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What sensor would tell ECM to not allow spark?

Runnin'OnEmpty

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Here's a couple more thoughts:

Unplug the RFI capacitor from the coil pack connector loom, then try starting.
(It's attached to the coil mount and has it's own connector a few inches back.)

The PCM should have (2) ground wires exiting the main PCM loom and connecting
to a bolt near the center of the firewall. Check those for a solid ground.

If you have battery voltage at the coil pack positive wire, then what's missing is the
ground signal on the other three wires to fire the coils. AFAIK, those signals come
from the CPS through the PCM (where they're timed), then out to the coils.)
Fairly simple.

Also check the spacing between the CPS and the toothed wheel on the crankshaft.
There's a spec for that, but don't remember what it is offhand...
 



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410Fortune

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I know this seems strange but we MUST rule things out
What is fuel pressure?
 






Mbrooks420

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I think its the coolant sensor. When the coolant sensor goes bad the engine will not stay running when warm. Cold start, the engine (ECM) uses the default setting. The warm starts the (ECM) engine, uses the sensors input. I know there is a starter relay (95) that provides power too the ECM
It certainly uses this value to set the starting fuel mixture, and not just default value. That’s why they are often very hard to start when this sensor fails.
 






Postal_Dave

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I'm going out to buy a new Coolant Sensor. I'll give that a try. I'll let you know if that works.
I did a test on all the components that connected to a reference signal wire to check they're resistance. The Throttle Position Sensor was the only one that had low resistance. I need to find out what resistance it's supposed to have.
I also got good readings from 2 out of the 3 O2 sensors.
Once again, thanks guys.
Dave
 






drbenz

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1996 4.0 Explorer. I changed the spark plugs and wires. It started up and ran great until it reached operating temp then it shut down. It did Not sputter, it just turned itself off like you would do with the key. I tried to restart it, it would crank, but it created no spark. It would not restart again til the next day, and again, it ran perfect for 5 minutes. Then engine reached operating temp, and it shut itself off again. The third was was a repeat of the first two.

Since then I've changed out the camshaft position sensor, the crankshaft position sensor, the ignition switch, the coil pack, and the computer. Nothing has changed. I've checked every fuse and relay, all are fine. I've checked the wiring completely over and I'm getting the right voltage and continuity.

I believe that some sensor over heated in those 5 minutes that it ran and told the computer to shut down. Then finally, on the third day, it blew. That overheated sensor is keeping the computer from allowing the engine to spark.

So the question is, what sensor would not allow the ECM to start my Explorer? Would an exhaust sensor do that?
Thanks for your help,
Dave
 












drbenz

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Among other things it could be poor connection of the connection pins in the relay box to one of the relays or fuse but look at wire connections in things you might have moved first. Make sure they are tight.
 






DannyW

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Check the TPS. If it show the computer it's at or near WOT, no spark.
 






drbenz

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I see that my post didn't go through so I'll try again.
The reason likely is a connector pin that is getting hot and loosing contact. Years ago I had an Explorer come in with a no start and it turned out to be the connection of the main relay in the relay box. Use a spade connector to plug in instead of the relays or other wire connector to see if every socket has the same reasonable drag on it when pulled out. Wires that carry a lot of current are prone to this becaust of the heat that is produced so relays are first on the list but any of the connectors can have the issue. If you find that this is the problem after you tighten up the socket put some dilectric grease on the pins to help keep the issue from coming back.
 






drbenz

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BTW, this can affect fuses also.
 






5OHHH

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In the situation like this I would normally say start off at the very beginning. You have changed a lot of sensors without having codes or indications of them being bad sensors, sometimes aftermarket sensors could be the cause of certain problems as well. One thing I haven’t heard you speak about is the PATS system (passive antitheft system). I currently own a 2001. I have two sets of keys both original Ford, one of them will only turn the car on with the key facing One Direction. Why I couldn’t answer. It will crank but no start in the opposite. I haven’t been a Ford tech for a long time and I know that my key situation makes no sense but I can tell you that it actually happens. So maybe take a quick look at your keys maybe the communication between the chip and the receiver could be interrupted after sometime. Otherwise crank it until it gives you a code and start off in that direction. One other place you might want to look at is your grounds. This is consistent with loosing voltage/power/ignition with heat. I hope this helps
 






Jisumo

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1996 4.0 Explorer. I changed the spark plugs and wires. It started up and ran great until it reached operating temp then it shut down. It did Not sputter, it just turned itself off like you would do with the key. I tried to restart it, it would crank, but it created no spark. It would not restart again til the next day, and again, it ran perfect for 5 minutes. Then engine reached operating temp, and it shut itself off again. The third was was a repeat of the first two.

Since then I've changed out the camshaft position sensor, the crankshaft position sensor, the ignition switch, the coil pack, and the computer. Nothing has changed. I've checked every fuse and relay, all are fine. I've checked the wiring completely over and I'm getting the right voltage and continuity.

I believe that some sensor over heated in those 5 minutes that it ran and told the computer to shut down. Then finally, on the third day, it blew. That overheated sensor is keeping the computer from allowing the engine to spark.

So the question is, what sensor would not allow the ECM to start my Explorer? Would an exhaust sensor do that?
Thanks for your help,
Dave
Crankshaft sensor sir
 












spetersen

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This does not have a chip key does it? I don't remember when it came out, also is the plug gap correct? I have seen this problem on another car when the gap was bad.
 






joney

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I've read on this forum, multiple people replaced their coil packs, but the new aftermarket coil packs were cheap/no good and failed.
 






Nate Tidwell

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Often when coils fail, they get hot and stop. Then when it's cooked enough, it'll do the same thing
 






Mbrooks420

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This does not have a chip key does it? I don't remember when it came out, also is the plug gap correct? I have seen this problem on another car when the gap was bad.
No PATS on a 1996.
 






BenDT

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I would inspect the wiring and the plug to the crank. I would also change sensors. I use non Ford and out of the box many do not work. IF you know it’s the only issue aftermarket can be a cheap alternative. If the vehicle has many issues only go Ford. It really can solve all too many issues. Old/bad fuel pumps can overheat as well. Just like a starter on its way out. Cools down typically will start again.
 






dbcreed

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Not a sophisticated troubleshooting response, but I'd do whatever you can to rule-out the Crankshaft Position Sensor. My 1999 behaved the same way you describe, and a new $25 CPS solved everything. Just sayin'...
 



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Runnin'OnEmpty

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PostalDave, congrats on hanging onto your sanity so far...:)

If you're still getting NO codes, and battery voltage on the coil pack + wire, and
reference voltage at the CPS, then check for continuity at the CPS to PCM ground
wire. Since you've changed virtually every sensor and checked fuel pressure etc.,
this must be a wiring/ground/connector problem.

The coils fire when they get a momentary grounding pulse from the PCM, and for
whatever reason this isn't occurring.

If you haven't already, unplug the RFI condenser.
It may be shorted and preventing the coil grounding from "breaking".
 






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