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The riddle that stopped the truck from starting


JakeinUtah

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1993 4.0 4wd Auto

So I am stuck.

Short story: I don't have spark during crank, but I do when it runs. It runs well with no misfires.


Long story. Last week my girl, Sandy, would not start except with fluid. I didn't have a fuel pressure gauge at the time, but I pressed the valve stem in at the rail and no fuel came out. So I assumed my pump was bad. I replaced the pump. That seemed to help a bit, but still no dice. So I ordered a fuel gauge, and my pressure was only 10 while cranking, 32 running. I replaced the filter, no change. I replaced the regulator, now I have 32 during crank and running. Still won't start. I replaced the coil.

This entire last week she would die when braking hard from higher speed, some one suggested I had water in the tank. So I drained the tank, blew out the lines, and refilled the tank with HEET in it for good measure. It no longer dies when braking.

Symptoms:
-Won't start except with fluid
-No spark during Crank, but there is spark when it runs.
-It used to die when braking hard, but no longer since I drained the tank, blew out the lines, and refilled it with new gas.

Things tried so far
-Replaced fuel pump
-replaced fuel filter
-replaced fuel regulator
-replaced coil pack
-drained out old gas, blew out lines, put new gas in with HEET
-cleaned MAF
-Cleaned Idle air control valve
-cleaned air filter
-checked for vacuum leaks with the starter fluid method, couldn't find any
 


BlackBII

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How's your battery, terminals and grounds? The starter could be taking up too much power and not allowing the injectors to fire.
 

RonD

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Welcome to TRS :)

"Short story: I don't have spark during crank, but I do when it runs. It runs well with no misfires."

"-Won't start except with fluid"

If it starts by adding fuel manually then you have spark while cranking, just no fuel from injectors.

The 1993 4.0l uses an EDIS-6 module for spark.
It gets AC Voltage from Crank Sensor located by the Crank pulley, AC voltage because it is a "pulse" that the EDIS module uses to time the spark.
Crank sensor generates this AC voltage by the crank pulley spinning near it, the faster it spins the higher the AC Voltage.
The pulley has what looks like a gear on it, each time a metal "tooth" on this gear passes by the Crank sensor it generates an AC "pulse", there is 1 "missing tooth", that gap tells EDIS module when Piston #1 is at TDC, so it can time spark
This "gear" is called a Tone Wheel, same setup is used with ABS brakes and a few other applications

EDIS module is connected to the coil pack directly
EDIS Module sends the Crank sensor "pulses" to the engine computer, which it uses to time the fuel injectors.
Engine computer sends back spark advance and retard info to the EDIS Module, because computer has driver input data, like throttle position and air:fuel mix data

If the Crank sensor or its connector is failing it may not be generating enough AC volts at cranking speed, so EDIS module doesn't start spark, but adding fuel manually wouldn't change that??
If tone wheel is full of mud/dirt crank sensor may not be able to read it well
If crank sensor has shifted farther away from tone wheel then it could be sending lower voltage at cranking speed but OK when above 400rpm.

EDIS-6 modules rarely failed, not never but rarely, but they ARE the spark system, computer is not needed for startup
EDIS module is located on the Rad Support, could be on the back side or front side
My 1994 has it on the front side, drivers side can see it by looking up under the bumper
 
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JakeinUtah

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How's your battery, terminals and grounds? The starter could be taking up too much power and not allowing the injectors to fire.
I don't think it's battery related, It behaves the same way whether it is being jumped (it died once while cranking), has a fresh battery (I charged it over night), or anywhere in between.

If it starts by adding fuel manually then you have spark while cranking, just no fuel from injectors.

The 1993 4.0l uses an EDIS-6 module for spark.
It gets AC Voltage from Crank Sensor located by the Crank pulley, AC voltage because it is a "pulse" that the EDIS module uses to time the spark.
Crank sensor generates this AC voltage by the crank pulley spinning near it, the faster it spins the higher the AC Voltage.
The pulley has what looks like a gear on it, each time a metal "tooth" on this gear passes by the Crank sensor it generates an AC "pulse", there is 1 "missing tooth", that gap tells EDIS module when Piston #1 is at TDC, so it can time spark
This "gear" is called a Tone Wheel, same setup is used with ABS brakes and a few other applications

EDIS module is connected to the coil pack directly
EDIS Module sends the Crank sensor "pulses" to the engine computer, which it uses to time the fuel injectors.
Engine computer sends back spark advance and retard info to the EDIS Module, because computer has driver input data, like throttle position and air:fuel mix data

If the Crank sensor or its connector is failing it may not be generating enough AC volts at cranking speed, so EDIS module doesn't start spark, but adding fuel manually wouldn't change that??
If tone wheel is full of mud/dirt crank sensor may not be able to read it well
If crank sensor has shifted farther away from tone wheel then it could be sending lower voltage at cranking speed but OK when above 400rpm.

EDIS-6 modules rarely failed, not never but rarely, but they ARE the spark system, computer is not needed for startup
EDIS module is located on the Rad Support, could be on the back side or front side
My 1994 has it on the front side, drivers side can see it by looking up under the bumper
I'll go look for a gear looking thingy near the crank and the EDIS module.
 

RonD

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JakeinUtah

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Ok so tone tone wheel is clean, the crank sensor was a little oily but still plugged in. No corrosion in the plug. I cleaned everything for good measure.

I can't find the EDIS, looking online to track it down now.

Thanks so much for your help.
 

JakeinUtah

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I can't find the EDIS, looking online to track it down now.
I found it, and it looks very clean. There is no corrosion in the plug.
 

RonD

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Thats all there is to the spark system
Crank sensor/tone wheel, EDIS module and Coil pack

EDIS module and coil pack get 12volts with key on

What BlackBII was referring to is the voltage drop that occurs anytime starter motor is activated
You will get a 2 volt drop, so 12v becomes 10volts thru out the system, while engine is cranking.
If battery is older or bad, or starter motor is older or bad, voltage can drop 4 volts, and 8volts will cause weak or no spark

IF(big if) a 12v wire has some corrosion then it would show 10v with key on at coil pack or EDIS
And then 8v cranking, so................weak spark

And we are still assuming it is a spark problem from your observations, I am more on the no fuel side because it starts when adding fuel manually
 
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JakeinUtah

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Thats all there is to the spark system
Crank sensor/tone wheel, EDIS module and Coil pack
I'll head to the Pic-n-Pull and see what I can grab. Could the ECU cause this issue?
 

RonD

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No, but if the ECU is not getting the "pulse" from the EDIS module it wouldn't start opening the fuel injectors.
You would get a Check engine light and a code if this pulse was intermittent

The ECU or EDIS is not connected to the "starting system".
When you turn the key to START there is no "signal" to EDIS or ECU that tells them to "start the spark and fuel"
The Crank sensor starts the ball rolling for that, its pulse sets timing, and EDIS and ECU then know to start spark and fuel.

In 1995 and up the EDIS module(its equivalent) was moved into the newer type of ECU, so spark and fuel were both controlled by ECU
Crank sensor was the same, and coil pack, but coil pack and crank sensor both connected to ECU
 

JakeinUtah

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Ron, I'm going to buy you a steak dinner.

Replacing the crank positioning sensor did the trick.
 

RonD

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Good work :icon_thumby:

Thanks for posting the fix, and compliment, but YOU did all the work :)
 

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