I hope this is an easy question. I basically just got my car running on a new MS3 PNP. I used the fuel and ignition maps from my ms labs ms3. After I sorted out all my initial problems, my manifold developed some cracks before I got a chance to do any logging. Its cracked in 3 places. It idles well, but in cruise and boost it's lean. Mid 16s and 14s. My question is, would the cracked manifold give me lean conditions, or is my tune bad. It was good on the old ecu. I didn't think it necessary to attach a tune at this point. Second question, is any of the high heat JB weld useful as a temporary fix? Until Lars makes me a new manifold. Thanks.

 

Maybe in cruise, but I'd be weary of it reading lean in boost. My thought process is that with our smaller turbochargers, its normal to see exhaust manifold pressures in excess of 1:1 of your intake MAP. I'm not claiming to be a physics expert and have no clue if the flow might cause some sort of venturi effect and suck air in, but if the exhaust pressure is 10 psi (or more) higher than atmospheric I don't think it should affect the AFR reading that much, if at all. I'm sure others might know better, but it's almost always better to play it safe when you're unsure in this case.

 

Well, any cracks in the manifold can lead to escaping exhaust and give you a false lean reading. What were the AFRs before the manifold developed the cracks? How do the plugs look? What are your target AFRs versus what the wideband is saying?

 

I wasn't able to log afrs with this ecu, but with the previous one I cruised at 14.7-15 and in boost went rich as low as as 11. I haven't pulled the plugs. My target afrs are 14.8 for cruise and 12 for boost. They now are in the 16s for cruise and 14s in boost. Too lean for me to comfortably drive the car. I expect to get a new manifold from Lars in a week or so. In the meantime I have to do some maintenance anyway.