I have a 1986 ford f-150 with some strange problems. First let me go back a bit. When my friend owned the truck, it ran pretty good but he complained about a lack of power. I drove the truck and felt the same way. Flored, it would only go about 75 to 80 mph. We checked and replace the spark plugs, wires, cap and rotor. It ran a little better but still did not go faster than 80 mph. Later, the truck started running really crappy and eventually died. He gave me the truck and I had it towed home. I found that it had a blown head gasket and also found it had a cracked head. I replaced the head and installed new gaskets. The motor would not start. I check it out and found it was not getting spark. I found that I needed a new PIP sensor and a new Ignition Module. After that, it fired right up but still ran sluggish. Timing was set properly and all cylinders were firing properly. I still gave it another tune-up just in case replacing spark plugs and necessary compents. The truck still ran as if it was missing something. Not alot of get-up and running very rough and irratic at idle. I countinued to drive the truck and it got me where I had to go. Then, another problem developed. It got cold here and winter was coming in. Next thing I know, the truck had a sudden loss of power. It lasted that way through the whole winter. The truck was very sluggish taking off and very weak in speed. It was like the motor was struggling. I checked everything and it seemed as if it was ok. Now it is beginning to warm up and something weird started happening. I start out in first (automatic tranny) and it is still sluggish but then when it shifts to second, the motor smooths out and then the truck starts to haul butt. It only does this when the truck is hot but when I take my foot off the gas, the truck the bogs. If I move the shifter to second and then back to third, it starts to haul butt again. I cannot expain what is causing this but I have an idea it is computer related. I am really confused because in all my life of repairing vehicles, I have never seen anything like this. Just to let you know, the carb has been replaced with an origional motorcraft carb from the factory. It is eating gas really bad and I notice that when it is running good, the exhaust it not as loud but when it drops out and starts bogging, the exhaust gets really loud. Any help would be appreciated because I don't want to spend hundreds of dollars on the trial and error method to fix this problem. I did check the cylinder compression and they were fine on all cylinders. Please help!!

 

Check the cats, they may be partially clogged, also check the timing chain to see if it has jumped a tooth or two. How about the fuel filter and pump? Also check all your vacuum hoses and lines for leaks.

 

It does sound like it could be the cats. I have had the cat go on several trucks with similar symptoms like yours.
The cat will plug up and the inside workings will break down. Sometimes the pieces will totally restrict the flow to the muffler, and then sometimes it will only partially restrict it. This was in my past experiences. The pieces would clang around when I would shake the cat once it was off of the truck. Sometimes the the inside of the cat will just get plugged up period, without breaking down. Good luck. Jake.

Jakegypsum // Ford fleet, soup to nuts.

 

How's the fuel pressure? My '91 F-250 had a bad fuel pump, couldn't keep up with the initial load. Acceleration was horrible but it was able to keep up the speed once I got up there.

Dustin Siebert
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