New battery & Alternator causing Trans. Failsafe Prog

[upallnight]

Originally Posted by bcredliner

If engine performance changes under load it is not conclusive the problem is fuel delivery, nor is driving with MAF disconnected pinpoint the problem. OP has not been considering a vacuum leak since Indy did a smoke test. A problem with throttle position sensor should have shown up in diagnostics as should have a fuel delivery problem.

mcfee03 has already gone to someone with more experience who diagnosed a bad MAF. IMO rather than do any troubleshooting that's what he should do again to verify the used MAF is working properly and if necessary I expect Indy will check further for any other problems such as fuel delivery.

Fuel delivery problem would have shown up but only if the mechanic connected a fuel pressure gauge at the fuel rail. An OBD II diagnostic will not show a fuel delivery problem such as a weak or failing fuel pump. The OBD II diagnostic may have shown a lean condition, but there are many reasons for a lean condition, such as vacuum leaks or a weak fuel pump.

Since the trans fail trouble code have disappeared after the installation of the used MAF, I would just leave the new MAF in place. You can look at live data from the MAF. You can review the flow rate of air through the MAF to see how many g/s of air is flowing through the MAF. At idle the g/s should be around 3-4 g/s.

I would connect a fuel pressure gauge at the fuel rail see what the pressure is with the key on engine not running, key on engine running, and engine running with the revs at 3000 rpm. Does the pressure goes down when you rev the engine? Does it go down and then back up?

And last but not least, was the fuel filter ever changed? People have been known to get the return line on the fuel filter confused with supply line. This has mess up diyers on this forum as well as other BMW forums. The engine will not run right if the two line are switched.