Location to tap for Map sensor.

ronchinoy · Post by **ronchinoy** » Fri Feb 01, 2008 4:17 am

Depending on where you install you map sensor tap.
The results the ECU sees is different.

what do you recommend as the best point to tap.

On my existing car there are 3 possible points. And each gives very very different results.

1. Before the Throttle Body (Shows very high Boost.)
2. After the Throtell Body (Shows a little less boost but stronger vacum signal)
3. IN the Intake Phlem. This is where the stock Map sensor is hooked up.

4. On the manifold but next to intake port. (Shows 4-6 PSI less boost than the boost gauge. And shows the strongest vacum signal).

Each point seems to give different results.

AR 67202 · Post by **AR 67202** » Fri Feb 01, 2008 4:50 am

1. can't possibly work, as the throttle valve's job is to reduce the manifold pressure...

2 or 3 are best, since if you put at 4 there's no way of knowing if the other cilinders are getting a similar amount, and there will be too much variation in the signal (noise)

Jack · Post by **Jack** » Fri Feb 01, 2008 7:48 am

As stated above 2 or 3, but 3 is best, as it is the least likely to be affected by changes in throttle, etc. and best reflects what the runners will see. You can tee off the OEM tap, if it comes off with a hose.

The MS is relatively insensitive to hose length (volume). I used a plenum tap for my MS and it tees off to feed the fuel pressure regulator too.

Jack

73Eldo · Post by **73Eldo** » Fri Feb 01, 2008 8:18 am

Mine is a TBI V8 with a stock carb manifold. At first I had it hooked to a port that was on one of the runners that had a few other things hooked to it (like the parking brake release). It worked but I was having troubles getting smooth acceleration so I made a new port in the spacer block under the throttle body and after that it seemed to tune much better.

ronchinoy · Post by **ronchinoy** » Tue Feb 05, 2008 11:30 pm

My first turbo was a carbed engine.
Had a lot of problems geting it to run right untill we found the right spot to tap into.
Dont want to go thru the same circuss with the Mega install.

My earlier setup was carbed with a cold start injector. That would triger every time the narrow band o2 sensor showed the engine was lean.
Another cold start injector was hooked up to a tank with 50% alky and 50% watter and using a presure sense switch it would sprak anytime boost was over 14 PSI.

All done on bread board.

Ive seen a few Megasquirt installs where they are taping in very close to the Inlet port. (Strongest Vacum signal / weakest Boost signal.).
And the guys claim its the best spot to tap. I wasnt too convinced.