Spark Plugs Not Firing

[Postal_Dave]

Fix4Dirt: Thanks for making sense of the code reader for me. The one I was mostly worried about was the MAF sensor. It's good to know that the codes were good. All the error codes were cleared by unplugging the battery. I was hoping that it would forget whatever was telling it not to start, that trick worked three times but it doesn't anymore.

Josh P: That was a good idea and I think it helped narrow down the problem. The coil pack is receiving 12 volts before and during cranking but it is still not firing the spark plugs. So the coil pack is receiving voltage, it just isn't being told to fire.

I'm thinking that it's either a bad wire or the computer. What do you think?

 

[Josh P]

Do you have a test light?

 

[Fix4Dirt]

Fix4Dirt: Thanks for making sense of the code reader for me. The one I was mostly worried about was the MAF sensor. It's good to know that the codes were good. All the error codes were cleared by unplugging the battery. I was hoping that it would forget whatever was telling it not to start, that trick worked three times but it doesn't anymore

I'm thinking that it's either a bad wire or the computer. What do you think?

i see, it wouldve been helpful to have the codes before, that, theyre a good starting point, but thats alright usually computers dont go bad, its very rare,i forgot how to test plug wires...

edit: see josh post

 

[C420sailor]

KISS

If it ran fine before you works on it, odds are that it’s something you ****ed with.

Unseat, clean, dielectric grease, and reseat every connector you can get to.

Was the plug change just normal maintenance?

 

[Postal_Dave]

I changed the plugs because the code said that cylinder 3 was misfiring. I bought a full set of plugs and wires but just changed out the plug and wire for cylinder 3 to make sure. It ran fine, the codes disappeared, and I thought I'd change out the rest of the plugs since it was probable time.
The next plug, cylinder 2 broke the plug off in the engine. Lots of work to get it out and all the little pieces, but I did and I checked with an endoscope.
I got everything back together and changed out the plugs and wires then started it up. It fired right up and and it ran beautifully til the engine reached operating temp, then it turned off like someone turned the key to turn it off. After that it would turn over but it wouldn't fire til the next day. Then it fired up and reached operating temp and turned off.
The day after that, I used the heater to keep the engine temp down and it ran 3 times as long. After I turned of the heat, it reached operating temp and died. It has been a week now and it turns over but does not fire.

The question is, What sensor could I have touched that could make the engine turn off as soon as it reaches operating temp and is now keeping the engine from starting at all?

 

[410Fortune]

Crank sensor is suspect, I know you replaced it
Pcm is suspect
Eec and fuel pump relays are suspect

Eec relay is a big suspect here, like said before when it shuts down check for battery power at red power distribution wire

Next time it shuts off turn the key and listen for pump? Does it run? Could be a weak / failing fuel pump

Could also be ignition switch related

 

[Josh P]

A test light and multi meter would track down the problem. Test the crank sensor with the meter set to ac. The sensor if good will read somewhere between 0.4 and 0.9. If that checks out, take a test light, clip the clamp to the positive side of the battery. At the ignition coil pack, there is 4 wires, one is the power supply wire, you already checked that, the other 3 are the signal wires to file the coils. Probe them with the test light. If the light rapidly blinks, everything is good to the coil pack. If the light doesn't blink, you either have a wiring issue, like a break in the wire or the wire is pinched, rubbed through shorting out. A possible bad connection at the ecm or the ecm is bad.

 

[Runnin'OnEmpty]

I believe you have a faulty ignition switch.
(The one bolted to the steering column.)

 

[Postal_Dave]

Runnin'OnEmpty: I don't think it's the switch itself because all the lights and inputs on the dashboard stay on while I'm cranking it and it does crank. So the signal for the wiring of the vehicle to be "On" is there. Plus, back when the vehicle still started, it turned itself off when the engine hit operating temp. This in particular makes me not think it's the switch itself.

However, I'm beginning to think you're right that it is something to do with the wiring from the ignition switch. Mostly because the spark plugs fire when I release the key from cranking. When I quit cranking, it now backfires.
Also, when I turn the engine on, I hear the fuel pump charge the fuel lines. I hear it charge the fuel lines again when I quit cranking the engine. I've never noticed the fuel pump doing its start up pumping twice like that.

It's like the power management system is ignoring the the fuel and ignition systems while sending all the power to cranking the engine.

Josh P: I'm chasing wires now. The ignition coils are getting power, but they are not getting a signal to fire. According to the wiring diagram, the signal to fire should be coming from the EDIS (Electronic Distributorless Ignition System) Module. This is apparently separate from the ECM. Anybody have any idea where the EDIS is? LOL

Once again guys. I can't thank you all enough for your input. Even though we haven't fixed it yet, your input helps to give me ideas and a direction to go forward.
Dave

 

[Josh P]

96, the edis module is part of the ecm. 90-94 or 95 the edis module was separate. The ignition system is the crankshaft sensor, the wiring from that sensor to the ecm and the wiring from the ecm to the ignition coil pack. The next step is to pull the connector off the ecm, check the pins for the crankshaft sensor there. Using the ohms setting, you can run a magnet over the crankshaft sensor and see the value change on the meter. Usually no spark is from the connector to the crankshaft sensor. Most people get lucky by unplugging and reseat the connector. I realize you are well beyond this but I'm stating it for anyone that finds this thread in the future from a search. If you probe each wire to the ignition system to rule out an open or short the only item not ruled out would be the ecm.

 

[Josh P]

Also, when I turn the engine on, I hear the fuel pump charge the fuel lines. I hear it charge the fuel lines again when I quit cranking the engine. I've never noticed the fuel pump doing its start up pumping twice like that.

Same thing happens when you have a battery that is almost dead

 

[Turdle]

Some (electric part) ignition switches do indeed fail and cut power to ignition only. Very common on hondas

It'll crank over, fuel pump runs, but won't start.

 

[410Fortune]

I would check battery voltage, alternator (running) voltage and check battery terminals including the ground connections to frame and body

 

[CDW6212R]

Ditto, go back through the basics, and then the old age parts like the ignition switch and relays.

 

[Postal_Dave]

The Ignition Switch is Not the problem.

I really dislike my multi-meter right now. I left my ignition switch in the steering column while testing the switch. I turned the key and didn't get continuity on a set of prongs that my Haynes manual said that I should while in the cranking position. $30 later, a new ignition switch installed, and still the Explorer didn't start. I double checked the old ignition switch with the multi-meter, now I get continuity. So that switch wasn't the problem.

I also thought that it could be the battery so I charged it, no change. Then I put my deep cell marine battery in the Explorer. Once again, it turns over but it doesn't start.

Next I'm going to check the wires from the ECM to the coils. I'll let you know what happens.

 

[Postal_Dave]

Guys, I think I've narrowed down the suspects but I need your help to find the culprit.
I was double checking the relays and fuses in the Power Distribution Box. I noticed a couple of strange looking fuses that I don't think I checked last time. I pulled them and one was blown. I looked it up in the manual and it's the PCM Diode.

OK, the PCM Diode sits next to the ABS Diode, which was still good. So I swapped them out and tried to start the Explorer. Nothing changed, it cranked but it didn't fire up. I then pulled the Diode and now the second Diode was blown.

Whatever is blowing these Diodes is most likely the problem. The question is, What could be causing these Diodes to blow?

 

[Josh P]

Reverse polarity with the cables on the battery can blow that diode. A shorted sensor circuit is another possibility.

 

[CDW6212R]

Reverse polarity with the cables on the battery can blow that diode. A shorted sensor circuit is another possibility.

Ditto, I'd inspect the wiring for that diode, a short to those from something else seems the most likely cause to blow the diode. The diode is just a one way valve to prevent current from passing in one of the directions. They have a current limit, so it should be some extra current getting into that circuit.

 

[Postal_Dave]

Does anybody have link to where I can download a complete wiring diagram for the 96 Explorer? Chasing wires is driving me crazy and my Haynes manual doesn't have the best diagrams.
Thanks.

 

[Fix4Dirt]

Does anybody have link to where I can download a complete wiring diagram for the 96 Explorer? Chasing wires is driving me crazy and my Haynes manual doesn't have the best diagrams.
Thanks.

Post in thread '1996-2001 ford explorer / mountaineer workshop manual (5567 pages!)'
1996-2001 ford explorer / mountaineer workshop manual (5567 pages!)