We have another addition to the chapter: PPatty1 Welcome!

 

Thank you for the welcome to the Arkansas chapter! I own a 1983 Ford F150 300 I-6 engine with 4WD and 4 on the floor. The granny gear has been useful for pulling out stumps! I named her Peppermint Patty because she is one tough chick! Ha ha! Anyway, I am having an issue with the motor that I am hoping you all might have some advice on. I bought the truck two years ago from the original owner with 83,000 original miles on it and I have close to 94,000 on it now. He kept a log book on it for repairs and I have a complete history on the truck. I have had issues with it idling smoothly and wobbling when I shift into 4th gear under light acceleration. When I press down harder on the gas pedal, it levels out. I have noted the gas mileage has also been suffering. I used to get 18 with it, now it is only getting about a dismal 10mpg. I see the engine wobbling when I have it running in the driveway with the hood open. I had the carburetor rebuilt, put in two in line fuel filters, and put Stabil in the gas tank since I don't drive her that often. There are four little plastic vacuum modules that I can't see any part numbers that are about the diameter of a dime that I am wondering if they aren't functioning properly. I also have a new air filter, breather and PCV valve in it. There is one large vacuum module on the air intake and near it another plastic module about the diameter of a quarter as well. I had a new air pump, EGR valve and an a/c dryer put in last summer. It ran fine until I drove it to South Dakota in August to clean out my old house up there. I was about half way there, near Kansas City when I thought I heard a "crack" in the motor and it started running rough. I immediately pulled off the highway and checked the fluids for any leaks or at worst, a rod sticking out of the engine block. Nothing. I have heard of rods breaking in those old I-6 motors and they keep chugging along, but I am really hoping it is a vacuum issue. I have looked through the shop manuals Ford produced for that truck but I can't find the part numbers for those modules. The auto parts websites have also not been much help on finding those either. I prefer to fix it myself rather than paying a mechanic to do it, but I am not sure I can get this done myself. Have any of you out there had a similar experience with your trucks and what was the diagnosis? Thank you in advance for your help and recommendations.

 

Welcome to the chapter!
Pretty sure the problem you describe isn't going to be vacuum related. First thing I would do is pull the plug wires one by one with it running to pinpoint which cylinder is dead. From there run a compression check. Could be as simple as a broken rocker arm or pushrod, hopefully not a connecting rod.

 

Welcome to the chapterI'm with Jeff on the possible dead cylinder. Now the vacuem leak could/would lead to it having a rough idle..but right now I think that's the least of your issues.

 

Good afternoon everyone,


I tried the pulling of the wires with the motor running. It amazed me that the motor continued to run smoothly as I temporarily disabled each cylinder for a minute. The engine idle speed dropped a little as I did the test on each cylinder until I got to the one closest to the front of the engine block. The idle speed did not drop on that one. I know each cylinder is getting a spark as I managed to get zapped by each one. The plugs, wires, cap and rotor are all new too. I am hoping your idea of a broken rocker arm or push rod is the issue, as I saw they are easily accessible under the rocker arm cover. I tried to look up the firing order to determine the cylinder number, but no luck. But the physical location should be enough to relay to the mechanic as I don't have the equipment to do a compression test, nor do I like getting into the internal workings of the motor. Thank you again for helping me track down the issue. I greatly appreciate it.