I have a 97 F-250 and she's been having inconsistent rough starts, even in the summer. It's not turning over too long but when it actually cranks, it keeps cranking and the RPM's jump a lot. And it only does it 1 out of every 10-15 start-ups so far. I don't want to start throwing a new starter and batteries/cables if it's something simple. I'm not a mechanic, but I'm trying.

 

could be the relay on firewall is sticking, i would change that out first.

If you can catch it and have a meter handy, see if the fender relay has power or not going to it.

 

I'm not clear on what your symptoms are. Does it sometimes not crank at all, and other times crank fairly normally? Or are some starts sluggish, rough cranking with others others normal? Accurate and complete symptom description strongly aids good diagnosis, which disarms the parts cannon.

Fender relay failure usually will be flat out no-crank rather than extended, slow cranking. Fender relay takes the very low-current "crank" signal from the ignition switch, and boosts it to a moderate-current "crank" signal for the relay on the starter. Relay on the starter either gets a strong enough signal to switch high-current to the starter motor, or it doesn't get enough signal and doesn't switch current to the starter.

If your issue is some starts no-crank and others normal, and the number of no-cranks is increasing, I would strongly suspect the fender relay. Even if the the fender relay audibly "clicks", it can still fail to send signal to the relay on the starter. If the fender relay "clicks", you know it is getting "crank" signal from the ignition switch. It's possible that something in the switch circuit (switch, park/neutral or clutch safety switch, wiring) or +12 feed to the fender relay is intermittently failing, but I think those are far less likely than the relay itself.

Sluggish cranking is a different issue. That would be something like worn out starter, weak batteries, or corroded or damaged main positive wire to starter. If it cranks at all, you know that everything from the ignition switch down to the relay on the starter is adequate, at least for that cranking attempt.

Good cranking but no start is a whole universe of possibilities.

 

Pretty sure I got it figured out. It seems to have been the neutral safety switch. We'll see