me and my fiance both have dentside trucks.hers is a 78 f150 mine is a 79 f150.i pulled my 302 out and swapped it out with her 460.before i pulled hers just hit the key fire right up.put it in my truck and it cranks over really slow like the timing is way off.but if i unplug the coil itll spin over great but as soon as you plug the coil up it drags again.ive replaced harness with hers new solenoid and coil.any ideas im at a complete stand still with it.almost ready to set on fire lol

 

Starter power cable?

 

no it only drags when i plug the coil up.if i unplug the coil it cranks over normally

 

my first guess is that the distributor accidently got turned and advanced the timing. I would try retarding the timing while cranking the engine...if it starts, you can set the timing.

 

i can check that.but never touched the distributor

 

Clean grounds, good cables. Check the cable ends, especially if you have the wire molded in the battery connection end. Every thing 100 % wired correctly?

 

cleaned all grounds replaced battery cables everything seems to be plugged up in their proper connectors.its just got me confused.ive changed alot of motors and harness on these old dentsides and have never had an issue like this.

 

I would start with a load meter on the battery. Try coil unplugged vs coil plugged in. See what kind of readings it has and go from there.

 

I sense the thread starter truly has all ducks in a row by cleaning all grounding and installing new cables, etc and is not a wiring or connection related problem of any kind......

I only run CATerpillar batteries myself since 1999 and have superior grounding which means much larger interconnecting ground wiring and cables with clean and greased up interlinking connections bumper to bumper - frame to frame on all of my old 50 year old rigs that I run....which is why I rarely ever have electrical problems.

Out of all the CAT batteries I ever owned (9 total)....the lowest life span I had with any CAT battery was 8 years on one of them, the other CAT battery that finally perished on me lasted 19 years in my 76 Lincoln Mark IV.....the remaining 7 CAT batteries in my other rigs are still quite active, so no data there LOL.

I will go into detail upon why my one CAT battery only lasted 8 years as mark a. hit the bingo on his post above !!!

In 2014 with an 8 year old CAT battery in my 70 F250 (390), I was on vacation in northern Canada haulin' my cabover camper and all of a sudden with no warning my engine would not start after normal operating temperature but would fire right up when cold with no problem....

Took me a day to figure out that my distributor counterweight springs got weak and went to replace my distributor with a spare one I had onhand and accidentally packed a 429-460 distributor so I was SOL, anyway with all the intermittent 10 seconds cranking and 20 seconds non cranking intervals in between when the engine wouldn't start took a toll on the battery enough that was not noticeable later on - as I had to break out the generator and plug in my battery charger on two occasions to quickly provide a little boost to the battery to start the engine when totally cold, as my multimeter shows 12.45 to 12.80 readings and I'm like why is this battery now cranking a little slow at times....a nice Canadian observing me had a load tester onhand and showed me my 8 year old battery had adequate voltage but a slightly out of good range as the meter had read barely in the weak load zone when cranking as I worn down the battery enough to give me that minor problem....

Made it to my friend's cabin two days later in the Yukon Territory and he let me borrow a counterweight spring off his 66 Mustang 302 spare engine to get me home on.

I still use that weak load CAT battery for outdoor 12 volt lighting battery power source which is 15 years old now.

What gets me on this particular troubleshooting posts is :
-1- Distributor was never touched, so I do not suspect a ignition timing issue there with the engine swap....
-2- Even if the distributor rotor was positioned exactly right or positioned anywhere between 1 to 360 degrees off target - I would seem to think the engine should still crank over nicely or fire up and not act like it's trying to fire up all of a sudden (drawing power).

That's why I am with mark a. on this one and suspecting the battery load capacity (drawing power) could be the problem here - however the ignition coil wire intact slowing down the cranking power while disconnecting the coil wire and fully cranking is throwing me off while I never experienced that before, however we all seen first time out of character mishaps that cannot be explained either....

Could also be a combination of the battery load and starter problem, while an ignition coil adds a weaker enough draw on a load maybe, could also be ignition related after all by either an overlooked timing position issue or a ignition part issue

I would take your fiance's good battery and swap it in your rig and see if the problem persists....if it does, you know your rig has a drawing power problem or ignition timing problem somewhere ....
If your rig fires right up, you know the battery was the culprit all along !

 

thanks for all the help guys.i hope to be able to get back on it soon.i just got out of the hospital.had a blood clot in a major artery and still have one in my heart.

 

can anyone tell me how to test the dura spark module

 

 

thank you 77&79f250 i appreciate the info and the help

 

thanks for all the help its running now but gonna have to make a new post abot a new problem lol