1984 Bronco build thread

Hi Guys!

Sorry its been so long. Family health issues, work stuff, and life outside the four walls of my garage have kept me busy.

Here is where it sits - No additional tuning changes. it seems to run fine on 87, though Id be tempted to top it off with high grade if I was going to tow a trailer with it. Im running 14 degrees of base timing. Cruising AFR floats from 13.8-15 depending on load and moon phase, but spends almost all of the time between 14-14.5. Idle vacuum is still about 16inhg on my faulty gage which correlates to about 20 in reality. It no longer goes lean in 4rth (as in leaner than stoich at WOT) but I wouldn't mind it being a little richer under that specific condition. it will get down to 13-13.5 but it may take it a minute to trend that way.

the engine now has about 1300 miles on it. I replaced my thermostat gasket and I am not losing water any more.

 I drove it up to the mountains a few weekends ago for an off road fishing trip, one expression of the vehicles ultimate purpose. It did great on the highway, I think all of the head work and oversized valves really helped with accelerating from 65mph (2600rpm) to about 75 rpm. I consider that to be a major safety upgrade for the purpose of defensive driving, even though I seldom drive the vehicle that fast unless Im trying to avoid getting smacked by a honda. Off the pavement, the bronco is great. It will power up any hill in 2nd and its happy to pull hard and sling gravel in 3rd so long as you keep it above about 1000 rpm. because of how Im geared the 10-15 mph gravel road sweet spot straddles 2nd and 3rd so I end up shifting a lot but thats not the engines fault. If anything, the generous wide useable torque band 1000-3000 rpm helps compensate for my wide gears. Skinny 33" tires may be coming next time I need new tires, that may help a slight bit.

the bronco made 14.6 mpg on the way home, a drive consisting of about 80% interstate miles at 65-70 and the rest local highway driving at around 55. this is the same drive where I made 15.9 mpg a little over a year ago. I think the engine was probably running really lean back then though, I upsized about 6 jet sizes once I got the AFR running. While I would love for it to make better fuel economy, thats hard to complain about for a carbureted 4x4. I think it made closer to 10 mpg on the gravel. Perhaps there is still a little bit of tuning work that can aide in fuel economy. Also, the transmission and Tcase were rebuilt at the same time as the engine. the rear axle is fully rebuilt only 600 miles before that, so all of the bearings may still be tight? who knows. it might get better, but I wont be heart broken if it doesnt.

 I think Ill rebuild my carb next time the forecast goes to rain for a week. I doubt it can hurt, and it will make me more confident in my tuning work. A new vacuum gage is in the works, but I need to be mindful of how much cash this vehicle has sucked down. there are other more pressing things like side view mirrors that dont point right or a filler neck/cap that leaks gas when you park on a grade. it feels good to be back in a spot where I can make gradual improvements to the vehicle as I have time and cash, without having to leave it disabled long term.

I ordered some new type 9 mirrors from JBG, Ill report back on their quality and function once I have a chance to install them. For this week, life is all about my girlfriends final exams this week, work, and prepping for a 5 day backpacking trip in the prettiest place this side of the Mississippi, great smokey mountain national park.

It is awesome that you have it running so well.  And that MPG is nothing to be sorry about.  But, if you are running at 14.0 - 14.5 most of the time you can gain a little bit by leaning it to 14.5 - 15.0.  The reading I've done says that max MPG is at 15.6 but that there's not much difference between 15.0 and 15.6, so the high 14's are good.

But if you are running 13-13.5 at WOT you are leaving torque on the table.  Best torque is at 12.6 and it won't hurt to be a little lower than that.  So I think if you got the carb to provide more fuel when getting into it you might find that it pulls a bit better at 1000 RPM.  And that may help with the 2nd/3rd shifting.

And these things can be some of those "gradual improvements".  

Thanks Gary!

In 2nd/3rd @WOT it quickly gets on down to 12-12.5 afr. However, at ~2000 rpm, 4rth gear, WOT, It often floats around 14.-14.5 and then gradually makes its way down to 12.5-13.5. that may take a few seconds? its not great, because that's generally what happens when I shift into 4rth while accelerating to highway speed. Im kinda hoping that a rebuild might help some, but I dont have any good reason to think that would be true beyond hoping. as for leaning out the main jets, Im open to it for sure but Id want to wait and get a better idea of how the engine runs. As overplayed as this statement is, Id rather waste some fuel than damage my engine or shorten its working life. once Im positive I know whats going on, I may try shifting down a jet size or two. Id rather fix the 4rth gear bog 1st. it has occurred to me that I may be up against the tuneability limitations of my beloved 2150. If so, that's fine. I wanted a simple carb and I have one.

Side view mirrors -
my JBG type 9 mirrors came in, and frankly it was really disappointing. They seem to be equivalent to the absolute junkiest mirrors on amazon. The housings are plastic instead of metal, the boomerang shaped bar and brackets don't fit up to the bronco and the part they sold me as a "passenger side" mirror is identical to the driver side meaning non concave. At $100+ shipped I wasnt really too pleased especially considering that products of similar construction and quality can be had on amazon for about half as much. Fortunately, the rep at Jeffs agreed to refund the parts. Unfortunately, they did not agree to refund the shipping or return shipping even though the parts dont fit, and the passenger side mirror, in my opinion, does not meet that qualification. Not to mention the obvious cost/quality issue. So thats the end of that. I hate to complain, but I feel defrauded and dont want that to happen to you guys.

At this point, my plan is to either repair or rig the mirrors I have which appear to be aftermarket themselves. The easiest option would be to epoxy them in place. I suppose that there is probably an epoxy that could be removed later down the line chemically, or with heat?

I know that the general consensus is that these are "non reparable" but has anyone had any success with tightening up that ball joint so the mirrors dont flop down in the wind?

Another option might be to hunt down originals in the JY.

You might consider wicking in some Loctite.
That tightened up my mirror heads enough that they would not budge from wind or slamming the door but still allowed me to move the head around (with two hands)

If you really wanted to glue them in place I'd think cyanoacrylate (Crazy Glue) would be better than epoxy.
Acetone or MEK seems to dissolve it.

Thanks Jim! I hadnt thought about Loctite. any ideas on which loctite would be best? regular red or blue? I just read something on another site about using spray glue in a similar way. I have also come across people dimpling the balls with spring loaded punches or electric engraving tools.  

Loctite offers a green formula meant to wick into already assembled fasteners. (this is different from the green bearing retainer)
But if your mirror socket is super loose I would imagine red or blue would seep in there if you set it up so gravity is on your side and you swiveled it around to work it in

I didn't realize you could swing the mirror enough to dimple the ball in order to tighten the fit.
I have done that with spun bearing pockets but always used an anerobic in conjunction with punch marks.

I need to go see what these type mirrors look like.

I think Jim is right about Loctite.  Some blue should work well.

As for the AFR, you aren't far enough off on cruise to worry about, but that 4th gear WOT is pretty lean.  I'm not sure why it wouldn't go rich in 4th like it does in the other gears since I would have thought it is predicated on vacuum and not air flow.  And I would expect the vacuum to go low even at lower R's.

Do you have a vacuum gauge on it while driving?  It would be interesting to know how low the vacuum goes at different RPM/throttle combinations.

Ill try the loctite trick. if it doesnt work, Im out nothing.

I have a vacuum gage permanently installed but its not very accurate. I checked it against a fluke vacuum pump/meter and its really pretty dismal. At 20 inhg on the fluke, my gage reads 16 inhg. I dont have any other points, so Im not sure if that relationship tracks linearly down to zero. An upgrade to a more accurate (and backlit) gage is in the works.

when I had my shop vacuum gage (very accurate according to the fluke) zip tied across the hood I observed that it was very easy to achieve vacuum readings in the 0-2 inhg range in 3rd and 4rth.

I think you can use the gauge you have to do the tuning since you know that 16 is actually 20".  You really don't need all that much accuracy for vacuum, just repeatability.

So I'd be trying to figure out why your AFR goes down into the 12's for the lower gears but not in 4th.  And the question would be if there's a difference in vacuum for the gears.

in my thinking anyway. the greater the load the lower the vacuum will be leaving air flow to do the work of drawing fuel. velocity through the venturi being the mechanism. that would explain the difference in higher gears at least until the vacuum dropped enough to work the power valve.

On the mirror I got mine from LMC and think they fit the holes I had in the doors pretty good.
I did get the right side glass like the left side so I know what is next to me IS NEXT TO ME!

When I first installed them the ball was loose. Each mirror has 3 screws and I was able to tighten them up but lately the left side has been moving so I took up on the screws more.
If they need more then I will need to move the mirror head to get the screw driver on the screws.
I cant even get a 90* driver on 1 of the screws so hope it is tight.

If running a 2150 carb I take it not on a factory log intake do you think the intake could have something to do with the AFR in 4th?
I also wonder if you are more into the throttle in 4th and when you go WOT the accl. pump is in the middle of the stroke and cant pump more than in the lower gears?

When you WOT in 4th and it goes lean does it also bog?

I am running the factory carb & intake and in OD on the high way (65 - 70MPH) if I WOT IIRC mine will show it lean then rich. I dont have a bog or anything so I dont really worry about it but I am still working on my timing and then leaning out the carb as I feel it is to rich at mid 13's to mid 14's.
I would like to get AFR to mid 14's mid 15's and maybe get MPG up some from 15 - mid 15's to high 15's to mid 16's MPG.
Dave ----

Hi Guys!

Sorry about another long break. I accepted a new job on the far side of the state (in Cartersville Ga). The last month has been really wild. We have moved out of our house. My family and I renovated the house, put it on the market Friday, and it will be under contract today! We are waiting for the market to cool down before buying , or at least we will wait for our resolve to break. In the mean time most of our things (most of my tools) are stored away and we are living with family in the north Ga mountains. Its going to be a hectic and adventurous time, but also a good opportunity to spend time with family and enjoy having nothing to work on..

Gotcha! There will always be something to work on.

The bronco didnt get stored. currently, it gets to live at my grandparents house when Im not driving it. Just like clock work I have two new issues.

I have been chasing a minor coolant leak ever since the rebuilt engine went in. I finally found a tiny trickle of a leak under the thermostat housing. I redid the thermostat gasket using studs instead of bolts, and its sealed up tight. I thought I had the coolant issue solved until I took her for a spin the other night, then walked by a few ours later. out of habit, I took a look under the engine bay (you know what they say about fords) only to find a small puddle of coolant directly under the bell housing. I cant find any coolant on top, head gasket appears dry, thermostat looks dry, no dry coolant runs. At this point, I think it may be the rear block freeze plug. my first plan is to try to get my hands on a coolant system pressure tester (what is that things real name? Im sure you guys know what I mean). If it shows that the plug is the source of the leak, I guess Ill pull the transmission out, tip the nose of the engine up, and try to do the job under the truck. does anyone know if you can get to that rear freeze plug from underneath, or do you have to pull the engine?

it doesnt seem to be losing much. From cold start in Carrolton Ga, a 100 mile drive to Jasper Ga, and then allowing it to cool, the overflow reservoir lost a little more than 3/8" level, maybe half a cup worth of coolant? In any case, I need to plan a repair sooner than later.


on to the second issue -
My fuel system is just generally in rough shape. My gas tank is probably original. my filler leaks gasoline on the ground if you park the bronco on an incline with a full tank. finally, I think I experienced some vapor lock issues yesterday driving in light traffic at about 90F. we had driven about an hour then got into some slower traffic. all of a sudden while moving about 35 mph the engine began to buck and stutter and the afr flashed 20 for about half a second. I gave the pedal a firm push and the whole situation righted itself for about 10 seconds. then it did it all again. I got off the road and had a look, the inline fuel filter was about half empty. after a moment to idle we got back on the road and it gave us no more trouble. on the drive home later last night at closer to 70F we had no issues at all.

currently, Im using a carter block mounted mechanical fuel pump to feed my 2150. I have run all new 5/16 (?) black fuel hose from the tank to the carb. I have a 25 gallon tank.

what I think I want to do is install a new plastic 33 gallon tank with an in tank pump capable of supporting fuel injection down the road. I would then use a return style regulator to regulate down to 5-7 psi in the engine bay and recirculate the rest of the fuel back to the gas tank to help keep things cool.

in my mind, it seems really tempting to do this all with a factory style setup for a 90s EFI bronco with 33 gallon tank and in tank fuel pump, but with a plastic tank instead of steel.

has any one done this? Can I regulate down from ~60 PSI from a factory in tank pump to ~5 PSI?  I know that the EFI sender is not compatible with the bullnose fuel gage in the dash. I know there is a special fuel system for the 85 EFI 302 that I might should pay more attention to. Is this a case where it might be better in the long run to go the aftermarket route instead of using factory style systems?

Im open to suggestions, or success/difficulty stories.

ofcourse carb tuning is ongoing.

to expand a little on my current tuning situation - I havent made any changes since my last update here. Im now cruising on flat ground around 13.5-14 AFR. Im guessing that is just summer time weather and hotter intake temps. I plan to jet a few sizes leaner and see what happens to cruising afr. Ill target 14.5 or so. in the mean time, I havent been experiencing "lean out" in 4rth like before, but I suspect rejetting to fix my cruising afr will bring the 4rth gear lean out back to the front of the list of problems. I need to read and learn more about how my main metering system works, and if there is any adjustability I can take advantage of the make the mix richer when the throttle is more open. if more tuning work doesnt allow me to have good cruising afr and good WOT in 4rth, Ill try a full carb rebuild. if that doesnt work, Ill consider going to a 4 barrel with more tunability. Maybe even EFI if a gold brick falls out of the sky and hits me in the head.

yes, you are onto something with the in-tank pump idea. I am doing this regularly with builds and it is exactly how i have my bronco 2. i purchased a new tank and sending unit/ fuel pump for the earliest efi with the primary pump in tank and the high pressure on the rail. i only use the in tank portion and run lines to the filter, carb and return. im running a holley 600cfm on a 306ci small block.

Matt,
Ive thought a good bit about if I should go with a low pressure lift pump in the tank then add a high pressure pump on the frame later if I go to EFI. As I understand it, this is roughly how the 86 302 EFI fuel system worked. I think at this point Im leaning more towards using the later EFI fuel pump set up with a single high pressure pump in the fuel tank. The parts should be a lot more common and easier to find in the future, and only one pump to fail. If and when I upgrade to EFI in the future the single pump in the tank seems to be the better option.

that leaves me with just a few questions.
-does anyone know if the after market 33 gal bronco tanks for EFI are internally baffled?
-does anyone have experience regulating  60 psi in tank pump down to 5-7 psi for a carb? Im guessing that I will probably need two regulators. one return style regulator to get from ~60 psi down to 5-10psi, then a deadhead style regulator to more finely control pressure at the bowl. of course, this will require running new fuel lines.
-has anyone solved the efi fuel sender -> bullnose fuel gage issue yet? I read some discussion about using an arduino to "translate" that signal.

I don't think there are any baffles. I have not seen one yet with baffles. I do prefer the pumps with reservoir when possible. we just installed a 38 in an f250 last month. that one had no baffles either but it was an aftermarket tank .

I have experience using the later Fuel Delivery Modules, which is what Ford called the in-tank pump/return valve/fuel level sender, on a carb.  My first attempt to regulate the high pressure down to ~5 psi was with a return-style regulator and it didn't work well as I had rapidly spiking pressure.  I then added a dead-head style regulator after the return style and that worked perfectly.

As for the baffling, I have a 38 gallon Bronco steel tank and it doesn't have any baffling at all.  I didn't use it as it is for the Bullnose pump/sending units and the slots in the opening that take the "key" in the sending units is in a different place for Bullnose vs FDMs.

And the FDM's sending unit can be made to work with the Bullnose gauge with a MeterMatch.

Hi Guys!

Sorry,

This has turned into a really wild year. Between moving jobs, moving houses, and everything else. We have finally bought a new house, and we are mostly moved in. the last few weeks have been spent moving, painting, and installing flooring. Over the next few months Ill be doing more flooring, installing a wood burning stove for the winter, moving some walls around, and much more. On the bright side, the new place has a big workshop out back! I may not get to work on the bronco much until early 2023, but I couldn’t be more excited about the whole thing. I finally have most of my tools back. Its great to lay your head down in the same place every night.

Since my last update, I have pulled off the MC2150 and replaced it with a holley 390. While I think the 2150 is a great carb (simple cheap, good fuel economy), I was running into seemingly untunable issues. The 390 needed a few jet sizes on the primaries to keep cruise in the 14.5:1 range, and I swapped up to an 8.5 power valve. I also installed a rear metering block conversion kit to let me play with the rear jets. Otherwise, the carb has been working great! Cold starts are strong with the electric choke (running off of the 7v stator output with no issues). Fuel economy is about the same. Throttle response and drivability at lower engine speeds (below 1500rpm) is MUCH better with the relatively small front barrels. 0 to interstate merge speed time is significantly better as well. Soon, Ill begin playing with secondary springs to see if there is any drivability improvement hiding there.

The carb runs very rich, around 11:1 at WOT after the power valve opens. I may pick up a second primary metering block and experiment with modifying it to accept replaceable power valve circuit restrictors made from small allen head set screws.

As a matter of interest, I have found drivability to be much better with the carb tuned for leanest operation around 14.5:1 as opposed to leaner settings. There is very little flat ground around here and running a bit richer helps pull up long grades. On flatter ground Im sure Id favor leaner jets as well as a numerically lower power valve.

Fuel system upgrades are still on the docket, along with an electric fan conversion and gutting out the cab to blast and paint the pan. Now that Im pretty sure Im staying carb’d long term with the 390, my fuel system upgrades can be a bit more carb/low pressure focused.

Im still on the hunt for a vacuum motor for my factory style air cleaner. I did buy an in the box XC-120 from ebay, but the part that came out of the box was not an XC-120. On the bright side, the seller did allow me to return the part. For now, I just pay attention to the AFR and will plan to make jet swaps 3-4 times a year to keep things in range. Im still hoping to find the vacuum motor, I think I have everything else needed to make it work.

Im also on the lookout for a new gas tank cap. The rubber gasket on mine has rotted out completely and sharp turns with a full tank can result in spills. I don’t want to get another locking type gas cap, Im hoping to find a regular spin on. The applications are a bit confusing and I cant seem to lay my hands on one in person. I guess I have to buy and try.

Anyhow, its coming along slowly but surely! Thanks for reading, I hope everyone’s projects are coming along nicely.

 

StraightSix wrote

Im also on the lookout for a new gas tank cap. The rubber gasket on mine has rotted out completely and sharp turns with a full tank can result in spills. I don’t want to get another locking type gas cap, Im hoping to find a regular spin on.

Hi, about the gas cap, I bought two new ones (regular and keyed).
Here are the models (on the picture you see the old regular one, but the new is identical).
These two fit perfectly.

I'm in the same boat as Jeff - I have one keyed and one that isn't keyed.  But I never lock the keyed one so it works just the same as its non-keyed brother.