96 Explorer 4.0 No Spark

[2ranger87]

I did a search through past posts, and couldn't find anything that was helpful in my case, so here goes...
I have a 96 Explorer that has had an intermittent no start for years. Lately it has been getting worse, and up till now, it always started after several attempts. Now it will not start at all.

What I have done so far: Changed the crank sensor from another running motor, no change. Swapped coil pack, still no change. Both parts removed from problem truck re-installed into donor truck and it starts.

Swapped another PCM in and no start. ( ICM is integral with this truck)

What I found: MIL turns on with key on, goes out while cranking but comes back on after a couple seconds of cranking. Disconnected the crank sensor, lite on at key on, does not go out while cranking.

I have battery voltage at the coil pack, and have 1.5 volts at both crank sensor wires. (blue and gray)

Can hear fuel pump cycle, and definate fuel smell. pulled a plug and it was wet. (not surprising with all the cranking...)

I always suspected a possible ground problem, but see nothing amiss. Although I noticed a bare wire mixed in with the crank sensor harness that goes nowhere.

Any one else go through this? Any help is appreciated!

 

[RonD]

I know spark plugs were WET but................................

Just try 50/50 test
Spray some ether or gasoline into the intake and crank engine



Also pull out Starter relay from engine fuse box, so no crank
Put test light or volt meter on Coil Packs Red wire
Turn key on and you will see the 12v
Now turn key to START and you should still see the 12volts, if not you found the problem

Some ignition switches still had a Dual power path for RUN and START

 

[2ranger87]

Ya I tried the ether thing...no go. I did verify no spark by testing at the plug.

I couldn't locate the starter relay ( i'll have to do some research, it's not in the main distribution box). I did disconnect the trigger wire from the solenoid, and coil has power in both on, and crank position.

 

[RonD]

OK

The Waste spark system has 2 spark plugs wired in series so testing a spark plug wire for spark doesn't always work, unless you reconnect the wire to spark plug, i.e. and inline spark tester

I guess I would use test light on coil packs red wire, or battery positive, to any 1 of the 3 ground wires on the coil pack
Should light up with key on, then pulse dimmer when cranking, it will dim because of starter motor power draw, the flicker is what you need to see
Each ground wire is disconnected in the PCM once per RPM so just a flicker at 200 rpm
I don't think you would see it on a digital volt meter, maybe on an analog meter

Its possible all 3 of these coil "-" wires are grounded in the harness, long shot but not a no shot
You could try OHM meter test from one of these wires to engine ground key off, should be high ohms, then key on low ohms


There might be codes by now if you have cranked the engine over enough
1996 should have cam and crank sensor so would set a code if either wasn't working
And codes for coil pack not doing a voltage spike, when PCM disconnects ground(misfires)

 

[2ranger87]

Thanks for the info RonD.

I'll try an inline tester for the plugs, and test the ground wires on the coil pack.

I did recheck for codes, but none so far.

What is the purpose of the "floating ground" in the crank sensor harness? With the key on, should there be voltage at both terminals?

 

[RonD]

Crank sensor has a shield wire, it just protects it against outside interference, doesn't need to be grounded, but might be at PCM end
Crank sensor is a VR type, variable reluctance, like ABS or VSS sensors
These sensors Generate voltage they don't need voltage.

Cranking speed, 200rpm, should show .5-1.0volts AC<<<< AC not DC so switch meter over to AC
The volts are just for testing, the PCM uses the frequency and drop point for RPM and timing
The crank sensor reads a "tone" wheel, it has 35 teeth, 1 tooth every 10deg, which would be 36 teeth(360deg), 1 tooth is missing, that causes a drop in the generated voltage, that drop is TDC for #1, the timing mark for PCM

ABS or VSS tone wheels don't have a missing tooth because they don't need a timing mark, just the frequency of the teeth passing by them

 

[2ranger87]

Good to know about the shield wire. Makes sense that it would be wrapped in a foil tape as well.

This is where it gets weird though.
That voltage of 1.5 volts was a DC measurement, did it again at AC and came up with 2.5 volts. Both ac and dc were measured on each terminal with one probe on a chassis ground. This is with key on only, no cranking. ( I don't have enough hands here to test cranking cycles today)
There is no voltage present when I probe both terminals together in the connector, with the key on.

I will do a cranking test tomorrow and see if the values change. Should there be any voltage with only key on?

Again, I really appreciate all your info!