help!!!! 96 Xj wont start

[Lumpy Grits]

Interesting, and good to know! I wonder how typical that actually is?

Well, I carry a spare O2 sensor in every car/truck/Jeep I own.
Saved my butt more than once ...
LG

[Russ Chung]

ok.....I understand replacing it with a Napa store bought one.....I guess the question i should have asked.....with that o2 sensor disconnected.....would I get 12 volts to the coil.....or does it need to be connected to complete the circuit since one of the leads on the o2 sensor goes to the computer as a signal wire? I checked the voltage at the ASD on the downstream contact which would be the green w/ orange stripe. I should get 12 volts at that point, but I get .8 volts. I cant see any where else on the wire that would cause it not to see 12 volts unless the return wire from the o2 sensor to the computer has to be connected. Does this make sense?

Let's talk about testing the ASD relay:
1. You should always get 12 volts at pin 16 (red wire) because it is connected to the battery. You can test that by removing the ASD relay and measuring the voltage at socket 16. If you don't get 12 volts then the fuse is bad or the wiring from the battery is bad.
2. When the relay is closed, you will get 12 volts at pin 17 (green/orange wire)
3. But in order to close the relay, you must put the relay back in the socket and turn the key on. In order to measure the output voltage while the ASD relay is in the socket, you need to put a jumper wire into the socket at pin 17, insert the relay into the socket, turn on the ignition key and measure the voltage at the jumper wire. If you don't get 12 volts, either the relay is bad, or the circuit that energizes the relay is bad. Either way, you won't get a spark. If all you are getting is .8 volts, then the relay is not closing and the .8 volts is getting to the green/orange wire thru the rotor of the alternator.
4. I don't know for sure what the XJ computer does with the O2 sensor input, but I know that on my TJ, the computer doesn't pay any attention to the O2 input signal until the engine reaches operating temperature.

[Lumpy Grits]

Anything new?
LG

[kirkandsylvia]

Ok....thanks Russ. I will try it again. Can I just jump pin 16 and 17 and try starting it? I dont see why I couldn't do that also. Mr lumpy....no I haven't had a chance yet since last post. I have been out our property in Az trying to get it ready to move to, but should have some time this week. Will keep you all posted.

[Russ Chung]

Ok....thanks Russ. I will try it again. Can I just jump pin 16 and 17 and try starting it? I dont see why I couldn't do that also. Mr lumpy....no I haven't had a chance yet since last post. I have been out our property in Az trying to get it ready to move to, but should have some time this week. Will keep you all posted.

Yes. Jumping pin 16 & 17 would do the same thing that the relay would do when it is activated. The key has to be on.

[aw12345]

When you do that use a fused jumper just in case there is a short somewhere

[Russ Chung]

When you do that use a fused jumper just in case there is a short somewhere

That's a very good general rule. In this specific case, it is not absolutely necessary because the wiring diagram shows that the current going to pin 16 is already protected by a 20 amp fuse (located in the power distribution center). In an earlier post, I recall that Kirk said that there was some small (.6 ohms?) amount of resistance between pin 17 and ground. According to Ohm's Law that could result in a current flow which could be high enough to blow the fuse.

[kirkandsylvia]

So....let me start by saying "thank you very much" to Russ for stopping by today after his weekend out in Johnson valley We did get some stuff accomplished, but not quite done yet. We have determined that the crank shaft position sensor is good.....the cam shaft position sensor is good.....all the wiring has no shorts or open wiring. We can see the 12 volts coming out of the ASD when the key gets turned on, but the 12 volts goes away after a few seconds of the key getting turned on. It appears that the computer is shutting off that 12 volts due to something that we aren't seeing. I think we have exhausted every avenue that we can with the diagnostic equip we have. A p0340 code keeps coming up after clearing it and trying to start it. Swapped out the cam shaft sensor 3 times now since its under warranty. I cant see a sensor being bad 3 times out of the box. Did some testing on It and it seems to check out ok. Somewhere the computer is getting a signal or not getting a signal and is shutting down the ASD . Next step...is either find a live scanner or take it to someone that does have one to find out what it telling the computer to shut down ASD relay.
Anyways.....again.....thank you so much Russ for coming by. It is greatly appreciated.

[aw12345]

ECm turns on the the fuel pump relay for a few seconds, generally not the asd relay, that one gets activated by the ecm when the ecm receives a crank/rpm signal from the crank sensor

[kirkandsylvia]

ECm turns on the the fuel pump relay for a few seconds, generally not the asd relay, that one gets activated by the ecm when the ecm receives a crank/rpm signal from the crank sensor

Yes....youre absolutely right...the fuel pump relay does only activate a for a few seconds....but right now, the ASD relay for whatever reason is also only activating for a few seconds. It should have a constant 12 volts while ignition is on.....but its not. Hence the issue. I....we...double and triple checked it. We chased each and every wire tied into the "12 volt" supply that comes from the load or secondary side of the ASD for shorts...broken wire...12 volts. I get 12 volts for a second or two at the positive side of the coil, fuel injectors, exciter on the alternator. Only for a few seconds....and then to 0 volts. Getting more frustrated....but haven't given up yet.

[Russ Chung]

Let me add to what Kirk said. Here's a picture of the 96 XJ wiring diagram. If you click on the picture, it will take you to Photobucket and you can enlarge the picture to get a better view.
1. When we turn the key "on", the circuit which is highlighted in [COLOR="#FF0000"]red[/COLOR] is energized, which closes the ASD relay.
2. When the ASD relay is closed, the circuits highlighted in [COLOR="#DAA520"]yellow[/COLOR] are energized
3. Almost immediately, the ASD relay opens and the circuits are de-energized. Kirk said it shuts off in "a few seconds" but it seemed to me that it shut off in less than a second.
4. We used a jumper wire to keep the ASD relay energized but there still is no spark, apparently because the computer is not sending the signal to the coil to generate the spark.



Here's what I think is happening:
1. We turn on the key and the ASD relay closes and energizes the circuits -- it is operating properly
2. Then the computer senses voltage at pin C12 (that's the one that is smudged in the picture) and because it is smarter than we are, it knows that something is wrong, so it opens pin C3 which opens the ASD relay and de-energizes all of the circuits.
3. Even though we can fool the ASD relay by using a jumper wire to keep the circuits energized, the computer still has to trigger the spark and the fuel injectors and it is not doing so.

Additional information:
1. When we crank the engine, code P0340 appears immediately. That code indicates a problem with the cam position indicator circuit (which could be the sensor, the wiring, or the computer)
2. If we clear the code, and crank the engine, the code reappears immediately
3. If we clear the code, and don't crank the engine but turn on the key, the code does not reappear, BUT the ASD relay still shuts down.
4. We tested the CMP and the CKP according to Karstic's suggestion (see post #41) and for good measure, we replaced both of them
5. We searched the web for code P0340 and found lots of posts. They boil down to 1) bad CMP, 2) bad CKP, 3) open or shorted wiring, or 4) bad computer. So we tested 1, 2, 3, and tried switching both the original and the replacement computer.
6. The fact that the computer is shutting down the ASD relay almost immediately after we turn on the key made me think again that it's behaving like there is a security system but the 96 XJ did not come with a factory security system, and we could not find any evidence of any aftermarket security system.
7. We don't have the diagnostic tools to see what signals if any, the computer is receiving from the sensors. All we could do is check the wiring for continuity, open and shorts which we did and we could not find anything wrong. If anyone has access to a DRB tool or any other suggestions I'm sure Kirk would appreciate it. Otherwise, he will have to take it to the dealer to find out why the computer does not let the engine run.

[Lumpy Grits]

Russ, is there any way at all that this could be tied to a fault in the ing. key switch/circuit????
LG

[Russ Chung]

Russ, is there any way at all that this could be tied to a fault in the ing. key switch/circuit????
LG

I don't think it's a fault in the ignition key switch circuit; the ignition key circuit does only two things 1) energize the starter relay and 2) energize the ASD relay. It is doing both.

[Lumpy Grits]

The key switch area is the only thing that hasn't be bypassed/tested yet is all
I ask because I have seen dirt/crud in the switch cause a slow power to ground contact in other 'puter controlled cars/trucks that would lead to a no-start deal also.
Good luck and fingers are crossed!
Respectfully,
LG

[Russ Chung]

Kirk,

Here's more information about code P0340 that suggests some more tests that we can do with just a multimeter.

1. The P0340 code is set after "5 seconds or when 2.5 engine revolutions have elapsed with crankshaft position sensor signal present but no camshaft position sensor signal". That suggests that you should double check and triple check the wiring between the CPS and the computer for opens, shorts and continuity.
2. The troubleshooting manual has this warning in bold capital letters: CAUTION: DO NOT PROBE THE PCM HARNESS CONNECTORS. PROBING THE PCM HARNESS CONNECTORS WILL DAMAGE THE PCM TERMINALS RESULTING IN POOR TERMINAL TO PIN CONNECTION. INSTALL MILLER SPECIAL TOOL #8815 TO PERFORM DIAGNOSIS. Since we probed the harness connector extensively on Monday without use of the special tool, I suggest that you do a visual inspection to make sure that the terminals and pins are making good contact. You should also check the pins on the CPS connector to make sure that they are making good contact. Since we don't have the special tool be very careful whenever you probe the PCM harness connectors.
3. Here are more tests that can be done of the cam position sensor circuit with just a multimeter:
Test 1:
With the key on, engine not running, the CMP disconnected and the PCM connected, the 5 volt supply circuit violet/white wire should have between 4.5 and 5.2 volts. If the voltage is higher than 5.2 volts, the circuit is shorted to voltage. The black/light blue wire should be grounded.
Test 2:
With the key on, engine not running, the CMP connected and the PCM connected, the CMP signal circuit tan/yellow wire will have 5 volts when the sensor is lined up with the metal part of the distributor ring and 0 volts when it is lined up with the window part of the ring. If the voltage does not switch, then the cam position sensor is bad.
Test 3:
With the ignition off, and the sensor connected but the PCM harness disconnected, the resistance between the 5 volt supply circuit violet/white wire and the CMP signal circuit tan/yellow wire should be more than 5 ohms. If the resistance is less than 5 ohms, look for a short between the two circuits.
Test 4:
With the ignition off, and the CMP and PCM disconnected, measure the resistance between the 5 volt supply circuit violet/white wire and ground. The resistance should be more than 100 ohms. If it is not, repair the short in the 5 volt supply circuit.
Test 5:
With the ignition off, and the CMP and PCM disconnected, check for continuity of the 5 volt supply circuit violet/white wire between the PCM connector and the CMP connector. The resistance should be less than 5 ohms. Use care to avoid damaging the PCM harness connector. If the resistance is more than 5 ohms, repair the open in the 5 volt supply circuit.

I hope that one of these tests will lead us to the source of the P0340 code.