Hello everyone, I'm new to this forum and I have a question. I have a 1986 F150 5.0L EFI 4x4. Heres my problem, I just aquired this truck from my father and it set for 4 years and I got back on the road again and now it has a hesitation in it now. It seems to do it at higher RPM's, it does when you accelerate to pass someone or take a hill and if let off just a little it straightens out until you accelerate again. It seems to have plenty of power other than that, it runs great at take off and starts and idles smooth. I have pulled codes from it and keep getting a code that says no TACH signal, code 18, I have replaced the TPS, EGR position sensor, TFI module, both fuel pumps, fuel filter, complete tune up including new plug wires and checked and set the timing. I am at witts end trying to fix this with no sucess. If anyone has any clue about this had something similar happen to them please any advice is welcome. Thank you

 

my ranger did this after it too had set for along time and it took me forever to figure it out, 3 hours after I got it fixed the tranny ate second gear not the ranger is someone's rock crawler with a 460 in it , I found out that there was a pinhole leak in the fuel line that was causing it to suck air and not get enough fuel at highway speeds. I replaced the fuel line and everything worked great, for 3 hours. but now that I think about it your fuel pump/s is/are in the tank so you would notice a small hole in your fuel line it would be spraying fuel instead of sucking air. ok nm it was an idea even if a wrong one.

 

I've got the same truck.
1. pull the codes, see what comes up.
Also check your throttle position sensor. The haynes manual describes the process.
zanny

 

I would think the tach signal would come from the TFI module, perhaps you have a loose wire?

I assume you've changed the fuel filter as well? make sure you run some fuel system flush though your truck. 4-year-old gas would get to be pretty gummy.

 

My 1980 F-100 sat in a farm field for 7 years until I bought it 6 months ago, and an assortment of fuel related problems have kept me on the edge of my driver seat ever since.

I rebuilt the Holley 2 bbl carb, changed filters, drained tank, flushed lines, replaced fuel pump; then replaced Holley with rebuilt Motorcraft, then rebuilt Motorcraft, changed filters again, drained tank again.......

..... and never knew if I had solved the problem. Truck would run great for a few weeks or month, then die in rush hour traffic on one of three bridges I cross daily.

Once I am done reading this forum for new clues, my day will be spent dropping that damn tank again and pulling the fuel lines.
Because yesterday, at the peak of bumper to bumper rush hour traffic, the truck died without warning in the fast lane of four lanes about 250 yards from centre span of the Alex Fraser Bridge.

Thinking it could only be a vapour lock from a pin hole, I removed the flex hose from the screw-in in-line filter at the carb, and it began spewing a purple-ish black, molasses like fluid that consisted of a real fine grained black particle suspended in the gummy fuel.

In addition, the wells at the bottom of the carb's fuel bowl that the jets are mounted in were buried in the same stuff completely cutting off fuel flow.

I mustn't have drained and flushed the tank well enough, or maybe this substance could be manufactured in the tank itself much like the algea problem in diesel fuel. Not sure that's possible, but at this point of frustration, I'll check anything out....... crazy or not.

There is also a sock filter as part of the fuel sending unit located at the tank. There was a one sentence mention of it in my Haynes manual, but nobody I talked to was familiar with it. I enquired in this forum, and got two responses which confirmed its existence.

I sure hope you can identify the root problem faster than my 6 plus months. Otherwise, the honeymoon period with this truck has been delightful !

Good luck, and please post your findings.

JT

 

there is a brass screan(sock) on the fuel pickup tube in your tank
when you fill the tank turbulance mat be causing the sludge in your tank to float into the fresh gas then it settles to the tank and plugs the intank sock pull your tank remove the pickup sender assembly and wash the tank out really goodblow out the sock put heet or rubbing alcohol in the tank to absorb the moisture and change all your filters again sitting is the worst thing you can do to a truck

 

This might be the actual tank liner breaking down. I do know that some companies went to lining the tank to keep them from rotting out. Not sure if it's a DOT code but if that liner was faulty it could be breaking down from the outside of the tank liner to the inside of the take. Basically plastic goo similar to styrafoam plates and gas. Just an idea.

 

Hey everyone thanks for all the help. I fixed it last week. As it turned out all it needed was a set of injectors. I replaced all 8 of them and the truck runs like a new truck again.