Ideas as to huge MPG drop since overheating? - Page 4 - PeachParts Mercedes-Benz Forum

timmyr · #46 02-01-2011, 06:48 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 · #47 02-02-2011, 03:11 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 · #48 02-02-2011, 04:45 PM

When disconnected from the ECU, the o2 sensor reads 0.8v...very rich.

Has anybody ever tried eliminating the cold start valve? I'm wondering if I can find a threaded screw and simply plug up that port in the fuel distributor....

timmyr · #49 02-02-2011, 08:15 PM

I have consulted the book again and it says to test the starting valve for proper operation and for leaks.

to test for proper operation of starting valve:
1.disconnect fuel line from starting valve.
2. remove valve and then reconnect fuel line.
3. place the valve in a container.
4. it then says to simulate 10kOhm resistance at the coolant temp. sensor, using some sort of resistance substitution unit.
5. disconnect green wire on electronic ignition control unit.
6. crank engine while observing the valve eject fuel.

test the valve for leaks:
make sure the valve is dry, and that it is not dripping/leaking .
the book does not mention whether or not the car should be on or not, nor does it say anything about simulating a resistance at the coolant temperature sensor, which i would guess should probably be at around 250/Ohms =90C simulating an engine at normal operating temp. i guess that you should just make sure that the cold start valve isnt delivering fuel at normal operating temp. while it is out of the intake manifold.

good luck

DRBC43AMG · #50 02-04-2011, 09:09 AM

Suicide perhaps?

Just joking, but I have to admire your drive to get this problem resolved

ps2cho · #51 02-07-2011, 03:36 PM

Checked fuel pressures with the new EHA in again.

Cold
5.2bar // 5.7bar

Warm
5.1bar // 5.5bar

Dead on spec, so new EHA's do not need any adjustment from the factory. System is definitely in closed-loop, there is no doubt about it. That is why this whole scenario is just so confusing.

--------------

O2 sensor heater wire has 14v. Heater element is working.

--------------

Disconnected cold start valve at the fuel distributor completely. I simply removed the fuel line and used one of the fuel pressure test port plugs from a spare distributor I had to close up the fuel hole.
Drove car...no difference, still sluggish and duty cycle is still hovering 50-55%. O2 sensor probe when warm still reads .78-.82v so still running rich.

Everything fuel-wise seems to be checking out....this is bugging me a lot.

Next?

jt20 · #52 02-07-2011, 03:48 PM

You did not previously mention the sluggish performance. Perhaps you should update the current conditions?

I thought the work flow diagram was a great idea, why haven't you completed it?

Regardless, I have been watching this thread... its driving me nuts. I can't honestly say I am familiar with these engines, but here are my top interests:

- EGR, A minor malfunction could cause poor running... however, I am not so sure it would cause such a large drop in MPG. But disabling it should be easy enough.

-Brains... who is making the decision to run rich with sensor input (swap another good one to test for a few weeks)

-throttle position sensor (there is something to that effect, correct?)

-maybe an early exhaust leak or a late intake leak

ps2cho · #53 02-07-2011, 04:43 PM

I mentioned the poor acceleration + fuel economy earlier in the thread...
It just does not accelerate hard like it used to. It almost "feels" like the engine is being flooded during acceleration because it does not spin as quickly. Before I could give it light throttle off the line to about 2500rpm then kick down hard and it would really, really pull almost chirping the tires. I can't get anywhere near that close anymore.

Found the influencing variables for my particular model:
I've crossed off everything I've 100% ruled out.

O2 sensor is brand new, and it reads the same, albeit refreshes faster, as the old one.
No TPS, only airflow potentiometer. I will check voltage though to confirm (7v +-.10v at idle).
No EGR on 87 M103.

Any information on how to check:

-Altitude Sensor?
-Hall Sensor?

jt20 · #54 02-07-2011, 04:51 PM

The flowchart in post #37 is much more elaborate... is your model different?

Your chart does not mention EGR. Have you checked that already?

ps2cho · #55 02-07-2011, 05:01 PM

No EGR on an 87 M103.

That chart is for a 560 V8. The 87 model is KE-Jetronic, but without check engine light (only o2 sensor) and does not have the California emissions equipment that was included in model year 88. My 1988 300TE has all the California elements that is how I know. This chart is correct for my model.

jt20 · #56 02-07-2011, 05:22 PM

The chart does not mention the OVP. Wouldn't this affect the control unit if it was faulty?

ps2cho · #57 02-07-2011, 07:09 PM

Quote:

Originally Posted by jt20

The chart does not mention the OVP. Wouldn't this affect the control unit if it was faulty?

True.

I've replaced the OVP, and if the OVP was non-functional, CIS-E goes into open-loop so I know its all good.

Bought the MB recommended Hirschmann backprobe addons for my Digital Multimeter. I should be able to properly backprobe the airflow potentiometer now.

Shame the built in screw to hold the leads from the DMM is super, super tiny and now I have to go buy a microscopic screwdriver

never ends! LOL. Out I go again...

ps2cho · #58 02-07-2011, 08:14 PM

Potentiometer checks out to spec....Was hovering around 0.7v +-0.15v....I think that's close enough right?

-------------------------------------

I'm having trouble with this EHA Test Harness....I cannot seem to get a reading.
The EHA does not function with the harness plugged in because the engine note does not change and the system goes into open loop.

Any ideas what I could be doing wrong? If I can ensure that the EHA is not enrichening the mixture it will help a lot.

jt20 · #59 02-08-2011, 02:23 AM

Does this help?

Using EHA test harness

Your DMM leads are supposed to get the alligator clips.

The Test harness plugs into the engine harness.

It probably doesn't seem like it, but I really am trying to help.

tinypanzer · #60 02-08-2011, 05:16 PM

It looks like you're trying to measure the current draw of the EHA valve in operation, correct? And I assume that you've rigged your meter so that it lies in series with the voltage being supplied to the EHA as well?

If the answer to both those questions is yes, then you have set up the rig correctly. However, I don't think that's the problem here. I think that the EHA voltage is a pulsed current (somebody correct me here if I'm wrong) and a digital meter will have a hard time getting a reading on a rapidly pulsing signal, for current measurement especially.

Either that, or you've got an open circuit, or the impedance of the meter is too high for the circuit to be happy...

So, just to sum up where we are here -- The car is sluggish and runs rich. You've eliminated a ton of things, have you eliminated the fuel distributor, particularly a sticking piston? Also, have you eliminated plugged up cats?