Trouble finding Lambda and EHA current Range
 

Hi guys

I have a problem adjusting the fuel mixture in my 1985 190E 2.3L

I have just spent most of my day trying to figure it out, but so far no luck.

The car overall drives great, no hesitation, good response and everything, but I noticed that the economy gauge tends to lean to the right a bit while idleling in gear at a red light. This started happening after a timing chain change. The fuel economy is also not that great, and I noticed that when cold the car is a bit sluggish on take off, after 2K rpm, it flies.

So, I got my MM out and checked the lambda voltage. When warming up, it is a steady 4.0V, according to the manual this is correct, but when warm, the reading goes all the way up to 7.22V and stays there no matter what.

Similarly with the EHA current, on warmup, steady 8mA, once warmed up, it sky rockets to 16mA and won't come down at all.

Now from my previous reaserch this tells me that the mixture is lean, and the computer tries to compensate by enrichment.

I tried to lean out the mixture, I adjusted and adjusted but I get to the point when the engine bearly runs and neither the lambda nor the EHA current change one bit.

I had this problem before, but I managed to get things adjusted and the car ran great, it still does, but it seems to be running extremely lean and I can't correct this problem

I also went through the manuals checklist and made sure all the components function correctly. The MAF pot is a bit off scale, and I'm thinking of replacing it, everything else works just like it is supposed to.

Right now I'm really frustrated why I can't find the scale for computer to do what it is designed to, but I'm not sure if I'm missing something, or if it's the car.

Any suggestions to resolve this will be greatly appreciated.

xp

Have you checked the O2 sensor?

Only guessing
Tom

Testing the O2 sensor would be a good start.

A constant 7.2 volts would correspond roughly to a 50% duty cycle, which in the 124 world is either a bad sensor or wiring.

Try unhooking the sensor and monitoring its voltage with the engine warmed up and running.

O2
 

I thought it was the O2 also, when I unplug the O2 the voltage goes back to 4.0V when the car is warmed up. Checked the wireing also and everything is fine.

When I ground the O2 connector the voltage goes to 0V so everything works the way it should.

Also once I unplug the O2 and plug it back in the voltage drops to 4 and slowly climbs up to 7.22V, I can't get it to stop anywhere before that.

I'll try a different O2, this one is relatively new but it could be bad.

Anything else I could try?

xp

You should measure the voltage between the O2 sensor and ground with the engine hot and running. You can do this by disconnecting the wire from the sensor to the ECU and connecting your meter. You should see something in the .25 to .5 volt range.

If you are getting good voltage from the sensor, then I am at a loss because the ECU seems to be working and setting the fault when the engine warms and it goes into closed loop.

The only other thing that I can think of is that you may be so lean that the sensor is generating no or very low voltage and the ECU thinks it's dead and is setting the 50% fault code. What happens if you richen the mix a bit?

Re: Trouble finding Lambda and EHA current Range
 

I'm scratching my head on this one. If you think it's lean already, then why are you trying to lean it out more?

Good question.. I missed that.

oops
 

Sorry, I meant to say richen the mixture not lean it out further.

In either case, I tried both, none did a thing to the lambda control.

Then I measured the voltage coming from the O2, and it was very faint, never went over .25V, so I got a new O2 sensor and now everything is back to normal, I adjusted it, lambda fluctuates beautifully and engine purrs like a kitten. Not bad for a 19 year old car.

I'm just suprised that this O2 went bad after such a short time. I had it in the car less then a year.

If anyone is interested, it was a Neihoff O2 sensor for the Ford mustang. This time I got the Bosch one and the car seemes to like it a lot more.

xp