It looks like there is a configurable threshold on the LM1815. I stuck a 470ish resistor from pin 5 to pin 8 on each LM1815, and adjusted the cas pickups close to the flags (since the signal wasn't strong enough to trigger without them close). The result is MUCH faster start, much more reliable idle, and the LC-1 no longer provides interference with the signal.

Reference the following thread :
http://www.msextra.com/viewtopic.php?t=24137

 

Thanks for the report. Looks like the adaptive threshold of the LM1815 is susceptible to noise? What's the tooth-sensor gap you are running to get it to trigger properly?

 

I have had quite a bit of noise on the RPM signal since day 1, thought it got better when I had removed the wideband (I only install it while I'm tuning). I completely changed my ignition map recently, reinstalled the wideband to retune fuel, and the RPM signal got super-erratic during cranking. Even at 8k RPM there was a 300+ RPM oscillation.

A good friend (Peter F) sent me a link to the above thread on MSEXTRA, and we discussed options to try. First we verified that the RPM signal cleared up (mostly) when I remove power from the LC-1 (which it did). Then we wanted to check the clarity of the signal from the CAS itself. Luckily, he has a CAS from a 2nd gen and was able to scope it. He said that he got a more robust signal with the sensors closer to the flags. I modded the LM1815s, and tried to crank, and got no fire at all. I then adjusted the sensors to 0.25mm (just because that was a shim I had), and the car cranked immediately and reliably, even with the LC-1 powered. Unfortunately, I did not measure what the tooth-sensor gap was before I adjusted them, but I can say they were quite a bit further than 0.25mm - possibly 1.0mm or more.

The result is that the car idles flat at 850 RPM, has virtually NO RPM spikes, and make a much smoother data log for all values (since RPMs are stable, everything gets more stable). I'll give it the old Trial by Fire this weekend at Carolina Motorsports Park with NASA

 

DBgeek ,are you running your MS with a patch harness to the factory ecu harness or a new harnsess?

 

I am using a 3-4 inch patch harness that has factory harness plug on one end (removed from a dead ECU) and the MS DB37 on the other. The primary reason for doing so was so that I could swap back and forth to the stock ECU for comparison, or if I happened to fry the MS . The aux reason was that I was already running a short patch harness to run the S5 engine/harness/ECU in the S4 chassis, and I already knew the wiring.

 

My lm-1 did something like that also, just wondering if you're lc-1 is a 6 or 7 wire and does the lc-1 sensor signal bounce around?

 

7-wire, with the power and signal grounds landed to separate chassis grounds. I had to turn on 1/6 second averaging to get a relatively steady A/F signal.

 

is it as steady as this worse or better or about the same?It is at 1/6 also!
thanks

 

I'll throw the sensor back in and take a datalog. As I recall, it was not near as smooth as that.