 Testing a four MPS, one holds vacuum but it's erratic |
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| Mark Henry |
 Feb 18 2021, 01:56 PM
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#1
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that's what I do!  Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada  |
Hi All!
Ethan just tested four MPS on a '74 2.0 we have here and it seems one holds pressure but it runs erratic. We tested the three other MPS and they tested good. I know that even if an MPS tests good, old MPS's the diaphragm's often fail once pressed back into service. Would the Tangerine MPS diaphragm kit help this, or is there something else likely going on? |
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| JeffBowlsby |
Feb 18 2021, 03:11 PM
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914 Wiring Harnesses Group: Members Posts: 8,519 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None 
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QUOTE(Mark Henry @ Feb 18 2021, 11:56 AM)  Hi All! Ethan just tested four MPS on a '74 2.0 we have here and it seems one holds pressure but it runs erratic. We tested the three other MPS and they tested good. I know that even if an MPS tests good, old MPS's the diaphragm's often fail once pressed back into service. Would the Tangerine MPS diaphragm kit help this, or is there something else likely going on? Open it up and see. Bet the diaphragm is ruptured, or at least the case is not vacuum tight. Another issue may be corrosion on the coil shaft, or a distorted plate spring. When vacuum is pulled is it a smooth transition or is there any point where there is a pinging sound or sudden jerk of the increasing/decreasing vacuum signal? If so, that is not good and could be cause of the erratic behavior. That MPS could be unrepairable if this is what is happening. |
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| Mark Henry |
Feb 18 2021, 03:23 PM
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Thanks Jeff, I see Chris' kit also has a couple of O-rings and a gasket.
I'll dig into it but I'll just order a kit. |
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| DRPHIL914 |
Feb 18 2021, 04:10 PM
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Dr. Phil Group: Members Posts: 5,767 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States
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QUOTE(Mark Henry @ Feb 18 2021, 04:23 PM) Thanks Jeff, I see Chris' kit also has a couple of O-rings and a gasket. I'll dig into it but I'll just order a kit. more than likely its torn, it might just be a small tear, so will run but not well. even hold vac fine . someone recently had this happen, had a couple they opened up, both had diaphragms torn but held vaccuum. I would order 2 kits, rebuild 2 so you have a spare. the paper gasket and the o-rings will make sure you have a good seal once rebuilt with new diaphragm. i have 3 operating MPS right now for my 75 2.o d-jet. One was rebuilt by Jeff B for me and tuned then tested i believe on his car. In comparison to my one that i now have dialed in, that one still runs a bit lean. in fact every one i have ahd in my car or that was tuned to factory spec was too lean and had to be adjusted. but every car is different. Phil |
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| Mark Henry |
Feb 18 2021, 04:22 PM
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Thanks
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| MikeM |
Feb 19 2021, 11:20 AM
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Senior Member Group: Members Posts: 564 Joined: 16-May 10 From: Calgary, Canada Member No.: 11,733 Region Association: Canada |
Mark...I have one that has failed electrically. There is always that possibility.
Mike |
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| Mark Henry |
Feb 20 2021, 12:45 PM
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#7
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Thanks, yes I figured as much.
The one that's erratic is believed to be the original one on the car, numbers are correct so I'm hoping to repair it. One of my good ones has a Tangerine kit in it and worst case I could use it, but it's part of a complete system I have. |
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| mgphoto |
Feb 20 2021, 01:46 PM
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"If there is a mistake it will find me" Group: Members Posts: 1,339 Joined: 1-April 09 From: Los Angeles, CA Member No.: 10,225 Region Association: Southern California |
I’ve rebuilt about a half dozen using Racer Chris’ kits. Very simple, you will need an induction meter to set up the basics with fine tuning done using an o2 meter.
Factory manual gives the values for the two coils resistance, if the coils are bad dump it. FYI 1.7 and 2.0 difference is a spacer ring in the 2.0. Also if you radius the edge of the ring the where it contacts diaphragm it will flex better and last much longer. |
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| 914_teener |
Feb 20 2021, 10:44 PM
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914 Guru Group: Members Posts: 5,200 Joined: 31-August 08 From: So. Cal Member No.: 9,489 Region Association: Southern California |
I had one that was partially cracked.
Would operate and run fine...and then not. |
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| warpig |
Feb 21 2021, 12:20 PM
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#10
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Member Group: Members Posts: 290 Joined: 2-August 10 From: Portland OR Member No.: 12,002 Region Association: Pacific Northwest
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Had a similar prob. Rebuilt MPS and would run erratically. Put the old one back in that won't hold vac., runs good with a slight hiccup around 3k. Been driving it whenever the sun is out for a couple years now and no issues? Not sure what the prob w/ the rebuilt one was or remember what rebuild kit went into it.
@cary |
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| r_towle |
Feb 21 2021, 06:25 PM
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#11
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Custom Member Group: Members Posts: 24,584 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States
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Order kit (s)
Wait for arrival Then open MPs |
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