I am a newbie in Durham NC.
I have been reading every thread I could find pertaining to my issue and have had no luck, so I'm posting.

78 F100 351 5.8 Duraspark.

I have ruled out no gas- plenty of fuel at the carb, filter new, fills up a water bottle quickly when hose disconnected and ignition key on.

I have had two mechanically inclined friends helping me. It seems like we have checked everything that relates to spark.

Ignition coil- good
Spark at plugs- yes
Cap and rotor- new
Duraspark unit- new
Plug wires- less than a year old, tested with ohmmeter and seem fine
Plugs- a little dark and oily, but not gummed up or so bad that they would cause a no start situation.

Electrical- Battery, alt, voltage regulator less than a year old.

I have read some about the pickup coil being a possible culprit- anybody have an opinion on this?

It has been driving seemingly fine until recently- some backfiring and hesitation when first driving in the mornings.

Somewhat suddenly, it took multiple attempts to start after I drove it 30 minutes and then it sat 30 minutes.

The next day more of the same after a 30 minute drive and then a short rest, except that it would just stall out after starting. Start up, stall out, repeat multiple times over a few blocks.

This second day I was on my way to get my kid at school and a little desperate to get there, so I started it and floored the gas pedal which allowed me to crawl (this made me think it was a fuel flow issue). Crawling along it would accelerate up to normal speed in 100-150 yards and stay there until I braked, then crawl with pedal to the floor and up to normal speed after 100-200 yards. On uphills, 5-10 mph max with the pedal to the floor.

I got to school and repeated this driving experience to drop my son at his after school activity, then pointed it home to try to get it to the driveway and look at it.
I didn't make it, stalled out on the side of the road.
At this point I was thinking fuel, so I disconnected the hose at the carb and had plenty of fuel there.

Got it towed to my house and it's been there a week, had a couple of friends come look at it with me. One, we took the carb apart and checked the float, and the choke, the other we tested ignition components and timing, which is at TDC.

Today I went through and tightened the intake manifold bolts a little, just to be sure there wasn't a vacuum leak there. (I replaced the head gaskets last winter.)

When I turn the key it cranks and cranks like a champ, sounds like it wants to start, but won't.

Seem like spark. Open to suggestions.

Thanks,

Mark

 

Have you visually checked the spark? With the coil wire about a ¼" away from an engine ground, while cranking, the spark should be a strong, blue-white spark that is consistent, not weak, orangish or intermittent.
But from your description of the symptoms, what I actually suspect without being there is the timing chain.
Run a compression test and let us know what the results are.

BTW, welcome to FTE. Lots of good, knowledgeable people here.

__________________

 

I would check the drive gear on the Distributor. this happened to me one time and the pin that holds the gear to the shaft was broken.

 

Also, if you want to test the pickup coil in the distributor:
There are three wires, black, purple and orange. The black is ground. Get a multimeter or an ohm meter.
Resistance between the purple and orange wire should be 400-1000 ohms, between either purple or orange and ground should be over 70,000 ohms.

 

Thanks for all the responses. I forgot to mention that we checked the timing. We lined up the mark and you can see the top of the piston in the #1 spark plug hole.

We also visually checked the spark as suggested. I didn't put my eyes on it, my friend Arlen was under the hood and he said it was fine. He was a certified Jaguar mechanic at one point, so I trust his eyes.

Thanks for the suggestion on the pickup coil, I will try the test. (Lord knows I've tried seemingly everything else.)

I have never pulled a distributor before, so I'm a bit timid about that, but I will do it if is potentially the issue as Savoy suggested.

Thanks again, it's nice to get some support and feel a little less like pulling my hair out.

 

If the pin has sheared in the distributor driven gear, you don't necessarily have to pull the distributor to check. Take the cap off and try twisting the rotor. It will normally turn a little bit because of the centrifugal advance but it shouldn't turn much more than ~20°-25°.
And visually checking for top dead center won't diagnose a bad timing chain, you need to run a compression test to verify that the cylinder compression is uniformly low.

 

I will do the compression test Sunday and report back. I'll check the rotor too as suggested.

Cheers,

Mark

 

hammer how many miles on this engine? if every thing else checks out I would check that the timing chain has jumped a tooth and it will do that with lots of miles and when you shut them off [possible cause for back firing] heres how to check for play;
remove the dist cap put a 15/16 socket/breaker bar on to the crank bolt turn the engine 1 way [by hand] then go back the other way watching the rotor if the crank is turning before the rotor moves that is the slop in the chain [with a new chain/gears the crank/rotor should be turning exatly the same time either way] I have had two chains jump on me with trucks I just bough and they always jumped when I shut them off also any spark problems I have had I just replace the dist with a 1 wire hei unit simple install and they work

 

The first two things I thought of were timing chain and distributor gear. Mike and Savoy beat me to it. The compression test is good, but a fast way to get an idea of how much slop is in the chain is pull the distributor cap off and look at the rotor. Turn the engine by hand in one direction until the rotor starts to turn, then turn the engine by hand in the opposite direction and see how far you can turn the engine before the rotor starts to move again. Any more than 15 degrees of rotation and the chain has too much slack. (or the pin is sheared on the bottom of the distributor)

 

I had the same issue on another ford vehicle. Replace the distributor it will cure the issue and the motor will run a lot smoother also

 

Thank you for the tips.

Tomorrow is Sunday. I will check for timing "slop" as recommended and maybe replace the distributor. I plan to do the compression test too.

I'll report back. Fingers crossed. I need this truck for my work and it's been down over a week now.

 

Here's something else to think about.
If it turns out to be the chain and you replace the chain and timing gears, also plan on pulling the oil pan.
Those pieces of nylon cam gear have to go somewhere. Usually what happens is they get sucked up in the oil pump pickup screen and clog it, making your engine lose oil pressure.

 

Well,

I'm not totally clear where to calculate the degree of "slop", but when I pul on the alternator belt to crank the motor and move the rotor, there is some slack when I shift directions.

watching a gear on the flywheel on the front of the alternator, it moves from about noon to 10 o'clock before the rotor starts to move.

"More than 15 degrees" was mentioned here. How to guage that?

thanks,

Mark

 

Twisting the rotor itself, it moves about 15 degrees.

 

That sound like just the centrifugal advance, using the alternator pulley as a gauge won't give very accurate results because the alternator pulley is much smaller diameter than the crank pulley so it will rotate further than the crank on any revolution.
Guestimating the diameters of the pullies, that doesn't sound too bad either.
You still need to run a compression test to check the timing chain.
Did you ever check the distributor pickup coil?
This isn't a very scientific or technically correct test, it's more a "seat of the pants" test but, how does the engine turn over when you're starting it? Does it sound like normal, or does it seem to spin real easy, almost like the plugs are out of it?
If it sounds like it normally does then that would move the timing chain to the back of the line and I would tend to suspect the ignition. If it it spins real easy, that moves the timing chain to the front.