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too_low 04-27-2013 09:12 AM

Ugh... No spark
 
98 jeep Cherokee drove it for about a minute from parking lot to parking lot stopped to put it in reverse and it just quit and wouldn't even try to start back up. we pushed it back into a parking space checked fuel pressure and it has it and checked for spark off the coil and there is none. so i'm thinking cps because it happened so suddenly and without warning, but any other ideas or confirmations would be greatly appreciated.. thanks in advance.

CJ7-Tim 04-27-2013 09:29 AM

Test the CPS.

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 when it cools back down.

Symptoms-
- Starter cranks and cranks but engine won't start up
- 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 should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed.

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 lose communication.

If you buy a new CPS, get a genuine Jeep CPS, or the premium one from NAPA. Cheap crappy “Lifetime Warranty” parts are often out of specification or even failed right out of the box. They usually also have a shorter service life than better quality parts. Buy good quality repair parts and genuine Jeep sensors for best results.

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.

Crankshaft Position Sensor Connector (CPS/CKP)

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http://www.fototime.com/78EA763821BA137/standard.jpg
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http://www.fototime.com/269D7600706B48F/standard.jpg.
CPS Testing

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 the 10K-or-2OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCEDURE 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 is on the passenger side, near or
on top of the Transfer case, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.

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http://www.fototime.com/554D75F2A0D08B0/standard.jpg




buildin1XJ 04-27-2013 09:31 AM

Do you have reverse lights when you shift into reverse? If not may be the neutral safety switch.

tjwalker 04-27-2013 10:16 AM

Test coil and crank sensor for starters (along with checking all major fuses), but the crank sensor fails more frequently than the coil.

too_low 04-27-2013 11:33 AM

thanks for all of the help the symptoms point toward a cps/ckp the nss is not attached to the tranny its duck taped to the fender well and stuffed full of cigarette butts (dont ask previous owner was a moron) so i dont have reverse lights anyway. but it just cranks and cranks and wont fire and the voltage gauge doesn't read correctly..

too_low 04-28-2013 09:28 PM

Replaced and tested the old cps (it tested good but my friend had a spare) and that didnt fix it. replced the coil even tho the old one tested good it was cracked so i replaced it too that didnt do it either. i also checked the voltage for the trigger lead for the coil and both terminals went from 8.7 volts (key on) to 6.9 volts when it was cranked over and grounded to the battery im not sure if thats right i thought one was suppose to stay constant while the other one drops to half voltage to trigger a spark :confused: but im not sure.. so it looks like im down to an ecu or a "cam sensor?" (the one in the dizzy) is there anything else i can try before trying a new brain??

BlackBetty01xj 04-28-2013 09:57 PM

sounds like the cam sensor. pep boys 48.95. i got one today lol

too_low 04-29-2013 01:16 PM

thanks for all of the help so far. I checked the cam sensor and replaced it, still no spark. i also put an ecu in it and it still didn't help. i also rechecked the voltage for the trigger lead at the coil and both positive and negative terminals read 0 volts until cranked over and when its cranked over they both jumped to about .3 volts, so i think that's working properly now but it still doesn't have any out put at the coil.. im going to recheck the coil and see if its faulty (its an auto zone coil so its i wont rule it out..)

i did notice that when i unplugged the cps and cycled the key a few times the fuel pump relays and the fuel injectors would click when i reconnected the cps i dont know if thats a good thing or not but i need this thing to get home from collage in two weeks and i am all out of ideas. is there any connectors or other little modules or relays that i need to wiggle or prod at??

CSaddict 05-10-2013 04:25 AM

Check power at the A2 and A22 pins on the C1 connector (the black plug)at the PCM with the key on. Also on ohms check to see if you have grounds on pins A31 and A32. I just went through this and fixed it. Was a broken wire.

too_low 07-31-2013 09:51 AM

Ok, thank you for all of the help. i know its been a long time but i figure i should give some closure to this weird issue.

i finally broke down and took it to the dealer and had them work on it. i had got it running on my own sort of.. just enough to limp it in. it spark knocked really bad when under a load. i dropped it off with all of the spare parts i had collected on the passenger floor board. the head mechanic worked on it for about 4 hours and this is what he told me

the timing was 30 degrees ADVANCED
so he reset that
the original 1998 ecu was fried
when it fried it shot a full 12 volts thru everything
this (this really only affected the 5 volt sensors) caused the fuel pump fuse to blow the cps to get taken out the throttle position sensor was cooked and the oil pressure sensor was done for as well.
he mixed and matched all of the parts on the floor board and made it run prefect again
he put a 99 ecu in it, and jumperd a cps in as well as a throttle position sensor

the truly terrifying part is that the timing was advanced. i have driven this jeep for over 2 years and put over 30,000 miles on it and i have never touched the dizzy. the old owner had never taken it apart either because he had always taken it to a shop to get fixed.

but anyway that's what happened to it..

on a side note all computers are compatible from late 1995, 1996, 1997,1998 and 1999. i plugged the 1996 ecu into the 1998 and it did exactally what the mechanic said it would do. it ran like dump for about 10 or so minutes until it got warm and the ecu adjusted or "relearned" the parameters and it was fine. neat huh?

tjwalker 07-31-2013 05:28 PM

Great to hear that you are rolling again. Base timing on the 4.0 is controlled by the computer, (not the distributor) so if the computer is fubar, that might have been the base root cause for all of this. You can't properly adjust timing on the 4.0 like older engines by twisting the distributor....

But moot point. You're rolling again. Let us know if you have any further issues.

JWELK 08-01-2013 08:10 AM

Voltmeter off?
Check the coil. Should have lo resistance pin to pin on the plug, several 10's of thousands from either pin to the Hi voltage tap.
I have/had the same problem, same symptoms. I awaiting a PCM. The PCM caused the alternator to full field. This gave me 17 volts to the battery, which in turn toasted the coil, among a couple of other things. The key seems to be "low voltage, just barely moving past the 9" reading on voltmeter.
I have yet to measure the field input to the PCM, it is on the list. One side of course is 12 volts, the other, regulated side, should have a hi resistance, I'm expecting to find it shorted. As an aside, I have read, "if you disconnect the plugs on the PCM without disconnecting the black battery, this causes the false data to be written to the uprocessor". This is irreversible.
FWIW this is a 99XJ, 4.0, Auto

Regards,

Jim W


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