86 f150 300 I6 brake booster/vacuum problem
Thread Starter
|
Freshman User
Joined: Sep 2016
Posts: 27
Likes: 0
86 f150 300 I6 brake booster/vacuum problem
Today I discovered my brake booster was bad after noticing the brake pedal went to the floor when started and front brakes apply. After doing a little research I found out that the booster is also the reason the truck has idled rough since I bought it and recently the truck would crank but not start without starting fluid. In my research I found out to plug the line and truck will start. It did! And a good easy start and the idle smoothed out! After running a few minutes the idle went 2000 and won't come down and runs horrible. Of course I unplugged the vac line immediately but know I'm afraid something is really wrong. The choke does not seem to be springing closed like it should but it's brand new. I just rebuilt the carb and the engine really runs excellent when I don't try to experiment!!!!!!! Have not replaced the brake booster yet but im really worried about this high idle issue. Please help I need advice I'm kinda lost on this one. Thank you all in advance!!!!!!
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Welcome to the forum, 86f1504.9rookie!
You are describing several things [problems] which is hard to diagnose, but let's try to start... When the idle went to 2000 RPMs, was the brake booster vacuum line still plugged at this time? The choke not closing properly could be just being adjusted improperly. Do you have electricity to the choke heater? Do you have the hot air tube from the exhaust manifold to the choke housing?
By the way, the 1986 was originally computer controlled [ignition timing and carburetor]. Is yours still original? These engines "hate" vacuum leaks... have you checked places other than the brake booster for possible vacuum leaks?
Open this link and see if it helps: https://www.ford-trucks.com/forums/1...ent-101-a.html
You are describing several things [problems] which is hard to diagnose, but let's try to start... When the idle went to 2000 RPMs, was the brake booster vacuum line still plugged at this time? The choke not closing properly could be just being adjusted improperly. Do you have electricity to the choke heater? Do you have the hot air tube from the exhaust manifold to the choke housing?
By the way, the 1986 was originally computer controlled [ignition timing and carburetor]. Is yours still original? These engines "hate" vacuum leaks... have you checked places other than the brake booster for possible vacuum leaks?
Open this link and see if it helps: https://www.ford-trucks.com/forums/1...ent-101-a.html
Last edited by 1986F150six; Sep 29, 2016 at 01:16 PM. Reason: Added link.
Thread Starter
|
Freshman User
Joined: Sep 2016
Posts: 27
Likes: 0
Welcome to the forum, 86f1504.9rookie!
You are describing several things [problems] which is hard to diagnose, but let's try to start... When the idle went to 2000 RPMs, was the brake booster vacuum line still plugged at this time? The choke not closing properly could be just being adjusted improperly. Do you have electricity to the choke heater? Do you have the hot air tube from the exhaust manifold to the choke housing?
By the way, the 1986 was originally computer controlled [ignition timing and carburetor]. Is yours still original? These engines "hate" vacuum leaks... have you checked places other than the brake booster for possible vacuum leaks?
Open this link and see if it helps: https://www.ford-trucks.com/forums/1...ent-101-a.html
You are describing several things [problems] which is hard to diagnose, but let's try to start... When the idle went to 2000 RPMs, was the brake booster vacuum line still plugged at this time? The choke not closing properly could be just being adjusted improperly. Do you have electricity to the choke heater? Do you have the hot air tube from the exhaust manifold to the choke housing?
By the way, the 1986 was originally computer controlled [ignition timing and carburetor]. Is yours still original? These engines "hate" vacuum leaks... have you checked places other than the brake booster for possible vacuum leaks?
Open this link and see if it helps: https://www.ford-trucks.com/forums/1...ent-101-a.html
Thread Starter
|
Freshman User
Joined: Sep 2016
Posts: 27
Likes: 0
After playing a little bit today I discovered the carb mounting bolts were a little loose which will cause A LOT of problems!!!! The choke had backed off and had no spring action to the carb flap. Also it's kinda amazing how dirty the carb has gotten in six months which made it a little sticky. My big question I have right now is where to find the screws for the choke housing and is that gasket essential? The gasket is really making it difficult to adjust the choke and from what I read on another post the choke has to adjusted for the weather changes. I really love this truck and want to fix all the stupid things that were done to it from the kid before!!!!
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
Welcome to FTE, Rookie. 
As David mentioned, the original carburetor from the factory was connected to the computer, but what you describe makes me wonder if that carb is still there. Can you please post pictures of the carburetor from all angles, and one of the distributor, too? Thanks.
A speed shop or decent auto parts store should be able to help you with the screws.
As David mentioned, the original carburetor from the factory was connected to the computer, but what you describe makes me wonder if that carb is still there. Can you please post pictures of the carburetor from all angles, and one of the distributor, too? Thanks.
A speed shop or decent auto parts store should be able to help you with the screws.
Thread Starter
|
Freshman User
Joined: Sep 2016
Posts: 27
Likes: 0
Got some screws today! Where the air filter bolt to the carb stripped out a while back so that top piece is off but it's the regular Carter yfa 1 barrel. After checking at a better trusted parts store the choke is suppose to be an electronic one hooked to the computer as you both said. That choke is $68! Is it worth that much? or should I just keep the bimetallic one I have now. It does have the exhaust heat tube to the choke.
Thread Starter
|
Freshman User
Joined: Sep 2016
Posts: 27
Likes: 0
Trending Topics
Thread Starter
|
Freshman User
Joined: Sep 2016
Posts: 27
Likes: 0
Another question I have is if I replace the valve cover gasket will it solve that dirty oily head and the bolts to the valve cover stay wet with oil all the way around the rim. Or is that oil coming from somewhere else? I know it doesn't have a cracked head. I have heard oven cleaner is best for cleaning the motor up does anyone have an easy chemical they use?
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Before replacing the valve cover gasket, check the bolts for proper tightness. Often times, they vibrate loose and sometimes are just finger tight or less.
Any oil from the valve cover gasket drains downward and backward, as gravity and the fan do their job. And, it does make a mess as time goes by.
Any oil from the valve cover gasket drains downward and backward, as gravity and the fan do their job. And, it does make a mess as time goes by.
Thread Starter
|
Freshman User
Joined: Sep 2016
Posts: 27
Likes: 0
Valve cover bolts were loose quite a bit! Then I broke one off but it's the front one so should be easy to get out. I guess your not suppose to tighten them very much or my bolts are just getting old
Posting Guru
Joined: Jul 2015
Posts: 2,239
Likes: 5
From: Northeast Ohio USA
7 ft lbs (84 in lbs) on the Valve Cover Bolts is what a manual says.
Ford 4.9L-300ci-S6 Torque Specifications - TorkSpec - Knowledge for the Motorhead
Ford 4.9L-300ci-S6 Torque Specifications - TorkSpec - Knowledge for the Motorhead
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
You're over-tightening, they're not spec'd to be very tight, I think the spec is in INCH-lbs. Basically, just snug the things down, overtightening distorts the cover and creates a non-flat surface to meet up with the gasket (which you will need to repair, a ball peen hammer works well for that).
On the positive side, that's a feedback carburetor you have there and the distributor is also original, so at least that part hasn't been mucked with by a PO.
I don't recall the automatic choke wiring on one of these things but here's the EVTM from Gary's site and you can look up the wiring in there; if it was computer-controlled, I'd expect it to depicted under the Engine Controls section:
1986 EVTM - ???Gary's Garagemahal
On the positive side, that's a feedback carburetor you have there and the distributor is also original, so at least that part hasn't been mucked with by a PO.
I don't recall the automatic choke wiring on one of these things but here's the EVTM from Gary's site and you can look up the wiring in there; if it was computer-controlled, I'd expect it to depicted under the Engine Controls section:
1986 EVTM - ???Gary's Garagemahal
Thread Starter
|
Freshman User
Joined: Sep 2016
Posts: 27
Likes: 0
Oh boy!!! I can't get a drill into the hole for that front bolt I broke off. I'm going to find a long skinny drill bit or take the valve cover or thermostat housing off which I really didn't want to do right now.
Now I need some advice. I was taking the old brake booster off and it was easy and got all the nuts and clip off. But the brake line were so rusted they broke off. What's the most economical yet right way to replace the lines? Can I replace them with hard rubber lines or is that going to cause more problems. I can get the set of metals for around $155 but I don't have that money as I just gave $110 for the booster and master cylinder.
Your help and advice is always appreciated highly as I'm just a rookie with an old horribly rusty but trusty FORD!!!! Thank you all very much.
oh and I did find the plug for that electric choke. It's actually at the bottom of the one picture above!!!!
Now I need some advice. I was taking the old brake booster off and it was easy and got all the nuts and clip off. But the brake line were so rusted they broke off. What's the most economical yet right way to replace the lines? Can I replace them with hard rubber lines or is that going to cause more problems. I can get the set of metals for around $155 but I don't have that money as I just gave $110 for the booster and master cylinder.
Your help and advice is always appreciated highly as I'm just a rookie with an old horribly rusty but trusty FORD!!!! Thank you all very much.
oh and I did find the plug for that electric choke. It's actually at the bottom of the one picture above!!!!
Moderator
Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
Auto parts stores (at least halfway-decent ones) usually have that tubing in pre-cut lengths but make sure you get the correct ends, thread size matters a whole lot here. 
Coil up any excess length if needed upon installation.
Be sure to use the correct wrenches for this, Flare Nut wrenches are the term I seem to recall (and there are one or two other names for the same thing). Those fittings are soft metal and it's real easy to round off the corners using standard wrenches.
Coil up any excess length if needed upon installation.Be sure to use the correct wrenches for this, Flare Nut wrenches are the term I seem to recall (and there are one or two other names for the same thing). Those fittings are soft metal and it's real easy to round off the corners using standard wrenches.
Laughing Gas
Joined: Aug 2010
Posts: 983
Likes: 49
From: Northern Kentucky
I recommend the Nicopp lines as they are easier to work with than steel lines. Be careful bending them as they bend very easy: use a large radius bend rather than sharp bend. They cost a little more but are worth it because they wont rust out