Hello everyone,
I just joined the community last night but have been a big fan of this website and in particular this forum for quite awhile as it has helped me with my f150. So a great big thank you all for all the wonderful in depth information you have shared with me and lots of others who haven't bothered to join but still utilize the site.

1986 F150 4.9L I6

I am well aware of the crappy computer Carb/Dizzy situation with the 84-86 f150's and that a Duraspark II conversion would fix the issues i am having now. Unfortunately though i am without any cash flow at all to do the conversion.

What i really want to know is what are some of the common problems that would cause the computer to go into the "limp" mode and stop adjusting the timing.
I sheared a pin (in a 3 week period i have sheared 3 pins, cleaned out pan, can and pick up tube, sheared another pin and then finally bored it out and stuck a larger solid pin in there) and re-timed it and the computer stopped adjusting the timing. My f150 came from a buddy that is very prone to "Jerry Rigging" things together and the owners before him definitely did a lot of questionable work under the hood as well. Nothing is right under the hood and i would like to know where all the sensors are so i can make sure the emissions lines are intact so i can get this running right again.

 

Welcome to the forum.


This pin you have had issues with is this for the gear on the distributor?
There is a post of someone else that keeps having the same thing happen. I don't know if he ever found a fix or not. Do a search for it in this area for it, maybe look for distributor pin.


I don't know anything on the sensors that truck may use. I know you said money is tight but may want to pickup a factory manual for the truck as it will have a lot of information on this type of stuff.
Dave ----

 

Yes it was the pin that held the drive gear on to the distributor. I will look into the other thread you were talking about and see if i can add some input or take something away from it myself.

It would definitely be helpful to have a map of vacuum hoses for the emissions but i was really hoping for more information on specific problem areas that effect the computers timing. I have a Chilton repair manual (worth its weight in gold) for the truck but it doesn't really help me with trouble shooting anything.

 

If not helping in trouble shooting then what good is it? J/K
That is what most say about chilton books and why the factory book.


As for the vacuum hoses there should be a sticker on the radiator support. I cant remember if there is a ledger of what the abev. are for on it or not.
Dave ----

 

I actually found a list of abbreviations for vacuum route diagrams yesterday and i saved the link in my notes for future use. I found it on either this auto forum or another one just like it. I am not really sure if i have a sticker under my hood with the hose diagram or not, i know there is about 4 or 5 different stickers on it but i don't remember vacuum lines being one of them.
I am not too worried about that stuff so much right now anyway because i am currently stuck in Dallas because of a broken distributor. The plate that fastens to the rod the rotor slips onto at the top cracked all the way around it and now it doesn't spin along with the rest of it anymore. On my way down the ford started running rough right before i hit the state line and i had to pull over and turn the distributor a hair to get it running right and get me the rest of the way. I stayed a couple of days and then about 25 miles into my trip back home to Tulsa my truck shook and died on me. I thought i sheared another pin in my distributor but after i got the truck towed back to my in-laws place (thanks to AAA free towing up to 100 miles, up to 5 times a year, best $80 i ever spent!) i took the distributor out and the pin did not appear to be sheared. It took me awhile before i figured out what was wrong with it. I initially thought that since i put a larger solid pin in place for the shear pin that the synthetic fiber blend (phenolic?) timing gear stripped out on me and i was really up *****s creek. I was able to get my old lady to crank it over while i watched the distributor and saw that it was turning until i reached down and tried to stop it with my hand and saw that the rod that the rotor slips onto was free spinning inside the metal plate so i took it out and saw the crack all around it allowing the distributor to spin while it set still. I can try to put a tack it back together or just buy a new dizzy i guess.

 

Sorry to hear of your break down.
It sounds like you can figure out what is wrong and ability to fix it with the right tools.
That is better than most as they need to rely totally rely on others.
Dave ----

 

My 85 F150 has that same Electronically controlled carb junk too. I have never had a pin sheer on me though. My problem is when it's not above 50 degrees my truck won't stay running on its own! I can even put my foot down and the rpms still start going down. You have throttle it for about 5 min to get it to stay idling and let it warm up for 10 min. I am curious on how the computer would screw up the timing though.

 

The computer adjusts the Carb and it can only tweak it so much. If something trips a sensor i have read that it switches to "limp mode" and will be good enough to keep it running but not very well. This is only on the 84-86 models with the damn electronic ignition/timing/emissions. That is the reason everyone does a "duraspark II" conversion and basically uses the older style vacuumed distributor/Carb combo. I just recently learned all of this myself so i haven't begun to do any of that but that is the plan for it. With that being said i forgot to mention that i have 4.9L I6 engine in mine and i don't know if any of this carries over to the other engines. If you haven't heard any of this stuff before you should check out the "sticky" section, its got all the information you would need for it and i would check out the emissions section in your Chilton/Haynes (you should have one for every vehicle you own).

 

Mines on a 5.0 302. It will run fine when it's T operating temperature. Other than that it just sucks.

 

I'm also working through issues with an 86 w/4.9 and the feedback carb. I've got it running now but I'm getting 10mpg so I'm pretty sure it's in limp home mode as well. Have you tried pulling the OBD codes? Most of my problems have been vacuum related so far.

 

The feed-back system is absolutely great when working as designed. It has been known to return better gas mileage than the EFI. The trouble is that the system and its associated parts are 30-32 years old, now, and it was only used for 3 years, so obtaining some parts is difficult at times.

My son has a 1984 with the 4.9L and feed-back system and it still works well. My 1986 with 4.9L and feed-back had much wrong with it and was converted to the Duraspark system.

If any vacuum hose(s) or sensors are broken or missing, the computer cannot "see" what is going on and for safety reasons, locks the timing at the static setting [10 degrees BTDC] and adjusts the carburetor to run at its richest setting. The result of this is poor performance and awful gas mileage. The first two tanks of gas in my truck with non-functioning feed-back system was 11 and 9 MPG. Yuck!

There is a MAP sensor located by the battery. An Oxygen sensor is located in the exhaust manifold. Located in the thermostat housing is a temperature probe which measures coolant temperature for the computer [not for the gauge or idiot light]. There are many vacuum hoses to control things like the EGR valve and ventilation system. Often times, people take these loose in an attempt to "clean-up" the engine bay or to make the engine "run better". If any of this is not as designed, your system will not work correctly.

Sometimes, people remove the original air cleaner assembly and put on a chrome aftermarket one, for looks. This, too, can cause running problems, especially in cool damp climates.

 

The EEC-IV and feedback carburetor system you have is not "crappy" at all. That system is basically a "bridge" between carburetion and modern electronic fuel injection. Gas mileage, emissions, and power is better with these systems than the earlier (pre-1984) carbureted mechanical systems. The EEC-IV engine computer has the ability to adjust the air fuel mixture, ignition timing, and emissions equipment with more accuracy and efficiency.

Just like any modern electronic fuel injection system.

The *only* reason to swap to the earlier DuraSpark II system is if your truck is missing components or if you wish to modify your engine. If you have a stock engine that is functioning correctly, and you are not interested in modifying it, you will not gain anything by reverting back to an earlier DuraSpark II ignition system.

To do the swap correctly, you would need to replace the carburetor, distributor, and the entire ignition system. This will render most of your stock emissions equipment inoperable, as these components relied on the engine computer to function, and the engine computer cannot control the emissions equipment without input from the stock carburetor, distributor, and engine sensors. Keep in mind also that this is technically ILLEGAL, and your truck will not pass an emissions inspection if that is required in your area.

If you are running *any* aftermarket carburetor, your truck will not run correctly. Your truck has to have the correct feedback carburetor in place to relay information back to the engine computer, or your truck will not run correctly.

If *any* of your sensors are missing or defective, or if *any* of your emissions equipment is missing or defective, your truck will not run correctly. The engine computer will lock the timing and air/fuel mixture into a "FAILSAFE" mode and throw a code.

Just like any modern electronic fuel injection system.

That is the typical problem with these vehicles. Not only are they well over 30 years old, but most of them are NOT original anymore. You cannot modify or delete anything on these earlier EEC-IV-equipped vehicles without upsetting the engine computer. If *anything* has been tampered with, your truck will not run correctly.

Just like any modern electronic fuel injection system.

That sounds like a choke problem. Even though you have an engine computer and a carburetor with a feedback sensor on it, you will still have a mechanical choke system. Check and make sure your choke stove is connected. You should have a fresh air tube coming off the back of the carburetor air horn and connecting to the choke stove chamber of your passenger's side exhaust manifold, and an insulated hot air tube coming back up to the choke cap.

If you don't have that, your truck is relying on the electric assist choke, which only works above about 60 degrees.

 

LARIAT 85 I appreciate you clearing that up for us. You are absolutely right for correcting me on the "crappy" remark. Pretty much all of my vacuum lines on my vehicle are no longer there. As a matter of fact i need to buy a new distributor for the thing today. Can i buy a vacuumed distributor and use my existing Carter YF carburetor?

And again LARIAT 85 thank you so much for that information, i can not imagine what i would have done 20 years ago when i would have been at the mercy of my immediate pool of associates for advice.

 

Would be better off purchasing the Cardone replacement dizzy and just figuring out how to redo the vacuum lines? The "Jerry Rig" guy also was kind enough to toss out the air cleaner system and put a 4" filter on the Carb i get to replace every month or so if i have been driving the truck.

1986F150six Thanks for your input as well, i didn't mean to leave you out of the praise earlier.
I really appreciate the information that everyone is sharing with me. I truly love my truck, its exchange hands between "Jerry Rig" and I a couple of times because we both kind of needed the money and we both would hate to see it go to someone else. I will say real quick that "Jerry" has bailed me out quite a few times from installing new clutches for me pretty much single handedly to pulling me out of a mud pit a few times so lets not judge him too harshly, he is a better man than me.

 

I will look under the hood and check everything. Thanks so much, hopefully I can figure this out!