Working on the Alda and manifold line, I just discovered that the overboost switch (I think that's what it is--on the firewall, with a line in from the ALDA and a line out to the banjo fitting on the manifold) is not working at all. The inlet from the manifold was totally plugged, and I can't seem to get it cleaned out.

I hooked the two tubes together, bypassing the switch, and the car runs very significantly better.

Is there any danger in running the engine without the overboost switch, until I can get a new one? Or is the switch repairable--I can't find any way to take it apart.

I seem to recall someone saying that they permanently bypassed the overboost switch. True?

Advice would be appreciated.

From here:

"An important point to remember regarding the overboost sensor switch is that there is a "reverse" release or venting that takes place which is important. When the car is decelerating, you still have a lot of boost which is not needed. During this time, you don't need the accompanying fuel that would normally be injected at a given boost level [due to receiving "false" information on boost "needs"]. The overboost sensor switch vents the boost at this point so that the injection pump is not getting the signal to continue fuel flow at that particular boost level. This is specifically noted here since it has been noted that these switches are bypassed by unknowing do-it-yourselfers who, in addition to causing the engine to consume excess fuel during deceleration, put their engines in jeopardy by removing this catastrophic failure device."

Sounds like good enuf reason to me NOT to bypass it.

__________________
Chris
1985 300SD - 'Grace' (198K mi.)
2018 Honda Civic Sport
2018 Honda CRV LX
2010 Honda Fit Sport (RIP)
2013 Honda Accord Sport (Sold)
1996 Lexus LS400 (Retired)
1995 Ford Contour SE (Retired)
1976 Porsche 914 (Sold)
1972 Datsun 240Z (RIP)

I guess the question was more if it was problematic to drive the car temporarily with the overboost bypassed. Or better to leave it hooked up and non-functioning (line from manifold to Alda plugged) to drive the car temorarily (until I get a new switch).

Speaking of new switch, I can't find one list on FastLane. Is there another name for the switch, or does FastLane just not have them? Anyone know?

Thanks,

What year car do you have. I will send you the one I took off of my car for shipping cost. Took it off about a year ago. I just run the boost signal tube straight to the Alda. I did run a test to see what kind of boost I get wide open and it never gets above about 8.5 psi.

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Jim

Hi Dweller,

I hope you won't mind me chiming in on your thread. I am going through the same problem. The overboost protection switch is cronically clogged. I run a paper clip in it from the bottom and then blow through it with a can of compressed air, only to have it clog again in a short time. Would it be OK to spray carb cleaner or other solvent into the switch for a good soaking and then blow it out?


Also, is the EGR valve contributing to the gunk? I have not disabled it as yet...

Many thanks,

Steve (8C>

I don't know the answer to your question. Mine seems to be totally inoperative--the electromagnet won't budge the plunger. I'm soaking it in liquid-wrench, but that doesn't seem to be doing anything. I know there are some rubber parts inside, and I'm not sure if they'll be affected by carb cleaner or liquid wrench.

Well....I'm finally understand a little more about how this stuff is hooked up and what the names are.

I grounded the overboost switch (on the intake manifold) and can hear the overboost VALVE clicking. This allowed me to blow thru the valve when the switcfh is ungrounded. When grounded, if I blow thru the VALVE, the air is vented to atmosphere like it's suppose to....so the VALVE is apparently working.

Only question I have is that there definitely IS some amount of restriction when blowing thru the VALVE. I just can't figure out if it's because the diameter of the hole in the VALVE is so small or if it's being partly blocked.

Anyone know what the tube going from ALDA to some blue valve thingy is?

__________________
Chris
1985 300SD - 'Grace' (198K mi.)
2018 Honda Civic Sport
2018 Honda CRV LX
2010 Honda Fit Sport (RIP)
2013 Honda Accord Sport (Sold)
1996 Lexus LS400 (Retired)
1995 Ford Contour SE (Retired)
1976 Porsche 914 (Sold)
1972 Datsun 240Z (RIP)

"Blue Shiny Thing" is the vacuum amplifier! A search of this term should lead to a couple of threads where this is discussed by "gsxr" if I recall it is used to condition the vacuum to the tranny modulator. Good Luck!

Sorry for my ignorance--what's 8.5 psi relative to the 1.1 bar that's dangerous?

1.1 bar is ~ 16.2 psi at sea level, so he's well within range.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)