car is running poorly and wondering if it might have something to do with a lean or rich engine.

How can I diagnose this so that I know I am in the right direction and it is not one or the other?

I’m trying to avid testing map sensor, looking for vacuum leaks, investigating fuel system etc if I can just know by looking at some other parts of the car. I take it a check engine light does not always accompany a lean or rich engine?


  • First check the plugs.
    – Solar Mike
    Commented Nov 14, 2020 at 14:02
  • And as you don’t have a cat then looking at the exhaust pipe colour also tells you.
    – Solar Mike
    Commented Nov 14, 2020 at 14:07
  • I do have a cat but I was just asking about decats etc. Commented Nov 14, 2020 at 19:46

1 Answer 1


If your car is running rich you should have a strong smell of gasoline from your car.

Have you considered using an air/fuel ratio gauge? Personally, I prefer to see the exact number.

I have the air/fuel ratio gauge wired into the back of my glovebox and keep the gauge inside.

This article is for carbureted engines specifically but the first suggested gauge works on EFI systems too. https://drivinggloves.net/best-air-fuel-ratio-gauge-for-a-carburetor/

Hope this helps 👍

In addition to help with your 'colored smoke question' in the comments.

Black smoke means your engine is running rich

Blue smoke means your burning oil

White smoke is a sign of a blown headgasket

I'm not sure about a lean mixture producing smoke - sorry.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .