No start on 81 4.9 inline six

[Dfather99]

I'm have a problem getting my truck to start it will crank but not start. I have spark I have fuel. Carb was rebuilt because I believed that was the problem but no change.

The engine turns over and rotor in the distributor turns as it should. It sometimes sounds like it is going to start and will just spin faster.

The only thing electrical I have noticed is that it will crank in any gear.

New plugs and wires caps etc.

It ran rough before it died.

Not sure if there is a ground strap that could cause this.

Thanks

[mat in tn]

does it try to start if you prime it with small bit of gas? that would be indicative of not enough fuel or fuel pressure. another possibility could be the quality of gas. meaning is it new or are you reviving it from a long rest.

[Dfather99]

I've tried it with starting fluid and sounds like it wants to start but does not fire. The gas in it is less than a year old. I figure it would start on starting fluid.

[ratdude747]

On my 1984, if memory serves, there is a ground strap between the firewall and the back of the block.

Suggestions:

Look for vacuum leaks. I've had issues with my 1984 300 having large vacuum caps rot away creating a massive leak that would result in hard starting and no idle at all. These were all on the vacuum tree on the back of the intake.

Get a timing light, cap off the vacuum to the distributor, and check base timing (you'll need a buddy or a remote start switch, obviously). Had a kinda similar situation the last few weeks with a 302-powered boat I'm fixing up- in my case, the timing got off due to an ignition upgrade (and lazy me forgot to recheck it). Ran very rough last fall (when I began work on it- had been off the water for 10 years due to ignition issues) but wouldn't run at all this spring. Changed out the fuel, rebuilt the carb (which did have issues!), and replaced the rest of the ignition to no avail... only to find my timing was way, way off. Acted like a carb issue, but nope.

Verify that ignition has power in crank. Ignition switch issues on these are not uncommon, and there are separate circuits for "hot in run" and "hot in crank and run".

Cranking in any gear means the neutral safety switch is bad or has been bypassed. Part of the starter relay control circuit.

[Gary Lewis]

Actually, an 81 didn't have a neutral safety switch.

[1986F150Six]

Dfather99 wrote

I'm have a problem getting my truck to start it will crank but not start. I have spark I have fuel. Carb was rebuilt because I believed that was the problem but no change.

Do you have spark at the right time? Try advancing or retarding the timing. Maybe have someone turn the key [in neutral] with brakes on and you rotate the distributer until it fires. Remember, on the 300/4.9L engine, rotating the distributor CCW advances while CW retards timing.

[Dfather99]

I did try the above.

I think what I am going to do is turn it over with the Cap off and see if the rotor is skipping. Perhaps some teeth on the cam gear are off or shollow. Again it's sounds like it is trying to start but was turn on it's own. So white smoke comes out of the carb every now and then after cranking

[mat in tn]

white smoke out of the carb sounds like timing of the valves. verify the rotor button rotation for sure. if the white smoke seems to be in sync with any irregular pulse or attempt to fire then that may well be a strong clue.

[Rockhauler]

I've had a couple ignition modules work just fine then one day shut truck off and wouldn't restart replaced the module and truck fired right up. But I've also had the module still work but cause hard starting and running rough. I now always carry a spare module in the truck after getting stranded and nowhere nearby to purchase a new one.

Also double check you have the plug wires in the correct order on the cap.

Paul