running track pipes causes lean mixture & damage?

[M5zealot]

My engine rebuild is going great. Not too much wear or damage to the engine, which I attribute to Mobil 1. Cam shafts look virtually new! #3 and #5 cylinder did suffer damage. Small chunks broke off due to old age. Another customer at the shop told me my damaged pistons were caused by lean mixture because I was not using a converter. He said the ECU needs to "see" a converter because it's adjusting for the backpressure. I have heard this before. I do have a Dinan Chip and cam gear (Euro headers waiting patiently to be installed too!) and I would think the chip took care of the lean issues. The engine did last 250,000+ miles before this damage so I really don't think his diagnosis had any merit. So, the solution I feel is get a cat that will blow in few thousand miles or get a Euro muffler w/ more back pressure. My head hurts and I just don't know who to belive anymore! Any suggestions?

[lkfosteraz]

The ECU can't see exhaust pressure. It either uses a signal from the oxygen sensor when running closed loop under moderate load or the air flow meter in open loop conditions (i.e. cold start or WOT). Reduced backpressure can improve scavenging, but the system should compensate. With carburators altering the exhaust affects scavenging and you could get into a lean condition, but fuel injection got rid of that problem.

I have heard that the AFM only works up to some nominal speed beyond which it runs off of a map, but I can't confirm that. If it was the case you could get into a lean condition.

Looking at the issue another way, if what he said was true all six cylinders would show lean.

[M5zealot]

Thanks, I agree with you 100%, all six should have some damage. Oxygen sensor is in the one of the track pipes. Thanks for your input

[ajwong]

Here are my a/f mixtures on the dyno with and without a track pipe. Both are way rich at high rpm's actually.


Track Pipe Dyno Results<img src="http://home.comcast.net/~wong.andrew/pics/sig.JPG">