Problem of the day. Post it up!

[davidt]

Hi there,

Strange thing going on with my MS2. Fitted a different turbo to my 1972 Superbug and now the MAP sensor reading under boost is about 4 psi lower than my VDO boost gauge reading. Problem was not happening prior. Only replaced the turbo and exhaust piping.
When driving under boost, VDO will show 7psi (waste gate pressure) but Tunerstudio only shows 3psi.
Have updated to firmware release 3.4.4 and it made no difference. Turn ignition on and connected a pressure vessel so I could send a fixed amount of air pressure to the MS2 and VDO (both sense hoses are connected to the same fitting in the inlet manifold), provide pressure and I get the same boost reading. But when driving the car under boost, Tuner studio reads low. Barometric and MAP sensor read the same 101kPa when ignition is turned on. Tried different MAP sensor calibrations, no difference when driving. Tried older tunes, no difference. Retried the pressure vessel 3 times and no difference.
Acceleration feels like 7psi, not 3psi.
Using Tuner Studio release 3.1.05 just as before.
I have been using Tunerstudio with this car for around 11 years now and have never had this issue.
Can't work out how to attach the tune file as it comes up ads invalid.

Help!

David

[madmike]

I'm sure you checked for exhaust leaks right?

[davidt]

No exhaust leaks. I don't care what actual boost I get as I have a manual boost controller and will be increasing to 13psi once I am happy with the new tune.
The problem is the discrepancy between the VDO gauge and the MAP sensor but only when the engine is running, not when the ignition is on and the engine is not running.

[madmike]

Hey Dave, You may just want to post this 'down below' cuz some guy don't/won't see this,,,

[davidt]

Hi everyone,

Problem fixed.
The new gauge arrived and was reading 1psi lower than the old VDO gauge. That was fair given its age.
But the original issue remained.
I removed the MS2 and pulled it apart. Nothing out of the ordinary here. So I was worried that the MAP sensor might be faulty. So while it was out I connect a new plastic vacuum line and ran it to the R/H/S inlet manifold. Went for a drive and viola, Tunerstudio is now matching the gauge.

So it looks like there was a restriction to the vacuum signal to the MS2. Possibly a build up of oil or carbon in the hose.
When I was using the pressure vessel to compare readings, there was a consistent and long supply of pressure that was able to leak past the restriction and therefore gave the same readings. But during driving, the boost pressure was only for a few seconds before I had to change gears.

Sounds so simple now hey.

Thanks to everyone for your contributions and help with this confusing issue.