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joepowles 04-01-2009 09:20 PM

Good Crank w/o start, dead gages
i've been searching all over for weeks for someone with the same problems i'm having and cant find anyone so it's time to start my own thread :)

like the title says. I have a new battery and the engine cranks great, but with no spark, and no pulse at injectors while cranking. I have checked all the relays under the hood, they all work, i've replaced the ign. coil, and dropped in a new distributor along with a new crank position sensor. through my self diagnosis i have come to the conclusion that my ecu is going bad or i have a short somewhere in the wiring harness i cannot find.

a little more on the problem.
My jeep runs, and when it runs it runs like a top. but randomly it seems, while driving, stopped, or parked with ign off. this problem will start up. if i'm driving at the time, my engine will turn off, my voltmeter, fuel gauge, tach, spedo, oil press, and water temp gauges will all drop to zero or dead positions, obviously if the engine just shut off the tach and oil press will read zero but i'm sure the gauge isn't actually reading correctly. lol. this of course is the most frustrating of the situations of this problem acting up, and i'm getting sick and tired of it happening, thus this post :)

how i "fix" it.
every time i go to start my jeep the first thing i do is turn the ignition on and stare at the volt meter. if it jumps up to 12v i know it'll start otherwise it jumps up maybe an 1/8 of an inch, 1 to 2 widths of the needle. then drop back down to zero. if it reads zero it will crank but not start. one of two things i do usually solve the problem and get it drivable again. 1 I turn the key on, off, on, off till i see volt meter come on. or i go under the hood to the ecu with the key on and unplug the black (i think), on the right side of the ecu towards the engine. anyways i unplug that and plug it in untill i hear what i think is the injectors click in. then when i go back inside my volt meter is up and the car will start.

when the problem happens.
it seems almost as it is completely random, but it does seem to increase when it is humid outside. the last really bad rain we had i couldn't start my jeep for 2 days. causing me to miss a day of work... ouch

oh one more thing. when my jeep wont start and i have the ignition on. if i turn the hazards on, NOT turn signals, with every flash of the hazards my vold meter gauge will jump slightly up

Sb5551 04-01-2009 09:44 PM

When your gauges go dead, does the odometer read no-bus?

I had a cherokee in the shop that read no bus, the crankshaft position sensor went.

On my jeep when I had the same problems as you, my computer had taken a crap I cant remember if it read no bus or not though.

joepowles 04-01-2009 10:01 PM

Oh one more thing. 97 sport 4.0L AT

not sure what it means to read no-bus. i'll look it up

joepowles 04-08-2009 05:05 PM

ok found out some more but still no solution yet.
1 - odometer does not read no-bus, so no problem there
2 - I found a friend with a known good ecm swapped em out and still had the same problems. so that leads me to believe my ecm is still good.

so now i'm looking for a short in the wiring harness i'm guessing. I dont know exactly where to start without just ripping the whole harness out. any suggestions?

tdm 04-08-2009 05:24 PM

Sounds like you have possibly found your issue...The black plug to the ECM. If playing with it make a change and lets you start the engine, I would begin there. Completely clean the plug and ensure that you have good contact when plugged in. Maybe even use some dialectric grease to help.

joepowles 04-08-2009 06:27 PM

every plug on the ECM is very clean, and i've put dielectric grease on each plug. i tried that first. *shrug*

that goes for all the relays under the hood too i've gone threw and cleaned all i could think to with no results

tdm 04-08-2009 06:36 PM

Is it possible that one or more of the wires have "backed out" of the plug? I'm not sure without looking (some plugs are molded), but on most of these type of plugs the wire end is crimped on and then inserted through the back of the plug...they snap into the unit and are only held in place by the little tabs. Sometimes they will back out just enough to create an issue.

joepowles 04-08-2009 07:00 PM

thought of that as well and i took apart that plug completely. there was nothing wrong with it from what i could tell

joepowles 04-08-2009 07:00 PM

thanks for your help and ideas though :)

crazyredneck 04-09-2009 06:08 AM

i know that it may sound kinda dumb, but have you checked ALL of your grounds? from the motor, to battery, then the frame to motor, and the body to frame?

slf41002 04-09-2009 11:06 AM

Well it could also be the ignition switch itself or the wiring going down the column from the switch but I would say you are headed in the right direction at this point.I would have to go back and look to see but I had the same issue with my Dodge Dakota and ended up being the main feed wire to the computer.I had to search the Internet for the harness color codes and find the main wire that feed the computer.It did the same exact thing as your for a while but one day it would not start at all and after 3 days being dead I hooked a hot wire to the battery and defibulated its heart:D As soon as I hooked the hot wire to the wire to the one that I found to be the feed wire it fired right up(now this was after sitting dead for 3 days)I traced the original wire down to find nothing wrong with it so I ran a new wire and it is still running fine that way(that was over a year ago)!!!!!!

coppage 05-10-2009 10:18 AM

Just read your message after I started a thread just like it. My symptoms are exactly the same even on rainy days. I also noticed that my fuel gauge shows empty along with the amp gauge reading 0. Any luck yet?

rrich 05-10-2009 10:40 AM

Sounds like either a supply problem or a ground problem.

I think you can use some "T" pins from your wife's sewing basket.
Use a wiring diagram to find which terminals on the ECM are hot and grounds - there are more than one.
Back probe the "T" pins into those wire connections.

Then use a digital voltmeter - record the voltmeter readings KEY ON when it's in the condition it will start. Leave the pins in -- Then next time it won't start, take another set of readings.

The one that's "different" would be the culprit. Then use the wiring diagram to see where it goes and measure at the other end.

It sounds like a connection, like maybe a splice is not right.
Tough to find, but a good wiring diagram, a voltmeter (use a digital meter, they are high impedance,) and patience will resolve it.

SGT DELTA 02-18-2013 10:25 PM

Wondering how this was solved
Hi guys,

My 97 Sahara is having this same exact problem. Did anyone figure out the problem? Can you please share the solution with me?


Buz 1 02-19-2013 02:42 AM

i've been having the exact same problem. the red wire with white marker in the black plug is the main power wire to the pcm. u'll notice that it's a 14 gauge wire, where the rest are 18g.. it enters a plug located right next to the pcm that continues along the firewall into the cab. if u read the fsm it shows u how to pull the plug apart & pull connector out to service.. i just applied dielectric grease to each connector but haven't had a chance to test. seems to be a common issue.. '97 tj...:)

SGT DELTA 02-19-2013 07:19 AM

Thanks Buz,

I'll try that next. I also need to try my other ignition key because the one I'm using seems to be a little worn out.

I'll post my results when I get them.

Buz 1 02-19-2013 12:07 PM

i should have also mentioned that to test ignition switch check fuses 9,10, & 11 (behind glovebox) for power, both with key on,, & while cranking. if all good ignition switch is good(tks to 'rubi)...:)

BigCrave 02-19-2013 12:21 PM

If turning the ignition key off and on helps, I would look into the swicth itself. If unplugging and plugging back in connector to the ECU works, look into that.

Falcho 03-09-2013 10:19 PM

Greetings all,
So my 97 TJ was running just fine. I parked in at the end of December. Went to start it today, battery was completely dead. Once I charged it, I got the no gas/voltmeter working, no start situation. Im at a loss. All I did was park it for 2.5 months. Did any of you come up with something I can try?

Buz 1 03-10-2013 07:21 AM

well,,, if u read this far through the thread u should know what plug we're talking about. mess with it with ign. switch on & heater blower off so u can hear real well,, & u'll be able to hear the sensors click & the fuel pump run when they get power. i 1ce again pulled the plug apart & lightly crimped connectors a10, a11, a19, & a20, all 4 of which control the iac( m-lite on since i bought it.) earlier i had crimped a2, a4, a22(fused +), a31, & a32(both grounds). if u look at the face of the plug that goes into the pcm u'll see that each connector is numbered.. also,, before i crimped anything i filled each female connector with dielectric grease. it's working better since...:thumb:

Falcho 03-10-2013 03:42 PM

I played with the pcm connectors best I could, which was unplug and replug at this point. I have no garage, and I am in Alaska, and its too nippy to play around trying to disassemble the plastic connectors, which always break at these temps. Anywho, plugging and unplugging had no effect whatsoever. So, until I get another 40 degree day I guess the jeep will have to sit.
Hoping to check the ignitions fuses while I wait, I can do that with no damage. At this point, weather restricts me. Good thing the jeep is not my primary vehicle at this point....

Falcho 03-16-2013 05:12 PM

It warmed up enough today to break out the meter. The CPS is not getting 5 volts. So, it appears the problem is in the pcm. I have scoured the internet for any way to test a pcm, and it seems to be apparent that there is no test available, you just need to buy one and hope for the best. Im not at that point yet, since the cold is keeping me from doing anything more then the absolute minimum to check things. (30 below wind chills today with clear sunny sky). One person said it could be the ignition switch not sending a signal to the pcm, due to a failure. Again, too cold to tear the steering column down.
The pisser is that this thing ran fine since the day I bought it, until I let it set for 6 weeks, and the battery went dead. I find it hard to believe that sensors, or wires or what not just magically failed while sitting frozen. And since I find dozens upon dozens of references to this exact problem, with no particular cure, I really dont even know what to try next. I sure dont want to give it to the jeep dealer, thats like setting money on fire.
Any new suggestions kids?

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