B20 MSnS issue (voltage/RPM signal suspect)

[spe1983]

I have set up my B20 with MSnS controlling both fuel and spark using a pertronix hall sensor w/ the pull up resistor(copied sberry). I'm using the 3.0 board's coil driver to control the timing.

It appears at random time I am getting a drop/spike of the rpm signal, verified in megalog viewer and on the small 240 tach I added in my 142. This throws the timing out of whack and causes a serious stumble.

Reviewing the log I noticed a voltage drop anywhere from ~2-5 volts from the constant 14V put out by the alternator almost each time this happens. The rpm signal can spike to like 6.5k or drop ~.5-1k RPMs. I have double grounded my MS box and don't have any reseting issues. Also I just replaced a broken valve spring and removed the head, I don't recall having this stumbling issue prior to the repair but it was running rough due to the broken valve spring.

Does anyone have any ideas or suggestions?

[Matt Cramer]

You might want to put a stereo power filter on the MS's 12 volt wire. I had to do this on my Dodge Dart to keep it out of voltage weirdness.

[spe1983]

power filter on the MS's 12 volt wire.

Interesting, sounds like a good idea. After reviewing the wiring in the car and the logs some more it might be external maybe in the wiring. I have the 12V feed for the pertronix, the pull up resistor, and to the MS all coming from the same relay(original d-jet on/off relay). I also noticed that maybe only half of the voltage drops recorded in the log actually result in the RPM signal going haywire.

Like I said I don't remember this being an issue prior to pulling the head. I think Ill try upgrading to the latest firmware and going from there. If there is any other ideas please let me know. I am not discounting the alternator or external voltage regulator, but I don't think it's them quit yet.

[Antique Swedish Steel]

Maybe the D-jet relay is failing?

Joel

[spe1983]

Maybe the D-jet relay is failing?

Close. I went and checked the relay ready to wire a direct +12V line to bypass the relay and found my piggy back spade terminal was grounding out my MS, injectors & pertronix +12V on the metal body of the relay intermittently. I rotated the terminal 180 degrees and had about 2 stumbles on the way to work today instead of bucking a backfiring every couple seconds. Going to datalog this afternoon on the way home to see if its fixed. Silly issues causing problems once again.

[B-lennium]

please buy a new relay, don't trust old electronics!

[spe1983]

Didn't work. I thought it did, but yesterday afternoon on the drive home it did the same thing. So today I switched up the old relay with a new unit, and no change as well. I'm going to check all the wiring and see if there is something else going on. How frustrating.

[Antique Swedish Steel]

Check relay ground wire?

Joel