Need Help on Air Fuel Ratio !!!!!

[mntngts99]

I have a 99 gts had corsa cat-back put on one year ago. Just had it in for service and the tech found that the sensor valves are not switching, he said that there stuck on lean. Went to a dyno service to have a look and the Air Fule Ratio, at a idle was almost 15, under excelleration it drops to 10. Is it the sensor valves, or a map sensor or what????? Does the cat-back have any thing to do with it ??? Any info or help would be nice. Thank you

 

[Joe Dozzo]

Not certain what a sensor valve is...

Perhaps he meant O2 (oxygen) sensors? These monitor exhaust gases and feed info to the computer which controls air-fuel mixture.

Your car should have 4 O2 sensors, 2 (1 on each side) up in the exhaust manifolds (or headers) and 2 (again 1 on each side) in the exhaust pipes just ahead of the rear muffler.

The cat-back system, by itself, should not impact the O2 sensors - unless one might have been damaged...

If an O2 sensor has gone bad, I would expect the "Check Engine" light to come on.

 

[Nexus-6]

For what it's worth, when we dynoed my '02 GTS with the VEC1 zeroed out my car ran nearly as rich (cruise speed up to 2500 it was about 14~15 as well).

It dropped off the charts it was running so fat right at 2800 or so. We finally got it dialed in with the VEC1 to hold steady at mid 12s but stock it was FAT.

I know these things run rich up top but MAN - it was REALLY rich...

 

[Jerry Dobson]

Sensor Valves are what they are called when your car is out of warranty so you can't replace them yourself. In warranty they call them O2 sensors

FYI: you wont get an accurate AF reading with Cats. Putting the sensor rod up the tail pipe on a cat car will not be accurate. You need a 02 **** on the header.

Original post was 15 idle and 10 under load = That's pretty normal.