Wont Start, What am I missing?

[ryanmcb]

I have a 91 with a 350. Truck started running real rough until it died. I thought it was fuel so I replaced the fuel pump. Still wouldn't start. I poorer fuel in the TB and it still won't start so I moved to ignition. I replaced the ignition module in the distributor and coil, still won't start. I tried changing the ECM that is mounted next to the TB with another good one that I have, still won't start.
what am I missing? I am not sure where to go from here.

thanks in advance

[ChevyTech]

See if it has good strong blue spark.

[ryanmcb]

No spark at all from what I can tell. That is what got me started replacing the ignition module and the coil.

[ChevyTech]

Take a test light and make sure power is getting to the ignition coil when the key is on.

If you have an ohm meter, test the resistance of the pick-up coil in the distributor, with it unplugged from the module.

Pickup coil testing
500 to 1500 ohms between terminals.
Infinite from one terminal to ground.

Inspect the magnet on the pickup coil to see if it is cranking into pieces. It should be one part.

On these distributors the housing/upper bushing area can get so worn out that the shaft will move sideways so far that the points on the pickup coil pole piece get hit by the reluctor points on the shaft. When this happens the ECM receives compromised signal for RPM and timing issues. See if the distributor shaft wiggles sideways.

Around 1989-1990 the distributor shafts didn't have the groove in the shaft to direct oil "back" down into the engine. Oil will get into the pickup coil and can damage the coil windings. Any of the distributors can do this if they get very worn.

If there is oil coming up the shaft and getting out onto the pickup coil – replace the distributor.

These distributors can also have problems because of loss of magnetism needed for the pickup coil to work. Check the magnetism by taking a small end wrench and touching it to the reluctor (the round part on the distributor shaft just below the rotor) and make sure you can feel the magnetism as you pull the wrench away.

If you remove the distributor to replace a pickup coil you should be able to feel the magnetism as you slowly turn the shaft and the reluctor points line up with the points on the pickup coil.

[ryanmcb]

THANK YOU. I was thinking about the pickup coil so this is very helpful

[400sbctruck]

Ignition/fuel relays and possibly the reluctor pickup coil. U can check pickup coil signal with tach meter or even a multimeter and watch for needle to bounce -digital meter is useless unless it has tach setting.

[ryanmcb]

well it was the pick up coil. I had an extra distributor so I just replaced the whole thing and the truck fired right up. Runs better as well since I had already replaced a bunch of other parts trying to narrow down this issue. Thanks for the help!

[ChevyTech]

You’re welcome, and thank you for letting us know what fixed it.