Ideas as to huge MPG drop since overheating?
 

It all started after the overheating issues I had...I ran the car at ~110C a few times while trying to figure out what was going on. I used the heater to keep temperatures down, but it never hit the red line.

Water pump and radiator later it is resolved and now purs at no higher than 95C in 115F heat here in Phoenix.
Could the overheating have done anything else?

Car idles smooth, no misfires....I have dropped from ~20mpg (~300mi to tank) to 12-13mpg (210mi to tank)

I've done a full tune up in the last 5k miles when I bought the car. All filters and fluids, rotor, cap, plugs wires, ovp...Duty cycle is ~45-50%.

Car drives fine although power seems slightly down, but nothing else out of the ordinary.

Any ideas how I can track down whats happening?
For my 87 260E

Failed engine/CIS temp sensors?

I replaced the 2 prong sensor 6 months ago after it cracked. A failed CIS temp sensor exhibits poor cold starts, but once warm no difference. I have no starting issues.

Just probed O2 sensor...Reads 0.8v. Definitely running rich according to O2 sensor.

Since the duty cycle reads 50-55%....what could be causing this rich condition? Injectors leaking? :confused:

Consider replacing the coil.

How would the coil be causing overfueling?

Do a compression test.

I think what he meant here was that since the oxygen sensor is in the exhaust system, which is after the cats it will only tell you if the exhaust gas is rich with fuel. The coil could have been damaged internally from the high heat and is no longer producing a powerful and 'complete' spark to burn all of the fuel/air mix in the cylinders before it is extracted out by the opening of the exhaust valve. A weak coil would leave an engine producing less power and give the impression to the oxygen sensor that the engine is running quite rich.

Other than that... :confused:

Is there a way to test the coil's output?

Whilst its possible that its the coil, in my experience, they either work or they don't. If the coil was failing then it would not start well, and misfire at higher revs.
We did a compression test a while back, admittedly before the overheat, but I see no rerason for anything to go bad.. its not like you fried it...

My guess would be something in the FI domain.
You already checked the temp sender, so that was a start.
Do a fuel pressure test, see if something is odd... you know what it was before, see if it changed.
Maybe the EHA went bad?
Leaking cold start injector?
I am also concerned about vac leaks... remember you had that idle hose fail, even tho it was replaced when you got the car.

Another issue is use... are you are doing more short trips with the A/C on full... could be a factor?

Went right for the EHA...and noticed it was wet. I checked O-rings and they looked OK. I removed it, cleaned all the surfaces and retightened the bolts (need new bolts too...these are getting stripped)-- But upon reinstallation I noticed this!

It seems to be weeping out a hole in the rear :confused:

Is this a 'weep' hole? Either way, looks like I need to replace it. It was quite handsomely dripping out when the car is running. Guess this could be it?
Although maybe I don't understand how that would cause an overfueling situation? I would have thought it would make the car run very lean?

http://w124-zone.com/downloads/photo...a-weephole.jpg

When EHAs go bad, it seems that they can cause all sorts of issues including lean and rich conditions...

I think if you replace this EHA with a good used unit or a new one, you will have solved the problem... but we shall see.

Well, if the EHA is failing to properly adjust upper/lower chamber pressures, then I suppose it could wind up being either rich or lean, depending on which "direction" it was failing.

I would still check the temp sensor by measuring its DC resistance, and comparing it to the temperature/resistance chart. The symptom you have seen with a bad temp sensor is what happens when it fails completely. If its value has drifted, that might give different results.

It's also possible that something got disconnected when the work was done. Also, on an M103, there is always the possibility of vacuum leaks even in spots you have already fixed.

In the case of buying a new EHA, does it require adjustment to set to factory settings or is it plug'n'play?

--
In regards to engine temp sensor...
Do you measure resistance with it at operating temperature? Compare it to the cluster sensor adjacent to it?

I replaced the engine temp sensor about 4 months ago, but I'll check it just in case also. Regardless though the EHA is a problem for sure.

http://w124-zone.com/downloads/photo...A/new-eha2.jpg
http://w124-zone.com/downloads/photo...A/new-eha1.jpg
http://w124-zone.com/downloads/photo...A/new-eha3.jpg

Going to put it in right now and report back later with the results.

Posted pics so you guys have the part #'s now for the screws. Although the dealer will not sell them separately, it may be possible to find them elsewhere now!

Nice, what did that beast cost? :eek:

Dropped $220 on it...


So after driving for the day and some adjustments back to 50% duty cycle (initial start was out of compensation adjustment -- Had to richen up for it to even begin reading), the car STARTS much faster and returns to the idle much quicker than before, but I am still plagued by the O2 sensors reading of rich (.81v - .88v)
Could we be looking at leaking fuel injectors? The mixture obviously believes that everything is fine.

Power is about the same at the bottom end, feels a little less at the top end.

Ideas from here?

I am reading that normal O2 sensor readings should bounce from 0.1 through 1v -- Lean to rich. Since I am getting a consistent RICH reading with no LARGE fluctuations, can I assume the O2 sensor is bad or carbon-fouled and giving inaccurate readings?

Hi..
did you test o2 heater coil?
here is from Mr. Arthur Dalton
The 3 test for heater are Resistance, short to ground, and current draw.
All these test are with connector unplugged.

test 1:
Ohms across white wires.. this is heater coil R test.
test 2:
Ohms across either white and gray. This is a heater short to ground test. There should be NO reading.
Test 3:
Bring 12v from battery to the white wires with an amp meter in series ..this is a heater current draw test. Looking for specs I mentioned in early post.

If all these test are OK, the heater circuit in the O2 sens. is OK
If any fail , replace the sensor.
These test only verify heater part of sensor and passing of these does not test the 02 sensors capacity to generate a sig to respond to rich/lean conditions

He talked about 95 E320 but I think it work the same way on your car too. Your o2 probably has 3 wires.
1.signal wire
2. heater core
3. ground
and the case of O2 is the ground also.
The heate coil R should be low (about 2.6 ohms on my car)
The current draw should be 1.2-2.2 A
The 12 volt supply to the heater core has to be measure when engine is running. You won't get it if the key is on ii positoin.

I too had a problem with idle and gas consumption (from 22 avg down to 13.5mpg and my o2 read up to .9 volt). After many months and many test, finally I got it fixed. In my case (M104 engine though) I don't have the 12 Volt to heat the o2 and another signs that point me to believe my ECM is bad (car is running though). After got the used ECM, everything is seem to be fine now. I will write what I found when I run the car more.
Don't know if this will help you, just my suggestion.

When you refer to heater coil, are you talking about heated O2 sensors? If so, these are not heated.

It is 3 wire, 2 white and 1 black. I assume 2 grounds and 1 sensor/12v wire. Does the test still apply?

I actually just found I have a brand new sensor from the 1990 Mustang GT that I can splice in. Forgot I bought one. Maybe I'll just splice it in and rule it off. The one I have in there may be original....Or at the very least has 50k on it.

http://w124-zone.com/downloads/photo...A/new-eha3.jpg

I'm from Wisconsin...what the hell are "Torx cheese-head screws" anyways? They better not smell like Limburger or that whole job is going to stink to high heaven before you're done!!! :rolleyes: :D

Yes, I mean heated o2 sensor, you should have heated o2 sensor too. 2 white (heater coil) and one black signal wire. One white should be +12 V and th eother white is grounded(remember this is when engine is running) The black wire is signal wire which use the case(of o2 sensor) as a ground. You can do bench test by take the o2 sensor out and put 12 v ( I used battery terminal ) and in just a few minutes you can feel the sensor is hot. I would do the current draw test too.
If you look at this diagram, you'll see what i mean.

http://www.autolib.diakom.ru/CAR/Mercedes-Benz/1988/300TE/WIRING%20DIAGRAMS/3160.pdf

Left corner bottom, under ovp relay
Like I said, I too suffer from drop MPG, got a new o2 sensor but no fix until I did the o2 sensor test and found no 12 V for heater coil which led to another more test.

Got the sensor out...


Anything jump out color-wise? New one I am splicing in as comparison.
Looks really rich am I wrong?
http://w124-zone.com/downloads/photo...ensor/o2-4.jpg
http://w124-zone.com/downloads/photo...ensor/o2-5.jpg


Test 1: Across both white wires = 4.6ohms.
Test 2: White Wire + Black = O.L.

Is test 1 a little high?

Either way I have a new sensor I found in my box I forgot I purchased. I will splice them in.
Which of the two white wires is the +12v? Or does it not matter and I am good soldering them together in no particular order?

Here are those tests....

http://w124-zone.com/downloads/photo...r/o2-test1.jpg
http://w124-zone.com/downloads/photo...r/o2-test2.jpg

Test 1: Heater coil resistance test -- I am not sure if that resistance is too high?

Test 2: The heater circuit is working. Hooked it up to my 12V battery /w amp meter inline....After about 30seconds the O2 sensor was too hot to touch.

That O2 sensor looks very bad. I took out mine on my '91 300E and it was original and just looked heat treated from being in there so long. Spliced in the same O2 you have there and had an instant improvement in idle but had to adjust air mixture to fine tune. I think I may have an EHA issue too but going to replace injectors, seals, fuel filter, and fuel pumps first. Always have hard cold and warm starts for some reason. Idles fine once started.

Drove last night got it all warmed up with the new sensor and I am still plagued by the rich reading.

So it is definitely running rich, it is not just a bad reading.

Ideas where to go from here?

Tested the coolant temp sensor tonight. I replaced this sensor about 6months ago because the old one broke. I know it has gotta be functioning fine.

Cold'ish: 1900ohms 5 minute drive 2hours earlier. Not stone cold.
Warm: 535ohms (79C @ cluster) 10 minute drive

Looks right....So cross that off the list I guess :confused:

As George560sel wrote, check that you have 12 volts being supplied to the O2 sensor with the car running. Your tests have only proven that the heater in the O2 sensor works when supplied with 12 volt source, not that the O2 sensor is being supplied by the ECM with 12v source necessary to operate the O2 sensor's heating element. Mark

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.

Fuel pressures are dead on....

http://w124-zone.com/downloads/photo...2010/fpt-4.jpg
http://w124-zone.com/downloads/photo...2010/fpt-5.jpg

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?

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?

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.

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

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?

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

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...

• http://i.imgur.com/MmPfTl.jpg

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

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 :)

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.

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

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....

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.

Did the injectors fix it?

Earlier on someone had underhood fumes issue diagnosed to a leaky EHA.
wonder if you had tell-tale smell of fumes .
mak

Finished up the injectors....
No difference unfortunately. The mixture went way off, so something changed for the better I hope.

It's just so confusing why this happened after the running hot incidents...
I keep wondering if compression or leakdown was affected, but I'm not burning any oil or anything.

Fuel filter is about 10k old...

Any thoughts on next?

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

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

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....

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

Suicide perhaps? :eek: Just joking, but I have to admire your drive to get this problem resolved :)