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I have Howell TBI on my 401. I'm suspecting vacuum leak from break power booster. High pitch sound in the cab goes away when I disconnect vacuum line to my booster. I have replacement part on order. What is typical MAP sensor reading at idle (~ 700 rpm)? Mine is currently reading somewhere in 35-45 kPa range. I would expect MAP sensor reading to improve once I replace power booster.
That high pitched sound is likely coming from the air inlet near the brake rod.
Sometimes spraying brake-kleen around where the rod enters the booster, (With the engine running) while pumping the pedal several times clears out and dirt/gunk that is preventing the valve from seating properly.
Worth a shot in lieu of buying a new booster...
And yes, the vacuum leak with definitely affect the MAP sensor readings.
Pulling the booster vacuum hose and plugging it should get your MAP readings back up to normal.
60-70 is about right for a good engine below 3000', which is equivalent to 20" on a gauge.
1977 Cherokee Chief - The Blair Jeep Project III
A collection of parts flying in close formation
Tatsadasayago wrote:That high pitched sound is likely coming from the air inlet near the brake rod.
Sometimes spraying brake-kleen around where the rod enters the booster, (With the engine running) while pumping the pedal several times clears out and dirt/gunk that is preventing the valve from seating properly.
Worth a shot in lieu of buying a new booster...
And yes, the vacuum leak with definitely affect the MAP sensor readings.
Pulling the booster vacuum hose and plugging it should get your MAP readings back up to normal.
60-70 is about right for a good engine below 3000', which is equivalent to 20" on a gauge.
60-70 MAP is not what you should be seeing, I think you're confusing the conversion with pressure vs. vacuum.
If stock cam, your MAP reading might drop a tad lower after fixing the vacuum leak, but not much.
Really depends on your engine and tune.
Manifold vacuum and pressure got me confused a bit until I saw this nice little picture from AA1Car.com site.
I think my break power booster is original and since I have new one coming soon, I'm going to change it out. None of the auto parts store where I live stock this anymore. I hope I can just move my master cylinder out of the way enough to remove booster without having to disconnect break lines. Has anyone change out break booster before without disconnecting break lines from the master cylinder?
Tatsadasayago wrote:You are disputing that 60-70 KPa is equivalent to 17-20" of manifold vacuum?
When tuning a vehicle or reading a MAP sensor value 0 is greatest vacuum / 100 is no vacuum
Typically stock engines idle ~30-40
Decel would be ~20, 60-70 would be a slight engine load, 100 would be WOT
Yeah, if you are careful, you can move the master forward and down without crimping the lines. You only need about 2" space to get the MC clear, but need to get it downward out of the way so the booster can come out.You will find the hardest part is worrying the booster nuts off the studs...long time with a wrench from under the dash. Deep sockets usually aren't deep enough for the first inch or so.
1977 Cherokee Chief - The Blair Jeep Project III
A collection of parts flying in close formation
Tatsadasayago wrote:You are disputing that 60-70 KPa is equivalent to 17-20" of manifold vacuum?
When tuning a vehicle or reading a MAP sensor value 0 is greatest vacuum / 100 is no vacuum
Typically stock engines idle ~30-40
Decel would be ~20, 60-70 would be a slight engine load, 100 would be WOT
100 Kpa on a MAP sensor is WOT aka: barometric pressure.
I'm not sure where you are getting your 30-40 numbers but we'll agree to disagree.
1977 Cherokee Chief - The Blair Jeep Project III
A collection of parts flying in close formation
The only person in this thread who may be wrong, so far, is me. I made an assumption on Howell's strategy without checking (actually that makes me wrong regardless of the outcome).
There are two different ECU strategies. So it would depend on which strategy that Howell follows.
To find out what is correct, hook up a vacuum gauge and compare.
Same strategy as a zillion other cars on the road...all the below use the same MAP sensor as typical GM TBI
ACURA 1996-1997
BUICK 1985-2004
CADILLAC 1985-1996
CHEVROLET 1985-2004
EAGLE 1988
GEO 1990-1993
GMC 1985-1998
HONDA 1994-1997
ISUZU 1989-1997
JEEP 1985-1995
OLDSMOBILE 1985-2004
PONTIAC 1985-2004
SATURN 1991-2002
Howell did update to a newer style MAP on newer systems, but it functions the same, just a smaller GM sensor used on newer GM vehicles.
Since a pic is worth a thousand words...and much faster/easier than trying to convince people or explain it...
I replaced my break power booster couple of days ago. Took O'Reilly's way too long and a few phone call to get the part that I order in early August. I also had to run over to my favorite nuts and bolts store to get the correct nuts. Booster was shipped with 9/16" nuts that was boogering up the threads on the stud. Studs turned out to be metric 10mm. I was not happy with O'Reilly and I will not buy from them again.
My idle improved quite a bit. I still need to hook up my computer to see the sensor reading yet.