What sensor would tell ECM to not allow spark?

[Postal_Dave]

Turdle: I've replaced the ignition switch and verified it's not that by turning the key to On, then using the solenoid under the hood and a heavy duty screw driver to jump leads and make the starter engage. I still got spark at the end but nothing while cranking.

Danny: I've checked the throttle position sensor and back probed the voltage, (I was hoping it was this) however, the voltage coming from the sensor is correct for starting.

5OHHH: I have the basic flat keys. There isn't a chip reader in the keys. Also, the sensors I've changed out I've replace with Motorcraft parts or other top rated parts for Fords.

Jisumo: I replaced the CKP with a Dorman CKP. I bench tested it and I back probed it. It was creating 5 volts A/C when cranking. I will say that I'm temped to buy another one to try because it's one of the only things it could reasonably be.

BenDT: I inspected the wire, made sure I had continuity to the ECM harness and made sure it wasn't grounding out.

Joney and Nate: I replaced my coil pack with a motorcraft coil pack.

Runnin'OnEmpty: I pulled the RFI plug and checked all the wires to the coilpack connector, no signs of the wires grounding out. 12 volts is getting to the coil.

I'm going to work on this thing just a couple of more days, then it's off to the junk yard if it doesn't fire up.

Thnaks guys,
Dave

 

[BenDT]

Dave I feel the pain. With the stock plugs... stuff happens. I personally have had those symptoms all be related to the crank sensor. At least change the plug before letting it go. The headlight switch is a great example of Ford pooping the bed. And unless you do backflips to rectify the issue, putting in a new plug is the easiest fix. With this things position to road debris and flying screw drivers while scraping off water pump gaskets etc it really does take a beating. If all else fails trade it on Craigslist. Im sure someone wants something off of it and with all the new sensors and work it should attract some reasonable offers. My ex never has left me when I “needed” it and I have always felt the same when wrenching.

 

[Runnin'OnEmpty]

..........
Jisumo: I replaced the CKP with a Dorman CKP. I bench tested it and I back probed it. It was creating 5 volts A/C when cranking. I will say that I'm temped to buy another one to try because it's one of the only things it could reasonably be.
..........

You mean point 5 volts (.5), right?
If the 96 has a 2 wire CKP, then I believe the output specs are between .5v to 1.5v.
That particular CKP does seem to be on the low end value, and if there's resistance
in the wiring or connectors, that could weaken the signal even more.

You mentioned that it tried to start once when you let off the key? That would also
indicate a weak signal.

I agree it's reasonable to suspect the CKP, although it's a mystery why there's no
code stored...???

I'm sure you've disconnected the battery negative terminal and left a door open for
about 10 minutes? This resets the PCM and discharges all capacitors.

 

[EB4X]

Do you have an engine temp sensor on order or picking one up tomorrow .... ?

 

[410Fortune]

I don’t think turdle was suspecting the ignition switch on the starter circuit side of things
More on the power up the pcm relay which distributes power to all the engine sensors via the solid red or red/green wires

The ignition switch in the steering column (not the key tumbler) has about 4 main power circuits running through it, if the one that controls the eec/pcm relay has issues then….

Need to rule that out

 

[Turdle]

Yes, ignition switch is a very common failure on hondas, and while this is not a Honda in question, the symptoms are identical. I recently repaired an old Mazda b2200 with same issue.

 

[Postal_Dave]

Yes, I did put in a new coolant sensor. Not the one for the gauge but the one for the computer. Nothing changed.

One of the first things I changed out was the ignition switch. Not the key holder but the wiring switch. After I did that I took the old switch and tested it with the continuity tester and it was fine.

Here is a video of the Crankshaft Position Sensor being checked. Please see if anything there is wrong with the results. I start off with an Ohms test. The probes are in pin holes 21 and 22 of the PCM harness, which is what the CKP is connected to.


BTW: Here is a really dumb question. I noticed this when I was making that video. The dash lights and gauges all worked the same with the PCM harness disconnected as they do when the PCM is connected. So the stupid question is, how can you tell that the PCM is working at all? I did check the power pin to the PCM and it is receiving 12 volts, but that just says it's getting power, it doesn't say if it's working or not.

 

[Postal_Dave]

I did find one difference when the PCM is plugged in. The Check Engine Light comes on. LOL

 

[J_C]

Yes the volts test for the CKP looks good.

It's getting a bit cumbersome to keep track of all the info in 3(?) different topics.

I recall in one of them that you were blowing PCM diodes, swapped in a different diode and it blew that one too. Whatever happened with that? Did you get new diodes, and now it isn't blowing them, or they are still blown? Did you ever find the fault that blew them, because this is definitely something that has to be found, even if there's another concurrent problem.

You have to have good diodes installed for the PCM relay to work, then it seems like, as others have already mentioned, you either have a short in the wiring from the diode to the relay, or a bad relay, or a bad ECM and the fault only appears with temperature.

Bad ignition switch won't blow the diodes. Neither will bad CKP sensor, O2 sensor, temperature sensor, fuel pump, coil pack, etc. That diode only goes to the PCM relay coil (to trip the relay closed) which suggests the relay is bad (rare internal short condition) or wiring to it.

Which power pin? You can tell if the PCM is doing it's job based on whether you get a voltage change on any of 3 coil ground wires to the coil pack, "ground wires" meaning the PCM grounds them to fire the plugs so with a multimeter probe on battery positive and on any of those 3 pins, while cranking it should show pulsating DC voltage.

 

[Turdle]

On a hunch, disconnect all spark plug wires, except the testing plug wire, and, recheck then for spark. Disconnect wires from coil pack itself. Push them well put of the way leaving only one testing wire connected to plug you have grounded to battery.

 

[Postal_Dave]

Turdle: That is a good idea. I'll try that tomorrow afternoon. Right now the carport is too full of mosquitos to go out there for more than a couple of minutes.

J_C: The Power pin for the computer is pin 97. Also, I thought I mentioned this in the other thread but I guess I didn't. The reason I thought I had a blown Diode was because of an ID10T error. Yes, I was stupid. This is shameful to admit. I thought I was checking continuity correctly with it but I wasn't. (For anybody that doesn't know, like I didn't, Diodes only allow current flow in one direction) I treated that thing more like it was a fuse. So they weren't blown and nothing was wrong with the box.

After I bought new Diodes though, I decided to play with the old ones. I connected one to my volt meter and my car battery. I don't suggest doing this because an angry genie came out of the diode in a puff of smoke.

 

[Kidd7]

You gotta keep that magic smoke in there, otherwise electronics don't work.

 

[RWAG]

Had a dealer installed Clifford anti theft system that was never used on a new 98 Expedition that gave me all indications that the ignition wiring module was bad. Turned out anti thieft was bad. Gave me: intermittent crank no start, no crank/no power, no crank-start with start relay jumped, no crank-no start with start relay jumped. In between these malfunctions it would start and run fine intermittently.

 

[Postal_Dave]

Well guys, I'm giving up. I'm going to call the junk yard in the next few days to come get it. I'm going to get a few parts off of it like the horn, jack, and I definitely want my gasoline out of the tank. They said they'd give me $340. I can take the PCM back because it had a 30 day warranty so I'll get $50 back there. That should cover all the parts I've put into this failed effort. It's kind of sad because this was a good working truck for the 23 years I've had it. ( For some reason I feel like I'm putting down a very old dog.)

Now I'm going to need to find something new that can tow around 2,500lbs, has a V6, and gets decent mileage.

 

[J_C]

^ There's always the option of paying a mechanic to diagnose it then DIY fix? Given the current vehicle market, I wouldn't want to give up on one with only a no-start issue.

 

[Josh P]

$340 won't buy much car in the current market conditions. A good mechanic would have it figured out within an hour or two.

 

[Fix4Dirt]

what about a v8 X? the gas mileage hit isnt big imo. or if not OHV manual, those also never die but like josh said 340 wont buy much today.

 

[Postal_Dave]

Oh no! I wouldn't try to buy a car with that little amount. I'm retiring in about a year and I was planning to buy a new truck or other vehicle that can tow a camper and travel the US. I don't think I could trust my old Explorer for that. However, I was trying to make my old Explorer last another year and hopefully use it as a trade-in when I was ready to buy my retirement vehicle.

 

[Josh P]

My point is, if you throw in the towel now, you get $340. If you fix it, it could be sold for a lot more as a running vehicle. Never know, the next owner might be in desperate need and it will take care of them as it did you for all these years.

 

[C420sailor]

I’d definitely bring it to a good mechanic and ask for a diagnosis. Great idea.

As for V6 vs V8, my V8 Explorer gets slightly better mileage. Much better for towing, too.