Last resort, posting from my phone:

Replaced coil - ran for 24 hours, had one difficult start.

Next day it'll crank but not start, jump started - still nothing. Disconnected the alternator fuse dorked around, went to start it and it fired right up, ran fine that day on errands. Slept went out to start it up, nothing. DPFE code, went out and replaced it with a new part and hoses. Broke a spark plug wire so I replaced all those.

Coil, Wires, DPFE have all been replaced.

Still no spark when I put in a test plug.

I'm going to pull the negative cable off the battery to reset, and see what happens. (No change.)

I can't locate my crankshaft position sensor, otherwise I'd replace that too.

Appreciate anyone and everyone's input.

(1998 Mazda B4000)

 

Just left it for 20 minutes charging and disconnected from truck. Fired up after a 3 second crank.

I doubt it'll start tomorrow, I hope it's fixed. If it isn't, thoughts?

 

Do you have a test light or volt meter?
If so pull off coil connector.
The end wire will have 12volts with key on, so test both end wires.
Other 3 wires are intermittent grounds controlled by computer.

If no 12v then there is a 25amp fuse in the engine fuse panel that powers the coil and EEC(PCM) Relay.
Check it.

If you have 12v then listen for fuel pump when key is first turned on, it will come on for 2 seconds if EEC relay is working.
EEC relay supplies power for computer and many other systems via a 30amp fuse in engine box.
So no EEC relay would mean no spark as well.

Yes, CKP(crank position) sensor is what "tells" computer that you are trying to start engine, so no CKP pulse would mean no spark.
It is behind the main pulley and has two wires coming out.
It will at about the 10:00 position behind pulley.
CKP sensors rarely fail, not never but rarely, check wiring first.
I have never come across an intermittent CKP, it either works 100% or doesn't work at all, wiring on the other hand could show that symptom.


EDIT:
reading your last post I would check the battery wiring to Power distribution box, it is reading like the cranking engine power draw is dropping the voltage going to the power box so coil is not getting enough voltage during cranking.
Also make sure the Ground connection for the box and battery are all clean and tight, 12volts is only 12volts if ground is good and tight.

Battery voltage needs to be above 12.2 volts, engine off, engine on the voltage should be no lower than 13.5 volts after a idling for 5 minutes, right after startup battery voltage will be 14+volts for recharging then it should drop down to 13.5v

below 12.2v means battery is at least 5 years old and due for replacement, or alternator has lost some fields(charging ability)
New battery will be 12.8volts, 100% of amps are available
12.2v means only 50% of the amps are available

 

i would say that the engine to cabin ground strap has corroded badly enough

that liitle voltage is getting to where it needs to

 

I had it towed to a local shop.

They haven't had an issue with it in 72 hours.

Could there have been a short that got disconnected when removing accessory wires before reinstalling battery?

They think it may be crank shaft sensor. But as stated above it shouldn't work intermittently...

 

The next time you have a no start I would test if you have 12v at the coil when key is on, if no this would point to ignition switch problem(under the steering column)

CKP sensor wiring would be more likely than the sensor itself, but moot if you don't have 12v at the coil with key on.

The CKP sensor is connected directly to computer, so it needs to be on to start spark.
The EEC relay closes when key is turned on, this relay supplies power to the computer and also the fuel injectors, so test if you have 12v at the fuel injectors the next time there is a no start.

EEC relay is in the power box in engine compartment, could be labelled ECM, PCM, CMP, they seem to change label every 6 months or so, since 1986, lol.

 

Worked for a week.

Had no issues.

Went to start it up this A.M. to head out to work and it cranked/turned over, no spark/fire. Came back 8 1/2 hours later to the same. Pulled out my GP's volt meters and wasn't getting 12v on analog or digital meters. Ran to O'Reilly's and bought my own volt meter, ignition switch, and some more tools ('cause, you know, never enough.). Pulled the plug to the coil and retested, 11.5v 11.75v 11.4v depending on the ground I used. (Engine block, battery, wiring in the plug, respectively.) Hooked it back up and tried starting it; I had forgotten to put the red plastic piece back in so it didn't start. Put the red plastic piece back in the plug and plugged it up, turned key and instant fire.



I need it to stop working again so when I change the ignition switch I can know whether it was faulty or not, or is that asking too much?

Ideas are greatly appreciated. I move in 4 days. I need my truck 100% reliable.

 

What is the "red plastic piece"?

 

Standard Motor Products S-658 - Auto Parts Network

No idea what it's called. That's similar to the plug/terminal. The red plastic pieces lift out, I assume to allow for testing of the wires?

 

the red clip ensures electrical contact between the pins

 

Voltage was 11.75 - 11.95 today. Started right up.

Is it ever too much to ask to have a consistent and measurable failing?

How difficult would a rewire of the power supply to the coil be?

Should I just replace the ignition module/switch behind the driver side panel?

 

i would dis-connect the battery

then unbolt the fuse panel and look for any corroded connections to / from the fuses

you have a semi bad connection somewhere leading to the ignition coil

 

I would test your meter on another vehicle or even 9v battery

Battery voltage at the battery needs to be above 12v
Battery has 6 cells each cell has 2.1v so 12.6v, if a cell drops below 2v then it will drain the battery, since that is not happening I would check the meter.

 

I found something loose directly connected to the engine. Has two wires coming off of it. Next to the coil. White in color and it is easily rotated.

 

Cleaned connectors at fuse box. Voltage to coil is 12.2.

Until it fails again, I'm calling it fixed.