1981 F250 4x4 4spd 351m. Drove out in the woods the other day and got back the truck wouldnt start. Single clunk when you turn the key. Swapped solenoids same thing. So Push started and drove home. Changed to a brand new solenoid same thing. Changed the starter ( had one on the shelf) Same thing. Single clunk no start. Changed the positive terminal and wiring and negative terminal and wiring And i get a starter that engages the bendix and does nothing no matter which starter or solenoid combo. Voltage is good and so is Amps...Engine is not seized either. Any suggestions before i rewire an entire truck?

 

Also changed batteries and fuses ( NO fusable links) And also forgot to mention i get a puff of smoke off positive battery terminal when it clunks.

 

I noticed a little oversight in your post. I think you meant to say this:

"Voltage is good unloaded..."

Here's something I've learned the hard way over many years of chasing sparks. A voltage reading on an unloaded circuit doesn't mean a whole lot. It's gee-whiz information to some extent, certainly not conclusive. If low, yeah, you've got a problem. But if voltage reads normal in an unloaded circuit, that can be misleading. You want to get a voltage reading with the circuit under load.

Fortunately, this guide tells you everything you need to know when dealing with a slow or dead starter system:

https://www.ford-trucks.com/forums/1...w-starter.html

Last I heard, the author was being considered for a Nobel Prize because this guide has been such a help to humanity in general. Not really the actual medal, or cash award. Rumor was it was only a $20 Starbucks gift card, but hey, it's something.

Forgive me as I get up on my soapbox, but make sure the poor battery is fully charged prior to any testing. This is very important, so please don't skip this step. Don't waste your time with a trickle charger. It won't cut it. If you don't have a proper charger (suggested min 10 amps), most auto parts stores will charge your battery for free.

[/soapbox mode off]

You mentioned having replaced the battery terminals. Do they look like this?:


I have found that style very useful in some situations. Deep sea fishing, for example. They make great sinkers. Or if trying to keep papers from blowing away on a windy day. But as part of a vehicle's electrical system? Not so much.

 

There's your clue right there. Get a testlight or voltmeter and measure the voltage after the positive terminal WHILE YOU ARE TRYING TO CRANK IT. This usually takes two people, one to work the meter or testlight while the other is inside trying to crank it. If you have a problem with that terminal, your 12v will go to near zero when you try to crank it. A good place to put the meter or testlight would be the large + terminal on the solenoid.

 

That's another YUGE clue. Run the tests in the guide linked above.

 

I Understand the basics of electric in auto's. Starter works out of the vehicle..Solenoid opens and allows current to flow. Ive already replaced the Grounds from frame to block and block to battery and frame to battery. Ohms measure out no matter where i touch the block or frame. Including the starter. When everything is installed im getting little to no power from the solenoid to the starter and the positive terminal smokes every time. Brand new 4 ga copper lead with crimped sealed lead terminal and copper terminal on the solenoid. This truck has worked fine until now, The symptoms are a bad wire yes i understand that from your write up. But These are brand new 4ga copper stranded wire. Sealed soldered crimped ends. No issues with voltage drop. Thats why im baffled.

 

Changed positive cable to 2ga copper with leads i soldered ..fired right up. Then solenoid took a **** and sent the starter into the flywheel on a test drive..Now its time to drink white russians and see if i have a spare flywheel on the shelf. Moral of this story is Anything Napa sells is absolute garbage on a ford. Napa 4ga positive cable brand new had a hot spot midway and the lead seems to not be very conductive of amps. Napa Starter solenoid ( "premium" gold plated one) Got stuck and damaged a brand new starter and probably flywheel.

 

Just to add to your automotive electrics knowledge, you can't ohm out these large wires and call them good.

Let's say on the bad positive cable you had, you put your meter on ohms and measured from one end to the other of that cable, and got 0.1 ohms. Normally you would call that good right? Most meters have a hard time measuring that low anyway. But watch this;

You most likely have at least 100 amps running through that cable when the starter kicks in, maybe more. So your voltage drop through that cable is going to be E=IxR or voltage drop = 100amps x 0.1 ohms. which equals 10 volts. So you would have only had 2 volts going to the starter when it was activated. Enough to make it "clunk" and that is about it.

 

You know NAPA has 2 lines of parts, the cheap line and the better line that is more money.

I was having issues when trying to start I would get 1 clunk from the solenoid each time I turned it to start. After 3 to 5 clunk it would then crank & start.
When I rebuilt the truck little over a year before I installed all new battery cables and all connections were like new.
It came down to the old / used solenoid so I replaced it with top of the line NAPA one and never an issue again.

So dont be calling some parts from a store bad as most have 2 or more lines (levels) of parts you can buy.
You have to ask for the higher level / better part or they give you the lowest one as that is what most want.
Just today I had 4 different oil filters to pick from, from $5.99 up to $12.49.
Store brand 1 level up was $9.49 and the lower Wix was $10.49
Dave ----

 

I don’t recall what solenoid have on there now but After blowing up a couple NAPA golds I think I had better luck with the NAPA silver.

I’m wondering if the start signal wire is bad? Next time it goes clunk try jumping 12 volts to the S terminal on the solenoid to see if it will turn over that way.

 

Oh another thought the solenoid needs to have a good ground to the fender.
I went back over all that before I replaced my solenoid.

Funny I pulled the old solenoid to make sure it was grounded and it worked for the first 3 "test" tries.
Picked up all my tools and went to start the truck to put in the house garage and "CLUNK"!
Right then and there I told myself "time for a new solenoid" and on the way home from work picked one up from NAPA, top of the line one.
Again been fine for 6 months now.
Dave ----

 

Well there's your problem... you let the magic smoke out.

I'm sorry. That was unhelpful. But it was funny the first time l heard it... like, 40 yrs ago.