Greg ( I don’t know if you are on this forum) sent me his MPS to rebuild. It had its original epoxy and rivets intact. The outer case was moderately oxidized but he said it functioned good, he was just being preemptive in sending it to me. And I’m glad he did.

I first checked for leak down several times. It was steady and solid, very very good, almost perfect. Only the slightest almost imperceptible leakdown occurred up at the highest idle vacuum range, but oddly when down near the WOT range the vacuum level dropped quickly like rock.

I checked the electrical and calibrations at all vacuum levels. Spot on and perfect.

But then I opened it up...Surprise! The diaphragm was torn about 240 degrees of its circumference. I cannot explain how this MPS worked at all, much less how it held any vacuum. This is not the first time I have seen this. Seems maybe 10-20% are like this from the MPS’ I have opened.

And let’s be sure to thank Chris at Tangerine for manufacturing the diaphragms. Without these many DJet systems would be unusable.


Takeaways: If you are ‘testing’ an MPS - the mouth suck test is not accurate or reliable - don’t bother. Even using a vacuum pump with gauge is not foolproof. Also the outer case condition is not an indicator if what’s inside I’ve seen too many that are clean on the outside and either corroded inside or unrepairable. The only thing I am comfortable with anymore is complete disassembly with full internal inspection and checking it’s specs on my test equipment.

To test an MPS:

1. Verify the resistance of the two coils and each coil for no shorts to ground. ~90 and 340 ohms.
2. Vacuum pump and pull to 18 in/HG. This is a sealed vessel, there should be no leakdown if the seals and diaphragm assembly (including the gaskets and center adjustment screws) are 100% intact. None. With a very minor slow leak, the MPS will still function OK, given the way the MPS works. the constant vacuum will still move the diaphragm, it wil just be slightly richer than its calibration is set for. Ultimately the MPS fails rich when it does not hold vacuum.

More and more frequently the MPS's I am seeing can be corroded internally, the coil springs are warped or deformed, and the cases leak in odd places - around the 4 pole electrical connection, at the check valve and occasionally other places. Repairing them to not leak even after rebuilding can be major effort of opening an resealing the case multiple times to verify a leak free condition.

Ditto, same with mine. I've got a driveability thread somewhere in here a year or two ago* where I was pulling my hair out trying to get the damn thing to start and run right. Checked the MPS with the Mity-Vac and it tested fine.

Chris rebuilt the MPS - on his recommendation - and it transformed the car's driveability.

Don't rely on the vac test. It's just not good enough.


Amen.


*Edit: it was actually 2016! http://www.914world.com/bbs2/index.php?sho...=291477&hl=

Thank you for rebuilding them and Chris for the parts!!!