rickyzZ28

Sorry this is kind of long:
I have a 98 Jeep Cherokee with a 4.0 and auto transmission. Here is my problem. I was out four wheeling last week and climbed to the top of a hill. I shut it off as someone else had a broken front u-joint to change. When I went to start it there was nothing. No spark and no fuel. Towed it back through the woods to my truck and got it home. When I got home it, I had the battery tested and it tested bad so I replaced with a new one. Next I went through and checked the grounds on the motor and did find one that was loose on the back of the engine on the dipstick tube so I cleaned it and tightened it up. It cranks over just fine so I do not think it is a problem with the NSS, but I did look at the wiring and do not see anything that is bad.

Next I did the OHM test on my Crank Sensor and it came back low so I originally ordered the Premium one from NAPA and installed it but no change. So I figured maybe I got a bad one and returned it, then decided to order one from the dealer. I got the one from the dealer and both sides OHM out at infinite, where on mine with it set on 20k Ohm setting it only had 6.xx Ohms between B and C pins. Now my gas gauge and fuel gauge are not working and I still have no spark. They did work before the CPS swap and when this issue first happened. I have Ohm tested and voltage tested every fuse and all are normal and not bad. I have switched the ASD, Fuel pump, and fan relays with no result.

The fuel pump will work if you jump pins 87 and 30 under the relay. I checked the camshaft position sensor and had only .32 volts on it with no change while cranking and found I am missing the 5 volt signal from the computer to all the sensors that need a 5 volt signal.

Because of this I went through and checked the grounds and voltage at the ECU. On pin A4 I had no ground so I jumpered a ground to the wire and still nothing. I then checked pin A17 and there is only .32 volts when there should be 5 volts. I have traced this signal from the computer to each connector and all of them have .32 volts. Pins A31 and A32 both have good grounds, but pin A8 does not have anything on it. No voltage and if you try and Ohm it out to the battery positive or ground there is nothing on it.

Finally I have scanned for codes and it had a code P070X and it said it was for something with the transmission. I mistakenly cleared it before I wrote the number down. I also did the gauge test by holding the trip reset and turning the key on and they cycled just fine.

Questions:
What could cause my voltage on pin A17 to not have 5 volts? Does the ECU regulate this?

Does this sound like a bad ECU?

What else besides a bad CPS can cause my fuel and volt gauge to not work? I saw to check the speed sensors on the transmission but I could not see anything physically bad. I did not Ohm each wire though.

What doesn’t make sense to me is that I have never had any issues with it not starting or stalling. This is a woods only vehicle so I am not in a hurry to throw parts at it to try and fix it, only advice on what needs checked next.

salad

Volt gauge on an OBD-II should *always* work as long as the PCM and instrument cluster have a good connection.

Kind of curious why you didn't check the NSS first?

Only 0.32V from the PCM on A17 does sound like a problem. Yes, the PCM regulates the voltage for this from the battery supply. Before replacing anything refresh all of the grounds and power connections in the engine bay.

Related info:
https://www.cherokeeforum.com/f51/cr...x-tips-153657/

Ground locations on 97+
http://www.naxja.org/forum/showpost.php?p=245993828

captainwoot

x2 /\ , does the 5v reference come back if you unplug the new crank sensor? any of the sensors could short and shut down the 5v from pcm.

salad

Excellent point

rickyzZ28

Thanks for the help. I thought since it is cranking the NSS would not be the problem. Is it possible for the NSS to cause a no spark or fuel but still crank? I have tried to start it in neutral and there is no change.


The 5 volt signal does not come back if you unplug the crank sensor. I also tried unplugging the cam sensor, coil, TPS, and Temp sensor and it still did not come back. What other sensors should I try? It does look as if someone cut the plug off the rear O2 at some point and hard wired it in. It has been like this for the past 4 years I have owned it with no issue and it is hooked up correctly but minus the plug.

salad

Whoops sorry, I was tired and didn't see that it was a crank no start.

Have you considered an FSM? I'll have to dig into mine this evening to find out what sensors hang off of that circuit.

rickyzZ28

No problem on the NSS, I was unsure if it could cause a problem like this so now I know. I have some of the wiring diagrams from the FSM, but not all. I have the pinouts for connectors A and C, but not B on the ECM. I found one for B, but it is from a 98 Wrangler. On it I see that there is a secondary 5 volt reference on B31 that I did not check. From what I can see the rest of the pinouts are the same. Can you check your book and see if B31 is the secondary 5 volt reference. Thanks for all your help.

rickyzZ28

Here are the 4 pins that share A17 5 volt reference primary.


White/Black 5 volt reference Pin A17: MAP, CAM, Crank, TPS



Got this from the scanner danner videos: B31 Violet/White: VSS, Transmission Governor
Any idea where the Transmission Governor wire is?

salad

Okay so this is from my 1999 but here's what I found for you ('98 should be the same). C1 A17 feeds splice S115, which powers gadgetry as pictured:



Maybe one of those has a short. FSM says S115 is "near MAP sensor", diagram looks like it's in the fuel injector harness, where the MAP and all that feed out of going over the intake manifold.

rickyzZ28

Well it has been zero or below here everyday since Tuesday so I finally got back out to look at the Jeep today after clearing off the 8 inches of snow we got last night. I unplugged all the sensors on the diagram and there was no change. The voltage did go up to .71 volts from .32 volts with all the sensors unplugged. I got ahold of a FSM that I forgot I had downloaded as well. I depinned B31 which is the 5 volt signal to the transmission and still nothing. I checked pins 30 and 85 on the ASD and Fuel pump relay and they both had 12 volts on both pins. With the 5 sensors unplugged I checked to see if there were any codes and I got P1694 that I found from research means the computer shutdown to prevent damage. I also did an OHM test on the wires to the CPS, MAP, and TPS and all checked out within spec.


I checked the voltage on A22 and it had 12 volts. I also went through and checked the C connector on the ECM and pins 1, 2, 3, 19, 20, and 26 all had 12 volts. I did find that pins C28, 29, and 30 only had 2.45 volts for the CCD. Pin C28 says it is CCD bus negative so maybe this is where the problem is from since it has voltage on it. I checked inside on pin 16 for the OBDII connector and had 12 volts on pin 16 like it should. Could there be a problem here?

CCKen

Here's a schematic of the CCD Bus that you can refer to for troubleshooting various bus problems.



I really didn't carefully read all the posts relating to your problem but I did scope in on the last post where you said "only had 2.45 volts for the CCD".

I can figure out if you were backprobing the PCM connectors when you talked about the voltages from the PCM, but that is the process.

You need to check both the CCD Bus (+) and (-) circuits at the DLC.

Refer to the schematic.

Readings are at the DLC and with key to RUN, engine not running.

Measure the voltage at pin cavity 3 to cav 4 and/or 5. You should get around 2.49 volts. Check cav 11 to 4 and/or 5. You should get around 2.51 volts.

CCKen

Deleted. Duplicate of above post.

CCKen

Read through this thread. Similar to your problem?

Check how he fixed it at the end.

http://www.jeepforum.com/forum/f11/n...o-bus-1923881/

salad

Nice... funny how stuff like that doesn't get mentioned in the beginning of threads.

CCKen