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i have a 95 jeep grand cherokee laredo 4.0 strait 6. it just turns over and dose not start, everything works(radio, windows, lights, etc.) but it dont start. i was told that the computer is bad, but i dont think it is. it does not throw any codes, and the check engin light dosent come on. the only thing i dont have is spark. i have power to the coil, and rotor but no spark. plugs, wires are good. i was thinking about changing the crank case sensor. as far as i know it is getting gas. i can get a new computer for $300 but i dont want to get one unless i have to.

if any one can help me please do be shy. i would realy appreaciate it!
 

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i have a 95 jeep grand cherokee laredo 4.0 strait 6. it just turns over and dose not start, everything works(radio, windows, lights, etc.) but it dont start. i was told that the computer is bad, but i dont think it is. it does not throw any codes, and the check engin light dosent come on. the only thing i dont have is spark. i have power to the coil, and rotor but no spark. plugs, wires are good. i was thinking about changing the crank case sensor. as far as i know it is getting gas. i can get a new computer for $300 but i dont want to get one unless i have to.

if any one can help me please do be shy. i would realy appreaciate it!
Would a bad computer throw codes, or light up a check engine light? I think the computer does all that, so I guess it depends on how bad it is.

Yeah simple cheap stuff first. Cap, rotor. CPS was my first thought but I'd have to do some reading to see if a bad CPS means no spark.
 

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Discussion Starter #5
ok so i changed the cps(camshaft position sensor), and i still have no spark. so this coming thursday i am going to get cap, and rotor. i was also wondering if a crankshaft position sensor would make it get no spark. i know if the crankshaft ps. is bad the motor will not start.($60) is this a common thing with jeep gc. to not start?
 

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ok so here is the deal i went today and did the trouble code diagnostic with the ignition key. it through code, 12, 22, 23, 24, and 55. 12 is when the battery is disconected i knew that one would show i needed the battery the other day.
22 is the coolent sensor voltage is too high or too low, test coolent sensor
23 is intake air temperature sensor imput is below the minimum acceptable voltage or abouve the maximum acceptable voltage.
24 is the throttle position sensor voltage is high or low, test the sensor.
55 end of code transmission

does any of this have anything to do with why i have no spark?
 

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Discussion Starter #9
the (tps) has nothing to do with spark. the only thing that the tps, coolant sensor and air intake sensor...have in common is the pcm. the pcm regulates the voltage to and from those sensors. sorry i did some research. so apperantly my computer is bad. so idk. how would you test a pcm. is it possible to do that. thank you
 

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I could be way off so correct me if Im wrong. But lets say the TPS was faulty and reading in that the position is open further then it should be doesnt the system help compromise by decreasing spark along with other things.

Just throwing thoughts out there.
 

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My money is on the PCM.

I had the same thing happen to the wife's ZJ earlier this winter.

Theres a diode in the PCM (i think it's a diode) that has to warm up and trip the fuel pump relay. Then the fuel pump will prime the fuel rail. This is common during winter... and the colder it is the longer it'll take to warm. But you can check this without costing you money. Here's what you do.

Turn on the ignition, do not go all the way to engage starter. Keep radio, heater etc off so you can hear. You will hear a click or series of clicks coming from pass side engine bay where the relays are. After this the fuel pump will prime the rail, and you can then turn the key the rest of the way to start the Jeep.

I found a rebuilt PCM on ebay for ~$80, installed in 20 minutes. She fired right up and no more issues since.

Good luck..
 

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When the battery in my Jeep died and I tried to jump it everything worked and the engine was turning over but the computer had lost its memory. I was told this was a somewhat common problem. I had to have a mechanic hook it up to a laptop and fix the computer.
 

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Doesn't. The. Computer. RELEARN. When. You hook. The. Battery. Back. Up? I. Thought I Saw that in Chilton. Service Manual ! Do you. Have to. Hook- up to a. Laptop just because you. DISCONNECTED. Battery?? Can. You. Hook. The. JEEPS. Computer to a. - Laptop? Who. Has. The. Software and. Laptop. To do. That? It. Does. Not. Seem. Very - USER. Friendly!! What IF you are in the. BOONIES. Somewhere? NO ROADS! WOW! I. DiD. NOT Know. The Computer COULD lose Memory?? Comments??
 

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Same problem, CPS Sensor?

My 95 Grand Jeep Cherokee died on me today. I turned a corner and it almost completely failed just as it switched from 1st to 2nd gear. The rpm seemed to not go up as I pressed the gas but they weren't completely on zero. I coasted to a stop and turned it off, tried again and it wouldn't turn over. There is power, it attempts to turn as if it doesn't have gas, clearly it has gas as I just put a 1/4 tank into it. It just never catches. I've tried unplugging the Fuel pump fuse for 2 minutes and resetting the fuel flow safety plug that under the dash near the passengers feet. Probably based on this feed?

Thanks for the input.
 

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My 95 Grand Jeep Cherokee died on me today. I turned a corner and it almost completely failed just as it switched from 1st to 2nd gear. The rpm seemed to not go up as I pressed the gas but they weren't completely on zero. I coasted to a stop and turned it off, tried again and it wouldn't turn over. There is power, it attempts to turn as if it doesn't have gas, clearly it has gas as I just put a 1/4 tank into it. It just never catches. I've tried unplugging the Fuel pump fuse for 2 minutes and resetting the fuel flow safety plug that under the dash near the passengers feet. Probably based on this feed?

Thanks for the input.
Welcome to the boards!

I would first check your 2 Engine Control fuses, and your Auto Shutdown relay inside the PDC just to the rear of your battery.

Just a suggestion
;)




BTW - feel free to start your very own thread on this...
http://www.cherokeetalk.com/forum/f9/
:cheers:
 
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