Engine problems/swap ideas 1981 4x4 custom bronco

I have recently purchased a 1981 custom bronco 4x4. It has the 4.9l 6 in it. I have had many problems out of this set up already. Least to say Im thinking about a motor swap. Im torn on the idea of continuing to tinker with it until its right but have had many problems while dealing with this one and just cant seem ( even paying my very well known mechanic to work on it ) to get it running just right. With all that said I would like to go with a v8 but im not sure. I dont have the time nor know how to do this myself. What would be the easiest thing to do...IE what motors will work best and fit easiest. Im completely new to Broncos all together. I thought of putting in a fuel injected motor out of a newer vehicle however I have found they are harder and more expensive to get in and running. I have access to a 302 and 460 but have thought of a 302 as well. Thanks in advance for your thoughts.

Well personally I'd go with the 302 In my experience they are easier to find parts for and more reliable, also I would stay with carburated since it already has one in it it will make the swap easier, you also need to figure out what transmission you have and see what mods u will have to do to get it to bolt up.

Hi Ben.., welcome..!

It's VERY likely the problem is NOT the engine per se, but in the peripherals.

(that is a very "stout" engine.)

Fuel, ignition/timing, electronics, computer.

You've not stated what issues you're dealing with..?

The more info. in..., the more help out.... >< <'>

Changing engines is not cheap or easy. /emoticons/[email protected] 2x" width="20" height="20" />

Well Im not convinced to swap motors yet. Right not the bronco starts up fine. However after putting in gear ( manual Shift) while letting off the clutch and pressing gas ( driving the bronco ) it dies off. It does this in both reverse and first shift. I know....I know....Give it more gas and it wont die. With that said Im having to give it alot of gas. I have not ventured past the road I live on due to this. Is it normal to have to give this motor that much gas? I dont have a rpm guage so I dont know how high im spiking but it is pretty high I would think. Thanks in advance for your suggestions.

Well.., with that, I would guess it's just an accelerator pump. (easy fix)

With air filter housing off.., you should be able to see the fuel squirt down inside the air horn. (Do this with eng. OFF.)

2nd guess would be a vacuum leak.

3rd would be timing off.

"Is it normal to have to give this motor that much gas?"

No..., actually, you're giving it more "air" (as throttle plate opens it's sucking more fuel thru the "main jet")

This could also be the problem if the main jet is plugged/partly plugged.

(It sounds like the idle circuit/jet is OK)

The accelerator pump actually floods the eng. a bit to give it a "kick" to get going.

Bully Bob said:

Well.., with that, I would guess it's just an accelerator pump. (easy fix)

With air filter housing off.., you should be able to see the fuel squirt down inside the air horn. (Do this with eng. OFF.)

2nd guess would be a vacuum leak.

3rd would be timing off.

"Is it normal to have to give this motor that much gas?"

No..., actually, you're giving it more "air" (as throttle plate opens it's sucking more fuel thru the "main jet")

This could also be the problem if the main jet is plugged/partly plugged.

(It sounds like the idle circuit/jet is OK)

The accelerator pump actually floods the eng. a bit to give it a "kick" to get going.

Click to expand...

Wow yeah thats a little beyond my comprehension level. Seems like it needs to go to a mechanic?????

Sorry..., didn't mean to "overstate." Some ford carbs. have an accelerator pump accessible from the outside of the carb. It's easy to replace.

Checking to see if it's squirting into the carb. is easy with air filter off & just moving the throttle by hand. (the throttle also activates the accelerator pump).

If the jet(s) are dirty..., that would req. internal carb. work.

Do let us know what you find...... >< <'>

Bully Bob said:

Sorry..., didn't mean to "overstate." Some ford carbs. have an accelerator pump accessible from the outside of the carb. It's easy to replace.

Checking to see if it's squirting into the carb. is easy with air filter off & just moving the throttle by hand. (the throttle also activates the accelerator pump).

If the jet(s) are dirty..., that would req. internal carb. work.

Do let us know what you find...... >< <'>

Click to expand...

The carb was actually just rebuilt...??

"(even paying my very well known mechanic to work on it) to get it running just right."

Even the best of us make mistakes. That I-6 is an "old school" very dependable engine. /

----assuming it's stock----

Maybe it is time for another opinion (mechanic). :-B

Good luck..

Bully Bob said:

"(even paying my very well known mechanic to work on it) to get it running just right."

Even the best of us make mistakes. That I-6 is an "old school" very dependable engine. //>

----assuming it's stock----

Maybe it is time for another opinion (mechanic). :-B/>

Good luck..

Click to expand...

Thanks for the help so far... Would it help to see pics to determine if its stock?

Bully, Im looking into keeping the 4.9l however do you have any experience with swapping the 1bbl carb over to a 4bbl carb using the offenhouser intake set up. Just curious if its worth it....

Where are we at this point..., is it run'n normal now..?

Also.., what's your goal..?

I'll assume you're look'n for "more power". What you're speaking of is more for a racing engine. Usually with more mods than just a carb. (like head work, cams, etc.)

But.., no, I don't have any exp. doing that to a 4.9 I-6. However.., you see I have a 1 brl. on my I-6 & it is every bit as fast as the V/8's I sold off.

Long/short.., a carb is just a mixing bowl to create a ratio of 17:1 (17 being air) air/fuel mixture. 17:1 (pretty sure it's 17.., I could be off a bit) being the optimum performance ratio for a gas eng.

Many times a larger carb will get less performance. Then there's the hassle of fitting linkage & air filters.

Your I-6 should have plenty of power if it's still somewhat fresh & in proper tune. Google its performance charts & go to a dyno shop for testing. Could save you lots of $$$$... $-)

No its not running normal yet. I have a guy going to look at it next week. May have to replace the just " rebuilt" carb just wasnt sure if that would be a good time to upgrade it or not. I have seen many guys post they are happy with the upgrade. But there are just as many that run the 1bbl and can get it running well too I guess. Im going to sell my daily driver soon and need the bronco to fill the gap ( I drive two miles to work so not a long drive ) So Im going to have to **** or get off the *** real soon. Im trying to reach out to a few guys and find someone thats familiar with the motor but have not found that guy yet.....

Well Im not the most patient person....And I like to tinker a bit even though I have no clue what Im doing at times. ( if its not a gun I dont know how to work on it ) I ventured out and pulled a few of the sparks plugs out ( I know I know remedial at best however It foreign to me) and whala one of the two I got to pull out ( bad storm moved in and had to stop ) would not have been firing. So I know I will be replacing the plugs and wires Sunday when I have time wheather permitting. What plugs and wires does this motor like. I have read where some guys get what they need out of the cheap and some who got the more expensive ones were not impressed with the performance. Thank you again for the help.

Good job..!!

Shame on me.., I assumed you already checked plugs. Plugs are a view into the "heartbeat" of any eng.

Rule of thumb with a strange eng. is to do the basics. Check fuel delivery, check ignition (spark), check the plugs/points/rotor/cap, (points if not elect. ignition), check air delivery, check battery strength (&/or charge it).

If the plug wires are bad.., & you intend on keeping the truck, get a good set of wires. Most auto parts have two or three grades of wires.

I'm using OEM silicone electronic supression wires. You don't need race quality.

Also you can test the OHMS on your wires..., if they test good, You can re-use them.

Im thinking after I do the plugs and wires I still have a clutch or carb problem given the driving issue. I dont think the plugs would be the cause of it stalling out on me. With that said Im completely stupid when it comes to this stuff....

When you get the plugs out.., keep a record as to which cylinder they came from.

You could take some pics of them laying side by side (un-cleaned) & showing the threaded ends.

And, a couple pics of the carb.

You'll be an "expert" when you get it runn'n proper. >< <'>

Bully we have confirmed the motor is shot. With that said I have my hands on a 302 that was built but never installed in any vehicle that dyno right at 350 hp . The question is one will the 302 bolt right to the trans that the 4.9 uses and secondly will changing the motor mounts be all we have to change out or will we have to move the posts in the frame as well? Thanks in advance for your help. Thanks

At this point, you're beyond my expertise as to a 4.9 I-6. I could only guess, if memory serves, that the trannie would bolt up.

I'm thinking the rear mounts would have to be moved but, the frame may already have extra holes.

It isn't just the (front) motor mounts per-se..., you have to cut the steel mounts off the frame.., then weld in the proper ones for the V/8. Again this assuming the V/8 is mounted different. Then the "replaceable" motor mounts go between the motor & mounts.

It's pretty important where the mounts are welded on..!!

Short answer is "YES"..., it's likely both front & rear attach points will have to be relocated.

Maybe someone will "chime in" with 4.9 I-6 to V/8 experience.

Then.., a rhetorical question would be; How'd they get a dyno reading W/O the eng. installed..?

Why would someone build such an eng., then sell it..?

Engines are engineered/built to match the veh. they're going in.

You may be better served, saving time-money-headaches, rebuilding the I-6.

What you're planning isn't really a novice project... /emoticons/[email protected] 2x" width="20" height="20" />