Spark Issue

[IHScoutman14]

I am having a problem with my spark. The problem is there is none . I am using the 7747 ecm with the ford duraspark conversion. What i am getting is just a single spark when i turn the key (confirmed by having the timing light hooked up to the plug wire from the coil) then nothing. What the fuel pump shuts off it will happen again ( i assume some sort of automatic restart or something). The weird part is that early last week i got it running and havent touched it since. I know i was having spark issues last week but it would still sputter and pop and eventually start running. Now i am not even getting a sputter (again cause the no spark thing). I have done the "key on" checks and the following are the wires that didnt check out.
A4- egr control 0volts
A7- shift light 0volts (shouldnt cause any problems i dont think)
C10- coolant temp 4.7 volts (its cold out 40-45 F. and this wouldnt cause the problem anyway)
B7- ESC signal 5.3 volts (should be 9)
D7- O^2 sensor signal (.4 volts again shouldnt cause the problem)
Both d14 and d16 are reading wrong too but thats probably because the throttle body isnt hooked up. The old carburetor is on to make the diagnostic process easier. (this does work by the way, i had it running sweet until i had to take the engine apart. My rockers ended up being severly destroyed).

I have started tracing all wires to and from the EST and the ESC. I have the ESC bypassed so B7 is tied to C14- the 5 volt ref. D off of the ESC is grounded as well. The ESC module that plugs into the wires is not plugged in however im sure it doesnt need to be because i havent ever had it plugged in.

In order to do the "key ON" checks, is it legit to have the engine turning over with the starter motor to get a correct reading? I am sure that getting those readings are going to be very important for diagnosing this.

It seems so weird that one day it works and the next it doesnt. Before i took the engine apart i had great spark, we hooked it up to a huge machine that gave spark readings etc. and it was strong. This makes me think i might have damaged something while i was working on my eng., however i cant find any damage anywhere. confusing!
any help is appreciated, i really just need to get this done!
thanks!
charlie

[IHScoutman14]

here is a little more insight which should help. With the engine turning over (not running but starter turning) i tested all EST wires
B3- EST reflow has .1 volts (should have 0)
B5- EST reference hi has 2 volts (should have 1.5)
D4- EST control has .15 volts (should have 1)- a problem!
D5- EST bypass has .1 volts (should have 4.75) a MAJOR problem!

So with that information, where should i go to next? All of my system gounds and whatnot are good, i checked them with the engining turning over as well.
thanks
charlie

[Bill usn-1]

I wouldn't put a lot of emphasis in the cranking voltage readings.
The ECM does not take control until 400 rpm. Till then it's the EST.

Since you have the ESC bypass hooked up the 5V on B7 is normal since it's tied to C14.

I would start with the basics on this one.
Go to this thread . I have the duraspark and the HEI troubleshooting links there. That way you will have the ref for the pick up ohms and both coils depending on which you are running.

Do all the basic resistance readings first to make sure you didn't lose a pick up or coil.

[IHScoutman14]

The duraspark pickup is in good condition and so is my coil. I couldnt warm the engine to operating temperature like the instructions say but the ohm tests still came out positive.
I have started doing ohm tests on all wires connected with the ignition system and so far i have found none that are damaged.
Here is a thought though. When i tore into my engine two weeks ago the front half was undercover and the back half was outside. As you may or may not know it rained like crazy here in washington for several days straight. My est is mounted on the heater core box near the firewall and though i tried to prevent it, it did get some rain splatter off of the the top of the scout. A day or two into the rain i started the motor and pulled it into the carport further. At that time it had a very hard time starting and would sputter and cough but eventually fire up. So then i let it sit for a week without touching it and it doesnt start at all. Do you think that the EST could have been damaged from rain water and then slowly corroded or something? just a wild idea....

What does the one spark right when the crank turns sugest? To me it says that at least the coil is ok. from there i dont really know

thanks again for the help
charlie

[Bill usn-1]

Coils can act in different ways when going bad.
I have had them still produce a blue spark when holding the coil wire near the block but when you hook it up to the distr cap it wouldn't even make it to the end of the plug wire to fire the spark plug.

Or it will fire great when cold but as it warms up the spark just fades away and the engine starts missing.
A good sytem will shoot a spark from the plug wire to ground about a 1/2" long.

One thing I noticed in your earlier post, you asked about Key On checks...that's just what they are. Turn the key on and take the readings.
The Engine running checks require the engine to be operating.


If you do not have the weather pack connectors on the EST it is possible for water and moisture to seep in and damage it.
Also you mention it is mounted on the heater box.
Grounding is critical on these EST's.
If it is mounted then it must be flat.
Meaning the small alignment tabs need to be removed and the lip at the connector end needs to be removed or it has to be mounted at the edge of the heater box so the lip over hangs.
The paint should also be removed frome under it and a thermal paste used under it to conduct heat away.

The heater box is on the body and not the eng so you must make sure the body and the box are properly grounded.

If you have an autozone nearby they may be able to test it for you.

If not I would recommend picking up a spare from the junkyard.
I prefer the factory GM ones.

[IHScoutman14]

My est is mounted flush onto the heater box with the mounting tabs hanging over so that part is taken care of. It is also grounded with a wire from the est to the engine ground so the grounding portion should also be good. I cleaned up the connections on the est a bit and it appears i do have the weather pack connectors on side where the two connectors are but where the dist. plugs into it it doesnt have the weather pack.
I will try to plug in known good coil and maybe pick up a useable est (i have a '90 suburban with the 7747 )
thanks

[Bill usn-1]

well i figured out my spark issue (the est was done) but now that i have installed the throttle body i am having some more problems.

Good to hear. Hopefully you took care of the heat transfer problem so it won't happen again.

[IHScoutman14]

yup it came with some heat paste stuff so i used it, checked my ground and it should be good. Came with a 5 year warranty too