I've had my '95 E320 Wagon for 3 years now, and love it! I have a lot of little kids, and it's way better than a minivan!

CEL recently came on right around when I noticed MPG drop from 24 to 20, and it just now failed UT state emissions, HC and CO% are high both at idle and at 2500 RPM (CO% is 4-6x the MAX and HC just over 2x).

I've built the code reader described in these forums and right now (after a recent reset) it's code 3 (LED blinks) and code 13 (using reader on pin 8). Exhaust smells like unburnt fuel (hence the MPG drop), likely indicating rich fuel mix rather than lean. Motor doesn't have any stutters and sounds smooth both at idle and rev'd.

I'm eager to dive in and figure out what it could be, but would love advice from some of you experts!

Could this be just a bad O2 sensor, or would that have triggered a different code? I tried testing that based on post (green wire under passenger-side) and found it was staying at .5v when disconnecting vacuum line, revving engine, etc. Is that a likely bad O2 sensor?

What else should I test with these symptoms? We use 10% ethanol in UT, which is what I first thought was the cause of the reduced mpg, though we drive it only once every couple weeks, so it took a while to notice.

I don't know what those codes are, do you have a chart?

95 might have a OBD2 port under the dash, have a look as you will get more codes and sensor values.

If this has OBD2, there will be a front and rear O2 sensor, you need to measure the front one.

Pull the vac hose off the fuel pressure regulator and see if liquid fuel is coming out.

Also, measure the voltage at the mass air flow sensor, if it fails, it may still run but go into limp mode.

mileage drop is a strong indicator of bad O2... cheap and easy fix ...no obd2 port on that car

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1989 300ce 129k
( facelifted front,updated tail lights, lowered suspension,bilstein sports, lorinser front spoiler, MOMO steering wheel, remus exhaust,stainless steel brake lines). (Gone)

1997 s320 154k (what a ride). Sold with 179k miles. Replaced with Hyundai Equus

1994 e320 Cabriolet 108k



1972 280se 4.5 153k Owned for 12 yrs, sorry I sold it


[/SIGPIC]

Yeah, no obd2. The led code is "bad lambda" the blink code is "o2s, fuel mix lean or rich". I assume rich based on mpg drop and smell from exhaust.

I'm not 100% sure which vacuum hose is fuel pressure regulator, can post a picture later of the one I think it is, but it was bone dry. Car runs and starts really smooth so the o2s being out and mix being constantly rich makes sense.

Question, can I test the voltage change on o2s without having it connected under the passenger seat? I've seen people say both connected and unconnected and want to make sure it doesn't matter to the voltage readings.

Any way to easily check if the catalytic converter is bad too? (I hear that can cause o2s to fail, etc.)

Will retest today and put in a new o2s today if it fails, just scared of what else this might need done to pass emissions!

Yeah looks like $100 or so, that'll be my first target today.

The pin 8 code 13 fault indicates the engine computer has reached the maximum limit to which it will enrich or lean out the mixture. Your car is obviously running on the rich side. The code does not directly implicate the O2 sensor; the computer is not seeing an open circuit or otherwise implausible signal from the O2 sensor.

There's quite a few threads on this fault, here's one: M104 pin 8 code 13 question

I suggest using google to dredge through past threads here, search on "m104 pin 8 code 13 site:peachparts.com" for reading fun.

Good luck.

Thanks, a good list of info! But unless I'm measuring the o2s wrong (or unless those other things can make a good o2s stop fluctuating and stick at .5v) I'm pretty sure that the o2s is bad, but there could be way more going on too and I could be testing it wrong!

Look for the fuel injector rail ( chrome tube running front to back ) at the very front, there will be a chrome can about 1 1/4" dia with a single vacuume hose attached to one side, pull the black hose and have a look.

If you check O2 voltage with wiring connected, you will see the 0.500 volt bias from the engine computer. If you disconnect it, you can measure actual O2 voltage and the computer will remain in open loop. This is where the computer runs in a neutral mixture range.

If your coolant temperature sensor for the engine computer has failed open, the computer thinks the motor is cold and is applying a rich mixture.

If the engine is running rich for a long period of time the car will clog , in extreme cases it will melt.
95 is on the the tail end of "bio degradable" insulation wiring , have a close look at exposed wires and lightly rub them, if the insulation falls off, you will need to replace the harness before any other work is done. Short term you might be able to cut the shrink wrap and tape up wires.

Yup, that's the one I was checking it's dry!

Now I'm less sure of this I just tested it again, after letting the car warm up, should this voltage range be in mV? When disconnecting the vacuum line (the same one as above), it holds steady at ~13 mV. Revving the engine for a second and letting off shows 300-400mV for a moment then back to fluctuating. I am not sure how much of this is a cheap chinese multimeter vs real measurements though, or if I'm measuring in the right range. I thought it should be .1-.9 V but got nothing but zeros in that range on my multimeter, so set it to 2000mV when testing, and it is jumping up and down fairly regularly.

Would this throw a code? How do I check this? I was going through coolant this summer more than I'd expect... maybe related?

Crossing my fingers that hasn't happened... can I see either of those visually? Is there a way to "unclog" it if that has happened?

I haven't seen this at all, I believe the former owner must have replaced it because I've read that's a big problem with these cars, and mine has over 200k miles!

2,000 MV = 2 V

O2 sensors make 0.500 to 1.000 V when the exhaust is rich ( low O2 content ) , 0 to 0.500 V when the exhaust is lean ( high O2 content )

This type of O2 sensor does not have a linear output. The cross over point between rich / lean is very narrow. There is no way to tell if you are slightly rich or fully rich.

When the sensor fails, voltage drops , the computer thinks the motor is running lean then starts to add more fuel. Do you ever see more than 300 - 400 MV ?



Not related. If a total open circuit it should trip a code, if off scale it might run rich but not trip a code. It depends on the code strategy.

The pipes would have to be removed to take a look or a back pressure gauge used. You probably don't have this issue. Cats can sometimes clear out during a long hot run.

I haven't redlined it or anything but "steady state" idle after 20+ minutes of driving isn't going above .02V and revving it isn't going above .4V.

Engine speed is less of an issue ( Though a fast idle of 1,500 RPM is sometimes needed to generate enough exhaust heat for a 1 wire sensor to work. ) 3 and 4 wire sensors have built in heaters and won't go cold at idle.

At this point I'd install a " known good part " and swap the O2.

This one is 4wires (heated).

Yeah, that was my plan, and still is... If I can ever get the old one out!! Wd40, penetrating lube, and several attempts at cold, warm and hot exhaust leaves a score of:

Oxygen sensor: 1
Wooo: 0

Tomorrow I will try again, possibly with a torch to heat up the threads... Unless I figure something else out...

Got the sensor off when outside temperature was below freezing. Put in a new one, unplugged the battery to clear the codes and drove 75 miles....

Fuel efficiency appears to be restored (yay)! Cel is still off and code on pin 8 is still "1" for no code! Crossing my fingers it holds up the rest of the holiday and then I can go get it to pass emissions!!!

It passed emissions test yesterday (barely... HC levels at idle were within 2ppm of the limit!). Thanks for all the help, and if anybody has suggestions to get the HCs lower at idle I'm all ears!