Crank position Sensor info??

[Kidd7]

99 Explorer v6 SOHC
I'm looking to see if anyone can explain to me how the Crank Position sensor works and what the ECU does with the data coming from it. It appears to me this is basically a wheel speed sensor that sends pulses as the crank rotates. Anyone looked at the output of this sensor? Using voltmeter or o'scope? I'm thinking the scope would be better here. What should I see from that sensor?
Here's the trouble: Intermittently, seems more often when the vehicle is warm after driving a while, the Ex will stall, idle roughly or seem to start in 3rd gear.
-When it stalls it will immediately start right back up.
-When it idles roughly it seems once you give it some gas and get the RPMs up over 1K or so, she runs smooth.
-When it starts in the wrong gear (seemingly) you have to give it a lot of gas, it moves real slow. Finally at about 3K RPM she'll shift and drive normally, shift through the rest of the gears and be OK.
Some years ago my mechanic diagnosed the Crank sensor and replaced it, it ran really bad at that point (before replacement).
This picture and the past replacement is what points me to the crank sensor:

That wire is one lead coming from the sensor and flaps around freely by the stud from the front of the engine. I have taped the wire and the stud to prevent shorting, but I theorize that the wire itself is corroded and the ECU is getting false data. I can see this being true because I assume things like timing, spark, injectors, even shifting is all based on RPM, which comes from the Crank Sensor.
Am I thinking correct? Way off base? Thoughts? Sorry its long and thanks for any help.

 

[koda2000]

From my experience with the crank sensor on my '97 SOHC, the crank sensor functions pretty much as does an ABS wheel sensor. I think it's referred to as a Hall Effect sensor.

The crank position's purpose is to fire the coil, which in turn sends the spark to the spark plugs at the correct time. I don't not know exactly how the ECU uses this signal, but it works the coil pack.

The crank sensor can be tested using a VOM and a magnet. I set my VOM to continuity test (beep), connected the wires from the VOM and passed a magnet over the tip of the crank sensor and received a tone as the magnet moved over the tip. This indicated to me that the sensor was working.

I was having an intermittent crank no-start, which I determined was being caused by no spark at the spark plugs. After removing and cleaning the crank sensor (which was pretty greasy) and cleaning the tone ring on the harmonic balancer, I put some dielectric grease in the electrical connector socket and and reinstalled the sensor. The truck started right up on the first try. That was almost 5 months ago and there has been to recurrence of the crank no-start.

Dirty sensor and/or tone ring? Loose/dirty electrical connector? Flaky wiring? IDK...

 

[Kidd7]

koda2000, That really helps. You're right it's a hall effect, couldn't remember earlier. So that sensor simply acts as a closing switch when the "tabs" of the tone ring pass over it. I'm assuming at this point it will be bouncing between 12v and 0v. I'll see what I can find.

 

[koda2000]

koda2000, That really helps. You're right it's a hall effect, couldn't remember earlier. So that sensor simply acts as a closing switch when the "tabs" of the tone ring pass over it. I'm assuming at this point it will be bouncing between 12v and 0v. I'll see what I can find.

Pretty much that's how the crank sensor works. I don't know what voltage is carried by the 2 wires connected to the sensor. I might be 12 volts, but it could be as little as .5 volt. I never checked the voltage. It all depends what the ECU is expecting to see.

Are you certain that your problem is no spark?

 

[Kidd7]

I really have no clue what my problem is. I'm looking at this right now because of the damaged wire. it makes sense to me that all 3 symptoms could be caused by this. it's difficult to troubleshoot since it's so intermittent and when it stalls it starts right back up and runs fine.

 

[Kidd7]

koda, do yo know the pinout of the ECU, mainly where the 2 wires for the sensor are? Also, is there a trick to removing the sensor?

 

[Kidd7]

I found this thread with pinouts, but the pics posted are for a 97. I'll see what I can find...
http://www.explorerforum.com/forums/index.php?threads/104-pin-pcm-pin-layout.162444/

 

[koda2000]

IDK about the pin-out. As far as removing the crank sensor, there are two 10mm bolts that hold it to the front of the engine. Remove the bolts and it comes right off. On the '97 the wire connector had a metal spring clip that I had to remove to get the plug out of the sensor. When I reinstalled the crank sensor I used a business card to space it away from the reluctor wheel.

Removing the two 10 mm bolts is a bit hard to do as there isn't much room to get your hands in there between the trans lines and fan shroud, but it's doable I went from the bottom.

If the wires to the crank sensor are damaged, can't you cut out the damaged section add and solder in some new wires protected by heat-shrink?

 

[koda2000]

There's a pinout on this link. It may be helpful, maybe not. See post #4.

http://www.turborangerforums.com/showthread.php?t=512

 

[imp]

@Kidd7 This was all easier with EEC-IV in the '90s. Mustangs with 5.0L HO engines still used a distributor. The "tone ring" consisted of vertical strips of metal about 1/2" high, which rotated about in the distributor bowl. The Hall Effect sensor "looked at" these strips as they passed by it, generating pulses which then "told" a TFI MODULE (Thin Film Integrated) to produce pulses sent to the PCM, which counted them continuously, and "fired" the coil primary at the appropriate moment, able to electronically advance and retard the spark timing.

The "kink"? How could the PCM know when a certain cylinder (#1 of course), was ready to fire? One space between the metal strips was WIDER than the rest! Every 8 pulses one came slightly later, this being needed for PCM to know EXACTLY how fast the engine speed was! Simple system, foolproof, have only seen one distributor go bad in all these years, but the TFIs went out from heat often enough that Ford moved them off the distributor bowl to a remote (fender apron) location, mounted on a cast aluminum heat sink, in '94 or '95. My '96 F-150 with 4.9L straight 6 (300 Cu. In.) had that same setup in the distributor.

Now, the Explorers have also that famous camshaft position sensor, exactly why, I dunno. Maybe you guys can tell me! imp

 

[1998Exp]

Imp, I am also old enough to remember that setup, with its failing TFI's. The interesting part is not that Ford moved them off the distributor because they were failing, but the fact that some idiot decided to attach them to the distributor in the first place, apparently to save a buck on a piece of wire and a connector. The metal body of that distributor ran at about 200 degrees -- and that was the 'heatsink' for the power transistor in the TFI, ha, ha, ha... Out of the curiosity, I cracked open the first one that I had to replace, and found that the failed power transistor chip had burned a hole in the conformal coating inside the module.
So why, in the world, they needed the crankshaft sensor when the camshaft sensor alone could have done the job? Here is my speculation: because of the 'wasted spark' system, there was no need to sense the camshaft position in systems with no sequential fuel injection (remember CFI?) When sequential fuel injection came, suddenly there was a need, so someone decided to make use of that abandoned hole where the distributor used to sit. And why not redesign the ignition system to trigger off the camshaft at the same time? It wasn't broke, was it? Somebody who actually knows the history of these things, please correct me if I am wrong!

 

[koda2000]

The camshaft position sensor is used for the fuel injectors. If it fails the engine will still run, but really poorly. I'm sure there's some reason why you need both sensors, but I don;t know what it is.

 

[imp]

@koda2000 Possible they were "testing the waters" cam-position wise in preparation for Variable Valve Timing? I'm guessing it would be mandatory to know where your cams were position-wise, if you were changing them about! That little issue, VVT, as well as Continuously Variable Transmissions are still on my "don't know yet, don't touch yet" list. Also known as **** List. imp

 

[1998Exp]

@koda2000 Possible they were "testing the waters" cam-position wise in preparation for Variable Valve Timing? I'm guessing it would be mandatory to know where your cams were position-wise, if you were changing them about! imp

That's a possibility. However I don't think they ever built a variable timing engine with a single cam in the block. As far as I know, to make variable valve timing you have to separate the intake from the exhaust, so a single cam won't work. I believe that early VVT systems only varied the exhaust timing, with the intake fixed, but even that requires a twin cam system.

 

[imp]

That's a possibility. However I don't think they ever built a variable timing engine with a single cam in the block. As far as I know, to make variable valve timing you have to separate the intake from the exhaust, so a single cam won't work. I believe that early VVT systems only varied the exhaust timing, with the intake fixed, but even that requires a twin cam system.

@1998Exp Mighty good points! Getting me interested in learning more. imp

 

[Runnin'OnEmpty]

.......... is there a trick to removing the sensor?

There is indeed a trick to removing the CPS. If you look closely there's a thin wire clip that surrounds the connector
plug, and this wire clip must be removed before the plug can be separated. Use a small pick or screwdriver to pry
up the clip and it will pop off.

I just went through this procedure on the way to a timing chain replacement, and it will drive you nuts trying to
unplug the sensor without removing the wire clip...

 

[imp]

There is indeed a trick to removing the CPS. If you look closely there's a thin wire clip that surrounds the connector
plug, and this wire clip must be removed before the plug can be separated. Use a small pick or screwdriver to pry
up the clip and it will pop off.

I just went through this procedure on the way to a timing chain replacement, and it will drive you nuts trying to
unplug the sensor without removing the wire clip...

@Runnin'OnEmpty A testimonial to difficulty encountered! How many of these I've read, and can't retrieve! Your work and reveal is very appreciated! imp

 

[koda2000]

The cam position sensor on my '97 had the same wire clip on it's plug as the crank sensor (and you can see it much more easily). Practice on the cam sensor clip and you'll figure out how to remove it.

 

[Kidd7]

Runnin'OnEmpty, Thanks for the tip about the clip. As FYI if it will help someone troubleshoot in the future. I unplugged the sensor and took some measurements.
With ignition in run position: both pins read 1.5v to ground
Resistance across the 2 pins = 19.84 ohms.
I was hoping to find something out of sorts here. I still believe I have / had a wiring issue. I cut the wire at the broken insulation, I didn't find any significant corrosion. I soldered it back together, covered in heat shrink and taped it up real good. We'll keep and eye on it and see what happens.