Economy Gauge poll for M103 owners - PeachParts Mercedes-Benz Forum

ps2cho · #1 08-24-2009, 12:42 PM

I have noticed that my wagon's economy gauge is very "sluggish" to move in general compared to my 260E which responds to throttle very quickly.

I was wondering if this should point to anything as to my lack of decent MPG (I get about 12mpg)?

Does your gauge respond quickly to throttle or is it a tad sluggish?

pawoSD · #2 08-24-2009, 01:11 PM

It moves "smoothly" but quickly on mine. It doesn't "dart around" if that is what you mean. It responds quickly to any changes I make with the pedal, or if the A/C engages....or if I add electrical load (defroster)....

ps2cho · #3 08-24-2009, 02:33 PM

My 260E is smooth, but quick....the Wagon is smooth, but NOT quick. It's almost like delayed.

RBYCC · #4 08-24-2009, 02:58 PM

Could be indicative of a vacuum leak.

eatlead · #5 08-24-2009, 08:24 PM

mine moves quickly

Lead
91 300SE (M103)

ps2cho · #6 08-25-2009, 12:22 AM

Quote:

Originally Posted by RBYCC

Could be indicative of a vacuum leak.

I checked the end that attaches to the intake manifold and it appeared fine...so the only other end to check is at the instrument cluster. I really didn't want to pry it off because it never quite sits as flush once removed due to the warping with time. I guess I gotta just bite the bullet and try it.

...although I doubt something as small as this could be my poor MPG, right?

RBYCC · #7 08-25-2009, 09:06 AM

Quote:

Originally Posted by ps2cho

I checked the end that attaches to the intake manifold and it appeared fine...so the only other end to check is at the instrument cluster. I really didn't want to pry it off because it never quite sits as flush once removed due to the warping with time. I guess I gotta just bite the bullet and try it.

...although I doubt something as small as this could be my poor MPG, right?

Vacuum leak could cause poor running and mpg.

You don't necessarily have to have a leak in hose from the manifold to the gauge.

The gauge will react to any loss of manifold vacuum regardless of where it is.

Disconnect the hose at the manifold and install a vacuum test gauge.
The readings should give you an indication of any potential problem.

I tee off from behind the dash econ gauge and feed a vacuum/boost gauge.
If you have a tight system, the gauge should react quickly and read dependent on true engine vacuum.

ps2cho · #8 08-25-2009, 10:41 AM

Quote:

Originally Posted by RBYCC

Vacuum leak could cause poor running and mpg.

You don't necessarily have to have a leak in hose from the manifold to the gauge.

The gauge will react to any loss of manifold vacuum regardless of where it is.

Disconnect the hose at the manifold and install a vacuum test gauge.
The readings should give you an indication of any potential problem.

I tee off from behind the dash econ gauge and feed a vacuum/boost gauge.
If you have a tight system, the gauge should react quickly and read dependent on true engine vacuum.

Yes. That's what I thought. It's just odd because I've done all the vacuum hoses....so I'm kinda at a loss. I even used the O2 sensor and plugged each of the vacuum ports then undid each one individually monitoring the O2 sensor for any change...and there was no difference.

I'll give the vacuum test gauge a try though and see what happens.

ps2cho · #9 08-25-2009, 03:25 PM

Do you happen to know if there any specific values that I could test the vacuum for?

MBeige · #10 08-25-2009, 03:38 PM

Could be a vacuum leak, or a clogged line. Clogged line would restrict flow so the response might not be as quick as the other one.

When you pry it out clean it thoroughly inside. Brake cleaner comes to mind. Of course clean it when it's disconnected from the car.

Then replace the two rubber ends with fresh ones. Not sure if the gauge has any corresponding values to it, to me it seems more of a qualitative gauge indicative of whether you're getting good or bad MPG. As long as it holds vacuum I would think you're fine.

tinypanzer · #11 08-25-2009, 09:19 PM

When I had my cluster out, I hooked a hose to the economy gauge and was able to suck with my cheeks and make it move through the entire range. It responds instantly. If your gauge behaves this way when removed, I would suspect a vacuum leak or possibly a partially blocked hose.

RBYCC · #12 08-26-2009, 08:59 AM

Quote:

Originally Posted by MBeige

Could be a vacuum leak, or a clogged line. Clogged line would restrict flow so the response might not be as quick as the other one.

When you pry it out clean it thoroughly inside. Brake cleaner comes to mind. Of course clean it when it's disconnected from the car.

Then replace the two rubber ends with fresh ones. Not sure if the gauge has any corresponding values to it, to me it seems more of a qualitative gauge indicative of whether you're getting good or bad MPG. As long as it holds vacuum I would think you're fine.

Gauge reads about 15 - 0 vacuum...

If the OP installs a test gauge at the manifold port he'll be able to determine if the problem is in the line or connector to the gauge.

If the test gauge remains low under throttle change then there may be a vacuum leak.

ps2cho · #13 11-01-2009, 01:33 PM

Quote:

Originally Posted by RBYCC

Gauge reads about 15 - 0 vacuum...

If the OP installs a test gauge at the manifold port he'll be able to determine if the problem is in the line or connector to the gauge.

If the test gauge remains low under throttle change then there may be a vacuum leak.

I just got my vac gauge today. Is there a normal value for idle and what would "remains low" be considered as?

86560SEL · #14 11-03-2009, 06:31 PM

Quote:

Originally Posted by pawoSD

It moves "smoothly" but quickly on mine. It doesn't "dart around" if that is what you mean. It responds quickly to any changes I make with the pedal, or if the A/C engages....or if I add electrical load (defroster)....

Same here on my 300SEL

azurite300E · #15 11-04-2009, 09:14 AM

I suggest to get a MityVac kit, that will enable you to measure manifold vacuum, test for leaks, and also test gauges and actuators, etc. Look it up on google or ebay. Very inexpensive tool but very very useful.