I have a 1997 Ford Explorer, 180,000 miles on it. It does have a surge at idle which I believe is the MAS, but could be wrong about that. The big problem is on occasion, usually after sitting overnight, it will not start. I pull a plug and there is not any spark. It has happened a few times and when I am troubleshooting it according to the Haynes Manual, I pull the electrical connection off of the coil packs to check for voltage. I have always had 12 volts on the + side.
Now, it seems as though when I plug it back in, it always seems to work again and I have spark. Obviously I have cleaned the contacts. Today for example was a typical time. No start, no spark at plug. Pulled off the electrical connector at the coil. Checked for 12 volts on + side - was good. Used a LED light and cranked engine over with key on to check for voltage on - side of electrical connector (this checks the computer I believe). When I used a LED light as stated in manual so u do not screw up the computer, I had no voltage. Not sure if it was getting good contact, I risked it anmd used just a regular test light.......light blinked fine on every - . Cranked it over and she started right up.
Soooooo, would computer be intermittant ? This only happens maybe 3 - 4 times a year at most. I also tried (before I figured out if I unplugged connector from coil pack it would work again) disconnecting the battery and seeing if things would reset - this did not work.
So, after along boring story - why would it get spark after I unplugged the electrical connector , waited a bit, then it gets spark ? Clean connectors is a given.
Thanks for any info as I do not have the money to just start replacing parts.
don4@charter.net

 

Might want to try this, buy a ten dollar multi tester, and when it happens, take all your plug wires off and test the amperage at between ground and the coil. YOu can't test voltage because as you know it's off the scale, and even testing on the 20 amp circuit might break some stuff, so get a tester you don't care about. I'm wondering if you're getting a few missing cylinders.

The problem being so intermittant (3-4 times a year) is perplexing though.

 

or hey if you're not being stupid you can hook a test setup with an old plug wire and spark plug and go down the line of coil nodes groundng each one for spark. The thing I said first is a little stupid when I thought of this.

 

Don, that sounds like a bad ground circuit between the PCM and coil pack. When you attach the test light, it restores the ground and everything works again for awhile.

Unfortunately, a bad ground will be hard to find. Like Amish says, get a cheap multimeter and check the resistance on the ground wires from the coil pack to the PCM. The trouble indeed could also be inside the PCM. Outside chance it could be in the CPS/crank sensor also.

Do you have any CM codes? Checking the codes would be the first step.

 

Don't discard the possibility of a loose wire in the plug. On my '92 I replaced the coil pack and the ignition module ($$$$) and thought I had it fixed each time (intermittent no start like yours). The Ex. would run perfectly whenever it would start up. After about 6 to 8 months and much consternation, I found out that there was a loose wire inside the connector that plugged up to the ignition module. I could move the wire, and it would start every time. I went to a junk yard and cut off a connector/harness and connected (spliced / soldered / heat shrink tubing ) it to my harness to replace the loose connector. It has started up every time since (knock on wood) and that's been 3 or 4 years ago.

 

thanks for the info. Actually, I like the loose wire in the plug theory. Actually makes the most sense as I just could not see why the PCM would be so intermittant. I will check all the wires thoroughly.

 

Yeah I like Jerry's theory. Before I read his post, this is what I was thinking.

Spark does not need the PCM. It will spark with just the crank position sensor telling the ignition control module where the rest of the engine world is. If you all of a sudden loose all spark, then gert it again, this is a fundamental issue. Like the ICM or crank sensor is not giving signal.

Only logical reason is an intermittent short or open circuit. You can of course perform a wiggle test. Start up the truck and giggle the connector on the ICM and see if it stalls or shutters a bit. The ICM is right in front of the battery.

Cam shaft sensor only sends a signal to the PCM that the PCM then uses to condition the ICM through the SPOUT signal. Without the Cam sensor, truck will still run.

Let us know what you find.