to coil by hooking up the grey/white wire, originally heading to the harness's "coil primaries splice."
Wrong.
Did not work or produce spark.
According to a wiring diagram (1994 cherokee 2.5l/4.0l) there is a "GRY" Grey/White wire sent directly as a 'single purpose' wire, ("primary negative power"); and there is a "DK GRN/ORG" Dark Green/Orange wire, ("primary positive power") that shares voltage with a number of sensors like the injectors and O2 sensor, channeled through the ASD Relay to ultimately end up at the ignition coil. Am I reading these diagrams wrong?
How do I power the coil, utilizing the ECU computer's original wires? I fear I have a short in my jeep that is preventing the "coil primaries" to function properly. I am also trying to not destroy the computers wires and other sensors sharing voltages alongside the coil. Is this even possible. I need the Coil to produce Spark with the Computer's original Wiring harness.
I cut into the Greyish Whitish wire towards the "coil primaries splice," put that into alligator clips onto the fresh[good] coil. I maneuvered wire around the ASD relay post#86 into alligator clips onto the fresh[good] coil, with the ASD installed. I also put it onto the other posts (#30, etc) and got strange, unsatisfying results:
Not. Making. Sense.
Replaced the cam CPS and crank CPS bought from dealer. No differing results.
Not. Making. Sense.
Then, with nothing else to doI checked and verified signals to and from a few sensors. I researched and found out that the coil is powered ON and OFF multiple times according to the computer's "primary negative power" "GRY" wire. This pulsing affect is possible due to the electromagnetic signals derived from the constant turning of the camshaft and flywheel 'Engine-On.'
The computer sends a supply, VREF signal to the crank CPS (8v positive) as well as a ground signal (12v negative?). The cps thanks the computer for the supply signal and passes on a 5v positive back to the computer [intermittently switches between 0v and 5v and 0v and 5v and 0v and 5v, ect when the tiny metal teeth on the flywheel interfere with the magnet built into the crank CPS. The computer then sends signal to the coil by way of the "GRY" "primary negative wire." This signal is only sent when 'Cranking' and 'Engine-On.' Therefore, the Coil activates the Spark Plugs ONLY with the 'KEY ON' and/or 'Cranking.'
Not. Making. Sense.
So then I disconnected the ECU from the wiring harness. I retested with the CPS disconnected, voltmeter grounded to battery. (KEY-ON of course.) The crank CPS's 1st wire had 01.08v. The CPS's 2nd wire had 01.40v. The 3rd wire had nothing. 0v.
I retested with the CPS disconnected, voltmeter connected to battery positive. (KEY-ON) The crank CPS's 1st wire had 07.45v. The CPS's 2nd wire had 07.90v. The 3rd wire barely anything .03v.
Not. Making. Sense.
Why is the cps sensor connector Giving Power it does Not Have?
I feel like I could chase this mystery for years. It seems to me like there is a short in the ignition system, somehow infiltrating the CPS connector/harness.
Does someone know how I can defeat this problem without getting a whole new wiring harness? Perhaps someone has been there before and was victorious?
Does the ignition switch commonly short to parts of the wiring harness/ sensors? The 02 and wires are fine. Grounds checked and cleaned. No reverse lights.
I need the Coil to produce Spark with the Computer's original Wiring harness. This seems to be the only and correct way to remedy this condition of Good Fuel, Good Turnover, iffy Spark. This is a great community. Perhaps someone can point me in the right direction.
Need this job.
Please and Thanks.
God Bless
My experience as a mechanic is probably a 4/10. I have basic tools and have done basic things the last few years to keep my cherokee going (8th owner) like the water pump, alternator, valve cover, filters ect. I haven't any money to pay a mechanic of course and have spent the last few hundred bucks on things that should have fixed my issues-or so I thought. 230,000+ miles
I have tested the coil direst to the battery - nice blue/purple spark
I have tested fuel pressure at the rail - good 34psi
brand new fuel filter
brand new starter
brand new alternator
brand new battery
brand new jeep cam sensor
brand new jeep cps sensor
brand new asd relay
Aggravating because it was a strong dependable vehicle. I took the jeep on a road trip and later had a hard time starting it. It ran fine but had a loud screech sound to it. When I drive it back home it would not start back up. Eventually with starting fluid I got it to start and stay on for a few seconds at a time while pulsing the gas pedal before it[computer/ASD I guess] would lower RPMS and just die. I discovered that the Alternator was making the noise. I could see it turn 'engine-on', but the belt looked odd the way it was moving.
During one of these starting fluid - "starts" I kept the engine going under the hood via the throttle cable and the belt broke and flew off. I tried turning the alternator pulley with my hand but could not. I guess it was seized. But I know this: the alternator got me home from the road trip, over 90 minutes of a drive. Therefore it must have been charging and doing it's job at some extent.
I bench tested the Alternator at the Advance Auto and it it said it was "internally shorted." I replaced the Alternator with a new one and also the Starter because it was getting kind of weak. (later the old starter failed the bench test when I could see the Gear barely push out). Cranking became easy at this point and the Engine ran rough for about 25 seconds (During one of these starting fluid - "starts.")
Cranks, turns over. NO START!!? Fuel good.
After confirming I had spark 3-4 times (not very strong spark- sorta orange) I replaced the coil. Then I got REALLY WEAK SPARK. So I put the old coil back on. NO SPARK. Put the new coil back on. REALLY REALLY WEAK SPARK. losing my mind at this point
Took my father's advice and hooked up the new coil to the battery direct.
NICE BLUE SPARK. I went to go unplug the old coil to 'battery direct' test it and the plug wire was BROKEN and corroded. I tested it with a voltmeter and found that the wire is the primary negative wire. The other primary (positive wire) was ok, but spotty. From this, I concluded my ignition system is suspect. No power to Coil = No Spark. I thought it was simple: provide "primary positive power" to coil via the ASD relay, and provide "primary negative power" to coil by hooking up the grey/white wire, originally heading to the harness's "coil primaries splice."
Wrong.
Did not work or produce spark.
According to a wiring diagram (1994 cherokee 2.5l/4.0l) there is a "GRY" Grey/White wire sent directly as a 'single purpose' wire, ("primary negative power"); and there is a "DK GRN/ORG" Dark Green/Orange wire, ("primary positive power") that shares voltage with a number of sensors like the injectors and O2 sensor, channeled through the ASD Relay to ultimately end up at the ignition coil. Am I reading these diagrams wrong?
How do I power the coil, utilizing the ECU computer's original wires? I fear I have a short in my jeep that is preventing the "coil primaries" to function properly. I am also trying to not destroy the computers wires and other sensors sharing voltages alongside the coil. Is this even possible. I need the Coil to produce Spark with the Computer's original Wiring harness.
I cut into the Greyish Whitish wire towards the "coil primaries splice," put that into alligator clips onto the fresh[good] coil. I maneuvered wire around the ASD relay post#86 into alligator clips onto the fresh[good] coil, with the ASD installed. I also put it onto the other posts (#30, etc) and got strange, unsatisfying results:
blue SPARK With the Key ON!
blue SPARK With the Key OFF!
No SPARK With the Key ON!
No SPARK With the Key OFF!
No OIL GAUGE!
No SPARK with KEY ON and CRANKING!
No TACHOMETER JUMPING on CRANKING!
CONTINUITY between "coil primaries connector" wires
Wahoo!
I reconnected the Greyish Whitish to itself and:blue SPARK With the Key OFF!
No SPARK With the Key ON!
No SPARK With the Key OFF!
No OIL GAUGE!
No SPARK with KEY ON and CRANKING!
No TACHOMETER JUMPING on CRANKING!
CONTINUITY between "coil primaries connector" wires
Wahoo!
No TACHOMETER JUMPING on CRANKING!
Yes OIL GAUGE!
OK?
No.Yes OIL GAUGE!
OK?
Not. Making. Sense.
Replaced the cam CPS and crank CPS bought from dealer. No differing results.
Not. Making. Sense.
Then, with nothing else to doI checked and verified signals to and from a few sensors. I researched and found out that the coil is powered ON and OFF multiple times according to the computer's "primary negative power" "GRY" wire. This pulsing affect is possible due to the electromagnetic signals derived from the constant turning of the camshaft and flywheel 'Engine-On.'
The computer sends a supply, VREF signal to the crank CPS (8v positive) as well as a ground signal (12v negative?). The cps thanks the computer for the supply signal and passes on a 5v positive back to the computer [intermittently switches between 0v and 5v and 0v and 5v and 0v and 5v, ect when the tiny metal teeth on the flywheel interfere with the magnet built into the crank CPS. The computer then sends signal to the coil by way of the "GRY" "primary negative wire." This signal is only sent when 'Cranking' and 'Engine-On.' Therefore, the Coil activates the Spark Plugs ONLY with the 'KEY ON' and/or 'Cranking.'
Makes Sense.
Earlier, when I had nothing else to doand checked signals to and from sensors, I discovered the crank CPS's 3rd wire was receiving less than normal voltage from ECU. The CPS's 1st wire was sending out almost 8v! Ground wire (2nd wire) seemed ok voltage-wise.Not. Making. Sense.
So then I disconnected the ECU from the wiring harness. I retested with the CPS disconnected, voltmeter grounded to battery. (KEY-ON of course.) The crank CPS's 1st wire had 01.08v. The CPS's 2nd wire had 01.40v. The 3rd wire had nothing. 0v.
I retested with the CPS disconnected, voltmeter connected to battery positive. (KEY-ON) The crank CPS's 1st wire had 07.45v. The CPS's 2nd wire had 07.90v. The 3rd wire barely anything .03v.
Not. Making. Sense.
Why is the cps sensor connector Giving Power it does Not Have?
I feel like I could chase this mystery for years. It seems to me like there is a short in the ignition system, somehow infiltrating the CPS connector/harness.
Does someone know how I can defeat this problem without getting a whole new wiring harness? Perhaps someone has been there before and was victorious?Does the ignition switch commonly short to parts of the wiring harness/ sensors? The 02 and wires are fine. Grounds checked and cleaned. No reverse lights.
I need the Coil to produce Spark with the Computer's original Wiring harness. This seems to be the only and correct way to remedy this condition of Good Fuel, Good Turnover, iffy Spark. This is a great community. Perhaps someone can point me in the right direction.
Need this job.
Please and Thanks.
God Bless
01-23-2018, 08:16 PM
#3
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Thread Starter
Join Date: Sep 2016
Posts: 3
Likes: 0
Received 0 Likes
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Year: 1995
Model: Cherokee
Engine: 4.0l
(shoveled out the doodoo, didn't get that job)
The culprit was the wiring.
The varying VREF and other signals especially upon cranking was due to a oil sludge-coated cam position sensor bundle of wires that I could not even see. When I removed the oil I could see what I think were originally 3 twisted wires, only 15%-20% strands of remaining, of those some were arcing at each other and the block (oh yeah dont forget the sludge too). I reached for the remaining bundle with my fingers and it turned to dust lol. One wire strand stayed.
This sensor was replaced and it wasn't working. (CAM POSITION SENSOR) It was not the sensor's fault - It was the wiring towards the other sensors/ecu trailing below the spark plugs - ending up at the throttle split between MAP/CPS(CRANK)/IAC if I recall correctly. Its amazing the abuse all these years of driving it like that, the ECU still works.
Anyways, I went to the JY first thing the next morning and got the wiring section I needed. After replacing it and cranking, the cherokee ran smooth, never been better. Ha it was the best tune up I ever did on it.
Don't give up on your crazy wiring and electrical issues and get rid of it. And my goodness please do not junk it - I see these jeeps at the JY makes me sad and mad at the same time. (If you have to get rid of it because of whatever the issue sell it to a teenager and you will make his/her life a blast, for the same $200 worth of cash!!!)
I hope this helps.
Peace
BasicXJ
The culprit was the wiring.
The varying VREF and other signals especially upon cranking was due to a oil sludge-coated cam position sensor bundle of wires that I could not even see. When I removed the oil I could see what I think were originally 3 twisted wires, only 15%-20% strands of remaining, of those some were arcing at each other and the block (oh yeah dont forget the sludge too). I reached for the remaining bundle with my fingers and it turned to dust lol. One wire strand stayed.
This sensor was replaced and it wasn't working. (CAM POSITION SENSOR) It was not the sensor's fault - It was the wiring towards the other sensors/ecu trailing below the spark plugs - ending up at the throttle split between MAP/CPS(CRANK)/IAC if I recall correctly. Its amazing the abuse all these years of driving it like that, the ECU still works.
Anyways, I went to the JY first thing the next morning and got the wiring section I needed. After replacing it and cranking, the cherokee ran smooth, never been better. Ha it was the best tune up I ever did on it.
Don't give up on your crazy wiring and electrical issues and get rid of it. And my goodness please do not junk it - I see these jeeps at the JY makes me sad and mad at the same time. (If you have to get rid of it because of whatever the issue sell it to a teenager and you will make his/her life a blast, for the same $200 worth of cash!!!)
I hope this helps.
Peace
BasicXJ
