1996 grand cherokee 4.0 engine ,Coil wont fire..

[wayne100]

This is my first post,So I hope I don't mess it up.I have a 1996 grand cherokee for about a year now.It has ran great until a couple of days ago.I was parking it and The engine just quit.Hasn't started since.It is 4x4 automatic and has the 4.0 inline 6 cyl engine.I am getting no spark from the coil.I changed the crank sensor and electronic module in the distribitor with new ones.I tried two different used coils from a salvage yard where I used to work.No spark.I didn't see a cam sensor on the engine.I unplugged several plugs and plugged them back up,Thinking maybe a bad connection.I removed the computer,But cant find anyone who can check it to see If its bad.I notice the computer case is corroded bad from moister.Where the two computer halves go together,There is a couple of holes from corrosion that could let moister get into the computer.I haven't checked the ignition switch on the steering column yet.I don't know if getting the computer reflashed would help or not.It also has a security system alarm on it.I don't know if that could cause this to happen or not.Any help is greatly appreciated.

[boomhauer]

NSS, i originally thought, but you say your getting spark. Just out of curiousity do you have reverse lights? A new coil and CPS not salvage ones as they are classic problems and you may be swapping bad for bad. -B

[Talyn]

I changed the crank sensor and electronic module in the distribitor with new ones.I tried two different used coils from a salvage yard where I used to work.No spark.I didn't see a cam sensor on the engine.

The electronic module in the distributor is the cam sensor. However it wouldn't cause a no spark issue as it is for the injection synch. Did you try cranking the engine over with the distributor cap off to confirm the distributor is spinning?

I just had a similar thing happen his weekend on my 95 ZJ. Just died on the road, would not restart. no spark. Replaced the CPS and it was good.

[Talyn]

NSS, i originally thought, but you say your getting spark. Just out of curiousity do you have reverse lights? A new coil and CPS not salvage ones as they are classic problems and you may be swapping bad for bad. -B

He said he isn't getting spark. Also, a NSS problem wouldn't even let the engine crank.

[wayne100]

I am not getting a spark from the coil.The crank shaft sensor and the module in the dist is new.The last coil I tried came off a running engine.I had the original coil checked at an auto parts store and they said it check good.He checked the primary and secondary windings with an ohm meter.

[RCP Phx]

Might get better info over at NAGCA.
http://www.nagca.com/forum/

[wayne100]

Thanks,Will check it out..

[kastein]

Are you getting a proper coil trigger signal at the primary? Check that. If you do, check if you get a proper coil trigger signal at the output of the PCM. If you don't, it's either the PCM or some sensor / sensor wiring.

[wayne100]

Thanks,Will check that out tomorrow..

[wayne100]

I believe I checked the coil trigger signal going on the coil plug several days ago and the meter read about 4 volts.I don't know If the coil requires 12 volts or 4 volts was right.I will check that voltage reading again today.I'm not sure how to check the coil trigger signal from the pcm.I have the pcm unbolted and just lying beside the firewall.I don't know If the pcm has to be bolted to maybe get a ground thru the three screws or not.Maybe someone here will know.I ordered a chiltons repair manual online.But will take 7 to 10 days to get here.I hope it will read which sensors to check and what the voltages,signals should read.Thanks for all the help.

[kastein]

You won't be able to measure the coil trigger signal very well with a meter, it's a very fast pulse signal. You'll need either an oscilloscope or a test light - preferably an oscilloscope, of course, but they're expensive. Really what you are looking for is the test light flashing brightly when connected across the coil primary.

[wayne100]

Thanks for the Information Kastein.I had an older oscilloscope,But gave it to a friend of mine.I can borrow it and maybe check the coil primary.Thanks for all the help..

[kastein]

OK. You should see about 12 volts most of the time and a spike to 0 volts (or within a volt or two) every time the PCM wants the ignition to fire.

[wayne100]

I found something else going on today.I removed the ground battery cable and cleaned it and when I was reinstalling it,I noticed that something is pulling quite a bit of voltage with everything electrical turned off in the vehicle.Not a few amps like the radio would pull,But more like the headlights are on.But the lights,ignition,everything is off.I'm wondering if maybe the alternator may have gone bad and maybe shorted.Does anyone know if I pull the red "hot" cable off the back of the alternator and then checked If voltage is still being pulled.If the voltage is not being pulled then,Wouldn't that mean the alternator is bad.Maybe some auto parts store can check the alternator.I wonder if that could stop the coil from firing.The positive side of the battery has a double cable,One going to the starter and one going to the alternator.Thanks again for any help..

[wayne100]

Today I used a INNOVA OBD 11 CODE READER with hopes of finding out what is keeping the coil from firing.When I connected the OBD plug to the plug on the vehicle,The tester turned on by itself.Maybe it is supposed to do that.But the the book that came with the OBD says to manually turn it on after turning the vehicle switch on.I have pressed the link button with the key switch on and off.It makes no difference.It won't show any codes.It only reads ERR that I assume means error.I read a thread somewhere that said the electric fuel pump could stop the coil from firing.I checked the little bleeder valve on the fuel rail and it shot fuel out about a couple of inches.Not real strong,But fuel did come out.I turned the key off and on a few times and fuel shot out again.I don't know If that means the fuel pump is good or maybe bad.The fuel guage in the dash quit working.Some times in the past had to play with the key switch to get it to work.I'm wondering if the electric ignition may be bad.I hope the switch is down on the steering column like GM.I hope someone can give me some input on this.Thanks everyone for the help..

[joe_peters]

Well, when the scanner fails to connect with the PCM in an XJ I always suspect a bad crank sensor--when they short to ground the dash gauges usually won't work, a "NO BUS" signal presents, and the scanner can't communicate with the PCM.

As your problem is no spark, but you have changed the crank sensor, I would concentrate on the rusted PCM and security system as your probable sources of the problem.

[joe_peters]

Another thought--do your gauges work? If they don't on the XJ and you get a "NO BUS", unplugging the crank sensor will allow the gauges to function--a very clear indication of the crank sensor as the problem.

[wayne100]

Thanks for the information.Although A parts house checked my coil and said it was good,My uncle has a 1997 gc and has the same coil.He took my coil and mounted to his motor and the coil would not fire.I have a new coil on the way.I also received my chiltons book on the 1996 jeep gc that should help.Another thing I want to mention again is ,The person who took off the crankshaft sensor said there was a metal bracket that the bolt went through the hole that holds on the sensor on.Another person who put the sensor back on left the bracket off said it didn't have to be used.I don't if it held the wiring harness or had something to do with the sensor working or not.Thanks again for all the help.

[wayne100]

Does anyone know If the metal bracket that the crank sensor bolt goes through has to be used to allow the crank sensor to work.Or it is for the harness .I mounted the new coil today,Still no spark.I am going to test the plug going to the coil with a test light tomorrow.Thanks for any help.

[wayne100]

Today I mounted the new coil and mounted the little bracket on the crankshaft sensor that was left off the first time the crankshaft sensor was mounted.And now after about two weeks,The engine started up.Now the engine runs,But very badly It backfires like timing off and has no power.Now my code reader is working and reading the code.It reads P1391.Intermittent ckp or cmp.I have replaced both the cmp and ckp with new ones.Tomorrow I will check the wireing and plugs on the sensors and harness.One thing I am not sure of is,My chilton book says to check the voltages on the sensors.That means checking from the center terminals to each of the outer terminals,One should show voltage and the other shows voltage when cranking the engine,My question is how do you contact the probe when the harness is connected to the sensors?I understand how to check the center ground ohms back to battery ground when plug is disconnected.I don't know how to test when plug is connected .Any help is appreciated

[willxj]

hey wayne i read thought some other forums about the code that was given, a couple of the forums said to disconect the battery to reset the computer and get everything synchronized and another said to remove the ckp or the cmp and re-install, in you case the crankshaft sensor. so i hope that this helps a little, but i would try to un-install and re-install the crankshaft sensor sense it sounds like it was installed improperly.

[wayne100]

Thanks for the info.I did disconnect the battery cable first thing when the engine started for the first time to reset the computer.That didn't help.The crank sensor had a metal bracket that the first person working on it left off.After doing some research,I found that the bracket was needed for the bolt to go through making the ground.A second person removed the crank sensor bolt and installed the bolt through the bracket then through the sensor into the bell housing .The sensor and bracket looks like it will only go one way.Very hard to install.Located in a hard place to get to.If after checking the cam sensor,plug,wireing harness,etc and it still runs bad,I will get the crank sensor removed and reinstalled.Thanks for the help...

[joe_peters]

Back probing connectors--special order "back probe" needles from Fluke, or straighten one leg of a small paper clip, hit the edges of the straightened end with a file or stone to "break" the edge--don't sharpen it--then slip that leg into the back side of the connector and hook your meter to it.

[wayne100]

Thanks joe.Will do.