Hi, my truck is a 78 F-150. The 351M has 241,000 mi but still ran great. One day I was driving and out of nowhere the engine starting running rough. I mean one second it was fine and the next it felt like it was stumbling. I got up to a stop sign and it stalled. It started right back up the idle was so low it sounded like it was just barely running. I was able to drive back home (15 mi) and I have even driven it since and the problem is not getting any worse or better. It idles so low even a turn of the steering while sitting still will kill the engine because of the additional strain put on it the power steering pump. First I suspected a leaking vacuum hose but I couldn't find anything wrong. I replaced the fuel filter, cap and rotor, plugs and wires so far, since it needed a tune-up anyway. That didn't help at all. The PCV valve seems fine also. The carberator was just rebuilt less than 1000 mi ago and never gave any problems afterward. The engine does this when the oil pressure is high and low. I've lost top end speed too. If I rev it up it is rough all through the powerband until I get real high, like 4500rpm and up and it smooths out. This is my only vehicle so and don't want to just guess and replace things becauese I also have no money. Sorry for the long post, but does anyone have any ideas? All help is GREATLY appreciated. Thanks.

 

Check your timing. It's possible you jumped a tooth on the timing chain sprocket. At 200K+ miles it's a possibility. My brother's 460 reacted much the same way when the chain got sloppy and jumped. Good luck.

 

Nick1, double check your vacuum hose "tree" at the rear of the intake manifold. You have to take the air cleaner off and lean over the engine to see it. Also check the hose running to the brake booster, and the booster itself.

"Nothing lasts forever except natural stone and old Ford trucks." (Willie Nelson)

 

Looking at the exhaust, does it seem like it's burning too much fuel? If it is, I would suspect a piece of dirt may have found it's way into the carb needle and it is trying to flood the engine.

 

Nick, same thing happened to me two years ago. When I pulled all of my plugs, one of them was very fouled and black. I pulled the valve cover on that side, and discovered that I had broken a rocker bolt. I don't remember if it was intake or exhaust, but one hour later it was fixed and running strong again.

 

Nick,

I had that happen to me once, turned out to be bad gasoline! Problem went away with the next tank.

Just a thought,
-Brents

 

Thanks for the ideas guys. This gives me some more things to check out. I really appreciate it and I'll let you all know what the problem was when I get it fixed.