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Unread 01-02-2013, 12:17 PM   #1
DMSewell27
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1997 ZJ 
 
Join Date: Jan 2013
Location: Frederick, MD
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Zj no start! Please help!!!

I recentley purchased my first Jeep. A 1997 Grand Cherokee 4x4 with 4.0 I6 and auto trans. Ran great for the first 18 days and then in the middle of my 4 mile commute from work to home it just died. I noticed then that both the fuel and volt gauges were inop with the ignition on. Had it towed to mechanic. He says his scan tool can't communicate with PCM. Replaced the PCM and it ran better than ever, for exactly 2 miles. This time when it died the fuel gauge is inop again but the volt gauge on the dash is reading very high, 16volts while an actual digital volt meter reading at the battery is 12.6. It will crank but will not start and the ASD relay is being triggered instantly at ignition on. And now for the first time ever it is showing me engine codes. I get codes...

12 - Battery Disconnected Within last 50 Key-on cycles ( this I know, just being thorough)
24 - Throttle Position Sensor Voltage Too High Or Too Low
22 - ECT Sensor Voltage Too Low Or Too High (ECT = Engine Coolant Sensor)
23 - Charge Air Temperature Sensor Voltage Too High Or Low (Intake Air Temp Sensor)
55 End Of Codes

I get those codes in that order.

I also noticed that when I attempt to crank and then leave the ignition on the Auto Shut Down relay in the Power distribution Center and the Evap solenoid on the drivers fender both click rapidly about 15 seconds after cranking and will continue to click for several minutes. I am very familiar with how to use a multimeter and have an oscilliscope at my disposal but I am unsure of the values I am looking for on each particular component. Any help here would be greatly appreciated.

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Unread 01-02-2013, 01:48 PM   #2
LunaMoona
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Location: Durango, Colorado
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With any vehicle that's cranking but not starting, the first things I check for are fuel and spark. Do you hear the fuel pump priming when you turn the key to the on position? Test your fuel pressure at the rail. Test your fuel pump relay to make sure that it's operating normally. If you are getting fuel, then check for spark at the spark plugs. If you don't have spark, diagnose and repair as necessary. If you do, I would diagnose your trouble codes--either a bad sensor or a bad wire going to the sensor. See if repairing the issues related to these trouble codes fixes your problem. I'm unsure of the values you will be looking for, but I'd use the search function to see if anything comes up.
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Unread 01-02-2013, 02:04 PM   #3
ratmonkey
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those codes together indicate a sensor supply voltage issue to me. that would be in the ecu. i would test the supply to each of those sensors and see what you get. but i'm betting the computer is a DOA unit.
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Unread 01-02-2013, 05:19 PM   #4
DMSewell27
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ok. Now I'm not at work and can be more thorough.

Thanks to LunaMoona and RatMonkey for the quick replies.

My Jeep is at a mechanics shop who works the same hours I do. This being my busy season, (I install remote starts, alarms, mobile audio and video at the local Mom & Pop 12volt shop) it is hard for me to get over there during his normal business hours. But if anyone needs advice with a stereo, remote start or anything aftermarket 12volt please feel free to ask.

What I have found so far is that there is no spark. And the fuel pump does prime but I have not checked fuel pressure myself. I tested the reference voltage at the TPS, CrankPS, CamPS, and IAC so far. All read between 4.96v and 5.1v. That was with my meter grounded at the battery. Should I instead be using the ground path at the sensor that leads back to the PCM?

The other thing I noticed is there are fairly new (not cached in "engine dust") aftermarket sensors everywhere I look. TPS, CrankPS, CamPS, distributor, ASD, trans and fuel pump relays.... EVERYWHERE!!! It looks as though someone was chasing this problem for a while, got it working good enough and pawned it off on me. The PCM I got to replace my factory one is a Cardone reman if that means anything to anyone.

Again, thanks for any help you can offer. I cant wait to get my Jeep back!
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Unread 01-02-2013, 05:49 PM   #5
LunaMoona
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Quote:
Originally Posted by DMSewell27 View Post
ok. Now I'm not at work and can be more thorough.

Thanks to LunaMoona and RatMonkey for the quick replies.

My Jeep is at a mechanics shop who works the same hours I do. This being my busy season, (I install remote starts, alarms, mobile audio and video at the local Mom & Pop 12volt shop) it is hard for me to get over there during his normal business hours. But if anyone needs advice with a stereo, remote start or anything aftermarket 12volt please feel free to ask.

What I have found so far is that there is no spark. And the fuel pump does prime but I have not checked fuel pressure myself. I tested the reference voltage at the TPS, CrankPS, CamPS, and IAC so far. All read between 4.96v and 5.1v. That was with my meter grounded at the battery. Should I instead be using the ground path at the sensor that leads back to the PCM?

The other thing I noticed is there are fairly new (not cached in "engine dust") aftermarket sensors everywhere I look. TPS, CrankPS, CamPS, distributor, ASD, trans and fuel pump relays.... EVERYWHERE!!! It looks as though someone was chasing this problem for a while, got it working good enough and pawned it off on me. The PCM I got to replace my factory one is a Cardone reman if that means anything to anyone.

Again, thanks for any help you can offer. I cant wait to get my Jeep back!
The TPS and the Cam Position Sensor are testing within spec. To test the Crankshaft Position Sensor, the meter needs to be set to Ohms. It should have a resistance somewhere between 125-275 Ohms. If it's out of spec by much, replace it.

If those new sensors are not OEM Mopar, that could be a big contributor to your issue. ZJs do not like aftermarket sensors.
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Unread 01-02-2013, 06:00 PM   #6
ZeeJay1997
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Quote:
Originally Posted by DMSewell27 View Post
Should I instead be using the ground path at the sensor that leads back to the PCM?
Yes, the PCM furnishes the ground from a single source and has a few splices.
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Unread 01-02-2013, 06:13 PM   #7
ZeeJay1997
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S127 Near Injector No. 3 T/O (4.0L Engine)
S135 Near Branch to PCM (4.0L Engine)
fuelmix.jpg  
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Unread 01-02-2013, 06:29 PM   #8
Oldfrog
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Just for grins, crawl under it with a flashlight and check the lower O2 sensor wires. ( at the CAT) They sometimes short and cause a fuse to pop.....but you might have a high resistance and intermittent short to ground causing the PCM and/or the ASD relay to act stupid. ( although they do that quite well on their own at times)

I will ditto the fact that they dont like aftermarket sensors....especially the CPS.
Cardone brand PCMs are probably the best available besides re-soldering your own.
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Unread 01-02-2013, 06:39 PM   #9
DMSewell27
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Quote:
Originally Posted by LunaMoona View Post
The TPS and the Cam Position Sensor are testing within spec. To test the Crankshaft Position Sensor, the meter needs to be set to Ohms. It should have a resistance somewhere between 125-275 Ohms. If it's out of spec by much, replace it.

If those new sensors are not OEM Mopar, that could be a big contributor to your issue. ZJs do not like aftermarket sensors.
Luna... By much? plus or minus 10% in my trade is acceptable. Same here?

I was a 1st gen Dodge Neon enthusiast in my younger days. Yes, one of those guys. And I see factory sensors in cars all the time at work. I would bet any money these are not OEM mopar sensors. No elongated, hyphenated part numbers. no pendastars, nothing. The don't even have the brittle fibrous plastic composite look. They look like hardened black epoxy and shiny knock off lego plastic. Sorry, I'd take pics if I could, but I hope you get the point.

ZeeJay! AllData! Awesome!

So, in testing for my 5v reference I should be using the black/light blue ground at each sensor for my meter to verify both the sensor's reference voltage and a good ground path (Ohms between negative batt terminal and Blk/lt blue with a 0.7 max?) back to the PCM through the factory wiring harness. Do you have the values each sensor should be sending back to the PCM or a list of resistance values they should meter disconnected or open load?

Thanks again guys/girls.

Last edited by DMSewell27; 01-02-2013 at 06:50 PM..
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Unread 01-02-2013, 06:56 PM   #10
LunaMoona
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Quote:
Originally Posted by DMSewell27 View Post
Luna... By much? plus or minus 10% in my trade is acceptable. Same here?

I was a 1st gen Dodge Neon enthusiast in my younger days. Yes, one of those guys. And I see factory sensors in cars all the time at work. I would bet any money these are not OEM mopar sensors. No elongated, hyphenated part numbers. no pendastars, nothing. The don't even have the brittle fibrous plastic composite look. They look like hardened black epoxy and shiny knock off lego plastic. Sorry, I'd take pics if I could, but I hope you get the point.

ZeeJay! AllData! Awesome!

So, in testing for my 5v reference I should be using the black/light blue ground at each sensor for my meter to verify both the sensor's reference voltage and a good ground path back to the PCM through the factory wiring harness. Do you have the values each should be sending back to the PCM or a list of resistance values they should meter disconnected or open load?

Thanks again guys/girls.
I apologize. I was actually looking at the test procedure for a 1987-1990 4.0l. Later years are a bit different. Here are the steps for 1991-2001 4.0l engines:

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 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.


------

Here's another way to verify a bad CPS, quoted from another post:

"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 loose communication. Don’t get tunnel vision and assume the sensor is bad (unless it tests bad with a meter). Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Check/clean/repair wiring or connectors as necessary."

------

CPS failure is very common on ZJs, especially on 4.0ls from what I've seen.
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Unread 01-02-2013, 07:13 PM   #11
ZeeJay1997
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Check the harness where it wraps around the back of the valve cover.

Also read through the green link in my sig. It may be something obvious and quick. I put some links in there that may help ypu out.

I posted the diagram because it is most applicable to the codes you are getting.
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Unread 01-02-2013, 07:31 PM   #12
DMSewell27
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Location: Frederick, MD
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Thank you all so much!

I have been lacking direction and only have my remote start/12volt experience to draw from. I know how to test circuits, I just need to know what to look for.

I doubt I will get to my Jeep anytime soon as I have a scheduled 9 hour day tomorrow with 14+ hours of work on the books but I will be sure to keep you all posted.

Below are a few things I just don't get. If anyone can shed some light on them... please enlighten me. I'll take anything from a hypothesis to known fact.

The other things I'm having trouble wrapping my head around are...

-The reman PCM "fixed" the issue for 2 miles
-Displayed the CEL for the first time ever after replacing the PCM. That includes pre start up, first 5 seconds the ignition is on. I even have an inexpensive Innova brand OBD2 reader i plugged up and pulled no codes before buying my ZJ.
-The Voltage gauge reading high. I understand it runs off of a Can bus network. I know how to test for Can High and Low wires using an AC volt meter but that is about all I really understand about how Can-bus works. OK, not totally true. I understand that everything in the can-bus system works off of codes. In it's most simple form, binary. a sequence of zeros and ones equals a command. All components of the Can-bus network can see all codes but the determine which ones are meant for them. For example the PCM receives Can-bus codes across the network about whether or not the doors are open but ignores them and lets the body control module deal with them. Oh fudge me in the goat arse... I'm over thinking it again
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Unread 01-02-2013, 07:45 PM   #13
ZeeJay1997
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No CAN bus on ZJ.

Be sure the PCM connectors are plugged in good.
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