boost gauge!
 

I put a gasser economy gauge in the 300D to serve as a boost gauge. It took a lot of finger crossing but it appears the gauge set I got at the PNP works as well as the original gauge set. So far no smell of burned electricals or crazy behavior but I haven't gotten the engine to operating temp so I don't know if the temp gauge is good. Fuel gauge reads about where it did prior but that's another thing to keep an eye on.

I've read about folks drilling holes and soldering and whatnot. I'm not sure what that's about. This was a straight gauge swap. I didn't transfer the economy gauge to the tri-gauge module in my car. Goodness, I'd rather replace a transmission... uhh... in a 126 :) Maybe the gauges will go south on me and I will have to do that custom work :eek:

Per jbaj007's instructions, I set the economy gauge pointer to 10 o'clock which worked well in the SDL. I had to tweak it closer to 9 o'clock in this car because the gauge wouldn't lift until close to 10 psi. At the current setting it reads about 5-12 psi which is the range that matters to me.

I must say the 124 keeps finding ways to confound me. The 126 has lots of room to get lines through the firewall and similarly lots of room to work behind the cluster. The 124 formed grommet is tucked under dash. There's an obscure line of sight from the engine bay and some wishbone bracket behind the gauge cluster that prevents a hand from getting to the grommet. I had to push the plastic line through the rubber boot with finger strength. My hands and forearms look like I refereed a tomcat fight.

Sixto
87 300D

I have no problems using an economy gauge as a boost gauge in my car.

Pardon the ignorance; but what exactly is an economy gauge?

http://www.speedofixer.co.uk/images/bmw_e39_whiite_s.JPG It uses either vaccume or boost to show a barbaric mpg average.

Exactly.

In this case, I repurposed the vacuum gauge to react to manifold pressure.

I pinched this picture from a 300E on eBay.

Sixto
87 300D

Does it still say "premium unleaded fuel only" on it? :repuke:

That seller is running the fuel tank dry! (if its reading right.... :D ;) )

Gas W123 gauges don't have that printed on them.

Sixto, does the gauge read "backwards" (higher boost to the left)?

Sixto and I both have 124s so some detail work would be required. Maybe a little touch-up paint? When did the "unleaded" warnings start being put in cars?

No, it stays in the black and moves into the red with boost.

OK, I got the 4-gauge panel from the instrument cluster of a 1986 or 1987 300SD today at Windsor Pick and Pull. I don't think the gauge panel will swap into my '87 diesel but I'll pull its cluster and compare. If that won't go, I'll try to build the vacuum gauge into my panel.

Incidentally, the SD gauge panel has only a gas pump symbol on it -- it does not say "unleaded" or have any words at all besides the symbol. If I can adapt this thing correctly, I can transfer the gauge face to my cluster and overwrite "ECONOMY" with "BOOST."

Success at this project will solve a worry that I've had for some time -- how to build boost, EGT, and volts gauges into the '87, which doesn't have as big an ashtray as the earlier W123 cars. You can get three gauges in a 123 ashtray but only two in a 124. With the boost gauge built into the instrument cluster, I can have the EGT and volts in the ashtray area.

Jeremy

You found an 86-87 SD? Midbadged, perhaps? The 86-87 SDL didn't come with an economy gauge. Maybe someone retired my gold 87 SDL which had the same mod :(

I had problems with an 88 or 89 300SE 4-gauge panel in my 87 SDL so I made sure to get an 87 300E 4-gauge panel for this mod.

In my case it's also an economy gauge. I figure I use less fuel in the black than in the red.

It's not a great boost gauge because it's highly damped. It's between 1 and 2 seconds slower than a VDO 0-30 psi boost gauge I used as a reference. There's only about a 7 psi spread between posts so you can't have it tell you how soon boost builds and how high it'll go. I just like to see it swing when I go up and down the hills on I-280 with the cruise control :)

And nothing but premium unleaded Diesel goes into the tank. So there :)

Sixto
87 300D

Not my field of expertise . . .
 

I am rather a dunce when it comes to the S-class cars, Sixto. It had trim panels on the lower doors so that makes it an SD or SDL, right? I found what remained of the instrument cluster (speedo gone) in the trunk of a 123 car I was "visiting;" the SD was in the next row. I took the cluster up there, sure enough, it had an empty hole in the dash that this cluster fit. So I assumed it belonged. Perhaps that was a coincidence and the cluster came from another car, but I don't know what it could be -- this P&P has mostly 123 and 126 models.

The cluster had a number in the plastic something like "87 xx1186," which I assumed was a date code. The 4-gauge panel was the only piece I bought; it has a date code . . . (running to the garage to check) . . . "5.86" on the PC board (looks like a QA stamp) so I assumed it was an '86 or '87 model. It has a 15-pin round plug/socket on the back of the PC board. The other three gauges are the same as my '87 diesel, temp in C, electric oil pressure in bar, fuel in fractions.

Comparing the photos (attached) to photos of my '87 3-gauge panel, it's clear that I will have to move the economy gauge movement and probably the gauge face to my panel. I won't know if it will be possible until I pull my cluster apart again.

Jeremy

Are all three 126 and 124 gauges interchangeable?