MPS, Rebuilding the MPS Options

[Ron914]

Hello to all who have helped me with this project . @emerygt350 ,@TJB/914, @Superhawk996 , @ChrisFoley , @rjames , @MDTerp
I am in the middle of rebuilding my MPS and have a couple of comments and questions .
First when I opened up the unit I found the most difficult job was removing the rivets holding the two halves together.
When I removed the retainer plate to take out the old diaphragm it was in two pieces .

I needed to take two measurements since I was replacing the stop screw , I needed to measure the the stop screw protrusion into the housing . The instruction sheet sent to me by a member had the measurements he must have made when rebuilding his MPS . His stop screw protrusion was 1.97mm and mine only measured 1.72mm.
His inner/outer screw assembly depth in the old diaphragm measured 6.51mm .
Here's one of my questions ?
when I measured mine I got two measurements depth to inner/outer screw assembly was 4.03
and depth to the washer outside the inner/outer screw assembly was 5.46mm.
Again there is a difference and since mine was never accessed before (epoxy over screw was not disturbed) is the difference in measurements ok and which measurement should I use I will try to attach a photo or two to help with my question.
this one .

I have not touched either of these measurements yet and awaiting any help/comments.
I think it's this one to the washer on diaphragm .

[Superhawk996]

There you have it, now you know why it was a leaker. Good job! (IMG:style_emoticons/default/smilie_pokal.gif) The last unit I did had a diaphragm do exactly the same thing upon disassembly.

The measurements are just to get you close . . . In the ballpark . . . Instead of being way out just randomly assembling. It will ultimately still need tuning which is why you have the tuning tools too.

Pay attention to reassembly directions - gasket placement matters. Chris’ instructions will get you there.

[Ron914]

There you have it, now you know why it was a leaker. Good job! (IMG:style_emoticons/default/smilie_pokal.gif) The last unit I did had a diaphragm do exactly the same thing upon disassembly.

The measurements are just to get you close . . . In the ballpark . . . Instead of being way out just randomly assembling. It will ultimately still need tuning which is why you have the tuning tools too.

Pay attention to reassembly directions - gasket placement matters. Chris’ instructions will get you there.

Thanks , I just needed some encouraging words , I will start assembly later or in the morning .

[MDTerp]

There you have it, now you know why it was a leaker. Good job! (IMG:style_emoticons/default/smilie_pokal.gif) The last unit I did had a diaphragm do exactly the same thing upon disassembly.

The measurements are just to get you close . . . In the ballpark . . . Instead of being way out just randomly assembling. It will ultimately still need tuning which is why you have the tuning tools too.

Pay attention to reassembly directions - gasket placement matters. Chris’ instructions will get you there.

I agree the measurements just get you close when you reassemble everything. I wouldn’t worry that your numbers are off from mine. I would just reassemble back to your measurements and use the same reference points when measuring the new parts.

[Ron914]

Well all done . I must say it was easier than I thought I was just making a bigger deal of it since this rebuild was my first . I actually found by using a heat gun to soften the epoxy it came out very easy . Even the threads cleaned up nicely with a little heat and a pick , no need for a tap to chase the threads came out nice and clean the screw removed easily . Here's a few more photos . Now for the fun part ,tuning my car to run better for my 2056 motor . More things to learn for me

[JeffBowlsby]

Another documented case of a completely fractured MPS diaphragm holding at least some vacuum. Amazing that it holds any vacuum at all, which affects the inductance values of the internal coils and ultimately injector pulse width.

[emerygt350]

Way to go. I mean you are disassembling the most important sensor in the system so a little worry is called for the first time you do it. I will send you some info on checking the curve.

[rjames]

Crazy that it could hold vacuum at all!

[Superhawk996]

Crazy that it could hold vacuum at all!

Mine did the same thing. It’s my belief that they don’t actually fracture into two pieces until you crack the case open.

I think it’s basically a giant stress crack but it’s not fully fractured. Thus the partial leakage.

Because there is the partial leak it basically prevents the diaphragm from moving anywhere near full travel - thus limiting further stress on the diaphragm when it’s assembled.

Then when the case is pulled open, it lets go all the way around. I can’t prove that but like you, seems to me if the whole thing was literally in two pieces it wouldn’t even hold the partial vacuum.

[Ron914]

Well I was optimistic that my car was going to run a lot better this morning after installing the rebuilt MPS but that was not the case .I reconnected the retard to the distributor and removed that resistor I bought from AA in the CHT circuit and started the car and it would barely start , changing the timing did not make difference in the rough idling .Quite different from before I changed the diaphragm in the MPS . The car was rocking back and forth and running very rough . I first checked my plug wires and found them all intact . I then removed the distributor cap and inspected it and could see that the 4 contact points and the end of the rotor were burnt .Did not know what to think of this but figured this must be the rough running issue . I had installed a Pertronix system and removed the point/condenser several months ago so I decided to remove the pertaronix and reinstall my points /condenser. I also cleaned up the burn marks on the cap and rotor ( I installed brand new cap/rotor and plug wires after the rebuild of my motor) . I have not tried installing a new set of plugs since it was running ok yesterday .


This did not make much change and after several hours of scratching my head on this one . I needed to take a break . Its going to be a busy weekend with Mothers day and another comitment so I may not get back. to this until next week .