Coil (-) into VR input = noise?

PSIG · Post by **PSIG** » Sun Jul 30, 2006 10:52 pm

Hey all - trying the "one size fits all" VR input for everything. Today I tried a coil negaitive input from a running HEI external coil (stock 'Tach' output wire on coil). Instant success!

However, the rpms bounce rapidly (jitter) about 800 rpm up and down at fast idle (1150 to 1950ish).

I started with R52 & R56 fully CCW and could get signal with the hysteresis in any position but lost the signal with R56 voltage pot about 13 turns CW. JUST before I lost signal I got a clean rpm reading. Super sensitive and if I breathed on it I'd lose signal.

I need this to work quickly so I need ideas. If I can't get a clean solid signal easy I'll probably get it from the 7-pin module R terminal. I'd like to get the coil (-)/VRin working though.

TIA,
David

MS1-v3.0, Extra 029s, fuel only, VR input only

PSIG · Post by **PSIG** » Mon Jul 31, 2006 4:32 pm

It looks like this. Anyone?

87quest-TSI · Post by **87quest-TSI** » Wed Aug 02, 2006 8:55 pm

I all,

I'm trying to do the same thing with using the - side of the coil going to the vr + input on the MS.
But I can not get a clean rpm reading.
I have tryed to ajusting the r52 and r56 with no luck.
I'm useing MS1 V3 fuel only.
What else can I or should I try?

Thanks

87quest-TSI · Post by **87quest-TSI** » Thu Aug 03, 2006 1:28 pm

Help anyone?

I have tryed a few more things today.
I had the shelding for the tac wire grounded on both ends, so I changed to to jest one end. It didnt change anything.
I also added a wire to pin #7 and went to ground with it. No change.
The car will start and run, but the rpm's in MTune are all over the place from Idle to 8000 rpms when the car is at a idle.
At 1200-1600 the rpm's in MTune has a stedy rpm reading.
Is there some thing I have over looked? or do I have to chang it to the hall?
OH.. I'm running B&G v2.0. Should I try a newer version?

Thanks.

87quest-TSI · Post by **87quest-TSI** » Thu Aug 03, 2006 11:57 pm

Well seeing as there was no help here I have changed from VR input to Hall input and now have a clean tac single.

scowman · Post by **scowman** » Sat Aug 05, 2006 12:14 pm

87quest-TSI wrote:Well seeing as there was no help here I have changed from VR input to Hall input and now have a clean tac single.

I did the same thing but I am still getting tach spikes at crank. It goes from 185 to over 20k and the back to 185 in an instant.

I am still at a total loss.

Any ideas?

87quest-TSI · Post by **87quest-TSI** » Sat Aug 05, 2006 3:42 pm

scowman wrote:
87quest-TSI wrote:Well seeing as there was no help here I have changed from VR input to Hall input and now have a clean tac single.
I did the same thing but I am still getting tach spikes at crank. It goes from 185 to over 20k and the back to 185 in an instant.

I am still at a total loss.

Any ideas?

Thats what mine was doing when I was trying to use the VR input.

What kind of wire are you using for the tach?

scowman · Post by **scowman** » Mon Aug 07, 2006 8:51 pm

87quest-TSI wrote:
scowman wrote:
87quest-TSI wrote:Well seeing as there was no help here I have changed from VR input to Hall input and now have a clean tac single.
I did the same thing but I am still getting tach spikes at crank. It goes from 185 to over 20k and the back to 185 in an instant.

I am still at a total loss.

Any ideas?
Thats what mine was doing when I was trying to use the VR input.

What kind of wire are you using for the tach?

I tried a shielded wire but that did not work either. Using regular automotive wire now.

Any ideas? Are you getting any help from anyone else.

jsmcortina · Post by **jsmcortina** » Tue Aug 08, 2006 5:21 am

When running from the coil negative there is often a lot of noise. Have you followed the Megamanual guides about putting a resistance in line ?

Seems the VR input is way too sensitive (pity) - so use the hall/opto input and use the right jumpers on TACHSELECT and TSEL.

Then either try a bunch of resistors or grab a 10k variable resistor and twiddle it until you get a reliable tach signal with no noise.

You can also try a slightly larger capacitor for C22 (?)

(None of this applies when controlling spark of course.)

James