More fun with MFI and LM-1

[analogmike]

Hi,

Still trying to get the engine running right, a few things:

1) We replaced the MFI belt pulley on the cam last rebuild
so they are ok, good idea to check this though.

Originally posted by jluetjen
Aren't AnalogMike's symptoms common for a stock MFI system mixed with an aftermarket "Low restriction" muffler? Basically the fuel requirement curve has been changed and the stock 3D spacecam doesn't adjust for it. [/URL]

The various muffler I have been testing are all different and are causing some changes. But even with a stock muffler I have the same basic problem - terribly rich 10 to 11:1 at part throttle as in traffic driving. And too lean at 6-7K full throttle.

We learned that headers into a megaphone works best, tunes out a lot of little dips in the torque curve that the stock or sport muffler have. Dr. Porsche was not bad for the noise limitations but open works best even with MFI. Your mileage may vary.

Does anyone have GOOD values for the LM-1 mixture readings for an MFI 911? i.e. idle, part throttle, wide open? I did not have the LM-1 when the engine was running right, so I nothing to compare to. But I know 10:1 at part throttle is too rich as the plugs and exchaust are fouled with black soot. I can't even picture that much gas (1/10th of the air) being squirted into the cylinders...

p.s. I let my car idle (nicely) for a while last night then used an infrared temp probe on the exhaust pipes. #6 was 200 deg cooler than the other 5! PLug/wire/leakdown were fine so I replaced the injector nozzle, will test again today. That can't have been helping but the LM1 sensor is on the 123 bank so it was not affecting my mixture readings.


THANKS!

thanks!

[Ron,K]

Mike,

I'm not sure this qualifies as "good" measurements but this is my latest log file from LM-1. Still looks a little rich to me, but I erring on the side of rich.

[Ron,K]

Couple of more charts from Logworks.....first is idle, second is WOT.

[RoninLB]

Originally posted by analogmike

p.s. I let my car idle (nicely) for a while last night then used an infrared temp probe on the exhaust pipes. #6 was 200 deg cooler than the other 5!

imo.. and based on my experience.
EGTs are somewhat scattered at idle and going thru the gears.

An diagnostic EGT info reading will happen at a steady 3k, 3.5k, 4k, etc in 5th.
Excellent stable #s will have a deviation between coldest and hottest of 40-60deg. Deviation of 100-150deg is ng imo. Below 3k EGTs are under the breathing range of our engines, generally, for educated info. A Nice engine will be Very stable between 3-4k. After 4k and WOT CHT becomes the dominating envelope, below 4k CHT shouldn't be a prob to begin with.. in other words high EGT, within logical limits, is ok&good if CHT is good.

A stable engine will allow a heat boundary layer to form on the piston head. Normal extremely high combustion temps will diminish as it goes thru this boundary layer to reach the piston head. Unstable, caused by ignition or fuel mix, EGTs will diminish this boundary layer allowing the piston to see greater amounts of combustion temps, ie: damage.

[Grady Clay]

I thought I would add this useful link.
It's focus is hot start but has some useful information (and one error - corrected).

“Any good MFI people out there” on EarlyS
Hot starting issues and more.
http://early911sregistry.org/forum/showthread.php?t=4355

Best,
Grady

[KevinG]

Grady -

I finally located my protractor set, and I have the top 3 of the five you show in your picture (posted on page 2). Hopefully, they are the correct ones for my 2,2 motor. Unfortunately, I only have 2 of the needles that go with them. One is a hand-made needle that appears to be a match for the top protractor, the second is an original for one of the lower two protractors. From your photo, the two lower needles (for proctractors #2 and #3) appear to be slightly different. Would it be possible for you to provide some measurements for the needles so that I can fabricate a replacement for the missing one?

Thanks!