Any help diagnosing my POS truck?

6BangBronk

Well-Known Member
Joined
Jul 15, 2005
Location
Durham
"Duke" (1976 F100 - 302 / 3 speed) has laid down on me. Here's the deal. I had timing issue and it backfired through card on top end and exhaust on bottom end. Pulled distributor and it was shot. I replaced with brand new and it cranks right up and I drive it for 2 days to and from work. Now it's having problems starting? But when you get it started it purrs like a dang kitten?
What it's doing is when I turn the key it won't hit a lick until right when I let go. Then it just hits on one cylinder sometimes hitting one more. Usually just one. At first you'd think the switch but I replaced and even checked the new one and the voltage to the coil is doing what it's supposed to. I jiggled in every direction so that can't be it? I checked compression since it's a 90,xxx+ motor and I range between 130 to 147 psi on all 8. I set the timing to the cam spec being 6 degrees BTC. I've had to do this on several occasions and never had an issue before? Which brings to me a possible stretched timing chain but I put a double roller on it when I rebuilt it 7 years ago?
I've replaced plugs (I just double checked the gap at .035) replaced wires, swapped coil, replaced rotor and cap. I swapped the carb 3 times to make sure that wasn't the issue but I did that last weekend before I swapped dizzies too and it made no difference. On top of that, I pulled one wire at a time after I replaced the dizzy and observed that the plugs and wires were good. I've tripple checked the firing order so it has to be good cause it runs so good when I can get it started?
I took the gas line off and it shoots gas well! Actually suspiciously too well but I don't have a gage to be exact? I have a new clear inline filter and the jets shoot good when you open the throttle plates on all three carbs. My exhaust is tight with no leaks. There's no difference if I give it starting fluid. Actually it hurts it and it won't hit until I let the gas settle. The motor still turns over very easily although I've ran the battery down and starting from a charger.
That's it? I got it started before and after work yesterday by pressing the gas as soon as I let go of the key. It didn't work for me this morning and I've been at it all day. I cleaned the K&N air filter and have been trying to start it today without an air filter and with the oil venting open (disconnected). If anybody hears a loud boom in N. Durham I shot the damn thing! :flipoff2: A vehicle never lays down until you need it most... Anybody got anything to add would be much appreciated!
:popcorn:
 
I think your issue is electrical. It's been a while since I messed with older engines, but it would seem to me that the coil isn't getting strong voltage when cranking. I remember some cars had a ballast resistor to reduce voltage to the coil, that was bypassed by another wire from the starter when being cranked.

See what voltage you're getting at the + side of the coil when you're cranking. It should be within .5 of battery voltage when cranking. Could also be a weak battery? (You said it turns over OK, but try a newer battery from something else)

Still using points, or have you converted to an electronic system?

There is another possibility that you're pushing too much fuel through the carb - may want to check the pressure.
 
Could be too much fuel, and when you floor it your allowing the air to compensate for the large amounts. Also could be coil input voltage, or possibly coil output voltage. Hows your choke?
 
What it's doing is when I turn the key it won't hit a lick until right when I let go. Then it just hits on one cylinder sometimes hitting one more. Usually just one.

I think your issue is electrical.

Me too Rich... Most systems like this have 2 wires feeding the coil:

- #1 from the ignition fed thru a ballast resistor for 8-9VDC running as full 12+VDC will cook the ignition module/condenser

- #2 fed from the "S(tart)" terminal on the solenoid... to provide full 12VDC during cranking

Had the same issue on mine shortly after putting it all together. Would only fire near then end of cranking. The issue is the resisted circuit only throws 8-9VDC to the coil when running, but that drops considerably when cranking (5-6VDC = not enough to fire the plugs). This is where feeding 12VDC to the coil via the solenoids "S" terminal comes in... it's *ONLY* energized during cranking (circuit opens when in "run" position)
 
How many miles since you changed the timing chain? I always set the timing by ear rather than to specs especially on an engine with high mileage. Check to see how much play you have in the chain by turning the crank back and forth and watching the dizzy.
 
It's the first year of electronic ignition with the ignition module but no ballast resistor just yet. Was Ford's experimental year with a "resister wire" somewhere in the wiring harness? Needle in the haystack sort of thing I hear. Especially after you see the spaghetti under my dash!
Here's the latest. After my assistant got home yesterday (my Fiance) I checked the spark and the coil releases a single spark to the coil when she let go of the switch after cranking. I suspected the wiring harness somewhere so I broke out the Hanes manual. I bypassed the switch by jumping the coil straight to the ignition module and directly feeding the hot. Then I wired a starter button to the starter relay and I got the same thing? So now I'm pointing towards that resister wire?
She brought me a new battery for my multimeter so I can check voltages today as suggested. I don't fully understand this electronic system even after searching for a couple hours yesterday online. I'd love to just abandon the whole thing.
Right before my big move to Durham the last thing I did on my Bronco was wire in a GM modulator with heat sink and all from a article on Ford Muscle that said it even boosted about 10 horsepower? But I never got to try it. It's all made up and shouldn't take much to swap it over so I may try that today. But time is running out for I'm getting married tomorrow :beer: and headed to Florida for the honeymoon. By airplane and rent-a-car.:flipoff2:
A buddy has loaned me his beater truck for now. If I don't get it fixed today I'll still need to attack it as soon as I get back. I hate borrowing a ride.
 
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