84 Bronco 3g alternator upgrade problem

[StraightSix]

Well, its been an eventful day or so. I was able to get the alternator installed and running! I did have to do some grinding on the mounting bracket. It reads a steady 14.38V from the battery ground post to the starter solenoid B+ terminal. It reads a steady 7.07V from the battery ground post to the electric choke plug from the stator. I did put in a size 4 ground wire from the back of the alternator to the battery ground post. Thanks for all of your help Gary!

 

Unfortunately the bronco is not running great now. The air/fuel induction system and the ignition system are either 100% stock, or close enough that my untrained eye doesn’t see anything glaring. It idled at about 1000 rpm before (which is probably a problem all its own). Now it chokes down to 200-300 rpm, then surges to 1000 rpm, and repeats over and over again. The cycle takes about 5 seconds. This is at idle with no throttle. It does this even after the engine warms up. If you give it some throttle it smooths out and runs at a steady rpm. Right now my theory is that I have cracked a vacuum line somewhere during the process of working on the alternator. Im open to any suggestions! This is the first carbureted engine Ive ever had other than a lawn mower so its all new to me. Maybe I should go buy a vacuum gage? Ill Be sure to read around about this issue here and on other forums, Im sure someone has run into it before.

 

Finally, I may have run into the ford 300 deal of a lifetime. A fellow on our local craigslist has been trying to part out an entire 96 F150 complete with an incomplete 300 6. The add has been up for a month or so. I messaged him yesterday about to exhaust manifolds and he told me that I had caught him as he was going out the door to sell the whole mess to the scrap yard! He said I could have the manifolds for free, along with anything else I wanted from the truck. Im headed over to see him this afternoon. This may be a better question for FordSix, but is the 96 long block or head useful for a carbureted build? I know that the chamber volume on the efi heads is a little smaller, and that the block doesn’t have a mounting location for the cam driven mechanical fuel pump. Is there anything else? I my bring the whole engine home.

 

I know I got a little off topic here, thanks for reading! If I don’t figure out the idle issue I may start another thread. Some time in the next few months Ill be starting a Motorcraft 2150 / OffenhauserC + Duraspark II + EFI exhaust / 2.5” exhaust to the back type of conversion on the bronco. Nearly all of the major components are already on my garage work bench. Ive seen where there have been a lot of great writeups on similar conversions in the past (one on FTE and many good write ups from AbandonedBronco on several sites) but many of these write ups seem to have been relieved of their photographs. Im hoping I can document it all here on the bullnose forum when the day comes for that job.

[Gary Lewis]

Glad the alternator works.  

On the surging, my experience is that a very lean condition causes that.  So you may well be right about the cracked hose.  Or maybe just a hose that has come off.

David/1986F150Six recommends "the smoke test" to find vacuum problems.  He blocked off the carb's inlet and blew through a large vacuum line, like maybe the brake booster one, after puffing on a cigar.  Very quickly smoke came out from a cracked vacuum line he couldn't see, and that was the problem.

On the deal, get everything you can!  I don't know about the head, but do know the intake and exhaust manifolds are sought after.

And on the writeup, one of the advantages of this forum software is that the pictures are part of the forum.  Many other forums just have links to the pics embedded in the post, so when you pull a post up your browser knows to go to the other site and get the pic.  But so many of those sites change, die, or require fees that the picture owner doesn't pay, so the pic is no longer available.  I know I ran into exactly that last night looking for info on behind-the-seat storage units - many of the pics are NLA.

I can understand why those sites do that as it keeps the size of the backup down, significantly.  But with the changes that Photobucket made a few years ago, and the probability that other sites will do the same, I like the way our software does it.  Basically, as long as the forum is here the pictures will be as well.  And I plan for the forum to be here for a long, long time.

[ArdWrknTrk]

.The surge is the classic sign of a bad MAP sensor, but I don't know if an '86 300 has one.

You might try disconnecting the computer from the carburetor, reconnecting it and then locking the timing.
At least this will tell you what system is causing the idle to hunt.

[1986F150Six]

ArdWrknTrk wrote

.The surge is the classic sign of a bad MAP sensor, but I don't know if an '86 300 has one.

You might try disconnecting the computer from the carburetor, reconnecting it and then locking the timing.
At least this will tell you what system is causing the idle to hunt.

Located on the inner fender by the battery.

[ArdWrknTrk]

Thank you David!  

And given the 3G install it seems a wire or hose may have been dislodged.
At least it's something to check?

[StraightSix]

Gary and Jim,

Those are both good starting points. It looks like I can get a MAP sensor for about 45 bucks . If it doesn’t run right after, I could just return it. Truth be told, since my plan has been to remove the majority of the factory induction and ignition system all along I haven’t taken as much time as I maybe should have to learn about the trucks factory sensors and their function. Ive mostly been reading about how to perform the carb and ignition changes I want.

 

If I try puffing a cigar I may turn green like something out of looney toons. Hmm, Who do I know that smokes? I guess just blowing and listening might help if it’s a really gross leak. And I can try some ether spray as well.

 

I may start by pulling off the carb. It was “rebuilt” by the previous owner and Ive always wondered if that had something to do with the really high idle. It has also bogged down and died on me twice. Both times were after long pulls up steep mountains for dozens of miles. One was at about 5000 ft in the Rockies and the other was at about 1800 ft in central Alabama. The Alabama break down occurred when it was about 95F, I sorta wonder if I didn’t vapor lock the carb that time. Im a little suspect that the carb my have something to do with all of that. Also, Im only getting 11 mpg which is surprising since I drive very gently.

 

The temptation is immense to just pull the factory intake, exhaust and ignition now and start putting on my other parts instead of troubleshooting the factory equipment. The catch is that I really want it all to be running reliably enough for a 500 mile round trip through the mountains with spotty cell service by 11/18. I just don’t know if I can make it all happen that fast. Im sure putting the “big pieces” together would take a few evenings at most but the little details could eat me alive.

 

Ill grab everything I can for sure, maybe even the whole engine. Its not clear at the moment if he wants to part with the truck or not. It’s a seemingly very clean 5 speed burgundy 1996. Its not really part of my financial plan but if he wants to let that go at a reasonable price I may have to snag it. It doesn’t have an engine at the moment but Im getting awful close to having 3 300-6 blocks in my garage. My girlfriend may be burying me in the yard in the wee hours of the morning.

 

[StraightSix]

And thank you as well David!

[1986F150Six]

StraightSix wrote

Gary and Jim,

Those are both good starting points. It looks like I can get a MAP sensor for about 45 bucks . If it doesn’t run right after, I could just return it. Truth be told, since my plan has been to remove the majority of the factory induction and ignition system all along I haven’t taken as much time as I maybe should have to learn about the trucks factory sensors and their function. Ive mostly been reading about how to perform the carb and ignition changes I want.

I have several used ones [supplied to me years ago by Jonathan/FordF834]. I will be glad to send them to you!

 

If I try puffing a cigar I may turn green like something out of looney toons. Hmm, Who do I know that smokes? I guess just blowing and listening might help if it’s a really gross leak. And I can try some ether spray as well.

https://www.ford-trucks.com/forums/1478167-vacuum-leak-detection-effective-and-inexpensive.html

 

I may start by pulling off the carb. It was “rebuilt” by the previous owner and Ive always wondered if that had something to do with the really high idle. It has also bogged down and died on me twice. Both times were after long pulls up steep mountains for dozens of miles. One was at about 5000 ft in the Rockies and the other was at about 1800 ft in central Alabama. The Alabama break down occurred when it was about 95F, I sorta wonder if I didn’t vapor lock the carb that time. Im a little suspect that the carb my have something to do with all of that. Also, Im only getting 11 mpg which is surprising since I drive very gently.


Read the introduction to this link [first two tanks = 9 & 11 mpg; sound familiar?]


https://www.ford-trucks.com/forums/1325963-gas-mileage-recipe-4-9l-300-a.html

[StraightSix]

Wow! Thanks! That is an incredibly generous offer. Let me take a look at everything when I get home. If it seems like I may need a MAP Ill let you know! I could even return it after I do my intake and carb etc.

And now I have some good reading to do as well! Thanks David!

[StraightSix]

Woah. That guys 84 300 with the vac leak sounds exactly like my situation

[1986F150Six]

A high idle is often caused by a vacuum leak. Look on the intake manifold in the area under the carburetor. There is a vacuum "tree" which has 6 or 7 ports, to which are attached several vacuum hoses. Not all ports are used as it depends on options. This area is covered with numerous vacuum lines [hoses and plastic] as well as wiring. One of the ports is angled toward the cab and is nearest the engine block and exhaust manifold [high heat]. This port is difficult to see and when spraying with carb cleaner, looking for vacuum leaks, is easy to miss. The rubber cap gets hard and brittle with age and cracks, creating what can be a large vacuum leak.

I found this condition on two trucks, both with what appeared to be original caps [1984 and 1986 with 4.9L engines].

[StraightSix]

Ok- I found two problems I believe. One was a vac hose coming off of the carb right at the throttle plate on the passenger side. It wasnt hoing anywhere, but I found a bent metal tube that goes from under the carb town to below the exhaust manifold that was the right distance so I hooked it up. My surge is gone but Im not convinced that hose is what fixed it. I also found an open port on the vacuum distribution tree you all told be about. It was indeed drawing a lot of air. The engine sounds different after plugging it but still idles at 1100. So Im headed to the gas station to do something I never thought I would do- buy a swisher sweet.

[StraightSix]

The "smoke test" showed me a leak around the bowl of my carberator on the front side between the main housing and the "lid". There was also a minor fuel leak there. I tightened down the few bolts there (they were barely finger tight), and my idle dropped from 1100ish to 1000ish. But I just saw a fuel drop drip from that spot. I guess that the fuel drip means that spot isnt sealed up. Maybe it got a little better when I tightened the screws. Is it likely that the vac loss through that spot would cause my high idle? Now I need to figure out what to do. I really dont want to spend a lot of time on this carb since its all coming out in about 35 days anyways for that upgrade but I dont think its wise to drive around with a fuel leak right over the exhaust manifold. Drats.  Im sure you can buy the carter 1bbl rebuild gasket kits at any decent parts store. With nothing else showing up on the "smoke test" Im sorta at a hault. As always, thanks for any advice.

Btw, I did get those free exh manifolds! The fellow was in a big hurry and didnt have time to talk about the rest but I srill think it was a really good deal.

[Gary Lewis]

If you have a drip from the carb between the body and the top then the float level is way too high.  WAY too high.  It really shouldn't leak there, but the fuel level should never be that high.

[ArdWrknTrk]

Ill add that vacuum leak above the throttle butterfly can not increase idle speed.
It would have to be at the base of the carb or somewhere on the intake manifold.

[StraightSix]

Thanks guys. I already talked myself into the rebuild kit for the carb and Ive picked ut up and just got back home. Sounds like I srill have a vac leak after that though.

[StraightSix]

Well, Ive got the "top" off of the carb and everything seems ok. The float/needle assembly looks fine, the old gasket was showing signs of a good seal all around and the fuel level in the bowl is about 3cm below the rim. Its seems pretty clean too. Im at a bit of a loss for where the air and fuel were coming from. Perhaps the air was leaking through the loose "lid" and the fuel was actually coming from the fuel filter that threads in right there?

[ArdWrknTrk]

One thing that's not at all uncommon with these carburetors is that the body comes loose from the base because vibration causes the screws to back out.

It's recommended to apply blue Loctite on the screws before putting it back together.

[StraightSix]

The fuel leak culprit!


The fuel has been leaking through the crimp on this two piece fuel filter. I can only assume that some air may have been escaping from the fuel bowl and that tightening the screws did solve it. Either way, everything but the fuel filter is put back together now and seems to be holding. Still idling around 1000rpm. Presumably I still have a vac leak somewhere.

[Gary Lewis]

I frequently liken these truck to onions.  We peel the problems, layer by layer, and cry.  But eventually we have enough onion rings for a Blooming Onion!  

So, one problem down and more to go.  Yep, you probably have a vacuum leak causing the fast idle.