In the workshop recently we had a Mazda 3 with an ongoing engine management light coming on . The fault first occurred on a long journey and emergency RAC services were called.
Diagnoses was vague and consisted of a list of items that may be causing the engine light to come on.
We were asked to investigate after a local garage were unable to be sure what was causing the fault the car ran well and when driven seemed to perform as normal.
Initial investigation using a logical diagnostic approach showed a lean mixture fault p0171 this had been misinterpreted as a possible air mass meter fault. The cause of the fault was quickly traced to an inlet air leak around number one cylinder.
A pressured inlet smoke test was used to find the leak.
With customer approval we stripped out the inlet manifold and found that the manifold gasket on number one cylinder had a section missing.
New gaskets and refitting the manifold restored correct running and mixture control.
Section of manifold gasket missing..
Plastic inlet manifold..
View of engine with manifold removed..