Won't start, no spark

[Jon94]

I'm buying a 99 Explorer 4.0 OHV from a family member. It cranks, but doesn't start and he's fed up with it, so he's giving it to me. I already helped him do some diagnostics but I still haven't figured it out. Here's what we found so far:

I put a fuel pressure tester on it and there's 65 psi at the fuel rail.

I put a spark tester on it and there's no spark. Although I only tested one cylinder; I suppose I should test the other cylinders?

I checked the resistance of the coil, and it's within spec. I threw on another coil anyway, but it still wouldn't start.

I have power going to the coil.

I tried using a test light to look for pulsing at the other 3 terminals at the coil plug. It barely lit up and pulsed a little, but I didn't really have a probe small enough to get into the terminals and I'm not sure I got good contact. Basically this test was inconclusive.

I tried testing the crank sensor. The wire harness has 3.5 volts on both wires. I hooked up the multimeter to the sensor and cranked the engine. The voltage fluctuated quickly between 6.5 and 8.5 volts. Not sure if that's normal; the Haynes manual didn't say what values I should be getting. I really should've used an analog meter, but I don't have one yet.

I replaced the crank sensor anyway and it still doesn't start.

I was beginning to suspect the computer, but they rarely fail and it still communicates with my scanner. No codes, but the battery was dead for a long time and the memory is wiped. (Has a new battery now)

The tach doesn't move at all when cranking, and looking at the live data on my scanner shows 0 rpm while cranking. Does that point to bad crank sensor? Should the scanner read rpm while cranking, or just when the engine is running?

I don't think it's a PATS issue; the theft light does not flash rapidly and there's no P1206 code.

I'm not sure where to go from here. Thoughts?

 

[imp]

I'm buying a 99 Explorer 4.0 OHV from a family member. It cranks, but doesn't start and he's fed up with it, so he's giving it to me. I already helped him do some diagnostics but I still haven't figured it out. Here's what we found so far:

I put a fuel pressure tester on it and there's 65 psi at the fuel rail.

I put a spark tester on it and there's no spark. Although I only tested one cylinder; I suppose I should test the other cylinders?

I checked the resistance of the coil, and it's within spec. I threw on another coil anyway, but it still wouldn't start.

I have power going to the coil.

I tried using a test light to look for pulsing at the other 3 terminals at the coil plug. It barely lit up and pulsed a little, but I didn't really have a probe small enough to get into the terminals and I'm not sure I got good contact. Basically this test was inconclusive.

I tried testing the crank sensor. The wire harness has 3.5 volts on both wires. I hooked up the multimeter to the sensor and cranked the engine. The voltage fluctuated quickly between 6.5 and 8.5 volts. Not sure if that's normal; the Haynes manual didn't say what values I should be getting. I really should've used an analog meter, but I don't have one yet.

I replaced the crank sensor anyway and it still doesn't start.

I was beginning to suspect the computer, but they rarely fail and it still communicates with my scanner. No codes, but the battery was dead for a long time and the memory is wiped. (Has a new battery now)

The tach doesn't move at all when cranking, and looking at the live data on my scanner shows 0 rpm while cranking. Does that point to bad crank sensor? Should the scanner read rpm while cranking, or just when the engine is running?

I don't think it's a PATS issue; the theft light does not flash rapidly and there's no P1206 code.

I'm not sure where to go from here. Thoughts?

PATS disables cranking. Therefore, if the engine cranks, PATS is not causing the no-spark. I was never "up" on the 2nd. gens too well, but here's a guess. The PCM must get pulses from the crankshaft position sensor in order to generate ignition pulses to the coil. You replaced the crank sensor, so I'm looking at the PCM. But, if you throw a different PCM in, it won't recognize your key, then you have no crank + no spark. I'm away from my shop, but will retrieve my wiring diagrams, and get back if any ideas pop up. Sorry to not be more help. imp

 

[1998Exp]

PATS disables cranking. Therefore, if the engine cranks, PATS is not causing the no-spark. imp

There are many versions of PATS, but according to my 1998 EVTM book, there is no PATS effect on the starter circuit in this model year. It's a fairly simple circuit, from the ignition switch, through the DTR (transmission range sensor), to the starter relay. Hence, cranking does not prove that PATS isn't the problem.

 

[koda2000]

The crank position sensor sends the signal to the PCM to trigger the coils. I had a problem with me '97 SOHC this past spring. I removed cleaned and tested the crank sensor and cleaned the reluctor wheel and it's been fine for 3-4 months now. I also put some dielectric grease on the plug contacts.

 

[imp]

There are many versions of PATS, but according to my 1998 EVTM book, there is no PATS effect on the starter circuit in this model year. It's a fairly simple circuit, from the ignition switch, through the DTR (transmission range sensor), to the starter relay. Hence, cranking does not prove that PATS isn't the problem.

Most interesting! I was going by 3rd. gen., which mine is, figured earlier would be similar. Guess they are skinning the cat every which-way. imp

Edit: Just thought of it......if PATS prevents spark, but allows cranking, the battery can be run into the ground cranking away for nothing. I think I lean towards the later way.

 

[koda2000]

Most interesting! I was going by 3rd. gen., which mine is, figured earlier would be similar. Guess they are skinning the cat every which-way. imp

Edit: Just thought of it......if PATS prevents spark, but allows cranking, the battery can be run into the ground cranking away for nothing. I think I lean towards the later way.

'99 PATS turns off the fuel injectors. Nothing else. The engine will still crank, but w/out fuel it won't will not start.

 

[jmvb]

'99 PATS turns off the fuel injectors. Nothing else. The engine will still crank, but w/out fuel it won't will not start.

98' SOHC PATS do the same. Not sure about OHV ones

 

[koda2000]

98' SOHC PATS do the same. Not sure about OHV ones

'98 ('98 being the first year for PATS) through '01 that's how PATS works, what engine makes no difference . After '01 IDK.

 

[imp]

'98 ('98 being the first year for PATS) through '01 that's how PATS works, what engine makes no difference . After '01 IDK.

I can tell you, 2004 lights up the instrument panel wrong key inserted, PATS light blinks fast, no crank. imp

 

[Jon94]

Update: Still haven't figured out the problem, but made some progress in troubleshooting. We can definitely rule out PATS as the issue.

The computer is definitely not sending any spark signals to the coil. Although, I have a question about that: I was using a remote starter button to crank the engine while looking for a signal. The ignition was turned on (all lights on the dash were lit up). The computer should've been sending signals to the coil under those circumstances, right? In other words, if the ignition is on and you use a remote starter button, the engine should start up and run if everything is working ok, right?

If that's the case, then like I said, the coil is not receiving signal from the computer.

I tried testing the crank sensor again, but I have trouble getting alligator clips into the connector to test it, and I'm not sure if the clips were touching each other, shorting out the sensor. So to fix that, I ordered a repair harness that plugs right into the crank sensor and has a pigtail that I can easily hook my multimeter leads to. So I'll test it again as soon as I get that.

Anyway, my crank sensor was producing only a few millivolts when I was cranking the engine. Can anyone tell me what values I should be getting from the crank sensor? Voltage while cranking, resistance across terminals, anything to base my findings off of?

 

[Jon94]

Some other thoughts: I believe the computer only takes signal from the crank sensor to determine that the engine is running, and to send the spark signals to the coil. It doesn't rely on data from any other sensor. (Someone correct me if I'm wrong). So I'm thinking the problem has to be either the crank sensor, the wiring between the crank sensor and the computer, or the computer itself. There are no other possibilities.

I ordered a Motorcraft crank sensor from Rockauto just now. Even if that's not the problem, I'll have peace of mind knowing I have a quality sensor over the cheap Autozone sensor that's currently on it. If that doesn't fix it, I think I'll be able to safely rule out the sensor and narrow it down to the wiring or the computer. At that point, I'll try to figure out which wires go to the crank sensor at the computer and check for continuity at the sensor connector. If that checks out fine, then it must be the computer. At that point, it'll probably be towed to the dealer for a new computer, unless there's a way for me to program PATS into the new computer myself.

 

[imp]

@Jon94 Can we rule out the camshaft position sensor? According to Ford Wiring Diagrams, it "provides information to PCM for fuel injector synchronization". What about spark? Anybody know?

Beware the wiring from crankshaft position sensor is shielded, twisted pair, w/g. This suggests the possibility the signal is not a simple on-off DC voltage, which might explain your questionable reading of a couple of millivolts.

Also in the ignition picture is the knock sensor. Might it if malfunctioning stop PCM from triggering the coil? I dunno. imp

 

[koda2000]

The crank position sensor sends the signal to the PCM to trigger the coils.

The cam position sensor has nothing to do with spark. I'm taking the OP's word for it that he's verified his issue is in fact no spark, therefore his problem must be the crank sensor, it's wiring or the PCM. I think the crank sensor and PCM are unlikely his problem.

 

[Jon94]

Update: I replaced the crank sensor again with a Motorcraft one, and still no spark. I checked for continuity at either end of the wires going from the sensor to the computer and I have good continuity. Everything is pointing to a bad computer at this point.

If I buy a new computer at a parts store, is there any way I can program the PATS into it myself? Or is my only option to tow the truck to the dealer? Could a locksmith come to my house to program it?

 

[Jon94]

Just thought I'd close this one out: problem was a bad ECM. I replaced the ECM with a junkyard one and I now have spark. Truck still doesn't run because the PATS still needs to be reprogrammed, but the real problem is fixed.