Ideas as to huge MPG drop since overheating? - Page 3 - PeachParts Mercedes-Benz Forum

ps2cho · #1 10-21-2010, 05:14 PM

Quote:

Originally Posted by macdrone

Hey I see you found alot of things that probably has alot to do with fuel consumption but you just fixed the A/C didnt you? 10% fuel consumption if its not on E/C setting for sure. That compressor is pulling huge power off you. Just watch mythbuster had a full segment on A/C and windows down. In town A/C is just sucking gas from you. Just so you know if you didnt. No offense or sarcasam I swear. I just didnt see you say anything about your A/C.

I did, but I ran several tanks full of gas with the A/C functional and lost only about 1-2mpg...so I was still getting 19-21mpg. 12-13 now is something different.

I will check voltage at the sensor while running like you said. Will report back.

ps2cho · #2 10-25-2010, 02:23 PM

Fuel pressures are dead on....

I hooked up my vacuum gauges for the heck of it....Anybody know the idle specs that I should be looking for at idle? Do mine look about right?

ps2cho · #3 10-25-2010, 03:55 PM

2 more tests done

1) Have 13.9v at the O2 sensor white wire.
QUESTION -- Only ONE of the wires showed voltage. The other did not give me a reading. Should BOTH white heater wires give voltage?

2) Probed EHA and it gave me a fluctuating reading between 8-10mv. What does this indicate?

ps2cho · #4 10-26-2010, 05:02 PM

Somebody recommended putting a sniffer on the exhaust. I have found a local shop that may be able to get a CO2 machine on the car for me...

Will that help me in any way figure anything out?

I think I will unscrew the O2 sensor and just physically feel if it heats up instead of guessing regarding the voltage on the wires.

timmyr · #5 02-01-2011, 07:48 AM

Quote:

Originally Posted by ps2cho

I think I will unscrew the O2 sensor and just physically feel if it heats up instead of guessing regarding the voltage on the wires.

You can check to see if you are getting 12-13 volts to your oxygen sensor heating circuit from the passenger side footwell. Just remove the floormat, and then find the two white wires, leave them plugged in and just back probe them (you should be able to do so on the connector, just look for the metal leads)

from reading up on the forum i came across another oxygen sensor test that you could try. i'm not 100% sure if it applies to your car but, what the hell, its worth a shot.
try this to check what kind of output(voltage) you are receiving from your oxygen sensor output wire when it is disconnected from the ecu. to do so:
1. make sure the car is at operating temperature
2. do not disconnect the oxygen sensor heater circuit(2 white wires) because the oxygen sensor will not output a proper voltage unless it is at proper operating temperature.
3. you can then disconnect the oxygen sensor output wire from the ecu, and then hook up your positive lead from your digital volt meter to the O2 sensor output wire, and the negative lead from your voltmeter to ground(i use batt. neg terminal). this should give you an idea of how the engine is running without the computer . a low reading could be a vacuum leak , whereas a high voltage would probably indicate a problem with your fuel delivery.

good luck

timmyr · #6 02-02-2011, 04:11 PM

I also found a chart in one of my Bosch books,called "Typical K-Jetronic Symptom Chart"

under "Fuel Consumption Too High"
it haas the following:
1. Cold start valve leaking
2 "Warm" control pressure too low
3 Basic idle setting incorrect
4 Lambda control system not functioning correctly

ps2cho · #7 11-16-2010, 03:59 PM

Want to keep this thread together for future searchers.

My o2 sensor readings. Does it show anything? I can't seem to make heads or tails of it.

http://www.youtube.com/watch?v=QAmRXaGyW0w

ps2cho · #8 01-20-2011, 02:42 PM

bump...

Any other ideas?
I'm gonna swap in a spare fuel distributor I have cleaned up and see what happens.

What are the chances the injector tips could have gotten damaged during the overheating incident?

Aquaticedge · #9 01-20-2011, 03:52 PM

Anything is possible. If you can take them out have a look at them. Have them pop tested to make sure they open at the right pressure. Id also suggest looking at the exhaust system. If you have cat converters they may be partially obstructed. High egt's and engine heat can melt them a little and cause your engine to work a little harder

JamesDean · #10 01-20-2011, 07:12 PM

Alright dude, Lets try this systematically:

1) Federal or Cali Car?
2) Duty Cycle Read out (x11) at op temp idle and 2500rpm?
3) If constant %, then we got a fault.
4) If not constant %, we're gonna test all the CIS-E mixture related devices.
This is from a 560SEL, but most of the same stuff is in the 124 m103. The m103 126 didnt have a nice diagram like this...

Make sure each component is working within normal parameters, then make sure the CIS-E computer is getting the data.

alienman · #11 01-20-2011, 09:29 PM

Wow, thanks for posting the flowchart! Now I have to figure out where the heck the EGR temp sensor and altitude sensor are on my 126

ps2cho · #12 01-21-2011, 02:18 AM

O2 sensor and mixture are responding normally....

45-55% duty cycle, O2 sensor 0.1v-0.9v. If I try to lean out the mixture, the engine becomes very choppy.

Brand new EHA and O2 sensor...all ignition components are new. No vac leaks. New fuel filter. That is why I believe it could be fuel related.

California, but as an 87 just has the O2 sensor light.

ps2cho · #13 01-22-2011, 01:22 AM

Read an interesting post by Stevefbl....
http://www.peachparts.com/shopforum/showthread.php?t=116704

Quote:

Originally Posted by stevebfl

Actually unless you are below 59 deg the cold start valve doesn't work. This means that the combined enrichment of starting and starting cold allows fuel to flow at cranking speeds. The amount of fuel is that which runs the car 20 miles to the gallon or about twenty minutes to a gallon at road speed.

If you think about that, you will see that the amount of fuel used in each stroke is quite small. It won't spurt. Even if the airflow plate is held way down the flow will be small.

The mechanism I use for basic setting of mixture after the fuel distributer has been replaced is to bypass the fuel pump relay and adjut the mixture till fuel rises in the threads on a removed fuel line. Once flow is noticed the mixture is adjusted lean till it doesn't flow. Key on engine not spinning there should be no flow. Push the plate down and there should be even flow from all six chambers.

Might give it a shot when I swap distributors tomorrow. Should be interesting!
May also try a shot at fuel quantity measurement...Might be worth just pulling the injectors.

I'll give a shot at cleaning them first too. A visual inspection may give an idea to if the overheating caused any damage....

hstuehmeyer2000 · #14 01-23-2011, 08:24 AM

Check the fuel pressure regulator. When it starts to leak it will vent into the intake via a vacuum line.

ps2cho · #15 01-25-2011, 10:46 PM

Quote:

Originally Posted by hstuehmeyer2000

Check the fuel pressure regulator. When it starts to leak it will vent into the intake via a vacuum line.

Regulator is good, no fuel going through vacuum line.

I received a new set of injectors + seals today. Gonna get them in tomorrow and fingers crossed that resolves it. I opted to check out my current insulators first before spending an unnecessary $35 on those suckers.

In any case, the car is long term so probably a good move anyway.