O2 sensors or fuel pressure regulator bad? - PeachParts Mercedes-Benz Forum

#1 08-11-2003, 04:45 PM

Hi guys,

Any thoughts about this one?

The car seems to run fine. Although I think there is a slight hesitation when I step on the gas hard now that I think about it. CE light came on and independent hooked car up to CS2200. The scanner showed that bank 1 and 2 O2 sensors bad.

He said that the scanner sometimes gave him bad readings about O2 sensors, because he said he has never seen all O2 sensors go bad at same time. He said it was probably the fuel pressure regulator that was bad.

I asked if that could be why my MPG was low at around 15mpg on a M119 with mostly freeway miles. He said yes. I have read the threads on fpr and I think it was Steve that said the fpr would not affect the mpg unless it filled up your crankcase.

I don't think my crankcase if full of gas. I just changed the oil and found no gas with it.

He cleared the code and said to bring the car back for him to check the fpr. Later that day the CE came back on. I asume that the code will be the same. Is he looking in the right direction for the problem? I am going to check the line for gas as recomended in the threads about fprs. I would like to fix the problem myself if it is the fpr. How much for the gauge to check fuel pressure?

Any thoughts would be appreciated.

Thanks.

stevebfl · #2 08-11-2003, 05:49 PM

This Steve would say that fuel pressure won't change mixture till all the systems capability to compensate was used up. Fast movement wouldn't be compensated for but a systematic loss or gain in pressure will be corrected for.

The pressure regulator is also known for leaking through its diaphram into the vent line which winds up in the intake of the rear of the motor.

The adaptation values are a big help here. A bad sensor is one making its own answers, this is pretty easy to monitor.

Arthur Dalton · #3 08-11-2003, 06:45 PM

As SB states , the system will correct for Reg pressure , but if the reg diaphragm is ruptured and allowing fuel to pass to the intake, this richness can be large enough to over-ride the systems corrective limits..[ adapt values ]
... on the same note, a vac leak can do the same thing in the other [ lean] direction...the leak, of course , having to be large enough to be non-corrected by the ecu limits..[ again,adapt values]

An easy test for o2 sensor reaction on these EFI systems
is to monitor an isolated o2 signal [ meaning unplugging the feed/sig line to the ECU] and watch the sig while disconnecting
and plugging the vac line to the Fuel Regulator..this causes an instant rich condition and should show up on your 02 signal as high voltage.
This verifies o2 sensors ability to recognize rich mixture condition..
For lean recognition test, simply creating a vac leak by removing a vac hose and watch for low voltage reaction...here one can simply put your thumb on/off the vac hose and watch the reading
speed change..
a little experince and you can tell a decent sensor , although a scope is killer for absolute diagnosis..

brookspw · #4 08-16-2003, 10:24 AM

Quote:

Originally posted by Arthur Dalton
As SB states , the system will correct for Reg pressure , but if the reg diaphragm is ruptured and allowing fuel to pass to the intake, this richness can be large enough to over-ride the systems corrective limits..[ adapt values ]
... on the same note, a vac leak can do the same thing in the other [ lean] direction...the leak, of course , having to be large enough to be non-corrected by the ecu limits..[ again,adapt values]

An easy test for o2 sensor reaction on these EFI systems
is to monitor an isolated o2 signal [ meaning unplugging the feed/sig line to the ECU] and watch the sig while disconnecting
and plugging the vac line to the Fuel Regulator..this causes an instant rich condition and should show up on your 02 signal as high voltage.
This verifies o2 sensors ability to recognize rich mixture condition..
For lean recognition test, simply creating a vac leak by removing a vac hose and watch for low voltage reaction...here one can simply put your thumb on/off the vac hose and watch the reading
speed change..
a little experince and you can tell a decent sensor , although a scope is killer for absolute diagnosis..

Sounds like what I need to do. Please explain in "I've done that before" English. I have a multi-tester.

1. What settings do I need to dial up on the tester?
2. Where do I hook it up to test the O2?
3. Exactly what am I looking for on the tester?
4. Explain where these are: "isolated o2 signal [ meaning unplugging the feed/sig line to the ECU] and watch the sig while disconnecting and plugging the vac line to the Fuel Regulator."

1991 190E 2.6 / runs great except minor, very short stumble on startup and lowered MPG (about 18 mpg).

Arthur Dalton · #5 08-16-2003, 10:57 AM

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As stated , this Test is for EFI systems....

brookspw · #6 08-16-2003, 11:00 AM

You mean, as in fuel injected?

If so, unless I have an invisible carburetor -- I'm fuel injected.

Arthur Dalton · #7 08-16-2003, 11:03 AM

No
As In Electronic Fuel Injected .....
New ball game

brookspw · #8 08-16-2003, 11:08 AM

Ok, thanks. On what wire in my footwell should I connect my meter to test for voltage?

Arthur Dalton · #9 08-16-2003, 11:51 AM

I do not have a diagram here of your sensor, but it should be the green seperate one .. the other two are heater circuit [12v.]
This will get you to o2 sensor signal, but the above procedure I have posted is NOT for your car ... it is for the original posters ELECTRONIC FI... and not applicable to your system

MARIO FARIAS · #10 08-17-2003, 12:36 AM

Thanks, Mr Dalton.

Please, Which is the procedure applied to 190E & 300E, 2.6, 1988
for checking O2 sensors and pressure regulator?.

Where to do the conections?

Thanks.

Mario farias
laprefar@cantv.net