Mi16 Problem

[piran21]

I have a problem with my 89 405 Mi16 (xu9j4z w/cat- motronic m1.3). The engine is and has always idled quite rough and unevenly. The exhaust smells terrible like it is running too rich or something. There is some black smoke at lower revs if it has been driven hard. If you rev it up and then let it come back to idle, the smoke is there sometimes. The smell of the exhaust is very strong and hurts the sinuses! The plugs and wires are new, as is the coil, ignition module, O2 sensor, exhaust manifold has been replaced. Also, the engine sometimes raises the revs by itself to like 2500rpm and stays there until you blip the throttle and it comes back down. Can anyone help me or suggest any other things to check? I have to do an emissions test very soon.

Thanks in advance.

Piran

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[alan moore]

Quite possibly the injection temperature sensor (thermister) is defective. The mixture is OK when the motor is cold, but when it warms up the sensor still tells the computer that the motor is cold. The O2 sensor will not overide this. It will be on or near the thermostat housing.

[piran21]

There's 3 different sensors in that area. Which one is it? There's a big one at the bottom of the thermostat housing with a brown connector, a medium sized one at the side, and a small single wire one with a red connector. i have an extra cylinder head, so i can try the spare one out. Can you clarify which one to try? Thanks

[PeterT]

There's 3 different sensors in that area. Which one is it? There's a big one at the bottom of the thermostat housing with a brown connector, a medium sized one at the side, and a small single wire one with a red connector. i have an extra cylinder head, so i can try the spare one out. Can you clarify which one to try? Thanks

The one on the bottom is for the cooling fans. The single wire is for the temp. guage. The other one on the side is the one you might need to check. I'd also be checking the AFM. Can you borrow one from another car?

[piran21]

Ok thanks, i'll check that sensor. I have a feeling that the O2 sensor wiring may be buggered somewhere along the way. How would i go about checking that? AFM is not easy to come by. There are only a handful of Peugeots in Canada. Any other suggestions?

[piran21]

anyone?

[PeterT]

There are two connectors for the O2 sensor. One is for 12V supply, the other is voltage back to the ECU (0-1V). The most common problem is corrosion of the 12V supply connector. The terminals simply cease to exist. So replacing the sensor won't fix that problem. This is also a problem on Motronic equipped 205's.

Even if the 12V supply is stuffed, the O2 sensor will still work when the exhaust gases are hot enough, i.e. above 2000 rpm. The 12V supply is needed to heat the sensor for idle/low rpm situations.

I doubt it's a temp. sensor problem, as the difference between cold and running mixtures is only a few percent. You're talking about black smoke?

Has the idle mixture screw been tampered with? It normally has a tamper proof plastic plug over it. If so, try adjusting this with an allen key, whislt monitoring voltage from the O2 sensor. The voltage should be in the range of 800 - 900mV. Over 900 is too rich, less than 800 is too lean, for idle.

[piran21]

Yeah sometimes, i have a little bit of black smoke. What does that mean?
I will try what you suggested in the mean time.

Thanks

[piran21]

What is the best method to check the voltage of the O2 Sensor? We already tried adjusting the idle mixture screw on the airflow sensor. It made no apparent difference in the engine's running or exhaust smell.

[PeterT]

What is the best method to check the voltage of the O2 Sensor? We already tried adjusting the idle mixture screw on the airflow sensor. It made no apparent difference in the engine's running or exhaust smell.

The voltage output should range from 0.6 (light loads) to 0.9 (full load and idle). As long as it's in that range, all is good. More than 0.9V is very rich. Less than 0.6 is very lean. You should see less than 0.6V under deacceleration, when the ECU cuts the fuel off.