Did altitude just blow out 2 MPS's?, Put the in my checked baggage...now won't hold vac. Options

[FlacaProductions]

I need to see what is actually leaking/causing the unit to not hold vacuum. I don’t believe it’s the diaphragm.

[Ron914]

I have been fighting MPS issues with my 76 D-Jet fuel injection for some time . I knew my MPS had a pretty good leak to start with by testing with a mighty vac . Pulled 15InHg
on my Mps and total Leak down was quick at first but then would slowly leak down to zero after ~ 12 minutes or less . I was lucky enough to have a member sell me an older CF kit he had been saving in his spares .
I have to say after doing my first rebuild on my MPS I learned a few things .
The round O-ring supplied with the kit does not seal as well as the original square edged o-ring (Chris changed back to a square edge one) . Vacuum can be lost at the electrical connection plug also Just to help a bit I filled the connection plug with some dielectric grease to help ge a better seal ,I also used a little around the threads in the middle of the diaphragm , o-ring and the paper gasket .My rebuilt MPS is still leaking since I have the old square o-ring installed but now it holds vacuum much longer and it takes overnight for it to go to zero during a test .
My old diaphragm failed in the outer circle . My engine still is not running well so not sure if I will need a different MPS down the road .

[Superhawk996]

But it would run. Not well.

Yeah the definition of “runs” seems to vary a lot. (IMG:style_emoticons/default/stirthepot.gif)

[emerygt350]

My car explores all the definitions frequently (IMG:style_emoticons/default/wink.gif)

That is plenty long for the vacuum. My rule of thumb is if I don't have any problems creating the curve of inductance vs vacuum, it's good. If it's leaking so that you can't take your time and carefully get that data, it's leaking too much.

[worn]

The whole thing is a sealed area. Two forms of movement, expansion and contraction of the diaphragm itself, and the vacuum driven movement of the whole thing.

Both sides are open to atmosphere when it isn't connected.
The diaphragm doesn't either expand or contract. It simply flexes.
Once the diaphragm is against the part load stop, it doesn't move any further. All the additional movement comes from the aneroid cell expanding.

Hi Chris. Is there any chance that you or another of our saviors, I mean vendors, could get another run of diaphragms made? What if we personally searched for beryllium? I now realize that beryllium is scarce in the universe because it normally breaks down during star fusion, but there must be some of it. I know it isn’t your problem, but you sure did us one heck of a favor! Thanks!

[emerygt350]

A raspberry pi that replicates the output at whatever level of vacuum is probably where we should go in the future.

[FlacaProductions]

short of moving to a Holley Sniper setup or similar, something needs to be solved concerning the MPS as it seems to be the weak link without a cuurrent/modern alternative.

Update on my situation - I think the square perimeter o-ring is the/an issue. The nuts/bolts weren't in great shape and have stripped/broken when I've tightened them up (they seemed looser than I thought they should be on initial tear-down) so maybe just new hardware will help but perhaps a new seal would be good, too. Anyone have the correct direct replacement source?

[emerygt350]

short of moving to a Holley Sniper setup or similar, something needs to be solved concerning the MPS as it seems to be the weak link without a cuurrent/modern alternative.

Update on my situation - I think the square perimeter o-ring is the/an issue. The nuts/bolts weren't in great shape and have stripped/broken when I've tightened them up (they seemed looser than I thought they should be on initial tear-down) so maybe just new hardware will help but perhaps a new seal would be good, too. Anyone have the correct direct replacement source?

Pretty sure you could cut your own from gasket material.

[JeffBowlsby]

A thin coating of high viscosity grease (silicone grease) on the diaphragm paper seal and case seals should solve most MPS leaks. Superglue on other cold joints such as the electrical port to case and diaphragm to armature should resolve the remaining leakage.

[ChrisFoley]

I just need a little more time, Warren. I expect to be producing them again before end of 2025.
Right now, a large number of exhaust system orders is keeping me occupied.

[emerygt350]

I just need a little more time, Warren. I expect to be producing them again before end of 2025.
Right now, a large number of exhaust system orders is keeping me occupied.

That is excellent news.

[FlacaProductions]

Yep - good news, Chris. They're gonna fly out the door.
I'm just waiting for the O-rings to land today and then I'll pick up new nut/bolt hardware tomorrow along with the LCR and then hopefully I can move ahead.

[rjames]

I just need a little more time, Warren. I expect to be producing them again before end of 2025.
Right now, a large number of exhaust system orders is keeping me occupied.

Excellent news! Thank you for making a part that is critical to keeping cars w/ stock FI on the road.

[FlacaProductions]

OK - new o-ring and nut/bolt hardware seems to have tightened things up considerably and it's barely (barely) leaking. I'm going to call it a win and move to calibration with my new LCR55A. (I think it's a good eBay purchase as it looks brand new, still. warranty card, instruction book, all the leads still tied together with a rubber band...)

[FlacaProductions]

ok - LCR has me back to a calibrated MPS.
The proof will be when I get back to Indiana in a few weeks and can put this one back in. You can bet I'll be carrying this one onboard this time.

Next project is to drill out the rivets on the other one that failed after being flown in the cargo area, see what failed and then proceed as needed.

[emerygt350]

Don't have any faith in those raw lcr values. Maybe it Will start, maybe it won't. Be ready with "the tool".

[FlacaProductions]

Yep.
I also will take the LCR/calibration readings from the MPS that is currently IN the car and is running fine other than the running-warm-at-highway-cruise issue that brought me to this point. I'll compare those to what i have now and maybe transfer them into this open/adjustable one.

[JamesM]

I just need a little more time, Warren. I expect to be producing them again before end of 2025.
Right now, a large number of exhaust system orders is keeping me occupied.

Needed if anyone is going to save d-jet cars. Since the supply of diaphragms dried up I have moved to recommending to customers that they dont put a lot of money in diagnosing d-jet issues because if the diaphragm turns out to be failed, or fails shortly down the line then its just a wasted effort because little can be done other than to gamble on another used MPS.

[FlacaProductions]

With nothing else to do on this front, I decided to see if I could improve the MPS that I put back together recently. It was leaking down vacuum a little faster than I liked.

First task was to dismantle the one that would not hold ANY vac. See the pic. I'm pretty sure the diaphragm had a leak. (IMG:style_emoticons/default/lol-2.gif)

So after Frankensteining the two and using what I thought was the best parts, I ended up with an MPS that holds solid vacuum and is calibrated to factory specs. I know it will still need adjustment but this is a really solid (re)starting point going ahead.

Couldn't have done it without the VAST knowledge and skills on this board - big thanks.

[emerygt350]

Smart move! Can't wait to see how it goes.