Help with spark please?

[Marco]

Hello.Hopefully someone in here may be able to assist with my current no-run condition!

PROBLEM:  Jeep sputters to a stop while on highway.Towed her back t0 my house in cochrane.

SYMPTOMS: 97 TJ 4.0

-Jeep has fuel
-fuel pump makes priming sound.
-fuel rail does make pressure(not sure how much should be?)
-New plugs.cap,rotor,coil
-Test plug against engine block..no spark
-(engine block ground good)
-check for voltage before coil.niether prong with or witout ignition
-scanner brings up 4 codes. TPS,AIT,COOLANT TEMP,AND BATTERY TEMP?
do these cause spark conditions even?
-tried rplace the TPS, still shows it on the scanner?
-tried crank sensor replacement anyway
-tried reseting codes
-tried disconnecting battery
-battery is fully charged
-ASD relay swapped

I am not all that sure where the spark should originate.any help or ideas would be excellent as my toy sits collecting dust! Can the actual computer just give up? Maybe the alpine alarm has shut something down?
Thanks in advance for any help.

 

[hps4evr]

something is telling your computer to not send spark to your coil. personally, i dislike alarms for this reason. if they arent installed properly then they can cause little issues like this down the road. but, there still may be something else causing the issue. check the wires going to the coil for power. trace the lack of power back to the source. good luck.

[cLAY]

It is possible that the relay that was installed for the alarm system to interupt the spark signal went bad.

Check under the dash for relays that don't look stock. Replace or try swapping them.

Or it could be your coil has failed. If you are getting codes from the computer I would wager its ok.

[cherojeep]

Hello

Start with checking your connections at the ignition module and coil and check connection's at the ECM,Make sure their is no green fuzz, If so clean it up.When you reconnect use some kind of grease sealant IE:silglide or dielectric.Do you have spark at your coil? Unplug your coil wire get someone to crank it if you have spark it's the coil wire,If not it is most likely the module.

Mike

[Marco]

thanks guys for your help.alarm looks like a professional install(nice clean job) and every thing else im tracing out is in great condition?  I also cant reset the codes im reading? If the computer has crapped out,where is it and can i replace it? thanks again,sure would like to go for a cruise lol! I also im thinking of just tearing out the alarm but i cant even see where the guy tied it in. i yiyi.

[cherojeep]

Hello

The ECM is commonly under the dash or by kick panel on the right side,But on early model's I have seem them under the hood.
There is a chance that those sensors all share the same ground,using a test light test for ground on each,I will go to the shop tomorrow and see if I can get a wireing diagram for you,there is a chance that the ECM provides a ground for them.I will let you know.

Mike

[XJwrencher]

Crank sensor mabey?

[streetvan1]

I would start by verifying not only the power at the coil, but also the switched ground input. You can do this with a test light. If there is power AND a switched ground, you have a coil issue. (IE: if the test light flashes while you crank the engine). If there is no flashing, then you have to move on to an eec or module issue. The only other thing that I would suggest is to make sure that there is not only no spark at the cylinders, but also, verify that there is no spark at the coil wire. You could have an issue inside the cap and rotor, although with the new parts you say you have, it's unlikely. Good luck.

Also, did you use a fuel pressure guage to verify the fuel? I'm not sure of the exact spec, but anything under 30 psi would be suspect.

[cherojeep]

Hello

This is what I want you to do,locate the computer it is on to of the blower motor on the right hand side of the engine bay/disconnect black connector from PCM and check if there is any damage IE corrosion,broken wires.If not using a Ohm meter check for resistance between ground and ignition coil driver circuit(gray wire in black connector)There should be 5 Ohms if it is higher check for broken or short in grey wire after any repair check for 5 Ohms again,If it is the same then check valve timing if valve timing is correct It may be necessary to replace PCM.

Mike

[Marco]

awsome.thanks for the ideas ill take a crack at it and see what i come up with.

[Marco]

ok ,so i replaced the pcm from another 97tj out of wreckers. It started!  but then stops right away? Having different opinions on "flashing it". Anyone have any ideas or know someone who can do this?

[Marco]

i also tried to do the pcm "reset" batt,headlights,ign sequence. Still only runs for a second or two then dies. Tried calling around and sounds like i need to get it towed in to get the pcm flashed?

[cherojeep]

Hello

Thats the problem with getting stuff out of the wreckers,You don't know what problems the vehicles had maybe that PCM is no good!
I would just go back and trade it in for another,Before you pay to have it towed in.
One other thing when you put your TPS in did you set it properly or did you just slap it in there.

Cherojeep

[Marco]

hmmm no. i Definetly just slapped it i there.New pcm doesnt brig up any codes and now i can read live data on it,so i think the pcm is ok.

[streetvan1]

PCM failures are very uncommon. Unless it was exposed to moisture in the junkyard, it's probably ok. If the TJ you pulled it from was identical in model year, engine, transmission, and feature group, then it should work. Otherwise, it may need to be flashed at the dealer, or it may not work at all. Get AMA and the tow will be free at least