I have a 95 JGC 4.0l/AT 165k mi

Driving on the highway, it just died and has not started since.

I have searched the forum for similar issues but have not seen any resolutions.


I am getting a bright blue spark @ the coil, but am getting a weak orange spark @ plug wires.

Never an issue in the 12k Ive driven it. Died without warning... no sputtering or other signs... just died.

Cap, rotor and wires are NEW...

I am considering the Crank sensor or the pickup.... I read a post where these were replaced yet the weak spark remained, that thread hadnt been updated so i do not know what happened there...

What do you think?

How can I test the pickup or the CPS?

 

I would check the resistance of the wires. A sensor doesnt provide any of the voltage in the system only signals.

 

Well, I replaced the part called a 'magnetic pickup' by Autozone, or the Cam Sensor by Haynes Manual. Very simple looking device, sits in distributor beneath the rotor, has a three-pin connector off of a 7" wire.

Whatever its called... it did not work. Still getting a very weak spark.


Are you talking about the Plug wires? If so, I have not checked the resistance. Only because it wouldnt make sense that the wires that were fine for 10k miles suddenly failed, or that the new wires that I put on AFTER the break down would be faulty as well. My luck is not that bad! But I will have a look next time I am under the hood.


What else is in the ignition system that I have not addressed besides the Crank Sensor? Would a faulty Crank Sensor cause weak sparks?

 

Are you getting any codes?

 

Right now I am getting a 12 and a 55... so basically nothing.

The Check Engine light was on at various times during the trip. However, when I broke down initially, I removed the battery terminals to inspect them. I think that any codes present at the time were reset by removing the battery cables. And since it wont run, it wont be able to resend the codes.

Or am I wrong on that?


***I also checked the ASD Relay, which I have read about in other posts... and its fine***

 

No your right the engine has to run to through codes. But it couldnt hurt to check anyways.

 

missread new wires sorry

 

How old is the coil.

 

The coil is not the original, it was replaced before I got the truck.

I took it off and had it tested and it passed, same results as when we tested a brand new one.


Im still looking online for the method in which to test the Crank Sensor... any ideas?

 

From my experience, If it was your crank sensor, you would get no spark at all. It tells the computer to send the voltage to the Ign. coil.

BTW, I'm having the same exact problem as you right now. Been out of commision for over a week.

 

The signal from the Crankshaft Position (CKP) Sensor is used to determine crankshaft angle, engine speed, and basic timing. Powertrain Control Module (PCM) also uses the signal from the CKP sensor combined with the input signal from the camshaft position sensor to properly synchronize injection.
If you have a strong spark at the coil you have confirmed that the crank sensor is working. It is difficult to determine spark plug spark strength simply by the color of the spark. See if you can borrow a spark plug wire/plug kilovolt test meter. Made by snapon or otc. Or you could simply put a timing light on each spark plug wire as you turn it over you will see a timing light blink which will indicate that you have enough spark . Did you check fuel pressure and injector pulse. Can you get your hands on a noid light to check that the injectors are working? Most overlooked is the fact the the fuel injectors have their own fuse, but in this case a shut down relay. Check that each injector has battery voltage with key on at dark green with black wire on each injector. If no power suspect broken wire between injector harness and auto shut down relay. Also be sure to check pcm grounds at the engine block on the right side about 8 inches behind the distributor.

 

So a good spark @ coil is indicative of a properly functioning Crank Sensor? Thats good news, I was not looking forward to digging it out and replacing it.
I checked the ASD Relay and it passed. I have not tested the fuse/relay for the Fuel Pump, although I should, I do have pressure @ the rail.

What is the correct voltage @ the injector harness?
What is the method of testing for Injector Pulse?

I will double check the ground strap again too.

Thanks! I appreciate the help.
Brian

 

With a multi meter you can back probe the injector wire and read the voltage,,,,...do not pierce the wire as this will cause problems down the road with corrosion and voltage drop. You should read battery voltage (between 11.56 - 12.6) . If you do not have a meter you can use a test light...bright glow of test light would be good voltage. The ground strap is not the ground I spoke of. That is the general ground for the block. The PCM/ECM uses a brown wire size 16g wire behind or close to the distributor. check that you have continuity between that ground and the ecm. (sorry about spelling errors).
I know you checked the asd relay, however just because it clicks and supplies power does not mean that that current/power has made it to its destination. Only by checking the injectors will you be certin. The ECM controls injector pulse by suppling the ground circuit to each injector so if you have no ECM ground, poor ground or loose connections at the ECM this could cause the problem. Did you check fuel pressure? Is the gas gauge lying? Does it turn over fast and steady but not start?

 

Crankshaft Position Sensor Connector

:

PROCEDURE

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C. Ohmmeter should be set to 1K-to-10K scale for this test. The meter reading should be open (infinite resistance). Replace sensor if you read any resistance. That would be the test you where trying to find online Brian. However I believe your sensor is good, never rule out a bad wire though.

 

I have not checked pressure with a gauge, I released pressure @ the valve on the fuel rail, then cranked the engine, I then checked the valve and there was pressure again.

The fuel gauge is correct as far as I know.

Yes, it turns over just as it always did, just no start.

I should get a chance to check out the grounds, and test the voltage @ injectors on Friday or Saturday. I will post my results.

thanks again