7.4 No start condition

[THase89]

Hello,

1996 3500 7.4 Vortec

Bought truck needing a fuel pump and starter. Replaced both, fired up and drove it for a few days until the drive shaft carrier bearing vibration went from very mild to wild.

Anyway, went to start it and move to the garage - wouldn’t turn over. Cause was a loose negative terminal on battery. Fixed.

Motor now turns over fine but will not fire. Here is what I’ve checked or fixed:

-Replaced fuel filter.
-Fuel Pump still primes and runs.
-Schrader valve shoots fuel out a solid 3 feet.
-Power to pink wires at fuel injection harness plug.
-Power to coil harness plug
-Pulled spark plug, getting spark when cranking.
-Tried half a can of ether directly into open throttle body, no attempt of the motor to fire at all.
-Tach moves when turning motor over.

Do the injectors need a certain amount of pressure before they’ll open? FPG ordered to get actual measurements on rail.

Can a “weak” spark create this condition leading back to a distributor or coil problem? How can I check that? Or is it possible?

Open to any advice on what to check. Ready to move it 30 feet into the garage...

 

[Matt Conner]

Hello,

1996 3500 7.4 Vortec

Bought truck needing a fuel pump and starter. Replaced both, fired up and drove it for a few days until the drive shaft carrier bearing vibration went from very mild to wild.

Anyway, went to start it and move to the garage - wouldn’t turn over. Cause was a loose negative terminal on battery. Fixed.

Motor now turns over fine but will not fire. Here is what I’ve checked or fixed:

-Replaced fuel filter.
-Fuel Pump still primes and runs.
-Schrader valve shoots fuel out a solid 3 feet.
-Power to pink wires at fuel injection harness plug.
-Power to coil harness plug
-Pulled spark plug, getting spark when cranking.
-Tried half a can of ether directly into open throttle body, no attempt of the motor to fire at all.
-Tach moves when turning motor over.

Do the injectors need a certain amount of pressure before they’ll open? FPG ordered to get actual measurements on rail.

Can a “weak” spark create this condition leading back to a distributor or coil problem? How can I check that? Or is it possible?

Open to any advice on what to check. Ready to move it 30 feet into the garage...

Check your compression, and pull your dipstick and see if you smell gas in the oil, low compression will cause a no start, I’m not sure how it isn’t firing on ether if it’s got spark.

 

[someotherguy]

Hate to advocate shotgunning parts but Vortec caps are known for failing internally and crossfiring. Try another cap. Be careful with the distributor body as the thing is just plastic and the tabs are probably already cracked where the cap screws go in. If they break you can reliably zip-tie the cap to the body.

If you've had a lot of rain recently or a sudden temperature change that can cause condensation then the cap might just be wet inside or there could even be moisture inside the distributor body under the cap. Been there, done that. Dry it out with paper towels and WD40.

Richard

 

[454cid]

Check the cap and rotor? EDIT: Looks like Someotherguy beat me to it, while I was reading another thread in another tab.

Does the engine sort of cough and kick back, or does it turn over smoothly?

 

[THase89]

It turns over nice and smooth. But absolutely zero indication of spark and gas coming together and kicking off.

Of course the distributor is in the most convenient place ever lol. I’ll pull the cap tomorrow and look at it.

 

[stutaeng]

I've been having the crank, but no start on my 99 Silverado 4.3 Vortec for about 2 years now. Mine only does it on wet/humid weather mornings.

Has 56psi of pressure and spark. I changed a few ICMs, cap and rotors, spark plugs and wires. A few weeks ago I replaced the coil and it has been find since.

Do you have an HEI spark tester? You can rotate the threads to see how far the spark jumps. Scanner Danner on YT has some videos on doing this with a test light.

Also, check the spark color. It should be blue/white? Not sure on this though, I think it could also be yellow.

 

[Erik the Awful]

The fact you tried ether and got no fire rules out the fuel system for me.

Make sure your distributor hold-down bolt is snug. If you replace your distributor cap and still get no fire, try disconnecting your down pipes. If your cat's clogged you won't move enough air for your engine to fire.

 

[THase89]

Distributor and rotor has so much corrosion I don’t know how it ran before. Replaced both, new ICM since I had the intake off and it fired right up!

thanks everyone!

 

[454cid]

Distributor and rotor has so much corrosion I don’t know how it ran before. Replaced both, new ICM since I had the intake off and it fired right up!

thanks everyone!

Save the old ICM as a backup.... they can poop out with zero notice.