300sdl, replaced overboost sensor, still hesitates
 

hello guys, I recently replaced all the vacuum fittings under the hood, new fuel filters and an air filter, and I also replaced a sensor which is mounted on the firewall in front of the driver. The car was hesitating at speed and I was told to bypass this and it worked. But I have replaced it and I only have two vacuum lines to connect to it and there are three nozzles. There is one on the bottom which I have connected to the sensor on the intake right over the #3 cylinder, the connection on the front of the sensor runs down the the IP and there is a connection on top of the sensor which was broken off the previous one. I have no idea what should be connected to this nozzle. :confused: The car runs better but feels as though it is starving for fuel alittle around 80mph. If someone with an 86 300sdl can pop their hood for me to let me know where the vacuum lines are supposed to go I would really appreciate it. Thanks for the help in the past with my car, and thank you ahead of time.

The connection on the top of the overboost protection valve should be capped. It appears to be a common port to the horizontal port immediately adjacent to it. Use one of those rubber caps available locally. The factory part has a hard plastic cap that is rigidly secured to the port in some fashion.

Mine has been bypassed since before I bought it. Apparently they fail or otherwise get clogged. I understood that it is not a sensor, just a valve that opens and closes based on a sensor. Did you replace it with a new one? Is it getting a signal?
Dave

i bypassed it for a couple of weeks and the car ran alright. I than replaced it hoping it would help the performance. The car is very sluggish until I hit about 3000rpm. It feels as though there is no boost. I think the next piece to replace would be the alda. What do you think

I doubt the overboost protection circuit is causing problems with the onset of boost. The darned system gets so gummed up that a more likely failure mode is that it will react too late. As someone suggested, remove the hose fitting on the manifold and clean it. Then TEMPORARILY run a clean hose from the fitting to the ALDA. See if that improves anything. Then check that the overboost protection solenoid has clean and clear internal passages. TEMPORARILY leave the solenoid electrical connector off (or pull the wire off the sensor on the manifold) and see if there is a difference with and without a signal to the solenoid.

If it's the ALDA, good luck. They're not sold separately. Also a PITA to set properly without the proper bench set-up. Lots of guidance in the archives to get it close enough.

Brian, thanks, I did not know that about the solenoid fittings.

Sixto
95 S420
87 300SDL

FWIW, my car had similar problems. It felt like the turbo effect was MIA until about 3,000 rpm. I replaced all the fuel filters, tank screen, boost related hoses, and even the cat converter. Although a new cat helped, the car was still not the way it was when I bought it.

After reading some of gsxr's posts on ALDA's I decided to remove mine and pressure test it. It would not hold any pressure. I got a similar ALDA off of an '82 turbodiesel (yes, it has the same part number as the one from my '87) and it held pressure. I swapped ALDA's and added an extra spacer and my car is finally running the way it was when I bought it.