so i was getting tach spikes at 7000 rpm and i tried to fix it, now its worse. what do i do now.

the setup: stock s5 na motor. MSI vs 3 pcb. 2nd vr conditioning circuit. 2 transitor ckts to control the vdi and aux ports. i think im running MS1/extra 029y4 code, i think this is correct but dont know how to check. using a temp plug and play addapter to connect the megasquirt to my stock wiring harness.

the fix: i added a .1 micro farad capacitor between ground and the 2nd vr signal input, where it comes into the vr conditioning circuit. i think its G+. now i get a nasty spike 5800 rpm and get big spikes between 6200 and 6400 rpm.

any advice would be great! is that the normal method for getting rid of tach spikes? thanks alot!

 

IT depends on the cause of the spikes... if you're getting really bad ones, I'd suspect your CAS wiring. Make sure that the shield is grounded on one end.

Also make sure you're using the 024 wheel decoder, not 025.

Ken

 

thanks! ill check the shield tomorrow when i have some time. i believe i switched to 024 style decoder and it helped a little but didnt solve the problem. i dont know how bad my spikes are, i have nothing to compare them two but the are usually about 1000 rpm. some times they will oscilate - spike down 1k then up then down 1k back to normal, and other times it will just spike up, or down. i attached some data logs if you or anyone else would like a look.

 

I don't see the attachments, but your problem really sounds like noise. I doubt it's settings if it's running well up to the point where it spikes, but if you could post settings too I'll have a look.

Ken

 

thank you ken. i will try to upload them again. i havent had much time to look for the shield to ground. i made a temporary plug and play harness out of a spare db37 and a ecu connector. i have jumper wires 3-4 inches long running between the two connectors. the conductors for the cas are not shielded at all at that point. i imagine that is where im picking up noise.