MPS mystery, huh Options

[r3dplanet]

Last winter I had some fun rebuilding my MPS unit, which is for a '73 1.7 liter engine. The MPS part number ends with 049.

According to the calibration tests on the pbanders website in conjunction with my trusty Meterman LCR55 and MityVac, the unit is perfectly calibrated. It holds vacuum without issue. The readings at 15, 4, and 0 in.Hg all match perfectly. And I mean perfectly. No variation from what the LCR55 shows to the pbanders table.

The mystery is that when I hook it up to the car the engine won't start. It tries to start and I can sort of force to keep going by blipping the gas, but it won't idle on its own. However, when I install another verified trashed out unit, the car starts right up and idles and climbs smoothly.

Um. Huh. I'm hoping that there's some other adjustment elsewhere in the system that my tired brain won't remember. Somehow maybe my car is adjusted to work around the (leaky) old MPS? Or maybe I didn't rebuild the MPS correctly. But it was in and out of the thing for days and I'm convinced the physical operation is correct. But I'm always willing to be wrong.

Confused.

-m.

[JeffBowlsby]

The calibration values need to be indexed for atmospheric pressure based on elevation from sea level. And is that the correct meter, seems to me its not 'Meterman'

[r3dplanet]

I was hoping you would chime in.

The Meterman is a Wavetek. Wavetek is the manufacturer, Meterman is the model.

Also, I live at 1017 feet above sea level so I don't think I should have to reindex the values. The pbanders values were taken at 1280 feet. It should be close to enough to start and run the car to my mind. Good thinking though.

-marcus

The calibration values need to be indexed for atmospheric pressure based on elevation from sea level. And is that the correct meter, seems to me its not 'Meterman'

[JeffBowlsby]

I was hoping you would chime in.

I would run the calc for the altitude elevation just top be sure.

Brads calibration numbers were derived by characterizing known NOS or excellent condition MPS units. My experience has been that different identical PN NOS MPS units have different calibrations right out of the box and the numbers can be different than Brads numbers. My experience is that Brads numbers seem to result in lean conditions and richening them up is beneficial, or maybe its just the specific engine I am running requires a richer setting due to age or wear. I cannot say for sure because there are many factors to consider. When I have the opportunity, I intend to do more research on this with the EFI Associates testers that I recently aquired from the Cap'n with their pulse width monitoring capabilities and hopefully derive better calibration information.