My Defi EGT D-Gauge readings seem to fluctuate when I turn my parking lights on and off when the engine fairly hot. It's strange because it seems to only do this when I've been running the car somewhat hard or when the engine's really warmed up. I'll come to a stop, watch my idle EGT temps, turn off the lights, turn them back on and the needle jumps up about 60 degrees F. It seems to jump up less the more time I let the car idle and cool down. The needle stays the same if I turn the lights on and off when the engine it cold, right after I've started the car in the morning. I followed the instructions on Evo Motorsports and tapped runner #2. I used the following wires for power: on the dimmer switch, green with white stripe = illumination, black with yellow = ground; under the dash fuse #10 = ignition/switched power, fuse #17 = 12 volt batter/constant power. It has me a little worried because at night when I'm using my lights and I'm boosting through several gears I've gotten the temps up to 1575 degress F or so. I can use the dimmer switch to change the lighting of the gauge, but past a certain point the needle starts moving down and shows zero, because of too little current I guess. Boost seems to be right on target at 19.5 psi WOT. Anybody know what's going on???

 

I have not noticed if my Greddy Electronic gauges do that, but I do know that when they were first installed, they would work sporadically and sometimes they seemed to work backwards These are the 52 mm Boost and EGT gauges. I think it was some kind of a bad ground or something like that. The installer did some more work on them and now they seem to work fine.....

 

Get a grounding kit and see if that helps, or try changing the ground for your gauge. Ground the gauge to the car, or the block just to see what happens.

Same thing happens with the O2 gauges, they change readings when lights go on or off if the wire choice is not proper. THis is true for any car, not just the EVO.

 

Changed the ground from the black/yellow dimmer wire to the chasis and that seemed to fix things. Can't dim the gauge lights anymore, but it doesn't really matter since I leave the dimmer at max anyways. Although the temps don't vary with the lights anymore, I can still reach 1550 degrees when running it hard through several gears. Should I be worried or might this be a consequence of where and how close to the engine I tapped the sensor?

 

1550 F is remarkably hot. I don't think I've ever seen even 1200 F in my EVO...... Of course, my car runs pig rich, that could be the reason.... I think you are approaching the limit there. According to some authorities, 1650 F should be the max you ever want to see. Are you running very lean?

 

To tell you the truth, I don't really know how lean I'm running. I've never been to a dyno and the car is stock performance wise (unless a lightweight battery, grounding cables, gauges, and a new head unit count). I'm actually still breaking the car in, still haven't reached 600 miles yet. Boost peaks at ~19.5 and 1550 F is reached when running it hard (shifting at ~5000 RPMs) through 2, 3, and 4th gears.

 

Well, that sounds really about right. You are not at the max and the whole idea is to run as lean as practicable. Seems like your car is running very well.