turbo pressure switch

[luckys420]

the turbo pressure switch on my 1980 300td ( its had a turbo adapted) is not hooked up to any thing. how and what does it hook up to? any help would be much appreciated thank you
lc

[sixto]

It should hook up to an overboost swtichover solenoid to interrupt the signal from the intake manifold to the ALDA.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

[luckys420]

would this be an electrical hook up? the manuals I have do not say anything about how it is connected.
thanks for the quick response.
lc

[sixto]

There's constant +12V to the solenoid. The ground circuit is closed when intake manifold pressure gets to the setpoint of the pressure switch, whatever that is (1.1 bar?).

How is the line routed from the banjo bolt at the back end of the intake manifold to the ALDA?

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

[R Leo]

The overboost valve electrical connections are shown in here:
Time bomb? overboost protection switchover valve

[luckys420]

thanks sixto, i am going to take a look at the routing today.
and rleo, thanks for the link it was insightfull.
lc

Is there a way to adjust this switch for a different psi/bar?

[R Leo]

The pressure sensing switch is a sealed unit. No adjustment is possible.

[sixto]

There's little to be gained from raising the pressure switch setpoint since the IP can't provide more fuel to give more power. Folks who max out the ALDA don't trip the overboost protection solenoid.

Has anyone experienced a real overboost situation?

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

[luckys420]

both ends were plugged. the one on the manifold has a rubber stopper on it as well as the ALDA. Can I put a pressure line on there and worry about the electrical hook up later? or is it best to do it all at once?
thanks, this is great help
lc

[R Leo]

From my reading in this forum, it appears that the wastegates on these turbos rarely (if ever) fail to the 'high side' ..ie: too much boost. I'd say there's probably little risk in temporarily bypassing the overboost valve in order to get some boost pressure on the ALDA.

However, I would invest in an inexpensive 0-30psi gauge, some rubber tubing and a "tee" to plumb in so that you can monitor your boost on a real-time basis.

Go here for the straight dope on building a simple boost gauge:
Time bomb? overboost protection switchover valve



BTW...the reason you don't have any of the overboost circuitry is because the 1980 model wagons didn't come with turbocharged engines. IMHO, I'd just plumb a boost gauge in that line to the ALDA and drive. Keep an eye on the gauge when climbing hills.

[R Leo]

Originally posted by luckys420
my 1980 300td ( its had a turbo adapted)

One more thing....
Do you know if this turbo was added to the existing engine? Or, was a turbocharged engine used as a replacement for the old n/a OM617?

If the turbo was added to the original engine, you may ultimately experience some complications. The OM617.952 engines (stock turbo install) have some significant differences in their design that allow them to tolerate the combusion conditions encountered when operating at full boost.

[luckys420]

i am not sure if it has been added or the entire engine replaced. any ideas on where to find engine id numbers?
lc

[sixto]

Put a line just to try it out. You might as well not have a turbo if you don't have that line.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

The reason I wanted to adjust the switch is to make a keen little light come on in the cab just to say "Hey, you've got full boost." Ya' know, impress the riders and make the car that much more "Unique".