What does a tuner do?

[funcrew]

When you pay a tuner to work on your engine, what exactly does he do?

The reason I ask is that my S52/OBD1 failed smog due to running rich. It is running on a TRM chip for an S50. I'm looking for solutions to get the AFR where it needs to be.

If custom tuning is what I need, how would I find somebody who is worth the cost to get it done?

[gstuning]

Reputation goes a long way.

But the reason your car failed emissions is almost 100% not a tuners fault as he does not mess with that region in your ecu. You should look for generic faults with the engine.

[hoveringuy]

I've been working with TRM for the last year trying to get my M54 tune nailed-down. One thing I can say is that no matter where the tune is, the ECU will ALWAYS adapt to 14.7 (unless WOT, open-loop when cold or sometimes idle)

The problem is not your tune.