What is this part?

[MikeTangas]

What is this, and what does it do?



While cleaning the engine and lubing the throttle linkage today, I noticed that the braided line was loose, cracked and disentigrating. I was able to cut back the end get a good connection.

I can find no refernce to it, other than seeing it in one picture in my manual. The braided line coming off the side passes through a grommet one the left side of the engine and goes into the deeper, darker regions - to where I couldn't tell.

Thanks.

[Mark DiSilvestro]

It looks like an intake manifold pressure sensor for the fuel injection.
Mark DiSilvestro

It IS the manifold pressure sensor. It senses engine load. It's the single most important input for the fuel injection system. Replace the hose. It's connected to a fitting at the back of the intake manifold.
If your book fails to mention this part...get another book .
Regards,
Randy D.

[MikeTangas]

Thanks guys. Now that I know what it is I can look in the book again (MB manual). Not knowing what it was, I had to do the old "look for the picture" method. I only saw one picture of it in the fuel section dealing with the regulator at the lower right of my picture. Ahh, something to read up on when I get home from work.

[MikeTangas]

In section 7-20/5&6 of the manual. No picture in the area but a nice detailed diagram of the sensor as well as a description of what is does. Thanks for providing the name of the sensor .

Now that I have repaired the sensor end, until I obtain some of the braided line, I will see if my mileage improves any around town. I expect it will since it was basically registering full load all the time due to the cracks and hole at the sensor end.

Next I'll read the entire section to see if there is a test to determine whether or not the unit is functioning.

[stevebfl]

If you didn't notice any difference then it must of still been sealing. Take the line off while running and see what happens. Any portion of a leak here is unacceptable.

[MikeTangas]

Well Steve, I could hardly wait to see what happened. As soon as I got home, I pulled the line off the sensor and the idle dropped to maybe 400 RPM, gauging by ear. Looks like the sensor is working. Next I stuck the vacuum gauge on the line to see what it was pulling at the reduced idle, ~7 inches hg. If I had had the right sized line I would have teed in and seen what it was pulling at true idle.

As I was checking the vacuum I noticed that if I moved my hand slightly I could hear a hiss. Checking out the line closer, near where it makes the down turn, showed several more cracks which opened when I moved. As soon as I reconnected the line, idle returned to normal.

I will be back and forth to San Diego the next four days, hopefully I'll be able to stop in the dealer and see if they have any of this line available.

As a note, the first item under high fuel consumption, according to the manual, is a defective pressure sensor.

[MikeTangas]

Well, no one around here had any of the proper line - not even the MB Dealer in Escondido. Now they could order me a roll of the tubing, but that was a little more than I needed so I declined.

The closest I could find in size was 5/16 fuel injection line. I got about 18" and went to work. I found that the manifold end was as badly cracked as the sensor end, and there were several holes along the run. The 5/16 was just a little big for the manifold fitting, but a small hose clamp took care of that and the sensor end fits fine.

With some extra line on hand, I was able to devise a large enough "T" and plug in the vacuum gauge. Now at idle it is drawing 15 inches HG.

[Thom Pintello]

Which brings up an interesting question Mike, is this part installed on earlier 2.8 liter 280 SEL models (1969)?? If so where would it be located? Many thanks.
Thom

[stevebfl]

Nope, only D-Jet EFI.

Originally posted by Thom Pintello
Which brings up an interesting question Mike, is this part installed on earlier 2.8 liter 280 SEL models (1969)?? If so where would it be located? Many thanks.
Thom

Like Steve said, it's only used on cars with D-Jetronic electronic injection. Your car has mechanical fuel injection.
Regards,
Randy D.

[MikeTangas]

I noticed today driving to and from work, that the milisecond of hesitation I have always had when first accelerating is gone. I had simply written the hesitation off as "an old car thing". It wasn't much, just a touch when first applying pressure to the pedal.

About the time I neared the office and started to actually wake up, I realized something felt different. On the way home I paid attention and quickly realized what was missing. The little holes/leaks definitely had some effect.

[stevebfl]

And what little gas mileage you got should improve greatly. Try going for 17in of vacuum at idle to get all there is. Timing will usually do it. Try moving the idle mixture compensation knob on the ECU while watching the vacuum gauge, get 17 in and your there.

[MikeTangas]

The ECU is located behind the right headlights, correct?

When I first got the car I was seeing 8.5 MPG around town. Now I pull 12.5-13 MPG, and see almost 16 MPG on the highway (80 MPH and A/C on). The car is definitely getting more economical .

[MikeTangas]

Just a quick update, my in town fuel mileage has increased to 13.5 mpg. Don't know what the highway mileage looks like yet, but it's bound to be higher now too.