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98 XJ 4.0 AW4 no start issue

b17gsr

NAXJA Forum User
Location
Ottawa, Ontario
Hi all,

New member with a new to us ride. This XJ currently does not start (does crank over) and has 370,000kms. When ignition is turned to on, only oil pressure gauge moves and odometer displays. Fuel pump won’t prime. Fuel pump works if relay is removed and wires shorted.

After more troubleshooting, including unplugging CPS and guess still not moving, I checked the voltage on orange wire at CPS harness (CPS unplugged). It reads 0.5V with ignition on.

Anything else to check before I search for a used PCM?
 
Failure of the PCM should only be considered after a thorough and in-depth diagnostics and trouble shooting of the more common and more logical causes for the symptoms. The symptoms strongly suggest a faulty CPS, but also could indicate a short circuit or other wire harness issues to any of the other 5 volt OBD engine sensors.

Start with the simple and basic stuff, Look at and feel along all the engine sensor wires. Check for chafed insulation from sharp metal edges, melted insulation from hot exhaust parts, and for failed wire splices. It would be a good idea to check for voltage and to check continuity between sensor and PCM for all the sensors. Also check their wire plugs for corrosion and bent or pushed back wire plug pins. Don't forget to include the O2 sensors as well.



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. Typical CPS lifespan is about 150-200,000 miles.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when the 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 NoBus displayed on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the sparkplugs.
- Fuel pump should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II trouble 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.
- Check the orange wire going to the CPS or cam position sensor for 5 volts with the key in the run position. A partial short in a sensor can cause the input voltage to the CPS (or most sensors) to be low and can trigger a no-start or no bus situation.
- 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 these relays as the cause of the no-start. Confirm that the fuel pump 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 exhaust 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. 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.

You must also perform 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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standard.jpg




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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 or 2 and 3 (See Images). 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/ohmmeter 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 .5 VAC, 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 wire connector.
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Thanks for the suggested debugging steps.

First thing I tried was moving the relays around. I know the starter relay works, and any relay moved to that socket continues to crank over the engine.

I did buy a new Mopar CPS, but haven’t installed it. With the existing CPS unplugged, no improvement in cluster operation and fuel pump still won’t prime for 2-3 seconds. If I plug in the new CPS (without installing it), no change.

I did find a damaged upstream O2 sensor wire and fixed it. Surprisingly the fuse was fine.

What other sensors are on the same 5V bus as the CPS? Or is it literally a question of unplugging every sensor and then checking for that 5V reference voltage?

Does the PCM need all signals / voltages to be in order before it primes the fuel pump? I confirmed all wires for the fuel pump relay are in good order, including the grounding wire back to the PCM.
 
I've had two 98 XJ. OK, still have the one. Sort of similar problem. I take it that yours is not throwing codes. On the first on, I found that the coil had gone bad. On the one I have now, the distributor went bad. But that did throw a code. On an '01, I chased my tail for a few months. A friend said it sounded like the ignition switch. I replaced that at it fired up after a while. I did replace the fuel pump before that.
The dash thing happens. That could be just the connectors to the dash. I think you need to determine if it is fuel or spark. Could be both though and that could be the ignition switch on the steering column. I looked for a way to test it, but didn't.
Did you check to see if you are getting spark at the plugs? Voltage to the coil? With the key on, fuel pressure at the rail? You can try to depress the Schrader valve and see if fuel sprays out. Wear safety glasses. Best though to use a pressure gage. Spray starting fluid into the intake?
 
Interesting info.

The only code I could pull was 1694. At the DTC, read 2.41V between pins 3 - 5 and 11 - 5 with ignition set to run (battery voltage was over 12V during this test). With ignition in lock position and negative battery terminal disconnected, resistance between pins 3 and 11 was 59.9 ohms. So that seems to check as acceptable, but the voltages should be closer to 2.5V.

I think the cluster is ok since everything works through the self diagnostic check. Not sure if that confirms the wired connections.

The fact that the fuel pump won’t even prime with the key turned to run leads me to believe I shouldn’t get spark, but maybe I’m getting some tunnel vision. If I bypass the fuel pump relay, there’s pressure at the Schrader valve. Need a pick up a gauge to confirm how much pressure.

The ignition switch does feel worn out. Definitely worth replacing it either way. Is there a way to bypass the ignition switch?

I’ll have to check for spark tonight at those locations (previous owner said he could start it by shooting starter fluid into the intake, but I haven’t tried).
 
Only info I can give is if you have NAPA parts stores up there. I found them to be a lot less on the ignition switch. Also, their Echlin brand is near OEM quality. It was only $7 more. I think $50. Another parts store was $100. So, check prices. If yours starts from starting fluid, then I'd suspect the fuel pump. I'd probably check the voltage to it. Mine had a bunch of mice or squirrel nuts around it.
 
Problem solve for the Check Engine Light OBD-II trouble codes before you install random new parts.


You should unplug each OBD-II engine sensor one at a time, and then see if the instrument cluster displays correctly.



P1694 Fault In Companion Module. No CCD/J1850 bus messages received from the power train control module-Aisin transmission.

Possible Causes:
CCD Bus (-) wire circuit open between PCM and TCM.
CCD Bus (+) wire circuit open between PCM and TCM.
Transmission CCD bus wiring damaged.
Faulty TCM.

Possible Causes:

When the CPS short circuits the engine computer (PCM) shuts down to prevent damage to itself. As a result, there is no communication (P1694).

Disconnect your crankshaft position sensor then put the ignition key in the on position. If the instrument cluster starts to work, once the CPS is disconnected, then you know the CPS is shorted. You can verify this by testing the CPS with an ohmmeter.

Follow the directions and test the CPS. Inspect and test the wire harnesses for damaged wires, broken wires, or chafed/melted wire insulation.

If the CPS/CKP is failed sometimes the OBD-II trouble 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 help 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.
- Check the orange wire going to the CPS or cam position sensor for 5 volts with the key in the run position. A partial short in a sensor can cause the input voltage to the CPS (or most sensors) to be low and can trigger a no-start or no bus situation.
- 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 these relays as the cause of the no-start. Confirm that the fuel pump runs for 3-5 seconds when you turn the ignition key to ON.
-- Inspect the wires and wire connectors at the O2 sensors on the exhaust pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will lose communication.
 
Last edited:
Good suggestions posted. A couple of other things to consider. It's my understanding that if the engine doesn't fire after so many revs, the computer shuts down the fuel pump. Some possibilities:
1. If the fuel check-valve, located on the fuel pump, fails; the fuel in the fuel-supply line drains back to the tank. Result? A longer start time is required to refill the fuel-supply line and then pressurize it. The computer doesn't know that and shuts down the fuel pump. The PO's suggestion of using starting fluid to fire the XJ is an indicator of lack of fuel. Simple fix is to use a small inexpensive aluminium check-valve downstream of the fuel filter to prevent the fuel form draining back into the fuel tank. My 88XJ has been running that way for a long,long time. I wasn't about to replace the $$$ fuel pump because an in-tank fuel check-valve failed when an inexpensive $5 exterior mounted check-valve solved the problem.
2. You getting some pressure in the fuel line could also indicate it's just taking a little longer to fill/pressurize the fuel-supply line. A clogged fuel filter could also slow down the fuel delivery to the injectors.
3. Check the color-codes of the electrical wires powering the injectors. The injector must fire in the proper sequence. If the wiring got switched, an injector may be firing out of sequence, i.e ejector firing for a piston that is not on the compression stroke before spark initiation.
4. It's also possible that some injectors are clogged or just not opening. If you can get it running, put some injector cleaning fluid in your gas tank.

Best regards,

CJR
 
We have NAPA Part stores around here as well. Good to know.

I was going to change the fuel pump, but it works fine when relay is by-passed (good voltage and ground at harness near tank). The only reason the relay isn’t completing the circuit is the PCM isn’t giving it a ground signal. I didn’t see it idle on starter fluid, so I’m taking that info with a grain of salt (he thought the fuel pump was shot, which it isn’t).

With the amount of fuel that came out of the Scrader valve each time I released pressure and by-passed the fuel pump relay, it should have enough fuel to at least stumble and start (if the fuel injectors are firing, another item to check...). I’m not even getting a sputter.

I’ll check for spark & voltage at the ignitor and report back.

Thanks
 
Problem solve for the Check Engine Light OBD-II trouble codes before you install random new parts.

You should unplug each OBD-II engine sensor one at a time, and then see if the instrument cluster displays correctly.

P1694 Fault In Companion Module. No CCD/J1850 bus messages received from the power train control module-Aisin transmission.

Possible Causes:
CCD Bus (-) wire circuit open between PCM and TCM.
CCD Bus (+) wire circuit open between PCM and TCM.
Transmission CCD bus wiring damaged.
Faulty TCM.

Agreed. I even tried starting the engine with the TCM unplugged and no changes (Fuel pump didn’t prime). When plugged, the TCM is giving me a transmission solenoid error code, so thought it was operating well. I’ll have to check if I still get the 1694 code with the TCM unplugged (and The other modules on that bus), then troubleshoot the CCD bus wires. The Airbag idiot light turns on and off, so think that module is working as it should (but better check).

I know there’s a newly crashed 98 XJ with 4.0 AW4 at a local yard, so I think both the PCM and TCM are likely still in good shape. Would be cheap parts and easy option to troubleshoot The PCM and TCM.
 
To summarize my ToDo list:
  1. Check for spark & power at ignitor
  2. Unplug all sensors and double check if there’s 5V on the sensor bus, and that the harness is intact.
  3. See if the 1694 error code disappears when unplugging the TCM, air bag module and other devices. Check if the CDD + and - bus wires are intact.
  4. Check if ignition switch working as it should
 
Will do. Fuses in PDC were fine, but will check again. Didn’t check all fuses in the Junction box, so got to verify all are in good order. After the recent snow, will be fun moving it away from the house to open the passenger door...
 
If the junction box is the inside fuses, then I want to say #11, or is it #10. Its been a few months since I dealt with that. But as I remember, the PDC sends voltage to it, and then back the PDC.
 
Yes, the inside fuse box is referred as the Junction Box in the FSM. I know fuse 11 is for the fuel pump and it was good when I was doing the testing. A sheet I found does mention power train control module as one of the devices connected to this fuse.

I assume fuse 10 works, since the back up lights work.

Time to move the XJ and check them all. Would be awesome if it was as simple as a bad fuse (then figure out why fuse is bad).
 
Had a bit of time to do some troubleshooting, but too cold to do more this evening.
  1. Checked all fuses in PDC. All were fine (battery voltage on bother terminals), except two fuses F20-20A and F23-15A, which are controlled by the ASD relay
  2. The F20 and F23 fuses were only reading 2-3V while cranking
  3. With camshaft position, crankshaft position, MAP, throttle and IAC sensors unplugged, measured around 0.5V on the signal wire with ignition on (instead of 5V) and 0.09V with ignition off.
  4. Gauges didn’t move the entire time. While trying to crank the engine, the tachometer didn’t budge.
  5. fuel pump relay never closed so pump never primed.
  6. At one point my son released the key from the crank position and it kept cranking, even when the key was removed. Had to re-insert the key and then it stopped cranking.

Based on the last item, I’m seriously questioning the ignition. Would it be the keyed portion or other part that’s faulty?
 
Also, switched the starter relay with ASD relay and results were the same. With ASD relay removed, voltage on pins 2 and 4 were battery voltage with ignition in on position.
 
If there are no signals to the PCM from the Cam and/or Crank sensor, the PCM shuts down the fuel pump. A faulty fuel pump check valve will crank and crank and the fuel pump will keep pumping until it starts.

Focus on the P1694.

.5 volts, or the meter was on the wrong setting and it was actually 5 volts. I have done this.

I would grab the PCM and TCM from the junkyard if they are low cost. I would buy a new replacement ignition switch. If nothing else you have spares or test parts in case they are needed and there are no donors available in the future.

I have no input about the voltages. I did have a 98 or 99 that would not start, one of the relays on the top of the passenger compartment fuse box had corrosion on the contacts. While checking all of the fuse, I pulled each relay on a at a time, cleaned the contacts and re-installed them. After that, it started and ran reliably.
 
My first goal is to get the fuel pump to prime when the ignition is on... Seems like something is corrupting the CDD bus and preventing the PCM from doing its thing.

I wonder if the 1694 was stored when I tried starting it with the TCM unplugged. Will have to clear code and check if it comes back. Do the codes clear if battery is disconnected?

Multimeter was set to 20V, since I was checking the signal voltage and battery voltage at the same time. Some other signal wires have a resting voltage state, haven’t found anything specific to the 5V bus.

Was the relay corrosion on the relay itself or the harness/socket? All 4 relays looked ok, will have to shine a light over the sockets to see if all look clean.

Just looked at the FSM, looks like a few more sensors also rely on 5V from the PCM (O2 sensors, coolant temp, oil pressure temp, fuel level, and likely more). I’ll have to unplug those and see if anything improves.

Yeah, used TCM and PCM will be cheap and helpful in future if not required at this time. Read another thread with similar issues and for that instance the PCM (used PCM corrected the 5V bus) and ignitor were bad.
 
This is an interesting problem. Here's a WAG. On the Renix system, which this year XJ does not have, if the ECU gets a wide open throttle (WOT) signal from the TPS,during crank, it opens the ejector circuit(i.e. closes ejectors) and opens other circuits as well. So if the computer logic on this year XJ is similar to the Renix logic some of your observations may be explainable. If the TPS is telling the computer it has a WOT on crank mode, the computer is opening up the ejector circuit to close all the ejectors because it thinks the engine is flooded. This could explain why you observed some fuel pressure but the computer closed the ejectors to prevent any fuel getting into the engine for a no-start. Getting spark without fuel doesn't start engines. I'd check that TPS. Maybe the spark circuit is also opened when the computer sees a WOT signal from the TPS. Anyway this is a WAG.

Best regards,

CJR
 
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