I have a 1985 F150 SuperCab 8ft Bed 302efi with AOD trans 2WD

I am at work while posting this so I do not have access to the truck or the Haynes manual.

After fixing some obvious problems with the truck to get it road worthy before I put it on the road, my father in law and I believe there may be a rather large vacuum leak. While idleing the truck as a very loud squeel/sucking sound in the engine compartment. While reading a couple of other posts about vacuum problems I discovered that the vacuum adapter on the firewall next to heater blower should be in use. Nothing is plugged into this adapter and I do not see any obvious vacuum hoses laying anywhere unplugged.

The previous owner so far does not have a very good track history of fixing relatively simple problems on the truck.

My 2 Questions hopefully are simple:

1. What should be plugged into this vacuum tree on the firewall

2. With the efi, could a vacuum leak cause a hard start when the engine is hot

PS. The truck does have all of the polution controls still physically attached.

Mike

 

I had a similar problem with my 86 F250 460/C6 truck...

Truck ran great then one day it had the problem you're describing.

What I found was a vacuum tree at the back of the engine, had a
port with nothing connected to it. I looked all over but couldn't find
a vacuum line anywhere that might have been connected to that port.

All I could figure was there was a cap on that port that had deteriorated
and fallen off, creating the vacuum leak.

Replaced the cap and all was well again.

If I remember correctly, the vacuum tree that you're asking about has
three ports on it, one for the source, one for the modulator on an auto
tranny, and one for the vacuum reservoir (the little ball looking thingy on
the fenderwell ).

At least that's the way it is on my carbed 86 460/C6

Scott

 

Thanks,

At the moment nothing is hooked up to it at all. The tree is as you described it. I guess I'll have to go fishing, hopefully my manual has good details and schematics. Good to know it may affect the tranny as I haven't driven it very far on the road yet and it would suck to find out when driving to work lol.

Mike

 

On my truck, there is a vacuum tree at the very back of the engine top side,
this is where I found the missing vacuum cap.

Then there is the vacuum tree or "log" that is on the firewall. The "log", I
believe, is feed by the above mentioned tree on the engine.

If the "log" isn't connected, there might not be anything connected to the
vacuum tree at the back of the engine either.

That's where I would start!

Scott

 

Thanks again Scott,

The back top of the engine seems to be where the sound is coming from so that would make sense. I will definitely take a look when I'm at home and will let you know what I find or don't find lol.

Mike

 

Sorry Scott,

I never got a chance to take a detailed look at my truck and my haynes manual doesn't have a routing diagram for the vacuum components, I will see if I can get the Chiltons manual from my brother in law.

Mike

 

There should be a decal under the hood with vac routing, unless it has been removed or painted over.

 

Does the sound get louder with rpms? Kinda sounds like a problem I had on an '84. It wasn't a vaccum leak though. The two small pipes that connected the exaust manifolds over the back of the bellhousing had rusted out, creating a whistling sound like you described. I'm not sure what they are called but I think they are part of the emmisions system. We don't have inspections, so I just crimped the thing shut and the noise went away.

 

Hello Everyone,
Sorry for the late reply but a lot of stuff going on lately. I put the truck on the road even though I could not find the vacuum leak. I think it may be the intake leaking after reading over some of the past posts and checking all of my vacuum lines.

When I put it on the road, I discovered that it likes to stall when coming to a stop or while going in reverse at low rpms. This is still mostely likely cause by the vacuum leak right? The plugs, cap and rotor are relatively new and the plugs themselve look mint. I did check gap so I was thinking its possibly a timing issue. While looking over the truck I did find hose coming from the intake right behind the butterflies that was plugged and not connected to anything. After checking over a parts truck we discovered it was for the gas tank. Oddly after repairing this, the restarts on the truck are MUCH easier than before. It would start after several seconds perviously and very slowly but now it will start right back up. Im not exactly sure what this line does but does this improvement make sense?

Also since I have to take the intake off would it make sense to inspect/change the timing chain? Is it that much more work, or should I wait until I have done the intake?

 

While, I put it off as long as possible but I started to remove the throttle body from the intake, and lo and behold 5 of the 6 bolts that hold the throttle body to the intake were tight, and the center torx bolt was about a quarter inch up and apparently cross threaded and stripped...........

So, nothing will get the bolt out as it is all but completely rounded out, and I don't have a drill bit that long so off to Sears tomorrow. After seeing how the carrier bearing had been "fixed" before I guess this shouldn't surprise me. Lucky, if the manifold itselfs is screwed up I do have an 86 parts truck.

Thanks again for the help

Michael

 

You can use a helicoil insert instead of making it bigger on that stripped bolt. I can tell you all a sure fire way to find a vacuum leak, if you dare. With the engine running, slowly pour transmission fluid into the intake, if you can get it there, and smoke will appear at the leak, exhaust side. Intake side, use starting fluid, just a little bit, spray around suspected site and if it's leaking, your rpm's will increase.

Hope it helps

 

Thanks for the info, but when I cleaned the area around the stripped bolt, I found three cracks around the perimeter of the bolt the go all they way through to the outside. Luckily I bought one on ebay for 38.00 after shipping so I don't have to strip my running parts motor yet. (saving it in case this one is completely shot, that truck is an 86 f250 302 with a bad tranny)

Mike

 

i thought my haynes book showed a schematic for vacuum but, i couldn't find it. anyway, i have an 86 f250 4x4 302cu in. there is a schematic on the panel just in from of the radiator. it gives emmisions data, firing order, etc.

maybe yours does also, good luck.