VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #1  
Old 06-17-2018, 12:03 PM
Gash's Avatar
Gash Gash is offline
 
Join Date: Aug 2009
Location: Goodyear, Arizona
Posts: 715
Default Low manifold pressure on takeoff?

I just did a takeoff where the engine only made about 15 inches MAP at full throttle, mixture full rich, 950 ft pressure altitude. The engine sounded the same, felt like it was making full power, and takeoff distance was normal. Fuel flow on takeoff was redlined, as expected.

The MAP slowly crept up to 20 inches while flying close to the airport at 3,000 MSL, full throttle. It never went above 20 inches though.

I tried unsuccessfully to Google this, search John Deakin's old articles, reading through my "Fly the Engine" book, etc. and am not finding anything. It seems the main discussion in other threads and articles is instead on high MAP. Does anyone have an idea what might be causing my low MAP on takeoff? I think I've ruled out a bad MAP sensor as I'm getting normal indications on the ground with the engine stopped.
__________________
Karl, Goodyear, Arizona (KGYR)
RV-7, Flying
Extra 330LX, Flying
RV-8, Sold
Bearhawk 4-Place, Sold
=VAF= donor 2018

Last edited by Gash : 06-17-2018 at 12:10 PM.
Reply With Quote
  #2  
Old 06-17-2018, 01:55 PM
vic syracuse vic syracuse is offline
Super Moderator
 
Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,355
Default Clean the line

Have you ever cleaned the line between the sensor and the cylinder? They can get clogged over time. I clean mine out every year.

Vic
__________________
Vic Syracuse

Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
EAA Homebuilt Council Chair/member EAA BOD
Van's East Coast Representative
www.Baselegaviation.com
Reply With Quote
  #3  
Old 06-17-2018, 02:00 PM
lr172 lr172 is online now
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 3,279
Default

Quote:
Originally Posted by vic syracuse View Post
Have you ever cleaned the line between the sensor and the cylinder? They can get clogged over time. I clean mine out every year.

Vic
+1
You would notice a difference in power and fuel flow if your were actually pulling that much vacuum compared to WOT and 29"

Larry
__________________
N64LR
RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress
Reply With Quote
  #4  
Old 06-17-2018, 04:46 PM
Gash's Avatar
Gash Gash is offline
 
Join Date: Aug 2009
Location: Goodyear, Arizona
Posts: 715
Default

Quote:
Originally Posted by vic syracuse View Post
Have you ever cleaned the line between the sensor and the cylinder? They can get clogged over time. I clean mine out every year.

Vic
Thanks Vic. I'll go take a look at it. What do you use to clean out the line? I would probably use 100LL unless there's a more elegant solution.
__________________
Karl, Goodyear, Arizona (KGYR)
RV-7, Flying
Extra 330LX, Flying
RV-8, Sold
Bearhawk 4-Place, Sold
=VAF= donor 2018
Reply With Quote
  #5  
Old 06-17-2018, 05:12 PM
vic syracuse vic syracuse is offline
Super Moderator
 
Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,355
Default Solvent

I use Brake Clean or any other solvent.

Vic
__________________
Vic Syracuse

Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
EAA Homebuilt Council Chair/member EAA BOD
Van's East Coast Representative
www.Baselegaviation.com
Reply With Quote
  #6  
Old 06-17-2018, 05:14 PM
dtw_rv6 dtw_rv6 is offline
 
Join Date: May 2008
Location: Martinsville, IN
Posts: 351
Default

I just went through this myself, and the guys above are correct. My MP gauge eventually stopped altogether. Pull the fitting at your engine connection first. Mine was packed with black gunk that was as hard as concrete. I used 0.035 safety wire and a good soak in MEK. An ultrasonic cleaner might accelerate this process.
Reply With Quote
  #7  
Old 06-17-2018, 05:16 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 4,520
Default

Your symptoms indicate black goo in the hose/line. 100LL works just fine.
__________________
Bill

RV-7
1st Flight 1-27-18
Phase II 8-3-18
Reply With Quote
  #8  
Old 06-17-2018, 05:33 PM
Gash's Avatar
Gash Gash is offline
 
Join Date: Aug 2009
Location: Goodyear, Arizona
Posts: 715
Default

Thanks everyone! I really appreciate it.
__________________
Karl, Goodyear, Arizona (KGYR)
RV-7, Flying
Extra 330LX, Flying
RV-8, Sold
Bearhawk 4-Place, Sold
=VAF= donor 2018
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 10:24 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.