where to ground LC1 on a 91
 

so i cant figure out which ground point is for the factory ecu or the main one?

any ground as long as its good should be fine...just ground it where the motor is ground under and to the side of the brake booster

If you are going to use megasquirt you want to ground the LC1 to the same place as your stock ECU which is near the throttle body.
If not going MS, it doesn't really matter as long as it is a good solid clean ground. Make sure the heater has a really good ground as well so that you don't get heater errors.

Does the LC1 take a 5v ref from the megasquirt? If not, ground is only half the battle in getting accurate AFR readings into the MS. If the +5v in the LC1 is different from the +5v in the MS, your readings will be off. I had that problem with my Zeitronix. +5v in the Zeitronix is actually +5, but in my megasquirt, the regulator puts out about 4.95, and the +5v pins on the ECU are only getting about 4.92v. I had to make a new AFR lookup table for megatune to correct.

-Mike

Pretty sure he's not even using MS, considering he has a rx7 afm still in the mix.

Good info though. I adjusted the .ini file to make my MS read the same as my AEM gauge.
Where is the regulator so i can check that on mine?

I've never seen any need to worry about the 5v side of things. Sharing grounds between the two makes sure they both consider 0v to be 0v, as they are using the same reference so there will be no voltage differential. The LC-1 will put out a 0-5v signal based referencing this ground as 0v. The MS is reading this on an input, the 5v from the MS reg doesn't come into play...

As long as 0=0, when you add 3v to that MS reads it as 3v and it's spot on. If they are grounded in different places there can be resistance between the two spots introducing a voltage differential introducing an error condition into the mix.... so the LC-1 may be sending 3v, but the MS sees it as 3.25v because of the differing grounds.

If it's grounded right, and configured right, it will be spot on. No need to make it any more complicated than that. If it needed to see the MS's 5v vref to be accurate then everybodys would be wrong all the time since it's not even an option to wire it this way.

The only reason i ask is because i can't get autotune or MLV to do what I want. I'm using an AEM 4100 series wideband and i've changed the appropriate .ini file so that megatune reads the same as my AEM gauge. Though when trying to use autotune it doesn't work as it should. I'll be cruising steady at like 13.5:1 and i have my target map setup for 15:1 in that are of the VE table. Though autotune does nothing and just continues to say "not near vertex" or whatever those 2 errors are. I've also adjusted the custom.ini file so that autotune has a range of 1500-6500 rpm and a map range of 30-255. I've run out of ideas on it.

im not running ms yet but im goin to hook them both up next week so i dont know where the ground is for the factory ecu

I think your ground should for the stock ecu should be on the hotside on the sheldf in the engine bay, a bunch of black wires which come into a block bolt down there, for you us guys that would be under the brake booster. I just grounded mine to where the engine grounds, right next to the clutch line and right near the ecu earth. I figured since the alternator grounds to the engine and the engine grounds there I am pretty close to the cource. It seems to be working fine.

Tim

Does that mean your LC1 has arrived Tim?

;)
Arrived, installed and done 4+ trips up cootha:bigtu:

I really can't speak highly enough of diyautotune, they are so helpful and my stuff arrived on monday, only a week since I ordered, not bad for the other side of the world:bigtu:

Tim