Clio 197 18% fuel trim

[shogun001]

Purchased my relatively high mileage (now 127k) just before Christmas last year. After sorting out the usual faults with them I had a look using the torque app at what the engine was up to.

I found that the long term fuel trim to be stuck solidly at 18.75% and hasn't changed over the 5k miles I've had the car. The short term trim varies from around +25 to -35(on WOT).

So far I've checked for exhaust leaks (manifold flexis known as a weak spot) and checked for the MAP sensor (no MAF) for leaks. When looking at lambda voltages they seem to stay between 0.075 and 0.75.

I'm guessing my next step is to create an artificially rich condition and see if the the ECU tries to adjust out? I've got a Renault CLIP on the way so am hoping that might show something?

Any ideas would be great!

[TooMany2cvs]

shogun001 said:

I found that the long term fuel trim to be stuck solidly at 18.75% and hasn't changed over the 5k miles I've had the car.

There might be a clue in "long term".

[Mignon]

The most likely causes of a long term fuel trim that high would be low fuel pressure or injectors getting a bit clagged up. I didn't think fuel trims could change at WOT from what they are before WOT because the ecu should be out of closed loop mode there. Fuel trims are set at stoich when the car is cruising. At WOT the ecu will still add that fuel trim to its base table but will have no way of knowing how accurate it is because the mixture is too rich for lambda sensor feedback.

[stevesingo]

Before looking for a problem elsewhere, look at the device that is measuring the symptom of the perceived problem.

Lambda sensors don't last forever.

[Belle427]

stevesingo said:

Before looking for a problem elsewhere, look at the device that is measuring the symptom of the perceived problem.

Lambda sensors don't last forever.

I’d agree, they can get lazy over time. I try to change them @ 100000 miles on something I care about.