What sensor would tell ECM to not allow spark?

[Postal_Dave]

So today I tried new wires going from the CKP to the computer. I disconnected the harness to the CKP and connected the new wire to the CKP and then cranked the engine to make sure it was making .9 volts AC. I then put pins in the back of the Computer harness and checked that there was DC voltage coming from the computer on those pins. I then connected the new wires to the computer, and tried cranking the engine, same as always, no spark. I connected my scan tool and then tried cranking while monitoring the RPM's. They got up to 213 RPM's then zeroed out.

So it's not the CKP, it's not the wires, it's not the computer. Something is telling the computer to not start, not to recognize the RPMs. The computer sees it at first, then something says, "Don't look!". The question is, What reading, or input, or lack of input would cause the computer to ignore the signal from the CKP?

 

[Turdle]

Oil pressure sender possibly.

 

[1998Exp]

This thread is too long for me to read completely, so just a naive question: any chance of an aftermarket anti-theft system installed on this vehicle? Most of those just cut off the starter, but some were more sophisticated.

 

[Lee's Automotive]

This thread is too long for me to read completely, so just a naive question: any chance of an aftermarket anti-theft system installed on this vehicle? Most of those just cut off the starter, but some were more sophisticated.

Nope he has stated its 100% original

 

[XploderPhil]

the check engine light should flash when you crank it over, if it doesn't the PCM is not receiving a PIP signal tell that engine is cranking over.

 

[Lee's Automotive]

the check engine light should flash when you crank it over, if it doesn't the PCM is not receiving a PIP signal tell that engine is cranking over.

True i forgot about that my sohc does that

 

[Postal_Dave]

Yes the check engine light flashes and the oil pressure gauge goes to operating levels.

I don't have an alarm system but I just remembered, because I haven't used it years, I did have a remote door unlock installed 15 to 20 years ago. I have no idea where it could be installed in the truck. It didn't have any anti-theft system attached to it though, so I doubt it could cause any problem with starting.

I realized that when I did my new wiring experiment today that I messed up. Even though I unplugged the CKP, if there is a short in the wiring to the CKP, it would still cause a problem because I didn't cut the existing wire and separate it from the system. So I'll try that tomorrow.

 

[C420sailor]

find that aftermarket system. They’re often tapped into a circuit that’s always hot using connectors that can make the wiring corrode

 

[Postal_Dave]

OK, I found the keyless entry remote system and carefully took it out. Man! Those installers knew how to play hide and seek with that system. I then hooked up the scan tool and cranked the explorer and it still only got to 200 RPMs then the computer quit recognizing the CKP again.

Guys, I hate to say this, but I think it's time to call it on this Explorer. Unless someone can come up with some brilliant idea to try...

 

[Lee's Automotive]

OK, I found the keyless entry remote system and carefully took it out. Man! Those installers knew how to play hide and seek with that system. I then hooked up the scan tool and cranked the explorer and it still only got to 200 RPMs then the computer quit recognizing the CKP again.

Guys, I hate to say this, but I think it's time to call it on this Explorer. Unless someone can come up with some brilliant idea to try...

Have you tried to leave the battery unhooked for a bit and then try again?

 

[Postal_Dave]

Have you tried to leave the battery unhooked for a bit and then try again?

Because I've only been cranking this, without getting it to start and recharge the battery, I unhook the battery after every try.

 

[Lee's Automotive]

Because I've only been cranking this, without getting it to start and recharge the battery, I unhook the battery after every try.

Ok well it seems like its time to find a harness for it let me research some more stuff

 

[Lee's Automotive]

@Postal_Dave Engine Wire Harness Fits 98 Explorer 4.0L 4WD Automatic 399362 | eBay

 

[Lee's Automotive]

I know i sound like a broken record but many different sources point to a no start with a bad camshaft position sensor some say it will run without it but others say it will not run without it

 

[Lee's Automotive]

Also, another question have you tried starting fluid or brake clean in the intake to see if it will fire?

 

[Lee's Automotive]

I'm thinking the reason your RPMS are dropping is because of a sensor shorting out which in turn drops the rpms from 200 to 0 maybe a shorted cam sensor is the cause of all of this

 

[Mbrooks420]

5.0 runs completely fine without it. No reason to believe the 4.0 isn’t the same. Why build a sensor failure into being stranded?

 

[Lee's Automotive]

5.0 runs completely fine without it. No reason to believe the 4.0 isn’t the same. Why build a sensor failure into being stranded?

Honestly just trying to rule it out because on ranger forums there's a few people that mentioned a no start without the cam sensor

 

[Runnin'OnEmpty]

IMU, the pcm takes the two sensors; cps and cmp to start. If one or both signals are missing, then the asd relay will shut off power to the coils and fuel pump as a safety measure, so the engine will not start.

You can check the cmp signal at che pcm wires; it should show a pulsing 5v every two engine revolutions.

Also pull the asd relay and give the female terminals a good shot of wd-40. It's non- conductive so it won't harm anything.

 

[Runnin'OnEmpty]

One other thing, try two or three starts without disconnecting the battery, then check for codes. OBD-2 needs at least two successive faults before storing a code...

Turn the key completely off, get out of the car and close the door between trys...