MPC (D-Jetronic) Pressure Sensor - Mercedes-Benz Forum
 
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#1 (permalink) Old 04-09-2010, 01:12 AM
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MPC (D-Jetronic) Pressure Sensor

My mechanic suspects that my Manifold Pressure Control(MPC) Pressure Sensor has failed (Bosch Part # 0280100100).

The car is running rich & is losing power under acceleration. Local parts supplier is showing the unit as no longer being in production. Will call the local MB dealership(the guys @ the parts counter are generally useless when I call) in the morning.

Has anybody experienced this before?


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#2 (permalink) Old 04-09-2010, 05:40 AM
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I just replaced mine on my 73 with an NOS unit. It is my understanding that you can get reconditioned units for around $3-400. I spoke with my supplier in Anaheim and was quoted $1250 with an MBCA discount to $1000 for a new unit (they are still available). Here in Canada they cost about $1880 and with taxes that comes to $2100.

It also looks like someone has messed with the screw behind the plastic cap, but only a better photo would tell. These things do ware out in time.
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#3 (permalink) Old 04-09-2010, 05:48 AM
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MB PN 002 542 28 17. And that is what they cost.
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#4 (permalink) Old 04-09-2010, 05:57 AM
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I have a spare that is tested and works fine, PM me and we can work out a deal.

With best regards

Al

Check out the W114, W115 /8 enthusiast forum http://www.stroke8.org

My 280SL restoration
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#5 (permalink) Old 04-09-2010, 06:18 AM
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Quote:
Originally Posted by alabbasi View Post
I have a spare that is tested and works fine, PM me and we can work out a deal.
I am just curious how you tested your MAP sensor?

I replaced mine only because I thought there might be a problem with it and the NOS unit that I got was at a very reasonable price.

The way I tested mine was to install the new one, tune the car up, check the emission readings and then hook up the old one to see what the differences might be. Here are the results.

As you can see, the LAMBDA and AFR are substantially better on the new unit, but there seems to be a conflict with the CO readings because with a AFR near perfect (perfect being 14.7:1), the CO should be just above .5%. I haven't taken the time to adjust the idle AFR using the dial on the ECU because it simply doesn't matter due to the fact that my car doesn't require any emissions testing.

BTW, the vacuum on my car is 19 inches with advance plugged and 17.5 with the advance connected.

Loren
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#6 (permalink) Old 04-09-2010, 06:28 AM
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Quote:
Originally Posted by ostkurve View Post
My mechanic suspects that my Manifold Pressure Control(MPC) Pressure Sensor has failed (Bosch Part # 0280100100).
There are some simple tests that can be done. They are in the shop manual. Basically, you can test two resistances and you can check that the unit holds a vacuum. If your MPS does not pass these tests and buy a used one, at least confirm that those readings are per specs. That does not mean it will work properly - many have been screwed around with and are no longer set correctly.

Go to section 07.4-040B of this link. It gives all the EFI tests and specifies the resistances for the MPS. To check vacuum use a Mityvac and pull about 20" vacuum - if it holds for say 30 min, then it is OK.

Does your mechanic know how to adjust the d-jet? You need an exhaust analyzer and the procedure for setting up the MPS and ECU (There is a post here somewhere that provides the %CO figures at idle and under load.)

You may have quite a different problem. I once had a rich running problem and it turned out that the trigger points (in lower part of distributor) had worn out and were not firing the injectors properly. The link above gives a basic way of testing -MB call them release points. But the key is that the points close for a period equivalent to about 100deg or so of a rotation. You can test this on the bench while turning the rotor slowly.

You can check if the injectors are firing properly by removing them and letting them fire into a container. The manual outlines the method.

PS: The manual link is for a different car, but same M116/7 engines.

Last edited by MBGraham; 04-09-2010 at 09:10 AM.
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#7 (permalink) Old 04-09-2010, 08:30 AM
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Ahh well mine was much more scientific then that. As I no longer have my 4.5, i've been slowly getting rid of my spare computers and map sensors. In this case, I asked a buddy of mine to to stick in his 72 350SL and drive it around for a while. He gave it back a few days later and told me that his car drove fine with it

Quote:
Originally Posted by lfedje View Post
I am just curious how you tested your MAP sensor?

As you can see, the LAMBDA and AFR are substantially better on the new unit, but there seems to be a conflict with the CO readings because with a AFR near perfect (perfect being 14.7:1), the CO should be just above .5%. I haven't taken the time to adjust the idle AFR using the dial on the ECU because it simply doesn't matter due to the fact that my car doesn't require any emissions testing.

BTW, the vacuum on my car is 19 inches with advance plugged and 17.5 with the advance connected.

With best regards

Al

Check out the W114, W115 /8 enthusiast forum http://www.stroke8.org

My 280SL restoration
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