4.0HO No Start, No Spark

[ihscoutlover]

Bill, your pic is for a Grand Cherokee, mine is just a Cherokee Sport(smaller cherokee). What I meant by shorting, was that I put the lead for #5 on the FP relay to ground(the negative battery lead, and that's where my wire got hot. I will post up a pic of the relay diagram that I have been working from here as the attachment. Pin 5 is supposed to be the ground from the computer, so if this wire is grounded to any ground point(battery negative included), then it should activate the pump. I didn't get the relay to activate, but the wire sure got hot.

Jeff

[Bill usn-1]

Yes the pin 5 of the relay DB/Yel wire should be the ground to energize the relay.

It connects pin 2 to pin 4 thru the NO-normally open contacts.

Looks like a standard bosch relay. You could unplug the relay and simply jump across pin 2 and 4 to see if the pump runs.

[Mt Hood Carl]

Originally Posted by ihscoutlover

...I am also on the hunt for a 4.0 computer from a 93-96 Cherokee with an automatic transmission...

A failed PCM is certainly one thing that would cause both no spark and fuel pump not running. I think you'll find 96 is OBD2 and so not compatible. Not sure about 95. In the unlikely event you don't find a PCM locally I have one for 94/AT. PM if interested.

[ihscoutlover]

Ok good news, the PCM might be ok. I reconnected the battery tonight, and jumpered the #2 and #4 pins on both the ASD, and the Fuel pump, with the fuel pump first. It pressurized the rail, but then nothing. I tried the same with the ASD, and no change either. When I connected the battery and then turned the ignition switch on, low and behold the CEL was on. Upon seeing this, I took advantage of the moment to retrieve the codes. First code, was a 12- this means the battery has been disconnected within the last 50 key-on cycles. Next was a 54, this one is no Cam Sync Signal at the PCM. Likely culprit here is the Cam sensor, so I will look to replace that and see what's up then. The last one was a 42, this indicates an open or shorted condition detected in the Auto Shutdown Relay Circuit. This could be due to me still having my jumper wire in place there, instead of the relay. I will work to clear the codes and see if I get something else to show up. Then of course the standard 55 which is the completion of ETC display on the CEL. Thoughts here, besides the Cam sensor??

Jeff

[Bill usn-1]

From the AZ link I provided.

OPERATION



See Figure 1

The Camshaft Position Sensor, or CMP sensor is located inside the distributor. The PCM uses the CMP signal to determine the position of the No. 1 cylinder piston during its power stroke. The PCM uses this information in conjunction with the crankshaft position sensor to determine spark timing among other things.

The CMP sensor contains a Hall effect device which sends either a 0.0 volt or a 5.0 volt signal to the PCM depending on the position of the distributor shaft.

If the cam signal is lost while the engine is running, the PCM will calculate spark timing based on the last CMP signal and the engine will continue to run. However, the engine will not run after it is shut off.








Fig. Fig. 1: Exploded view of a common camshaft position sensor and related components-1996 5.2L engine shown


TESTING


1. Make sure that the ignition is OFF , remove the distributor cap and turn the engine over by hand.


2. Verify that the distributor shaft turns. If the distributor shaft does not turn, the engine must be checked for proper mechanical operation.


3. Backprobe with a high impedance ohmmeter between the CMP sensor connector middle terminal and battery ground.


4. Verify that the resistance is less than 5 ohms. If the resistance is not as specified, repair or replace the wiring as necessary and continue the test.


5. With the ignition ON and the engine OFF , backprobe with a high impedance voltmeter between the sensor connector middle terminal and either of the end terminals.


6. Verify that a 5 volt or greater signal is present at one of the two terminals. If not as specified, repair or replace the wiring as necessary and continue the test.


7. With the ignition ON and the engine OFF , backprobe with a high impedance voltmeter between the sensor connector middle terminal and the end terminal that did not have the 5 volt or greater signal.


8. Crank the engine by hand and verify that the voltage reading alternates between 0.0 or 5.0 volts.


9. Install the distributor cap and crank the engine with starter. Verify that the voltage reading is 2.5 volts (averaging voltmeters only).


10. If the voltage readings are not as specified, the sensor may be faulty.

[Mt Hood Carl]

The FSM diagnostic procedures book says the "no cam sync signal at PCM" fault can be caused by any of these:

• open 8-volt supply circuit
• open sensor ground
• open or shorted signal circuit
• damaged pulse ring
• failed sensor
• failed PCM

[ihscoutlover]

Carl,

You and Bill both brought up good points. I will be testing the unit, however as a side note, I am wondering just how much play a distributor should have with the rotor. The reason I ask, is that I noticed when I removed the pickup coil(cam sensor), there were wear marks on not only the ring inside the distributor, but also on the sensor. I noticed a little bit of play on the rotor end, which makes me wonder if the distributor bearing is worn. I was gonna replace the cam sensor anyways, as the damage I am seeing may be from a worn bearing or gear or something to that effect.

I rechecked the trouble codes this morning, and 12, and 54 are still there, but the 42 is gone, probably from when I jumpered the connection. I am thinking the fuel pump may be bad, as it pressurized the fuel rail for a moment last night and then nothing else after that, and it hasn't since done it again. I will try and hook the pump directly to 12v and see what becomes of that. Then we can rule the pump out, but right now, I need to get a fuel filter so that if I need to get a new pump, it doesn't have to work so hard to get fuel up front. I'll keep you posted on more of my findings as I come across things.

Jeff

[Mt Hood Carl]

Sorry I don't know the spec limit for shaft play. But you found something I think since the sensor is hall effect type and should not contact the ring.

[ihscoutlover]

I kind of thought the same thing. Now its finding the cause of the no fuel pump running that I also need to address. I'm thinking the spark issue is partially to blame on this cam sensor, but only time will tell what's the true cause of what's the problem. Funds have cut my parts quest a tad short, till I can find a true cause/effect and see if that cures it. I was thinking the whole distributor, since it actually comes with a new cam sensor. I'll keep you all posted and see what I come up with.

Jeff

[Bill usn-1]

You won't get fuel if you don't have spark.
So if you jump the relay and the pump works then it should be fine.
But it will not be turned on by the PCM if there is no spark.

If the pump still doesn't work with the gnd applied to the relay then you may want to remove the replay and test it onn the bench.
The diagram is normally on the top or side of the relay.


If the reluctor is touching the pickup then you should probably look at replacing the distr.



Cardone Reman/Distributor

For your 1994 Jeep Cherokee 4WD 4.0L MFI 6cyl

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+Core: $32.00
Part Number: 30-4694