hp18racer

Thanks for the responses and for the data. I will post more when I have a chance to do some testing under load.

Laust Pedersen

What is the data rate in post #1?
I would double check the pressure pickup by T-ing in a (mechanical) boost gauge.
You may have oil in the vacuum line and (hopefully not) in the MAP sensor.
You definitely need a multiport Vacuum Manifold (new batch in process).

Laust

hp18racer

I believe 5 samples per second. Connected regulated pressure air going into the turbo, pressurized the entire intake, hooked up the laptop and collected data with the motor not turning. Pressure readings were very stable. Reading of the boost gauge and the computer track together.

333pg333

I know this is probably totally unrelated but those MBCs do get a buildup of gunk in them and need to be cleaned out from time to time. This had given us a few glitches in the past.

lejams

True. Have rebuilt the Lindsey MBC I've had for ten years once, seven years ago. I first had it under the hood and after a few years it failed. The internal plastic (Nylon?) parts didn't do well with the engine compartment temperatures. Moved it to the glove box.

Then in recent months, the MBC was slowly becoming imprecise until yesterday it stopped responding and wouldn't adjust down from 19psi. Had also been getting some seemingly erratic readings on the boost gauge for awhile. It seemed to stick a little on the sweep sometimes which I attributed to the gauge maybe acting up. Suspect now it might be related to the MBC failing.

So yesterday I took the MBC apart. The plastic tube-stem under the diaphragm was stuck, sort of frozen in there, and broke off while trying to dismantle it. After removing all of the plastic parts, I emptied what looked close to a tablespoon of carbon powder out of the housing. I was shocked at how much carbon debris was in there.

Ordering a rebuild kit from Lindsey for 15 bucks tomorrow.

lejams

Laust, glad your making these again I'm in for one when they're available.

hp18racer

The root cause of the erratic data in the original post turned out to be the ground cable. I replaced the battery to motor and battery to chassis ground cables and it smoothed out.