• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

vacuum 2.9


werewolf

Member
Joined
Dec 22, 2013
Messages
125
Reaction score
5
Points
18
Location
Odessa Texas
Vehicle Year
2002 & 1999 & 1
Make / Model
ford
Engine Size
4.0&3.0&2.9&351c
Transmission
Manual
My credo
take life day by day
This is most likely a dumb qustion. I was doing the sea foam test on my 87 4x4 2.9 yesterday. I used a can of spray in the intake to clean throttle body. then put 5.oz in the engine, it said 1.oz per quart of oil. Then i did the 3/4 can into the intake through the brake vacuum hose. But to my surprise when i pulled the hose off brake buster the engine rpms went up higher. I would think that big of vacuum leak the engine would try to die. It seams backwards to me.
 


adsm08

adsm08

Senior Master Grease Monkey
Supporting Member
Article Contributor
Ford Technician
TRS 20th Anniversary
Joined
Sep 20, 2009
Messages
34,623
Reaction score
3,613
Points
113
Location
Dillsburg PA
Vehicle Year
1987
Make / Model
Ford
Engine Type
4.0 V6
Engine Size
4.0
Transmission
Manual
2WD / 4WD
4WD
Tire Size
31X10.50X15
On a MAF system a leak as big as pulling the booster hose might kill the engine.

The 2.9, with the exception of a very few units built for California, used a speed/density system, which is less sensitive to air coming in through places that are not the throttle body.

MAF systems work by measuring the approximate amount of oxygen, not air, just oxygen, coming in by having an intake duct work of a known volume, and then inferring the temperature of the air by measuring the amount of power needed to keep one of the wires in the sensor 200* hotter than one of the other ones. It is very accurate, but it is also very sensitive to leaks after the sensor.

A speed/density system makes a calculation for the same information, but it does it using the temperature of the air in the intake and the pressure/vacuum of the intake manifold. This is somewhat less accurate than MAF, but it is less sensitive to air leaks.

The reason a MAF controlled engine will stall when you introduce a large leak is because it lets in a lot of air that the computer can't see, and that in turn leans the mix out so badly that the engine can't run on it. A speed/density system will "see" that air when the pressure in the intake goes up/vacuum goes down, and so it can compensate a little better.
 
You must log in or register to reply here.

Sponsored Ad


Sponsored Ad

Staff online

Members online

Total: 433 (members: 13, guests: 420)

Member & Vendor Upgrades

For a small yearly donation, you can support this forum and receive a 'Supporting Member' banner, or become a 'Supporting Vendor' and promote your products here. Click the banner to find out how.

Latest posts

Truck of The Month


Shran
April Truck of The Month

Recently Featured

Want to see your truck here? Share your photos and details in the forum.

Follow TRS On Instagram

Latest Album Photos

20240409_190831.jpg
20240409_190818.jpg
20240409_180824.jpg
20240409_182648.jpg
20240409_181010.jpg
20240408_175026.jpg
99 Ranger
20200706_161414.jpg
20240207_155117.jpg
20240207_155111.jpg
20240207_154537 - Copy.jpg
20240207_154500 - Copy.jpg

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store


Sponsored Ad


Sponsored Ad

Sponsored Ad


Amazon Deals

Top