I have a 1991 F150 4x4 5.0 EFI

I just recently purchased this truck, being my first "ford"

While under the hood (bolting the tranny back up) from the broken flywheel syndrom I noticed that almost all of the vacuum lines were unhooked and plugged, or melted.

Using the chilton and sticker under the hood i've got darn near everything hooked back up.. The only thing not hooked up is the "ACV" i think it's called an Air control valve.. but i'm not 100% positive.. it runs from the TaB selinoid & TaD selinoid (i know i can't spell em)

It runs like dog crap, until you get over about 2000 rpms.. Idles not too terrible, but since i got all the vac lines hooked up except the 2 that goto the ACV, it doesnt like to start the 1st try all the time..

The questions would be:

1. Where is the ACV located on the 91 5.0 F150
2. Would this not being hooked up to the Tab/Tad cause the truck to run this poorly.
3. Could it be something else? (any ideas)

Symptons:
1. Not starting very easily all the time
2. 7 mpg poor fuel mileage
3. Very bad hesitation between idle-2000 rpms above that range it runs just "ok" no real power though. You have to be super gentle with the pedal and virtually feather it to get it above 2k, and then your home free.
4. Lack of raw power (feels like a 4banger- yet it's a 302)

What i've done:
1. Air Filter
2. Plugs/Cap/Rotor
3. Flywheel
4. Tranny service incl. fr and rear seals and flush of fluids, and new filter.
5. Oil change & filter
6. Full Chasis Lube
7. New Battery 900cca
8. Vac line replacement (minus ACV) since i can't find it.

Any help is appreciated.. Thanx

~Pirg

 

one line from the tab or tad runs to over by the egr but down on the bottom of the cylinder looking thing behind the air pump that is an air bypass valve i believe? i'd have to go look at mine to tell ya for sure where the other runs too . i got rid of all the plastic hoses and replaced with real vacuum lines .

 

I'd really appreciate it..

According to the diagram, the yellow & pink lines run from the Tab & Tad to the ACV I'm not quite sure what it is, but heh..

The black runs from both the tad/tab to the black vac reserve..

I just have no clue where the "Acv" is.

I'm doing the plastic to real conversion as well.. being a 91' that I have all the plastic lines are super flimsy and crack / break too easy..

 

Sounds like the previous owner disabled a lot of the emissions stuff instead of replacing the broken parts. Now that you hooked everything back up right you need to fix whats broken to get it to run right.


TAB Is Thermactor Air Bypass, TAD is Thermactor Air Diverter, Thats an emissions thing that has to do with the AIR injection system. They control vacuum to the ACV (Air Control Valve) Which is hidden under the intake manifold I'm not sure if they will cause the problems you describe.

There is a vacuum motor controlled air duct somewhere in the air intake. A problem with that can cause Hesitation on acceleration, lack of power, bad gas milage (if stuck open), or even pinging. I wonder if the vacuum line to that is ok?

-Jon

 

Just checked my Ford manual a screwed up AIR injection system can cause backfire, surging, engine noise, bad fuel economy, exhaust smoke, or an unsteady idle depending on what component is bad, so that might account for part of your problem.

-Jon

 

I really appreciate the help F4.

So the ACV is located under the manifold.. No wonder i couldnt find it..

I can guarantee that none of the lines are hooked up to it, as they arent hooked into the tab & tad.

It does backfire a little, has horrid mileage, and sickening hesitation, not much in the pinging aspect, it may be very slight.

I'm not sure if they were intentionally disabled, because they were bad or not.. But the motor in it has a remanufactored sticker, so i'm thinking whoever put the motor IN it, didnt hook everything back together like it should have been. (and if they did) the lines that were from the tab/tad egr etc to the Vac Reserve can (Glorified Coffee Can), were melted.

I never thought about it, but i betcha gettin it all hooked up fixes the cruise control as well.. Since it wasnt working.. It is vac controlled right? 91 f150 5.0 4x4.

Also: I figure once i get everything hooked up properly, i'll get my code scanner back on it, after a nice clear and reboot. That "should" tell me if any of the pieces are bad/failing.

On the Vac Diagram it shows the Yellow & Pink from the TaB & TaD going to "ACV" and shows the ACV is connected to the Engine, and Cat (i assume thats cat converter).. I just couldnt seem to find the darn thing

Thanx again - I'll get under the intake tomorrow morning, and see if i can figure the darn thing out..

~Pirg

 

as i said . tha acv is in line on the large hose that is directly (cylinder looking)behind the air pump . the vacuum connection is on the underside of it . all of this is on the passenger side of the motor below the exhaust manifold . i got busy yesterday and forgot to look at where the other hose leads to (also hood was iced over) but i will look today and get back to you . the one i have described here would have been the pink (red) hose that was there originally . the other one was/is a yellow line(may have originally been green). both my maunals are at work also or i could tell you now where they go and it has been over a year since i replaced all the vacuum lines . you will also want to get a vacuum pump and test the TAB and TAD for leaks through them as one of mine was bad also and it caused some idle issues.
Good luck !