1972 280SEL 3/5 V8 D-jectronic - sawing sound when engine cold

Hi there, 

Hope you are having a wonderful weekend!

When I start the engine cold, there will be 1 to 2 min. sawing sound appearing from the engine. I read through the forum, thinking if it is vacuum leaking or faulty AAV problem. Therefore, I use smoke machine to test the vacuum leakage, turns out there is a little leakage at the throttle housing butterfly shaft, and the breathe hose at the right valve cover. Then, I bought temperature bulb from AAV parts.com and replace it, but the sawing sound is not going away.

Then, I check the vacuum at the intake manifold, and it shows needle reads 16.5 inch and remains steady. I tried to make the ignition timing forward from 0 BTDC to 20 BTDC, and the vacuum has no change at 16.5. I have two questions:

1) What are the solution to solve the sawing sound problem? Anything I am missing here apart from AAV and vacuum leakage?

2) How can I increase the vacuum back to normal 17-21 inch?

Thanks for the help in advance! Appreciate any of your comments.  

Hi Unknown,

would be great if you let us know your name. Makes it smoother to write each other.

The part that AAVpart.com sells does not look like the one you would need. Have a look for Bosch F 026 T03 038 and you will see the difference. ANd on top you need housing, sealring, cleaning, lapping and adjusting ...

If you do not have a level of 500 mBar vacuum, there can be many reasons. If you do not find a vacuum leak in hoses and manifold bridge - which is normally the case - you have to check cylinders by pressure loss test.

Pardon me, all I was thinking is that I want to make the question/ situation clear, therefore forgot to introduce myself. My name is Danny from Hong Kong, and I have a Mercedes 280 SEL v8 3.5 and a BMW 3.0 CSL, which are both D-Jetronic. This website has always been my go-to place for my car related questions, and it is full of friendly experts here, who helps DIY car owner a lot. Appreciate that!

Since I have several problems for the same car, would you recommend me to create multiple threads for each question or one thread for all the questions, so that to facilitate efficient discussion with all the detailed context?

Also, the reason why I bought the parts from AAVparts.com is that they confirmed me the parts they provides is matched and compatible with my original parts ID. When it arrives, it looks the same to me and I have no problem installing it. Do you think the new parts is what caused the problem? If yes, how could I check? do you think i should buy the Bosch F 026 T03 038 for replacement from your experience? Appreciate a lot for your input and guidance on this. Thanks a lot!

Best regards,
Danny Cho

Hi Danny Cho,

it is better to have multiple threads. DId you notice that the thermostat of AAVpart.com looks different than the real replacement? Ask them for technical data: From which min to max temperature does their thermostate move with how many mm/°C ?

Thanks for your prompt reply! I will purchase the correct parts BOSCH F 026T03038. Btw, the car only cranks but not running this morning, which looks like a similar problem that I posted before in my previous thread "D-Jetronic problem". I will check and troubleshoot, then make a quick update in the previous thread for further discussion. Thanks again!

Best regards,
Danny

Hi Danny,

careful! You cannot mount this part in your AAV. You also need a holder, sealing etc. fitting in your AAV. This part is just the thermo element inside that holder.