Hey everyone. Here's the background. This is my dad's bronco and he bought it in early 1986 with 9k miles on it so he's had it since it was nearly new. Anyway it is a 4 speed with the I6 4.9l. Here's the problem. About 5 years ago my dad was driving it and reved it up for some reason and it started running really rough right away and so he parked it and it hasn't been driven since. Anyway I have put a new rotor, dist cap, spark plugs and wires, battery cables and changed the oil and fresh gas with some carb/fuel system cleaner. Anyway from what I could see, the entire problem was because one of the 2 bolts holing the dist. cap on had broken in half therefore causing the cap to be loose. I think that was the problem and why it started running rough on my dad. Anyway when I put all the above on, it ran great and I drove it around for about 40 miles max and it it slowly started running a little rough and I pulled a plug and it was completely covered in black carbon so its running really rich and I believe fouling the plugs so that's why it's running rough. Here is the question. Could it be just because it hasn't been ran in a long time and has a lot of carbon build up in it? Could I clean the plugs and run it some more and maybe take a one plug out at a time and let it blow some of that junk out? It runs great when the plugs are clean. Anyway, any help would be appreciated. My dad's birthday was on 9/25 and he and my mom are gone on a month long vacation with their camper and will be back in about 2 weeks. I'm working on this for him as a surprise for his B-day and would love to get it going for him. Any help would be great!! Thanks!

 

Hey Arkdriver,
The '85 is a difficult one to diagnose because it's one of the few years (84 - 86) where they used the feedback carburetor setup, which is a system that uses a computer to monitor the carburetor, which uses those signals to set the engine timing and fuel ratios. If one of the systems starts to go out, the whole thing just fails (and since none of them are newer than 24 years, there's most likely things failing.)

This is why most people to a DuraSpark II conversion, which is pulling out the entire ignition system and getting a distributor, coil, and ignition module from a pre-84 and putting it in. (This'll also require a non-feedback 1bbl carburetor.) I did this a few weeks ago on my '84 and it took me $35 in parts from a junk yard, and 30 - 45 minutes to swap the ignition system over. It isn't difficult.


But, assuming that the system is fine, and it's just fouled up from sitting for so long, you could try Seafoaming the engine.
Seafoam's good stuff, and can get rid of a lot of carbon buildup. Get some at Napa, Schucks, Autozone, etc. and then follow the directions on the back for sucking it up a vacuum line and into the intake. It can clear a lot of stuff out.

I'd also fully recommend a carb rebuild, especially if it's been sitting for 5 years. You may have internal fuel leaks that are causing it to run rich, and it'll just keep fouling again and again.



Also, do you have a timing light to check the ignition timing?

Where are you located?


Lastly, if you want a 4.9 straight six specific forum, check out
https://www.ford-trucks.com/forums/forum52

 

Thanks for the info AB. I've thought about the conversion to the Duraspark II. But just don't know if that is something i want to try and do. Not sure I could find everything I need. I'm not the best mechanic in the world. ha This is really the first vehicle I have done much work on. And the seafoam is a good idea. I'll check it out. And I don't have a timing light but have a buddy that does. I'm in Alexander, AR.

And the bronco I'm working on looks a LOT like yours. ha Just put a white top on yours and they'd look a LOT alike.

(Before I cleaned it. It looks a LOT better now)

 

IF you decide to do the Duraspark conversion, I'll be glad to walk you through it, and supply a detailed shopping list. I was blown away by how easy it was, and how well it ran afterwards.

But in the mean time, definitely check out the seafoam stuff, and look into putting a rebuild kit on the carb. They aren't too difficult to do, and that little 1bbl is an easy one to start on.

My 300 was the first engine I ever worked on, and I knew nothing when I started. They're a great engine for beginners.

 

Awesome! Thanks for all your help! I think I'll start with cleaning the plugs and also the seafoam stuff and see where I sit after that.

 

Good thinking. Always best to start with the least expensive and easiest solutions first. If they work, no point in going further!

 

Hehe, that's cool. I've only seen maybe one or two besides mine that have that white stripe down the side.

Mine was a lot like yours, sat for about 4 or 5 years because it quit running. They sure fix up and clean up nice!

 

Yeah my dad always talks about getting it running and going, but he just hasn't done it. Hopefully he will be surprised when I drive up to his house in it when they return from their vacation. He loves this truck.

 

That'd be very cool if you could pull that off, I know how that'd mean something to someone who's had a truck like that forever.

Nice thing is, unless the engine's physically worn out, it's most likely something external, and can be taken care of. Just a matter of pinpointing what it is.

 

AB is right on, but before you swap anything, buy or borrow a code reader and pull the codes. You might find something easy to fix and not need to do the duraspark swap.
Another thing to check is the carb screws that hold the throttle body to the carb bowl assembly- they get loose from time to time. Take off the air cleaner and try to move the top of the carb right and left; if it moves, pull the carb and tighten the screws that hold the throttle body to the carb bowl.
AB is exactly right about the swap-it's way easy.
One other thing- I'd strongly suggest you buy a reman carb rather than trying to rebuild the feedback carb you have; it's pretty finicky, and it'd doubtful that a carb kit will help it much. But if you decide to replace the carb, swap to Duraspark like AB suggests if you don't have to pass an emissions test.

 

I worked on it last night and pulled the plugs, here is what they looked like after maybe 30 miles. ha



Anyway, I cleaned them, put on a new fuel pump and also took the carb off. I'm going to clean it up over the weekend and replace some of the gaskets and just make sure everything is working right on it. Going to put it all back together and then sea foam the engine through the carb to try and clean it up on the inside some more. Anyway, that's where I'm at now. Boy this is a learning experience and kind of fun to work on! Aggravating at times of course....but fun. here is the kicker though, I'm doing this as a surprise for my dad while he and my mom are on a month long vacation. Well they are on their way home but their plan was to stop off in Dallas and visit my brother and his family for a few days on their way back. BUT I got an email from my dad yesterday saying they are not stopping in Dallas now and instead will be home Sunday afternoon. Yikes! ha Another kicker....I'm leaving from work at about 2 today and heading to the deer woods until tomorrow night since its Arkansas opening weekend of bow season. Anyway....Going to be a long night Saturday night. ha

 

Friend,
Check your automatic choke and ensure that it's not closed too tightly. If it's all origional, you may need to drill out the rivets that hold the choke spring on and install screws. Let us know what you find.

 

Wow, those are some seriously fouled up plugs! It's running rich rich rich.

I agree with Wyowanderer, check the automatic choke and be sure its working properly. If not, it's cutting off the air supply, which causes a rich condition.
To check:
When the truck is ice cold and the engine off, remove the air cleaner housing and have the top of the carb exposed. Do a full open and close on the accelerator (by hand on the carb, or in the cab with the pedal). Look and see what the choke plate on top of the carb does. It should almost be completely closed (about 1/8" open).

Now, start up the truck and let it FULLY warm up. If you don't drive it to do this, it's fine to leave the air cleaner off. Won't hurt anything (unless you have random and unexpected dust storms ). Check the choke plate again. It should be COMPLETELY open and straight up and down. If it's not, it is a problem and your choke isn't working properly and needs to be repaired or adjusted. If it's open most of the way, but not all the way, you can fix it by moving the choke (which I believe is riveted on on the feedback style you have). When fully warmed up, rotate the choke until it barely makes it 100% open. If it doesn't open at ALL, the spring inside the choke has rusted and/or broken, and the choke housing needs to be replaced.



The other idea I can think of is that something in the emissions system, or some sensor is out, causing the computer to put the engine into into limp mode. If that's the case, you'd be best off to just pull it all and put in a Duraspark II setup because those components are $$$.


Good luck with your bow hunting! It's a bummer your parents are getting back sooner, I know what it's like to have a surprise going like that and not be able to pull it off like you want to.

And I agree, working on an old engine like a 300 is a blast! I didn't know anything about anything car related until I started working on my old '81. So much fun.

 

Thanks for the walk-through AB!! Just what I needed. I'll check it out.

 

That puppy is making more soot than my diesel.

I guess I have sort of a primitive way of thinking, because I'd just throw in a 35 dollar points distributor from Napa and rebuild an old 1bbl carb for it.