My 1986 F150 long bed dual tank 302 EFI auto trans has been running well since my mechanic replaced both fuel tanks, the fuel pump, selector valve, injectors, map sensor, distributor, plugs, and plug wires about three years ago just before he retired. Recently I noticed the engine spins over more before it starts and "idles up" longer before it drops to normal idle. The truck then runs fine but I now notice that if I drive about 25 / 30 miles after the initial startup, turn it off and let it sit for 20 minutes or so, that when I restart it the engine "chugs" like the air/fuel mixture is off. I drive away and when the truck gets up to speed (35 to 40 mph), all is fine and it is fine until I turn it off then it again goes through the same "chugging" behavior. If you have read this far, you can tell I am not a mechanical whiz but I can follow directions so if anyone has a helpful suggestion it would be much appreciated.

 

I'd suspect leaky fuel injectors. Throw some Techron in the gas.

 

Can do. Is there any way to tell which injector(s) are bad or must they all be replaced if the Techron relieves the sympton?

 

If the Techron works, there's no need to replace anything. The issue is the ethanol gas we have forced on us by dimwits that can't open a hood called politicians. Your engine and injection system is not designed for ethanol, hence the issue. New injectors will have the same issue shortly. Techron will most likely take care of it and you'll need to give it a dose a couple of times a year to keep it running right. OR, if you have non-ethanol gas in the area, use it instead. I have a station that sells the Gulf Isobutanol gas. It's not a cheap date at 4 bucks a gallon but the 302 in my Bronco thinks it's great.

 

Update:
Sorry for the delay - cracked a rib so things have been "on hold" while trying to heal enough to function. Better now so here is what I did. Bought two bottles of Techron, one of Sea Foam, and two of B-12 Chemtool. Disconnected the vacuum hose where it plugs into the brake booster and, with the truck running, poured 1/3 of the 15 oz can of B-12 into the vacuum hose v-e-r-y s-l-o-w-l-y. Completed this without stalling the engine. Turned the engine off, poured the rest of the B-12 into the front tank which was partially full of leaded hi-test and waited 15 minutes. Restarted the engine and drove the truck about thirty miles. Planned to let the truck sit for 30 minutes then try a restart but was unable to complete this plan at the time which was about a week ago. This morning, I started the truck, drove it about 15 miles on the interstate to bring the engine to full operating temperature. Stopped by the gas station, filled the rear tank (it was empty) with 87 octane ethanol-free gas, filled the front tank (it was about 3/4 empty) with 87 octane ethanol free gas, then switched over to the rear tank (did not shut the truck engine off at the station). Came home, shut the truck off, waited thirty minutes then tried to restart the engine. The engine started with no problem and ran smoothly (no chugging or missing). I poured a full can of B-12 into the rear tank then drove the truck up the interstate a short distance to mix the B-12 with the gas. The engine seems smoother and runs fine. I am very grateful to GLC and Labnerd for the helpful comments and hope this recap will be useful to other forum members. Thank you.

 

A bottle of Gumout for high mileage engines (with PEA) in the gas tank is a routine maintenance item for me, about every 6 months.