I recently bought my brother's 86 F150 off him for $200, it runs good, but the catch of the truck is that it will run great for 150 miles, i'll turn it off, start it and run maybe ten minutes and it will die. After fifteen minutes or so it will start back up and run great. The truck seems to have had a lot of work done on it in the past, like a hacked up wiring harness, and i'm wondering if someone in the past has tried to put a nonfeedback carb/previous gen ignition system on it and put it on wrong, causing this problem. It's got the 300 straight six/four speed/ four wheel drive base model.

 

When it won't start, you need to see if you have spark and fuel. If you are missing one or the other, then that will send you down the right path for troubleshooting.

 

Being as the truck is a 1986 model with a carburetor, it would have originally come with a feedback carburetor with a TFI ignition system, powered by the EEC-IV engine computer when it was new.

A hacked up wiring harness is hardly ever a good sign, and that is typical with these later feedback versions. A way to tell if the ignition was changed is to simply look at your distributor. Does it have an ignition module bolted to the side of it, or does is have a vacuum advance? If it has an ignition module bolted to the side of it and a wire harness attached to it, then it is the original EEC-IV/TFI ignition. Your truck will not run correctly if the feedback carburetor was changed out to a non-feedback carburetor and the TFI ignition is still in place!

 

Lariat knows of what he speaks. But even if so, it can be fixed! Does your distributor look like this:

 

Yes, as Galendor stated, it can be fixed! But first, let's take a look at how your truck was originally set up...

To meet tightening emissions standards, the 1984 - 1986 models equipped with the 300/4.9, carbureted 302/5.0 2V (later models were EFI), or 351/5.8 2V (excluding 4V "H.O." models), and some 1981 - 1983 California models came with an EEC-IV engine computer, TFI ignition, and an electronic "feedback" carburetor. Think of this system as a "bridge" between standard mechanical carburetion and electronic fuel injection: the feedback carburetor system.

These models can be readily identified by the distributor. Like the picture shown above, the ignition module will be bolted to the side of the distributor along with a plug wire harness. The EEC engine computer controls all the timing functions, so unlike the older models, it will not have a vacuum advance. These models also will have an O2 sensor in the exhaust manifold, a MAP sensor on the passenger's side inner fender, EGR and EVAP system solenoids, and a unique computer-controlled "feedback" carburetor, identified by a feedback solenoid and wire harness plugged into the front of the carburetor. Depending on the model, the EEC engine computer itself can be found under the dash or under the seat.

Using an O2 sensor and various other engine sensors and solenoids, the EEC engine computer controls the air/fuel mixture at the carburetor, engine timing, and all emissions. The computer reads the signals from all the inputs, and then actually adjusts the air/fuel mixture on the carburetor for maximum efficiency and performance. It works just like modern electronic fuel injection does except it utilizes a carburetor. And, like any other EFI system, if any of these sensors or emissions components are missing or removed, the system will not work correctly.

On these computerized "feedback" systems, you cannot just start taking off components and changing things as if it were not. Because of the EEC-IV computer, everything must work together. For example, if the stock "feedback" carburetor was replaced with an earlier, all-mechanical model or an aftermarket carburetor, the vehicle will still run, but the engine computer will not know what to do with it because it can't "read" what the carburetor is doing and adjust the air/fuel mixture. As a result, the EEC computer will revert to a fail-safe "limp home" mode and lock the ignition timing, which will in turn hurt emissions, economy, and performance.

What you need to do to get your truck running properly is to either put the original feedback carburetor back on, or you can keep your current carburetor and go all out and remove the EEC-IV computer and replace your entire ignition system with a "stand alone" ignition. By going with the latter option, most of your emissions components will be rendered useless, something to keep in mind if you have emissions testing in your area.

Note: If you have emissions testing in your area, ALL of the stock emissions and engine components - including the TFI ignition and "feedback" carburetor - must be in place and working correctly or it will not pass!

What you need to do is find out exactly what you have to work with, and based on this information, we may be able to help you to get your truck running great again.

 

Wow, thanks guys. The ignition module is still on the side of the disributor and hooked up. This truck has been pretty hacked up though because, if i recall correctly, when my brother bought the truck the A.I.R. pump had been taken off. It has since been put back on by a good mechanic. I wont have time to mess with it for a couple days, unfortunately.

 

If your wiring harness for the feedback carb and TFI ignition is ruined, it's fairly easy to replace, if you can find one at the JY. everything comes off each sensor/carb/distributer pretty easily, and you just unbolt it from the computer (under the dash on the six cylinder models) and snake it through the hole in the dash. Reinstall in reverse order of removal, as the manual says.
Resist the temptation to convert to Duraspark II unless that's your last resort, as the TFI system is emission compliant for your truck and delivers better mileage as well.
I'll bet you can fix your present harness, though, and you'll be glad you did. I've found the Feedback system to be complicated, but well within the reach of the back yard mechanic willing to learn how it works.

 

Should I start a new thread or comment on this I seen it’s from 2011 so.. I’m hooking up the original carb on my 85 f150 with the EEC IV system and I’m not sure what hooks to the two ports in the front of the carb.. it seems everyone on this old thread is very knowledgeable on this subject and I’d really appreciate the help! If I need to start a new thread no worries! ☺️

 

Moore, it is best to start a new post and in it make sure you put the year of the truck, size motor and what it is doing and if you can a picture of the ports you talk of.
We will be more than happy to help.
Dave ----

 

Alright I’ll start a new post! Thank ya! I’ll post pictures to.