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Scott, ASE Certified Technician
Category: Jeep
Satisfied Customers: 1638
Experience:  ASE Certified over 24 years, Indepedant, bumper to bumper repair all makes
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1993 Jeep Grand Cherokee Limited, straight 6 4.0 [Starting

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1993 Jeep Grand Cherokee Limited, straight 6 4.0 [Starting Problem] Engine will turn over and either will not start or will start, run for a second or two and die. Occasionally I'll get double horn honk when trying. Maybe the security system, as I have all the bulbs out, because the lights stayed just on and run the battery down. Changed the IAC valve, doesn't start or keep running. Only codes are 12 and 55. Anti-theft? CMP or CKP? Maybe PCM, but how can I narrow it down w/o replacing all these?   Like where are these items and which do I check for first?



First off, the code 12 calls for a slow read on the MAP, but that could have been set due to your running condition. Second, the code 55 is the "end of message code".


Now, Lets start with the basics. Do we have a good spark, { Champion RC-12-LYC} do we have good fuel pressure. {31 psi w/ vacuum @ regulator, 39 w/o}


Will the vehicle stay running if you hold the accelerator pedal open?


Are the plugs wet, and everything else is good, replace them. If you have no spark, or lacking, or too much fuel pressure, we tackle that.


As far as the Alarm, see attachments for checking. Maybe a good run on that will help. The double horn honk has be a little bothered.


Do these checks and get back with me. Busy day today, but I will keep checking between road tests.






Customer: replied 8 years ago.
Pulled plugs and cleaned them. They were NOT fouled or wet and look fine.

I will clean the fuel filter and see if I can dig up a pressure gauge to check the pump.

Vehicle will not stay running if I hold full open. Just stalls (that's even w/carb cleaner sprayed in as starting)and btw it seems to only begin to start occasionally. Not every time, but when it does, it's when does it's immediately upon turning the key.

So I assume it's got fuel and a good spark (checked w/plug pulled & grounded and just a wire from cap held off ground for jump). I had also cleaned the rotor & cap. As far as the double horn honk? Happened only once, so I may have clicked key to acc. three times by accident.

I will check the Alarm system today and enter results here later. BTW - I'm not in any great hurry. I have other vehicles and lots of patience! :D

I just want to get the problem solved! :D
Run the alarm check I sent, and let me know if that made a difference
Customer: replied 8 years ago.
Ran alarm check. Double honk w/lights flashing to begin with. Then turned it to off position for testing.

No door or hatch openings produced a honk. Then opened hood, no honk. Checked hood switch connector and wire at switch is broke off & corroded. But if I ground the wire it honks (so circuit is ok to that point).

Rear Hatch = no honk when opened or closed (occasionally has worked). Key locks on doors honks as well as inside switches, etc. Hatch key fails fails to honk and so I pulled panel and paper clip grounded the connection to get a honk. So that key sensor is bad.

Are these switches normally a closed circuit (grounded) or open when doors, hood, hatches are closed?

It just cranks now (no start), but the way I got it to at least start momentarily before was when I was checking the IAC (that's now been replaced) and removed & connected it to see if the plunger moved when ignition was switched on, etc. It would start and stall out on several occasions but wouldn't run longer than a moment. But today it doesn't even try to start!

From reading the page links you supplied, it appears if I remove the PCM connector, that may disable the VTA for 20 starts. So I tried that, so I'm thinking although VTA has some problems it's not the problem. Still haven't checked fuel pressure, but do you think the problem may be in Cam or crankshaft sensor and if so where are they located?

No. Your told me you had a good spark, and that information comes from the crank sensor. Get me that fuel pressure, and I will cook on something here.



Customer: replied 8 years ago.
I'm out in boonies in the N.W.! Just got back from picking up a fuel pressure tester. But the jeep in out in the open and we are having a heavy rain and hail storm. When it clears I'll get that pressure reading for you!   
No problem, we're expecting it here in NC. N.W. North Washington State?
Customer: replied 8 years ago.
Northern Idaho, just north of Coeur d'Alene. No rain for over three weeks and it's a lot than late April showers. haha It's a flood! :O
Stay dry. I'll be here
Customer: replied 8 years ago.
Ignition turned to on/run and pressure gauge attached to fitting on fuel rail got me 34 lbs! That seemed low, so I called my son about fuel filter and he admitted that he hadn't put it on last fall cuz it was too cold! So he told me where it was and I'll put it on now myself. I think I read somewhere that w/ just turning the ignition on w/o attempting to start it or mess w/ the vacuum line it should read around 39 lbs. Is that correct?
Customer: replied 8 years ago.
Maybe I better try again. So I need to come off the regulator? OK! ....and yeah you are the one, where I read the 39 lbs! haha
Customer: replied 8 years ago.
39 lbs cranking both with and without vacuum line attached! hmmm... am I doing this right? and 34 lbs w/ignition!
Look at the fuel rail, you will see a fitting that resembles an old a/c fitting with a cap {should be a cap on it} remove the cap and screw the gauge fiting on it. Then take a key on reading. What ya got.
Customer: replied 8 years ago.
34 lbs

Good enough for now. O.k. I am sending you a schematic in 3 pieces. We are going to have to see if your getting power/ground to specific places.


1. You stated you are getting a good spark. So, we will check for injector pulse. Take

your test light and test any injector at the dark green/black when cranking should

have power. Then check the other wires, {other than dark green/black} going to the

other side of the connections. Should be pulsing. Are they?



Customer: replied 8 years ago.
No Pulsing! either wire! :(
So no voltage at the dark green and black wire?
Customer: replied 8 years ago.
No! ...but why do I smell fuel out of the throttle body?

Good question. O.K. No power at the injectors takes us back to the ASD relay "auto shut down, top of page right (A7){look at the diagram}


Check Fuse #2 at the Power Dist Center. red wire, power key on


Check light blue/red wire at ASD for power key on

Customer: replied 8 years ago.
My PDC is not numbered and has 6 small fuses, 10 large fuses, 7 relays only a relay is marked as Auto Shutdown. All fuses are marked as other things on the layout of the PDC lid. So which would be #2?

When you say ASD are you talking the module on far side of relays in glove box. It is under a part of the glove box itself w/o visible access, unless I pull the dash apart. Maybe access on the other end of that light blue/red wire? Otherwise I can start pulling apart the dash to get at it!    

NO! Picture is worth a , aww helll, you know. Fire in the hole


Customer: replied 8 years ago.
Power at #2 fuse and fuse is ok w/ ign on!
When you turn the ignition on and off, does the asd click?
Customer: replied 8 years ago.
Relay in PDC clicks, but the ASD in glovebox does not!
ASD id not in the glove box. Look at the last diagram I sent. Fifth relay from the left ASD Auto Shut Down Swap it with a like relay, not the fuel pump relay, and see if it starts.
Customer: replied 8 years ago.
Ok it didn't start, but while cranking Air Bag dash light came on! hmmm... WTF?
Which realy did you swap it with?
Customer: replied 8 years ago.
ABS on on end and it's the same number. I just tried it again and not only is air bag light on, but it double honked at me!
Customer: replied 8 years ago.
You know that's about 20 start attempts from when I pulled the harness from the to the PCM! Does that mean anything?
Customer: replied 8 years ago.
I saw a mistake above on my last post. Then I clicked on edit and I was going to just straighten it out. But I noticed a drop down box where I can pay more for the answer, if satisfied. Does that go to you, or does it open it back up for others to answer it instead? I want to keep it all going to you for helping me. Just think you are going to deserve more when this is done! :D

No, however, I bet the battery is ready for a charge. O.K. Recap time.


1. No power to Injector CKT Dr,green / black


2. No power to coil, Dk


3. These are fed by the ASD


4. ASD has power at red {fude #2} and light blue/red{fuse #6}


5. The only thing not checked yet is pink at the ASD for ground from the PCM pin #61; however, you stated that the fuel pump works, so you are getting feed.


Check ASD Pink. Key on, do you have ground?


almost 2300 EST. I will check in at 0630

Customer: replied 8 years ago.
Just put it on the charger because it's somewhat low, yes! :D Now, I'm sure how you want me to check the pink wire to PCM. Am I supposed to probe the pink wire at the harness to ground? Or?   
we are looking for a ground signal, oh, and good morning.
Customer: replied 8 years ago.
I lightly probed pink lead to PCM to ground and it lite and a relay clicked!

the pcm is not turning on the asd relay. you probing it, put a slight ground on the CKT. You have reached the end of the probing journey.


Next up is a data scan. This has to have a data stream read to determin where the issue lies. Like I stated earlier, it may come to this, but now other systems, buss systems and things that input info to the PCM to actuate the ground to the ASD need to be investigated. The only way to do this is to get a live data scan.


Now, is the PCM bad.. ??? Won't know until a scan is preformed.

Customer: replied 8 years ago.
Do I have to take the vehicle in to get a live data scan or can I get a tool (rent/buy) one to do it here at home? Isn't there a connector/adapter and program so I can attach a laptop pc to the jeep to do a live data scan? Or? :O

By the time you paid fot all the programs and cables, you could but another 1993. What we did together was rule out all the "non scan" issues. Like I said, either the PCM or one of the other modules {ie. alarm/body control} is keeping this from starting.


The whole alarm thing has me bugged. I can't help to feel that there is a connection.

Hail Mary Pass. Close all the doors, lock and unlock with key right front then left front then start.

Customer: replied 8 years ago.
Hail Mary Pass was caught, but no start. So I messed with all the door switches figured out which was truly bad and will get those replaced even though that was not the problem. So I started throwing parts at it and that didn't work. (joking)So after going all you've said, I decided to look over any wiring/buses and pull the dash apart to get at that alarm module. Checked, pulled apart and reconnected all connections I could find and found that terminal bus in door hinge side wall under glove box. So I pulled it out where I could see it cleaned it some and put it back in. Pulled that vehicle theft alarm off and put it back on. Didn't think any of this did any good, but I wanted to see if I had pulse at the injectors. So while test light probing it begin to start. So I shut it down and put things under the hood back together. Started Right UP! :D

Thanks for your help, I understand a little more about this beast. Just hope it keeps running. But now I at least know it is most likely in or around the dashboard wiring connections!   

You learned a lot over the last week, sad part, everything we went through is about an hour and a half real time.


Hang on to those schematics, and if I can send you anymore, let me know.


Keep your socks and matches dry.



Scott and 2 other Jeep Specialists are ready to help you
Customer: replied 8 years ago.
I am a member of many forums on the web for vehicles, etc. I have never considered using a service like "Just Answer" before. But in dealing with you, one step at a time (in the info exchange to work this out), I've come to appreciate your time and expertise!

I have Favorited your "Just Answer" profile for referrals on other forums!

Thanks Again! :D
Thank you. Have a Good weekend.