Sigma Engine - Questions About MAP Sensors

[Squeegee]

I need some advice.

 

Some of you may have seen from my build log that my 310S chassis arrived without a MAP sensor installed on the chassis or included in the parts. Not a problem, Josh at RMC has requested one and it is on its way. I would like a little advice about installing it when it arrives.

 

1) I know it will be installed on the passenger side foot well. How do I attache it? Do I just drill two holes and use sheet metal screws, or drill two holes and use a nut and bolt arrangement?

 

2) What kind and size of hose is used for the vacuum side?

 

3) Where precisely does the hose attach to the manifold? I think I have figured that out, but a confirmation, preferably with pictures would be greatly appreciated.

 

Don't be afraid of insulting my intelligence. Advice like you would give a 3-year-old and LOTS of pictures are probably the best way for me to understand.

 

Thanks in Advance,

Dave

[ashyers]

Dave,

1) I'd suggest attaching it with 3M Dual Lock. No holes and removable if necessary. It's good stuff!

2) Whatever size vacuum hose that fits on the barb(s) should work fine.

3) I'm not familiar with the intake system on your Sigma.

 

Andy

[Squeegee]

Andy, Thanks for the suggestion about the 3M Dual Lock. I may give that a try.

 

In the meantime, if anyone who has a Sigma under the bonnet could just snap me a picture, it would be greatly appreciated.

 

My engine experience is with stove bolt Chevy six-bangers and pre-emissions Triumphs, so anything higher tech than that is a bit mysterious to me.

Edited July 30, 2020 by Squeegee

[11Budlite]

In the meantime, if anyone who has a Sigma under the bonnet could just snap me a picture, it would be greatly appreciated.

 

My engine is still in the crate and I couldn't find any pictures on the internet so can't help you there. I would think any port on the intake that is manifold vacuum (after the TB) and fits the hose size of the MAP sensor should work fine. When I get home from work I can check a little closer.

[Squeegee]

Thanks Bruce.

[Mark IV]

I have a 310R in the shop and can snap some pictures.

[I B Sevener]

On the 310S we just built I was advised by Nathan Down to just plug in the MAP sensor and leave the port open to atmospheric pressure. The car seems to run fine and we are at 6,000 feet above sea level so I am equally curious if this is incorrect. Here is a photo of the car

The sensor is simply stuck to the panel with double sided tape and seems to stay just fine.

 

I await the experts to guide me the rest of the way. Cheers,

[I B Sevener]

Here's another photo for reference:

[JohnCh]

Dave, is the MAP sensor used as a barometric sensor to adjust for elevation changes, or is it in lieu of a Throttle Position Sensor to feed intake air density information to the ECU for A/F ratios? I B Sevener's setup is the former and why it can be left open to atmosphere.

 

-John

[Squeegee]

Mark IV, I look forward to seeing the pictures, particularly ones showing the vacuum hose connections..

 

IB Sevener, Thanks for the pictures and info. It's starting to look to me like double sided tape or velcro picture hangers may be the easiest way to mount the unit. I am really intrigued that your engine seems to be performing with no connection of the MAP sensor to manifold pressure changes.

 

John, My understanding of MAP sensor function rudimentary, to put it mildly. My understanding was that the MAP sensor functions as a constant monitor of air pressure/density in the intake which in turn determines how much oxygen is being fed into the engine. Based upon this, the fuel injection system optimizes the feed fuel to make maximum use of the amount of oxygen available. Like I say, that is just my VERY basic understanding of what the device is designed to accomplish, and I realize I may be completely wrong. BTW, I am at about 350 feet above sea level, so no real compensation for altitude is required.

[JohnCh]

I'm not sure how the Sigma is set up in the 310. An ECU can be setup to use a MAP sensor as you indicate, and what I referenced earlier with air density within the intake. However, if you are running a Throttle Position Sensor, which many people do, you can then use a MAP sensor as a barometric sensor to identify the ambient air density -- i.e. altitude. The ECU then compares this reading to sea level and adjusts the fueling table based on a look up table. This is helpful if you tour and go through mountain passes -- or if you live in the mountains and head down to the seashore. I B Sevener is using the MAP sensor (or at least the pictured MAP sensor) in that capacity. If it were determining the air density within the intake to establish A/F based on amount of air passing through the throttle, then the vacuum port would need to be attached to the intake.

 

-John

[Squeegee]

Thanks

[JohnCh]

Just did a little digging and it appears the 310 uses the stock Ford intake with a MAF sensor, so it looks like the MAP is definitely intended as a barometric sensor.

 

-John

[Mark IV]

I was not at the shop today so I asked one of the "helpers" to shoot pictures. He got pictures but not the MAP. I'll get more Saturday. If you want any special pictures email me rick@timemachinesauto.com as my files are too large to post without reworking them.

[Squeegee]

This morning I heard from Josh at Rocky Mountain Caterham re: the MAP sensor.

 

" Hi Dave,

Just got the official word back from Caterham on the Sigma MAP sensor:

"The map sensor on the current 310 is designed to be left open to atmospheric pressure. This means that the corresponding opening on the inlet manifold should therefore be blanked off with a rubber bung. Regarding the ECU calibration, you are correct in your thinking, as the sigma ECU mapping is TPS based."

So, confirmed. Looks like hooking up the vacuum line basically just makes for a more complicated bung!

Josh "

 

There you have it, the definitive word.