measuring AFR and boost

[john930]

I have purchased an LM-2 to measure AFR's, boost and rpm. Can any one give me some advise on where it is best to measure the boost from and rpms. A single wire is needed to measure rpms, is there a terminal on the CD box or close by i can get an rpm signal off. Thanks for any advise.

[billjam]

John,
RPM wire connection is straightforward.
If you have the standard ignition control module, splice into the white/violet wire near its 6-pin plug.
I have a Perma-Tune module which replaces the original, but in the picture below you can see where I have picked up its white wire (equivalent to original white/violet). This connects to an LMA-3 under the RH seat (pink wire).



I was originally trying to measure vacuum and boost (MAP) because my LMA-3 has a MAP port, but I couldn't get a location that worked properly for me.
I tapped into the manifold and also tee'd into the brake booster line but both locations showed vacuum readings on my "clock" gauge at low boost when I was clearly getting boost.
The gauge also under-displayed full boost by about 0.4 bar so I gave up trying to get an indication of vacuum and boost and settled for boost only by teeing into the hose that goes to the waste gate.
This is probably the easiest location for you as well if you are only looking for boost measurement.

[beepbeep]

Originally Posted by billjam

The gauge also under-displayed full boost by about 0.4 bar

My LMA-3 required correct configuration of software to display boost/vacuum correctly in 3-bar mode. Maybe it's a software error?

[fredmeister]

The LMA-3 or auxbox should be very accurate with the internal MAP sensor. The set up is a PITA as you need to calibrate the gage with the laptop. With the car off and power to the auxbox does the gage read 0 psi as this would indicate atmospheric pressure. This would indicate the map sensor is calibrated.
I have a VDO boost gage that consistently reads 0.2 bar low on boost when compared to my auxbox gage. This has bothered me for awhile because I assume the aux box is dead nuts accurate and hard to believe the VDO gage is that inaccurate. Only difference being the auxbox hose is mounted off the fitting on the blow off valve housing before the throttle body and the VDO gage is tee'd off the brake booster hose in the trunk.
I cannot belive the pressure drop across the throttle plate is responsible for the 0.2 bar difference.
What do you guys think?

[billjam]

Originally Posted by beepbeep

My LMA-3 required correct configuration of software to display boost/vacuum correctly in 3-bar mode. Maybe it's a software error?

Goran, the gauge I was referring to was my mechanical Greddy boost gauge mounted in place of the clock.
I use the same hose connection to feed this gauge and the LMA-3 MAP port but as yet, I haven't yet been able to get the LMA-3 working properly. (It's currently on its way back from Innovate after some warranty repairs.)

The problem I had with boost readings was related solely to the point of connection.
With the gauge connected to a port on the manifold or tee'd into the brake booster hose, it correctly showed vacuum at idle and on over-run, but as boost came on (as indicated on standard tacho boost gauge and seat of pants) the gauge would still indicate vacuum until boost actually came up to 0.3 or 0.4 bar. From there, as boost increased, the mech gauge indicated gradually rising boost up to about 0.4 bar when the actual boost was more like 0.8 bar.
The gauge has been tested and is OK.
I have now connected it into the IC/wastegate boost hose and works just fine, showing my boost from 0 to 0.8 bar (but no vacuum of course).

The only thing I can think of that would cause such strange presure readings was that the connection port in the manifold was under some venturi effect whereby the air rushing past the port inside the manifold was reducing the indicated pressure.

[john930]

Bill
thanks for your advice, the picture is very helpful too.

john