‘94 Ranger 4.0 4x4 No Spark, Cranks Fine But Won’t Start

[Madmacks]

My son’s 1994 Ranger 4x4 V6 4.0 had blown head gaskets which we replaced. The truck is back together and cranks over fine, and has fuel pressure on the rails, but, there is no spark. We think it’s the crankshaft position sensor, but I’m finding conflicting info on how to test it. Here’s what I’ve done. First, I’ve watched the tachometer while cranking the engine (while connected to a battery charger in boost mode so we have plenty of cranking power). I would expect the tach to jump around a bit, or even go to 100-200 rpms while cranking, but it just sits flat, no movement at all. That implies the CKP sensor isn’t sending a pulse to the PCM. So I then crawled under the front and disconnected the 2-wire connector to the CKP sensor. I think one line should be hot and one ground in KOEO, but they both show about 1.5vdc in KOEO (maybe shorted together?).

The CKP is a Hall Effect sensor and as I understand it it should put out AC pulses when working properly. On the bench, when I connect my Fluke DMM to the pins and move a large bolt back and forth over the sensor pin I get reading pulses of between 0.02-0.05 volts AC. So a couple of questions...

Should the two wire lead have a reference voltage on one lead and a ground connection in the other? I don’t think they should both show 1.5vdc reading in KOEO. So what should these 2 wires read?

And what is a proper voltage reading when passing a metal object over the sensor while testing?

One other thing. One of my manuals says I should get a resistance reading of between 200 ohms and 2000 ohms between the pins on the sensor, and a different manual says not to ohm out the pins as the passed voltage could damage the sensor coils. I tested resistance before I saw the “don’t do it” manual recommendation, and got no resistance reading at all on my Fluke DMM. Should there be resistance or not, and did I jack it up by trying to test it that way? I still get the AC pulses, even after testing the resistance, so I assume it’s working, but what do I know! Help,

 

[franklin2]

It worked before you change the heads correct? I would go over everything again, I am thinking something was left unplugged. Make sure any ground wires are bolted back in place also. Just go over the whole thing again with a bright flashlight and see if something was missed.

 

[rumblecloud]

+1 Franklin2+
Sometimes the simplest things.
At the risk of offending you with a dumb questions - I'm a dumb kinda guy - so let me apologize beforehand:
But you've probably already traced back to the coil pack to make sure all is wired up nice and tight?

EDIT: Just looking around for answers to your question and do what I normally do when it comes to electrical-type issues.
Weigh the cost of replacement versus how much fun I am having trying to figure it out.

In this case Rock Auto

 

[Madmacks]

+1 Franklin2+
Sometimes the simplest things.
At the risk of offending you with a dumb questions - I'm a dumb kinda guy - so let me apologize beforehand:
But you've probably already traced back to the coil pack to make sure all is wired up nice and tight?

EDIT: Just looking around for answers to your question and do what I normally do when it comes to electrical-type issues.
Weigh the cost of replacement versus how much fun I am having trying to figure it out.

In this case Rock Auto

Yes. Things are wire up correctly, nothing unplugged. Voltage input to the coil. We will replace the sensor, but if the wiring harness is messed due to cracking and shorting that won’t help. Really want to understand what voltages and/or grounds and/or resistances should be on the wires and plugs. I don’t like replacing things for no reason.

 

[Madmacks]

It worked before you change the heads correct? I would go over everything again, I am thinking something was left unplugged. Make sure any ground wires are bolted back in place also. Just go over the whole thing again with a bright flashlight and see if something was missed.

Did that, several times. I’m looking for specs and testing info on the feeder wires and sensor.

 

[franklin2]

If you want to check some things without guessing, the first thing to do is pull the codes. The computer will look around and if it sees something is obviously not right it will set a code. It's not always right and it misses things once in awhile, but it may point you in the right direction. If it's missing the crank sensor signal, it may throw a code for that.

If you can't get any codes at all from it, that may be a sign you have a power supply problem or a grounding problem. The computer should at least talk to you and tell you it thinks everything is ok.

 

[Madmacks]

I'm working on that, my son is trying to find the reader I bought him several years ago.

Nothing personal folks, but does anyone have the ability to answer a direct question with a direct answer?

I am doing lots of other trouble shooting steps.

What I'm asking is, how to test the 2 wires leading to the sensor, and how to test if the sensor itself is faulty. I'm not asking for advice on other possible issues. Yes, I know the PCM could be bad. Yes, I know I can test lots of other components. Yes, I know I can visually inspect wires. Yes, I know I can pull codes.

Should the two wire lead have a DC reference voltage on one lead and a ground connection on the other? I don’t think they should both show 1.5vdc reading in KOEO. So what should these 2 wires read in KOEO and with key off?

And what is a proper AC voltage reading when passing a metal object over the sensor while testing it on the bench?

 

[franklin2]

You should get a A/C voltage of more than 1 volt when the engine is cranked over if the sensor is good.

 

[Madmacks]

You should get a A/C voltage of more than 1 volt when the engine is cranked over if the sensor is good.

Thank you... appreciate the specific reply...