I have a 06' Expedition 5.4L 3V. I currently have a crank, no start issue. I believe I have narrowed it down to the ignition system. I have used NOID lights on both the COPs and fuel injectors and only receive a flash about every second. I believe they should be flashing very rapidly.

Does this sound like a Crankshaft Position Sensor issue?

I am getting about 350 ohms resistance from the sensor but barley see any voltage change when I move metal across it. I was expecting to see .3V to 1 V.

Seems odd that it would give me a weak spark about every second. Any thoughts?

 

Just to be sure, your meter is set to AC voltage?


Doing a little math here but lets say the engine is cranking at, say 180 RPM. Divide by 60 would be about 3 rev per second. If you have a noid light on one coil it should trigger every other revolution, or about 1 per second.


Just curious, but does the Service Engine Soon lamp stay on while cranking or does it turn off while cranking?

 

No, The multimeter is set to DC voltage.

The check engine light turns off when cranking. I saw somewhere this indicates that the PCM is sending its ignition signals to the fuel injectors and COPs.

-More detailed info I am having a crank no start issue. The plugs are new and I get the NOID to light up about once every second on the COPs and Fuel injectors. If I let the vehicle sit for a day or more depending on how much I have tried starting it, it will start for anywhere from 1 to 5 seconds but run horrible and shakes while the RPMs hover around 1K to 1.2K. I first suspected a fuel issue.

The Fuel Pump Driver Module near the rear wheel appears fine, the fuel pump can be heard activating when you turn the key. No blown fuses. I was going to check fuel pressure at the fuel rail but the loaner gauge had a stripped adapter so I will have to wait to get another before I can test that.

 

A variable reluctance sensor (it is a 2-wire sensor, right?) generates an AC signal.
Actually, the light goes off when the PCM sees the CKP signal.
Try cycling the ignition key between OFF and RUN 3 or 4 times to fully prime the fuel pump and then crank it to see if that helps.

 

Yes, It is a two wire sensor. It appears I should have been using the AC setting. Got confused since most of the car runs on DC. It would seem this part is fine if the PCM is getting a signal from it and the flashing of the NOID light appears consistent with a cranking engine.

Cycling the ignition before cranking over does not help.

 

No, an AC signal actually reverses polarity. What have here is a pulsed DC signal.

 

I don't want to be perceived as arguing with you, alloro. You've got the experience with these Expy's and you know this electrical stuff better than I.


My experience is that a variable reluctance (i.e., 2-wire sensor) sensor puts out an AC signal which does reverse polarity. And a Hall Effect (i.e., 3-wire sensor) sensor puts out a square wave digital signal that actually turns on and off. (See below).


Part 1 -The Basics of Crank and Cam Sensors and How to Test Them

 

Feel free if you believe yourself to be correct.

I read the article and see where the confusion is coming in. They're calling the sinewave output of the crank sensor AC. (Many articles out there make this same error.) It's important to keep in mind that AC is a sinewave, but a sinewave is not necessarily AC. A sinewave is nothing more than a variable output voltage that repeats in a regular cycle. AC is a current where the outputs actually reverse polarity. The AC setting of a VOM is designed to read sinewaves, so when a variable reluctance sensor is being tested they suggest using that setting.

 

Here is another article that actually shows the wave form from a VR sensor. It is a sine wave, but actually goes negative and positive. Isn't that AC current?
http://fullfunctioneng.com/info/Hall%20vs%20VR.pdf


Anywho, suffice it to say, the OP should put his meter on AC to read the CKP signal?

 

The best to use here is an oscilloscope, but that's not something everyone has laying around in their tool box. An approximation might be an AC meter, but it won't really show an accurate value. It might be enough to determine if "something" is coming out of the sensor, but will not be enough to determine if that "something" is correct and thus from a properly functioning sensor. But I think the most common thing on these sensors is that either they work, or they're dead so if they do put out something then they are in most cases OK.

Try to measure it both in DC and AC, reverse the probes as well. This should give 4 numbers which could help determine if it's a dead sensor or not. If you want to go beyond that, then you may need a scope. If there's no codes stored in the PCM, that would normally mean that it indeed is receiving a signal from the crank sensor. If it is not able to determine the timing of the engine when cranking, it usually throws a code which would point you in the general direction of why..

 

Nope, that's just how a scope graphs it. The graph starts at zero reference (center of the sinewave) then plots the sinewave through the full 360 degree cycle. The voltage markings aren't showing the voltage level of the circuit, they're showing the voltage difference from the zero reference point.

 

Been outta town for a while, but I just wanted to wrap this up for future readers so that I don't mislead anyone.


On our trucks with a 2-wire CKP (aka a variable reluctor sensor), it does generate an AC signal. But as alloro points, the scope waveform starts at zero and doesn't show a minus voltage. There's a couple of reasons for that, as it depends on how your grabbing the CKP signal.


On our trucks, the Ford PCM supplies a bias voltage to the CKP circuit. They do this by supplying a DC voltage to the circuit for purely diagnostic purposes, because when there is no AC voltage on the circuit the PCM thinks the engine is not spinning, therefor they don't have a DTC for no CKP signal! But to aid in diagnostics, if the PCM doesn't see the bias DC voltage, it sets a P1336 to indicate there is an electrical issue with the CKP circuit.


If you are grabbing the CKP signal by back probing the circuit of a good CKP, you will see AC voltage from the CKP riding on top of the DC bias voltage. If you have your scope set to AC it will filter out the bias DC voltage and you will only see the AC voltage. If you have your scope set to DC voltage you will see the signal as alloro described, i.e, you will see the AC signal riding on top of (above?) the bias voltage so it will appear as a sine wave that never comes down below zero because of the approximate +1 volt bias.


Now if you take your reading with the CKP unplugged and reading the signal as it appears on the CKP pins with the engine cranking, with your scope set to AC, there will be no bias DC component and the waveform will be AC with equal portions above and below zero.


Hoping I haven't made it even more confusing. Someone with better verbal skills than I, please jump in and make it clearer....................

 

Epic fail. Seriously though, it seems like we're all talking about the same thing, just in different terms. As long as the problem gets solved, that's all that matters.