Where's the boost??? - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 09-25-2006, 01:28 AM

I thought I'd try out my new boost gauge before building it into the car so I ran a temporary line from the intake manifold to the gauge. I fired up the engine in the garage but got no response from the gauge. I revved the engine to 3000 RPM -- surely that would get the turbo to spin, but no, the needle didn't budge. What's wrong?

Here's what I checked:
Gauge and line -- attached it to my air compressor and carefully increased pressure. Gauge works fine, even appears to be accurate.

Manifold port -- removed fitting, stuck screwdriver in port, not blocked by carbon. Attached rubber vacuum line to fitting, tried blowing into port through the line, no blockage sensed.

I haven't tried putting the gauge in the line to the ALDA as it (the line) is old and I don't want to risk breaking it until I have a spare on hand.

Admittedly, my experience with turbocharged cars is slim, but the car runs well and I'm sure my mechanic would have said something when he checked it out in April if the turbo wasn't working. Does the car have to be on the road, with a load on the engine for any appreciable boost to develop? I must be missing something. Please help!

Jeremy

#2 09-25-2006, 01:31 AM

The engine needs to be under load to get readable boost.

pawoSD · #3 09-25-2006, 07:58 AM

Yep, you'll probably get no reading just reving it, my car generates about 4psi if I rev to 3500 or so, but I also restricted my boost line....

Take it out for a spin with the gauge and you'll get some readings.

Brian Carlton · #4 09-25-2006, 08:45 AM

Quote:

Originally Posted by ForcedInduction

The engine needs to be under load to get readable boost.

Agreed.

Jeremy5848 · #5 09-25-2006, 11:15 AM

OK, I'll go for a ride this morning and report back. I'm also concerned about the tiny 1/8 inch tubing that connects the manifold to the gauge; I think it will slow the response of the gauge, which is already heavily damped. Fortunately, upgrading to 1/4 inch tubing and fittings will be easy.

Thanks for the guidance. What a great group!

Brian Carlton · #6 09-25-2006, 11:40 AM

Quote:

Originally Posted by Jeremy5848

I think it will slow the response of the gauge, which is already heavily damped.

It won't.

Brewer · #7 09-25-2006, 03:21 PM

Where did you get the gauge? (not trying to help, I just want one also)

d.delano · #8 09-25-2006, 04:12 PM

Yeah where did you get that one
I got a $18 JC Whitney special that does the job
but I want one of those VDOs with 0-15psi boost press reading only like you got

Jeremy5848 · #9 09-25-2006, 06:53 PM

The gauge is from egauges.com. Their number 150-101. See this link:

http://www.egauges.com/vdo_mult.asp?Type=Turbo_Boost&Series=Vision&Units=E

The 15 psi "Boost" gauge is $32.50, not including tubing, which is available in several kits or you can roll your own. The input to the gauge is 1.8 male pipe thread which easily connects to either 1/8 or 1/4 inch tubing.

This particular gauge family, the "Vision" series, has really good lighting, something that us old farts with our weak eyes especially appreciate. The Vision series is also a good appearance match for the factory gauges in the W123 cars.

Jeremy5848 · #10 09-26-2006, 04:38 PM

Here are some initial results for the Boost and EGT gauges. I wasn't able to push the car as much as I wanted -- it's a cool day and the traffic was heavy, but I learned a few things. The photo shows my "installation" -- I didn't want to start drilling holes until I was sure the gauges worked. I'll get pictures of the gauges in operation when the installation is complete.

I fired up the car today and drove into town. The road to town has a 55 MPH limit so I was able to push the pedal pretty hard. The boost got up to 10 psi at 5000 RPM and then dropped back to about 7 or 8, even though I was still accelerating -- I suppose that was the waste gate opening. The EGT gauge got up to about 450F and the water to 80C.

Once in town, I parked and let the engine idle (800 RPM) while I made some notes. There is no boost at idle, of course, and the EGT dropped down to 360F while the water temp remained at 80C, which is where it usually sits in "normal" driving in this car.

On the freeway (70 MPH, level pavement) the Boost is quite low -- only 2 or 3 psi. The EGT stayed at 450 and there was too much traffic to allow heavy throttle up the little bit of hill that is the only high-speed slope in the area. I was able to get the EGT up to 650F (at 70-80 MPH) but even on the upgrade the Boost never climbed above 5 psi. I was surprised it stayed that low -- comments, anyone?

So the gauges work. Now I can build them into the dash. Stay tuned!

#11 09-26-2006, 11:18 PM

450* is quite low. I see between 600-800*f at a steady 60mph highway speed. 900* is common before 35mph during a spirited acceleration from a stoplight. I hit 1400*f before I reach 75mph.

Can you post a picture of where you have your thermocouple installed?

Jeremy5848 · #12 09-27-2006, 12:29 AM

Quote:

Originally Posted by ForcedInduction

Can you post a picture of where you have your thermocouple installed?

See the first post in this thread.

#13 09-27-2006, 01:37 AM

Ah. One of those "DUH!" moments.

Carson357 · #14 09-27-2006, 02:55 AM

Quote:

Originally Posted by Jeremy5848

The gauge is from egauges.com. Their number 150-101. See this link:

http://www.egauges.com/vdo_mult.asp?Type=Turbo_Boost&Series=Vision&Units=E

The 15 psi "Boost" gauge is $32.50, not including tubing, which is available in several kits or you can roll your own. The input to the gauge is 1.8 male pipe thread which easily connects to either 1/8 or 1/4 inch tubing.

This particular gauge family, the "Vision" series, has really good lighting, something that us old farts with our weak eyes especially appreciate. The Vision series is also a good appearance match for the factory gauges in the W123 cars.

where did you get the egt guage? from same site?

Ara T. · #15 09-27-2006, 07:04 AM

Interesting. Lemme know how much boost you get when you are going 70 mph and you give it 1/2 to 3/4 "throttle."