\'88 GW Not Wanting To Run...
I have an '88 GW, 360, auto, common as nails.
Everything was still in place under the hood, right down to the emissions hardware.
Since it came from an emissions testing state, this didn't surprise me, but did give me more possibilities that I needed to shine attention on.
I purchased this vehicle to get me back and forth to the gun range and occasionally tow a trailer with a CJ on the back.
It needed to be reliable above all else...
Last thing I wanted to do was get stranded while hunting, cold and wet!
I had problems with both drivability and starting,
The truck ran fine when cold.
When the truck warmed up, it liked to shut off at idle.
This would happen most often at stop lights, but sometimes when going down the road when you let off the throttle.
No sputter, no stutter, just shut off during low RPM operation.
Never did it during higher RPM operation, but did misfire.
Often when cranking the engine (intermittent problem), the ignition wouldn't 'Catch' until the key was released and returned to the 'Run' position.
No 'fire' when the ignition switch was in the 'Cranking' position, but would normally start when the key switch was released to the 'Run' position.
Thumbnail diagnosis and simple testing...
Since the engine didn't 'Sputter' or otherwise give an indication something was wrong, like low fuel or air restriction was the problem, I started with Ignition.
The 'Shut Off' was abrupt, like turning the key off. No warning that it was going to shut down, it just 'Did IT!'.
I started with testing the distributor Magnetic trigger.
Since the problem only occurred at low speed, a defective mag trigger was a very real possibility.
Testing consisted of a resistance test between both terminals and ground. Both open like the should be.
Then a resistance test between terminals...
The results should be between 400 & 800 Ohms.
The average is around 600 Ohms, and at 720 Ohms this one was a little high.
So I used a heat gun and heated the trigger to about 150°F.
Under hood temps can easily reach 300°F, so this is a valid test.
The resistance at 150°F shot up to over 1,200 Ohms!
I think I've found a problem!
Removed the Trigger and replaced it with a quality replacement unit...
The problem persisted, but one faulty part had been identified and eliminated.
Module had been replace in regard to a different problem, so I was making an educated guess that two different modules weren't causing the same problem...
So I did a resistance test on the ignition coil...
Ignition coils are VERY reliable, but so are ignition triggers.
Modules on the other hand...
The primary resistance of the ignition coil was acceptable.
The secondary resistance test was a little high, but acceptable.
A voltage test with the key on revealed the resistor wire was in place and working within specifications...
So I did a substitution test, substituting a 'Test' or 'Known Good' coil for the suspect one.
Problem went away! The part I suspected least was the culprit!
I still had the occasional low speed misfire, but they were greatly reduced and the stalling problem disappeared altogether.
So as a further test, I substituted a Ford style E-core coil in place of the stock 'Volcano' or 'Canister' coil...
The miss went away!
Absolutely reliable and constant ignition through out the RPM band.
After a through cleaning of the connectors (a must with this ignition system) the 'Cranking' problem was diagnosed by attaching a test light to the module 'White Wire' circuit.
Jumpers were made from wire and spade terminals so I didn't have to destroy the insulation on the wires.
This would let me know if the module was malfunctioning, or the harness was the problem.
The 'White Wire' is the 'Cranking' circuit to the module, and if it is not getting power, the module will not function.
DuraSpark modules have a 'Starting Circuit' that retards timing about 8° when cranking for easier starts.
The module was getting power during cranking.
This only left the module as the curate.
Changed the module and the engine often started within one full revolution when cranking.
(This is after a new magnetic trigger, terminal cleaning, and E-core coil)