I have a 96 F-250 with auto tranny and 460v8.

A couple of weeks ago....I noticed a slight pinging.....

I asked my mechanic about it.....his first thought was cheap gas.

Then a couple of days later I put some Sea Foam through the gas tank.

Did not make any improvement.

Again some days later....driving home.....it began to "surge"....I had to
hold it back from hitting the next car at stop lights.

I immediately took it to my mechanic....he said to next look for a vacuum
leak. I found a 1/8" vacuum line off. It comes off a "T" on the main
vacuum line behind the engine, near the firewall. I looked for 1/2 hour
for a connection point. Could not find one. Took it to the mechanic...
he looked for 20 minutes and could not find one. I then took it to the
Ford garage.....they could not find one....what the heck? I have looked
at diagrams online...in books....and none show this vacuum line.
I put a screw in it for now....but that did not help the surging.
In fact...each day it has got worse.... I changed the fuel filter....
The diagnostic showed the passenger bank O2 sensor to be bad (but
some vacuum problems can mask that).
The "check engine" light started coming on.....and it is difficult to even
keep it running now.

I even cleaned the throttle body with gumout.....put fuel injector cleaner
through the gas......it runs no better...

I was wondering if my putting the seafoam in the tank had consequences?

Does this mysterious vacuum line have anything to do with it?

Or can anyone pinpoint my problem? The truck is almost not driveable now.
It runs that badly. Idle or at highway speed.....terrible.

I hope someone can give me a clue. So far I have been replacing those
few components and not getting any results.

Thank you in advance.

 

Have a pic of said line and general area?

 

Pull the codes again, and tell us the exact codes you're getting. Saying the "O2 was bad" is not descriptive enough.

Can you get a picture of this vacuum hose?

 

Hope this helps
| Repair Guides | Vacuum Diagrams | Vacuum Diagrams | AutoZone.com

 

Thanks for responding folks.

I don't have the codes....the mechanic would have to run the
diagnostic again. (and charge me) (OBD1).

Specifically he told me the code indicated it was the passenger side
O2 sensor. But he said a bad vacuum situation could cause the O2
sensor to show code failure.

I will try to get a picture here soon. After the rain stops.

Thanks for the reference to Autozone diagrams....been there....nothing.

The mechanic also speculated that this mysterious vacuum line could
be a former owner adding an accessory. However....he said it looked
like it was factory done. (not amateurish).

 

You can get the codes yourself.
Just ground the STI wire and get behind the wheel with paper and pin.
Turn on the key and count the flashes the MIL makes.

For information on getting codes go to this link:
Fuel Injection Technical Library » How To Run a Self-Test

The line off the "T" should go to the canister purge solenoid.


/

 

There is really no code that says O2 sensor failure. The code would say something like Circuit Short to Ground, Short to B+, Open Circuit, Rich, Lean, No switching detected, etc..

You don't need to pay your mechanic to pull the codes. The only thing you need is a paper clip, a piece of paper, a pencil and your eyes.
Fuel Injection Technical Library » How To Run a Self-Test
Your diagnostic connector is on the drivers side fender, and it will have 3-digit codes.

edit: Looks like subford beat me to it!

 

Don't rule out the possibility of a failing "computer".

Read this.....click here:A9x ECM's (and same years ECM's) Failures Due to Age


It might be worth investing a little time to see if your "computer" is headed south.

A failing "computer" may or may not store ANY trouble codes.

It COULD explain the progression to "not driveable now" you're having.

Just something for you to check.

Bob

 

Here are the pictures folks, of the mystery vacuum line.

One is a photo of the engine itself. You can see the "T" highlighted
with red. You can see the vacuum line from the "T" stretched up toward the camera.
The 1/8" rubber vacuum line is about 18" long.



The second photo is an illustration obtained from the Ford Garage.
I drew in the missing "T" and vacuum line from their illustration.



I am still concerned about that seafoam. When I have used it in the past
on my garden tractors? If the gas tank, or any parts of the engine were
dirty? It would throw all that dirt and crap downstream. I usually had to
clean the plugs and float bowl of the carburator.
I was wondering.....if that engine/fuel system did have dirt built up.....
Would it end up downstream in the fuel injectors themselves?
I think that would make an engine run badly....and surge.....wouldn't it?

 

I think it was from the PO's intstallation of a "driveability vacuum guage" installed under the dash or on the drivers pillar.
Are there any mounting holes in either of those places ???

It appears to have been installed on the vacuum line going to the MAP sensor....ie why the check engine light is coming on and driveability issues.
Plugging it is probably the correct thing to do and hopefully the computer will re-learn itself within a few miles of driving.


Nonetheless, I'd still check your computer as I previously posted for the possibility of your driveability problems.

Bob

 

You've got the T you drew in on the parts drawing wrong. If you follow the hose from your MAP sensor, you'll see that it goes along side the T'd line, but is not part of it. You drew the T inline with the MAP sensor - which it is not.



Follow the hose, I think you'll find it goes to the PCV valve.

 

You should have to vacuum ports at the back of the throttle body.
The top one should go to the MAP sensor.
The bottom one should go the PCV valve on a "T" and the vacuum line from the "T" goes to the canister purge solenoid.
Did you look at the vacuum diagram above which should be the same as the one in your engine bay.
My vacuum lines on my 460 is the same as in the diagram and yours should be the same.

You have Fuel Injector Filter on the frame to keep anything like that out of the fuel injectors.

 

I looked at that purge sensor....It has all it's lines (in and out).

I do not believe I have the drawing wrong as I carefully looked at the distinctively
shaped plastic vac line on the truck (there is another illustration I did not show).
(My mechanic was there when this was drawn). And I know that all the hoses shown
on the illustration are not accurately represented (routings) on the truck itself.
This in itself can be confusing. (at least to me....I have a mechanic engineering background).

Plugging the hose had no effect on the terrible way the engine ran.

Maybe if the hose has nothing to do with the engine's performance.....we need to just ignore it and
pinpoint what other potential failures can occur in components that would cause the "surging" engine
dying at idle, and check engine light coming on after a couple of miles (becoming more progressive).

Potential computer problem noted. Mechanic also speculated a dying fuel pump.
What if the evap and canisters are not functioning properly? Would that cause this problem?

 

Does the fuel pump come on and off with the truck setting with the key on and the engine not running (not talking about the fuel pumps coming on when you first turn on the key)?
Does the engine start normal with high idle then drop back down to normal and then sometimes the will jump back up to about 1500 RPM and the CEL will flash about three or four times and then after a minute drop to normal or go to normal idle RPM if you put it in gear?
If it does the above and when you check for codes after the CEL flashes you do not get any codes?

 

Again, My take,

Bob