94 4.0 wont start very intermittent spark
 

Hi everyone,

I'm kind of at a loss, I have a 1994 Ranger 4.0 4x2 that has been in the family since new.

It had some issues, and sat in the garage for a while. The battery died, and I used the "start" feature on my cheapie Harbor Freight battery charger to jump it. Well the truck never started after that, so I decided to let the battery charge for a few hours and try again. It still wouldn't start, so I grabbed one of the plug wires, yanked it off, put a clean plug in it and checked for spark. there was no spark.... Checked the other wires, same thing.


Unfortunately, using the start feature fried the powertrain control module. I threw parts at it hoping to resolve the issue.

Ignition control module
Powertrain control module
Coil pack
checked all fuses and relays.

all seems to be ok.

Now there is very intermittent spark. There's no specific sequence in the irraddic spark that I am receiving when trying to start the truck. Do any of you fine people have any ideas?

First thing would be to check for battery voltage at the coil with key ON.
There are 4 wires on the coils plug in(12v and 3 EDIS ground wires), Red wire, usually, should have full battery voltage with key ON.
This voltage comes from the EEC relay in the Power Box(engine compartment fuse box)
Fuel injectors should also have full battery voltage with key ON, this also comes from EEC relay, so check at least one of those as well.

What starts the ball rolling for spark, on distributorless systems, is the CKP(crank position) sensor, on 4.0l it is located on passenger side lower front of engine behind main pulley.
On the crank, behind pulley, is what looks like a gear with teeth, one tooth is wider than the rest, that's matched with TDC for #1.
EDIS-6 module(Ignition control module) is located on the Rad support, this is what the CKP sensor connects to, it is also powered by EEC relay.
When you crank the engine over the CKP sensor sends pulses to EDIS-6 module, which in turn sends pulses to Computer(Power control module, PCM)
The EDIS-6 starts the spark when it sees the CKP sensor pulses, it doesn't need the PCM for this.
PCM starts fuel injectors when it sees the pulses from EDIS-6 module.

If you have any spark at all I would think CKP sensor is OK, bad CKP sensor = no spark at all, never heard of weak or intermittent spark associated with CKP sensor

I would also check voltage at coil while cranking engine, should be no lower than 9.5volts.
New battery voltage is 12.8v
75% life is 12.5v, about 3 years old
50% life is 12.2v, about 5/6 years old, time to shop for battery sale, next cold morning will get you "click, click, click", lol.