Author Topic: Manifold Pressure Sensor D-jetronic repair attempt.  (Read 11151 times)

oscar

  • W116 Addict
  • ****
  • Posts: 4,043
  • Location: Riverina, NSW, AUSTRALIA
Manifold Pressure Sensor D-jetronic repair attempt.
« on: 10 July 2006, 05:38 AM »
Hi all,

I wish I could say "successful repair".  I found a heap of links regarding d-jet last night and loaded with new found knowledge about the MPS I managed to detach, pull apart, stuff up a repair, reassemble and test drive all within an hour.  Here's two links worth mentioning.


10 pages all about d-jetronic from thebenzbin.com
Fantastic in depth article with photos on the MPS and how to pull it apart and adjustments


That second link really was a great help.  Assuming you've read the 2nd link and rather than repeat any procedure that's mentioned above I'll fast forward to the pics of my faulty diaphragm.

Internal side


 :o Without encouraging the split, I found the tear went 3/4 around the circumference of the diaphragm



In anyones language that diaphragm is cactus.  So how to fix this?? Buy a new MPS.  Seriously!!  But meanwhile, have fun being inventive. ;)

Solder?  Well I cleaned it then attempted to solder and managed to burn a hole in it. #$%@,   >:(
Plan B, Tape?  I ended up using a fine surgical tape around the crack.  No pics sorry it looks shite. It kind of works though.

I had a McGiver moment, my idea was originally to use gaffer tape, or similar, cut in a fine circular strip to cover the crack, so the diaphragm could still operate like a speaker does.  I'm still going to try this one if I find the right tape.

If you read up on that MPS link the following will make sense regarding idle, full load and part load.  As you're probably aware by now, a modification on a cracked diaphragm is unlikely to (definitely wont),  return it to normal operation.  Such is the fine balance of the flex of the diaphragm in response to vacuum versus the pretensioned springs that a change in it's flex properties will lead to improper fuel/air mixtures.  I found my patch job wasn't quite vacuum tight either.  Sucking the vacuum connection revealed a noticeable leak, not as bad as before but noticeable. 

So how does it go now.  Idling was fine.  Maintaining constant speeds upto approx 100km/hr was jerky, especially noticeable keeping low speeds like 50km/hr, presumably from the mixture being lean.  Accelerating was great.  Decelerating also no probs.  Part load mixture is the problem. 

In terms of part load, my theory is the diaphragm flexes easier now, which also leads to a shorter transition period to full load, hence the great sustained acceleration.  The thickness of the tape covering the diaphgrams edge has moved the part load stop towards the coils allowing the diaphragm to flex further and the core now to move further out of the coils causing a shorter impulse from the ecu to the injectors. ie lean mixture.  There is the possibility of now adjusting the inner screw to richen the part load but I'm not going to fiddle with the adjustment until I find a better way of "mending" the crack.

A few notes before I go. 

   Pulling apart and reassembling was easy and quick.  I sarted using a dremel to cut off the 4 rivets but halfway through the first one I used a power drill.  Much easier.  The MPS article mentions a drill press if you've got one.
   I used small thin machine bolts and nuts to reassemble.
   I also opened the MPS up without removing the epoxy plug.  The inner screw could also be adjusted this way, but when I get round to adjusting, the unit will be on vehicle with the epoxy removed.
   The MPS article also mentions Bosch's mistake in not rounding the edge of the keeper plate that contacts the diaphragm.  Amen to that!!  The crack on mine followed the sharp edge of the keeper plate exactly, which was minutely off centre.  The match between edge of plate to crack was identical.  If I get a good used MPS, I wouldn't hesitate in cracking it open in order to file or grind a smooth curved edge for that plate in an effort to prolong the life of the diaphragm.
   
BTW, where does one purchase a new diaphragm rather than a new or used MPS?  "They" rebuild this things so a diaphragm must be available and cheaper than a new MPS.  Cheers.

1973 350SE, my first & fave

Denis

  • Classic
  • **
  • Posts: 334
  • Location: Paris
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #1 on: 10 July 2006, 09:07 AM »
Hi oscar

Quote
"They" rebuild this things so a diaphragm must be available and cheaper than a new MPS

Dont bet on anyone doing rebuilds to tell you what they do, it is lucrative business with all those early R107s in the US.

I gave up trying to find the part ...

tell me oscar, did you put a torch to the poor thing ? I used a soldering iron but when I used a torch on a spare dead part (the kid in me likes to experiment), it just melted it into oblivion  :o

Denis

Paris, France

Nutz

  • Vintage
  • ***
  • Posts: 587
  • Location: Hawaii (Maui)
    • W123 Gassers
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #2 on: 10 July 2006, 02:23 PM »

Have you tried cold welding it ?

oscar

  • W116 Addict
  • ****
  • Posts: 4,043
  • Location: Riverina, NSW, AUSTRALIA
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #3 on: 10 July 2006, 06:56 PM »
tell me oscar, did you put a torch to the poor thing ?


Mmm. Um. Yes ::).  I'll confess.  Even though I said earlier I was going to use low melt solder.  The thing is, I tested my torch on copper wire which refused to melt, just glowed bright yellow.  Even though the wire is thicker, I thought I'd be safe.  Painted a little flux on and within no time at all the outer flange buckled and a hole appeared with the solder.  I then used a tempreature controlled electronic iron to remove the solder. 

So what now?  Epoxy!!

I thought of using araldite but thanks to your suggestion Nutz, whilst looking up "cold welding" I diverted to "J-B cold weld" the brand name. 
Cold welding sounds like it's ideal for bonding copper.  I have no idea who in town here has the know how to do it. I got the impression that you need specialised equipment for this too.  Is it something you could do at home?

JB Cold Weld isn't cold welding at all of course.  If you've never heard of it it's an epoxy with a lot of commercial hype behind it relating to it's steel like properties.  Well, there's only one thing that I know of that turns from a liquid to steel and that's molten steel.  From some "independant" posts on the net I came across, it sounds better than using any other epoxy. So off I go for now, results later.
« Last Edit: 10 July 2006, 06:59 PM by oscar »
1973 350SE, my first & fave

Nutz

  • Vintage
  • ***
  • Posts: 587
  • Location: Hawaii (Maui)
    • W123 Gassers
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #4 on: 11 July 2006, 12:06 AM »

I tried the JB Weld cold weld before and wasn't impressed with the way the part held together for 3 whole days  >:(

I meant REAL cold welding with vacuum and etc  :)

oscar

  • W116 Addict
  • ****
  • Posts: 4,043
  • Location: Riverina, NSW, AUSTRALIA
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #5 on: 11 July 2006, 01:30 AM »
I meant REAL cold welding with vacuum and etc  :)

I thought so, it's just that I got sidetracked onto a JB Weld link.  I don't know who I'd contact to have cold welding done.  Especially locally.  Other than that, from what I read, the process sounds ideal for copper and this join.  Speaking of locally, nobody stocks JB Weld but I bought Quiksteel.  Similar properties, epoxy type stuff.  I'm a bit disappointed to hear it didn't work Nutz.  Also I was thinking that the epoxy may be too inflexible for this type of repair. 

Good news of sorts.  Cracked open the MPS and found that one of the screws to the keeper plate wasn't screwed in all the way.  One I must have missed.  Tightened it up and voila!  Vacuum!!  Went for a drive and that jerkiness during coasting disappeared.  The diaphragm obviously still doesn't move as it should and the tape will give way sooner or later but it's an easy fix for now and later until I get a replacement.  WHilst it's working I'm going to leave it alone until it fails. 60km so far. :)

Back to diaphragm replacements, I have a question about other MPS's. Since d-jet was used on Jag's, VW's, porsches even deloreans, what's the chance of another model's diaphragm fitting our MPS.  I realise the MPS as a whole is model specific but from reading it sounds like a setup in the coils, core and springs that make the difference.  There's also differently shaped casings and some without this diaphragm but from seeing a few pics of other models' MPS's, I reckon the diaphragm may be the same.  Firstly look at that MPS from a Porsche 914 on that second link in my first post: every part inside compared to mine looked identical.

Porsche  
Mine       

A VW MPS

And another Porsche 914

My point is that perhaps I can broaden my search to find replacement diaphragm/s by looking up other car makes that used d-jet.
1973 350SE, my first & fave

Denis

  • Classic
  • **
  • Posts: 334
  • Location: Paris
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #6 on: 11 July 2006, 04:40 AM »
Hi Oscar and all

Quote
WHilst it's working I'm going to leave it alone until it fails. 60km so far.

I have clocked 1100 km so far on a similar fix but with a lopey idle.

I agree that you can get other MPS diaphragms as long as the center screws are set identically. Always hold the device by the center metal core when adjusting the screws to a known good unit. As you have seen, the diaphragm is so delicate that people that dig out the epoxy and twist a screwdriver in there are likely to tear up a weak but previously working unit  >:(

One would think that somebody could simply find a way of stamping a thin copper plate to make this diaphragm or fabricate a plastic unit with characteristics similar to the original.

Denis

Paris, France

Nutz

  • Vintage
  • ***
  • Posts: 587
  • Location: Hawaii (Maui)
    • W123 Gassers
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #7 on: 12 July 2006, 09:49 AM »

To keep you from purchasing a bad pressure sensor (LVDT) at a salvage yard,take a multimeter with you
and test pins # 7 to # 15 and the resistance should be 90 ohms. # 8 to #10 resistance should be 350 ohms.

Nutz

  • Vintage
  • ***
  • Posts: 587
  • Location: Hawaii (Maui)
    • W123 Gassers
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #8 on: 12 July 2006, 01:05 PM »
In addition, referring to Nutz's electrical check, which are the terminals he is talking about ? Regards, Styria


oscar

  • W116 Addict
  • ****
  • Posts: 4,043
  • Location: Riverina, NSW, AUSTRALIA
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #9 on: 12 July 2006, 04:01 PM »
Hi styria and Nutz,

A new MPS costs, drum roll please.........approx $1250US, $1660AUD.  Cheapest I found was $853USD, $1133AUD.

Styria, I used to doubt you when you'd praise K-jet over D-jet.  Not anymore :D

I've got a spare coming from MB Spares in Canberra.  I should've asked you Styria but I knew they had some and it got sent yesterday.  Hopefully I should get it before I have to go back to work on Saturday.  This unit was $150AUD with 3month warranty.  Spoke to them and was guaranteed this one held a vacuum and the coils were up to spec.  But I'll test again as you suggest Nutz, when I get it to double check.  I'm not throwing in the towel (yet) for alternatives. But a couple of days ago I thought to myself I'm going to get stranded somewhere if I don't have a working unit on hand whilst I experiment.

BTW Styria, I haven't seen them referred to as regulators.  On the net they're either MPS (like the title of this thread), "pressure sensor" and the only other is "MAP" sensor which is incorrect but used nonetheless. Part No. 0 280 100 012.  That 2nd link if in my first post has all you need to know about it.

Right now though I'm dreaming of a large sheet of copper, a stamping press, a bunch of jaguar, VW, porsche and MB d-jetters, all filling my bank account in exchange for a new diaphragm.  Styria, this may be an opportunity for you what do you think? I wouldn't know where to start.

1973 350SE, my first & fave

OzBenzHead

  • Vintage
  • ***
  • Posts: 721
  • Location: Northern NSW, Australia
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #10 on: 13 July 2006, 06:28 PM »
... I am sitting on all of these beautifully painted spoilers

Ouch!   ::)

oscar

  • W116 Addict
  • ****
  • Posts: 4,043
  • Location: Riverina, NSW, AUSTRALIA
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #11 on: 13 July 2006, 09:00 PM »

... I am sitting on all of these beautifully painted spoilers

I hope not literally speaking :D :D

Well, I got a phone call from work this morning to say my package had arrived.  I ducked over there, sucked on the new (used) MPS and yes, vacuum!!  I was too impatient to test the terminals.  I'll take MB Spares' word for it.  Threw it in and the difference was amazing. ;D ;D ;D

No difference in power, but ever since I've had the car I've been placing too much emphasis on ignition for causing problems.  My car has always had this leap from idle to acceleration which I've blamed on worn accelerator linkages, plugs, leads, timing and so on.  Fiddling with all of those never got rid of this relatively jerked marked change in acceleration and the occasional firing miss.  Having pulled apart my MPS and changing its characteristics I could easily see how much the MPS affects engine running as some symptoms worsened.

Now the car has very smooth transition to acceleration, which I can't remember it ever having before, and cruising at any speed is soooo much better. Yay for me. ;D

1973 350SE, my first & fave

Nutz

  • Vintage
  • ***
  • Posts: 587
  • Location: Hawaii (Maui)
    • W123 Gassers
Re: Manifold Pressure Sensor D-jetronic repair attempt.
« Reply #12 on: 13 July 2006, 10:55 PM »

Try disconnecting the harness on the ECU and test the resistance of the harness at the ECU side. Same resistance readings as the pressure sensor,terminal 7 to 15 @ 90 ohms and 8 to 10 @ 350 ohms with pressure sensor still connected. If different,repair the wiring.