Hi,

My Marea 1.6SX ´99 have a "rare" fail. When I drive my car, this have poor performance. I changed TPS, Air Temp sensor, cleaned throttle body, changed spark plug, leads, water temp sensor and I not find the cause.

I read very articles about the lambda and I built the lambda tester (lm3914) with 10 led and show this:

1. With the lambda connected to ECU, my tester show a voltage oscillation from led 1 to 5, each second the led up and down. the light not is stable.

2. If I disconnect the lambda probe of ECU this show the led always on in the 5-6 position in the tester, but if I run the car in 2000-3000 rpm the light down to 2-3 led position.

3. The light injection never on, I disconnect the lambda and run the car and never injection is light on.

What do you thing about this?

P.D.: Sorry for my english.

Thats what a lambda sensor should do so its not your problem.

check the heater and probe resistance with a multimeter. remove the black plastic cover at the back centre of the engine bay. there are 2 knobs you need to loosen to remove it. behind that cover you will find the lambda sensor wiring connector. disconnect it, and then use the connector to test the lambda sensor. make sure you use the correct side of the connector, you need to use the side that has the wires surrounded in a white sheath, this is the side that goes down to the lambda sensor.

the following pic gives more detail.

jug said:

check the heater and probe resistance with a multimeter. remove the black plastic cover at the back centre of the engine bay. there are 2 knobs you need to loosen to remove it. behind that cover you will find the lambda sensor wiring connector. disconnect it, and then use the connector to test the lambda sensor. make sure you use the correct side of the connector, you need to use the side that has the wires surrounded in a white sheath, this is the side that goes down to the lambda sensor.

the following pic gives more detail.

Click to expand...

Jug,

I tested the heater resistance and is correct. If I connect the lambda to ECU the lambda tester show a movement of led from 1 to 5 constantly.

In my country the fiat tester is very difficult to find. I connected my elm323 (Scantool) but don't work.

you should see the lambda voltage going up and down constantly, this indicates that the lambda sensor is responding, and the ECU is switching from rich to lean to keep the fueling correct. So its basically working. What performance problems do you have ?

stylers said:

you should see the lambda voltage going up and down constantly, this indicates that the lambda sensor is responding, and the ECU is switching from rich to lean to keep the fueling correct. So its basically working. What performance problems do you have ?

Click to expand...

I don´t know about up and down voltage!!!, I thought that the correct was one led turn on.

My marea have a rare problem. When the car is cold it have more power, but when hot don´t have the same power. Too the car have "jump" o accelerate or brake abruptly, if I go in traffic at 2 gear and release the accelerator brake abruptly and if put the accelerator jump abruptly too.

If I turn on the air conditioning then the car loses more power (much power).

I replaced TPS, spark plug, cleaned throttle body,air filter, fuel filter, air sensor, water temp sensor.

The light ECU are off.

Sometimes in the interior car smells fuel.

rafy said:

My marea have a rare problem. When the car is cold it have more power, but when hot don´t have the same power.

Click to expand...

thats not rare. its probably the lambda sensor

rafy said:

Too the car have "jump" o accelerate or brake abruptly, if I go in traffic at 2 gear and release the accelerator brake abruptly and if put the accelerator jump abruptly too.

Click to expand...

thats normal, use 1st in traffic, the rpm should not go below 1300rpm, if it does you get this problem.

rafy said:

If I turn on the air conditioning then the car loses more power (much power).

Click to expand...

thats normal, the A/C drains a lot of current which causes power loss. you will also use more fuel.