For the past 18,000 mi my truck has been making a roaring sound under hard acceleration. First I thought is was the fan staying engaged(bad clutch). It wasn't that. ,,,Next I thought it was the turbo going.............it wasn't that.
also along with the roaring sound, idle was rough and there was hesitation along with HARD shifting. I mean BAM every time it changed gears when I got on it. ........It started running crappier and crappier. Figured the Banks Chip was going bad so I pulled it. No change. Also was ready to take truck to the tranny shop.

Today I noticed the vacum line was dry rotted to the passenger hub. Since I have manual hubs I decided to just cap off the lines on both sides along with the hubs.

Since I did that the truck runs like a NEW truck. All of the above problems DISAPPEARED.

How could a bad vacum line cause all of those problems??? Or affect the ECM

Could it be a coincidence??????????

 

You would be surprised how much a bad vacuum line could affect the engine. I left one off one time on a little car and it ran like crap. Finally found the line put it on and everything ran great.

 

That's a strange one. I'm trying to think of any way that the vacuum leak would affect the operation of the engine and can't come up with any. The vacuum system is totally separate from the engine. We'll see if someone can come up with something.

 

My thoughts exactly. there's no vacum advance, no vacum operated shifter, no vacum operated secondaries.
Reminds me of the time when I swapped out the alternator. Later that nite when I turned on the headlights, they both blew at the same time, Thats never happened since.

The only other thing I can think of is the build date on motor is the same as my Ex-wife's birthday 2/19

 

That is the only thing that I can come up with. The vac only runs the hubs and the blend door for the heater.

 

unmetered air?

do diesels have a mass airflow sensor or some other sensor to measure airflow into the engine?

 

No mass air on the 7.3

As stated, the vacuum system is only for the HVAC and hubs.

With a very large vacuum leak, your HVAC would not switch doors correctly and would keep the recirc door open, which would make the blower motor sound loud. Are you sure it wasn't just the blower motor?

 

Otto,

I dare you to put it back the way it was to see if your problems come back.

 

I just disconnected my vac plugs last night, just to see, and you are correct the blower motor is much louder. The truck ran the same.

 

But that was on a gasoline engine.

These are diesels and have no manifold vacuum, or any other kind for that matter.

A bad vacuum line will have NO effect on a 7.3 engine's performance.

As others have said, it might affect your air conditioning or ability to auto-lock the front hubs, but nothing to do with the engine.

Different fuel, different ignition, different performance, different thinking.....

Pop

 

It was a long day I was not thinking of the difference, no vacuum for the engine. Just how vacuum seems to do lots of wierd things if not in perfect operating condition.

 

I am a manual transmission guy but is the automatic trans controled by vacuum? If you have a vac. leak it will not shift properly. I remember my old '86 F350 with a 6.9 and C6. It had a vacuum modulator on the throttle linkage and if it wasn't adjusted right it would do all kinds of things.

 

Nope. Nothing on the tranny is controlled by vacuum, either.

All electronic, with sensors to determine load, throttle position, RPM, etc.

Microprocessor determines when you should be shifting, but there's some really smart programmers at Ford behind the scenes writing lookup tables.

Pop

 

I just did as you suggested. The problems DID NOT comeback. However while driving I started thinking , perhaps the EBV valve was stuck and then fixed itself the same time I fixed vacum problem. It's the only logical thing I can think of which would cause all of the above problems.

Opinions ???????

 

After 2 days of perfect running the symptoms are BACK. Could the EBV be causing them???? (read 1st post please)

I do have a brand new Flex Fan to install to see if the fan clutch is causing the problem. Question: Is the nut on shaft clock wise to losen. (opposite of what you normaly would do)