5.0 cranks but no start after a day of sitting.

[Acgallen]

In a series of bad luck or whatever, my driveshaft disassembled itself from the transmission. Long story short, pulled the truck back to the house, started it and then let it sit. That was about 12 pm yesterday. About 12pm today i finished up getting the driveshaft back on with some new parts and went to start the truck. Fuel pump is humming, cranks over great, but wont start. I had to do some welding on the transmission yoke but i had the ground strap an inch away from it. I have also welded before on the truck with the battery installed with no problems. Yes i know i should just take the few minutes to take it off, but i didnt, and would like to know if that had a good possibility of frying the computer. I have 12 v at the coil when cranking, tried another EEC relay with no avail. I really cant catch a break with these things


Edit: After doing some research, I will add that my distributor and TFI are brand new, as are the plugs/wires and ignition coil. Stock A3M computer.

 

[RonD]

Spray some fuel into the engine and see if its a no spark or no fuel issue(50/50 test)

What year Computer are you running?

 

[Acgallen]

Spray some fuel into the engine and see if its a no spark or no fuel issue(50/50 test)

What year Computer are you running?

I have an A3M computer. I left for the day but i will try tomorrow. If it doesn't start with fuel, what's the next step? It doesn't have EDIS, so i believe it would be the computer that controls spark and fuel. Really confused on this one, its been running like a dream the past 500 miles.

 

[RonD]

A3M will be a EEC-IV computer so just does fuel, it has spark Load Advance but no wiring for distributor or coil packs

EEC-V had fuel and full spark control

If you have coil packs then you have an EDIS module, it runs spark on its own for start up

 

[Acgallen]

A3M will be a EEC-IV computer so just does fuel, it has spark Load Advance but no wiring for distributor or coil packs

EEC-V had fuel and full spark control

If you have coil packs then you have an EDIS module, it runs spark on its own for start up

Gotcha, I do not have a coil pack. I have singular coil that is getting 12v when cranking. I understand the majority of the ignition system, but not enough for me to understand how something overnight could go bad. Im 100% positive my fuel pump is pumping enough pressure and fuel to the engine. Its whether that I'm not getting spark or fuel / or both. Computers are super expensive so i would like to try everything possible to not have to replace that.

 

[RonD]

So you have a distributor/TFI system, that would be more normal with 5.0l A3M based engine/computer system

Well that's kind of the way things break, was working, then its not, 1 min or 1 day

Moving parts tend to make noises prior to breaking, lol
Electrics/electronics usually not big on making noise but can release the magic smoke

I doubt the welding caused any damage to the electrics, possible but not at all common

You can crank the engine over a few times, then pull any easy to reach spark plug and see if its tip is WET with fuel, should be
If so light with match/lighter, should burn fast and bright, its gasoline
If so then its a spark issue
If tip is DRY a fuel issue

 

[Acgallen]

So you have a distributor/TFI system, that would be more normal with 5.0l A3M based engine/computer system

Well that's kind of the way things break, was working, then its not, 1 min or 1 day

Moving parts tend to make noises prior to breaking, lol
Electrics/electronics usually not big on making noise but can release the magic smoke

I doubt the welding caused any damage to the electrics, possible but not at all common

You can crank the engine over a few times, then pull any easy to reach spark plug and see if its tip is WET with fuel, should be
If so light with match/lighter, should burn fast and bright, its gasoline
If so then its a spark issue
If tip is DRY a fuel issue

No spark. Tested with starting fluid first, nothing. Pulled a plug, no spark. Coil wire going to distributor gives 12v. Pip sensor is getting 12v from power wire. So my problem lies in the distributor? Or pip sensor?

 

[Acgallen]

So you have a distributor/TFI system, that would be more normal with 5.0l A3M based engine/computer system

Well that's kind of the way things break, was working, then its not, 1 min or 1 day

Moving parts tend to make noises prior to breaking, lol
Electrics/electronics usually not big on making noise but can release the magic smoke

I doubt the welding caused any damage to the electrics, possible but not at all common

You can crank the engine over a few times, then pull any easy to reach spark plug and see if its tip is WET with fuel, should be
If so light with match/lighter, should burn fast and bright, its gasoline
If so then its a spark issue
If tip is DRY a fuel issue

Swapped another PIP sensor in with no success. Pretty stumped on this one. Could it be the coil even though i was seeing 12 v go through the coil wire?

 

[RonD]

Yes, there is no accurate test for a Good Coil

But fuel injectors would still pulse open when cranking engine over, so spark plug tip would be WET with fuel

The PIP pulse goes to computer for injectors, and also ungrounds the coil's "-" wire to generate a spark
You can put a test light on the coil's "+" and "-" wires, these can be hooked to the coil or unhooked from coil for testing
Light should be on with key on, coil's "-" is grounded
When cranking the test light should flash rapidly as the TFI module ungounds the coil's "-" wire in sync with PIP from distributor's sensor


Works the same as the bad ol' days with Points in a distributor
A coil "builds up" a spark when it has both 12v and ground
A coil "releases" a spark when it loses either 12v or ground
Cutting the ground was what was chosen 100+ years ago
Points were the ground for coil's "-" terminal
As the distributor rotated a cam on the distributor shaft would push open the points, cutting the ground to coil, releasing a spark, then reconnecting the ground building up coil voltage for the next spark/cam lobe
Big pain the the butt because they needed to be filed/replaced and/or reset a few times a year if not more

Electronic "points" were a great improvement, present issue not with standing
But it works exactly the same way, distributor spinning sends the pulse to ground and unground the coil's "-" terminal, the PIP

 

[Acgallen]

Yes, there is no accurate test for a Good Coil

But fuel injectors would still pulse open when cranking engine over, so spark plug tip would be WET with fuel

The PIP pulse goes to computer for injectors, and also ungrounds the coil's "-" wire to generate a spark
You can put a test light on the coil's "+" and "-" wires, these can be hooked to the coil or unhooked from coil for testing
Light should be on with key on, coil's "-" is grounded
When cranking the test light should flash rapidly as the TFI module ungounds the coil's "-" wire in sync with PIP from distributor's sensor


Works the same as the bad ol' days with Points in a distributor
A coil "builds up" a spark when it has both 12v and ground
A coil "releases" a spark when it loses either 12v or ground
Cutting the ground was what was chosen 100+ years ago
Points were the ground for coil's "-" terminal
As the distributor rotated a cam on the distributor shaft would push open the points, cutting the ground to coil, releasing a spark, then reconnecting the ground building up coil voltage for the next spark/cam lobe
Big pain the the butt because they needed to be filed/replaced and/or reset a few times a year if not more

Electronic "points" were a great improvement, present issue not with standing
But it works exactly the same way, distributor spinning sends the pulse to ground and unground the coil's "-" terminal, the PIP

Thanks for the info. Tried a new coil, still nothing. Checked all my grounds again, seemed like nothing was off. I also swapped distributor caps, that didnt help either. It cranks well, and the spark plugs are wet, so im pretty lost.

 

[RonD]

Use a test light on the 2 coil wires, + and -, if TFI module is working it will flash the test light when cranking the engine over

 

[Acgallen]

Use a test light on the 2 coil wires, + and -, if TFI module is working it will flash the test light when cranking the engine over

Coil is most definitely getting power. Mentally im getting close to getting rid of this thing, only been headaches. Ive changed each spark component and nothing has worked.