Tach spikes - seems common but no easy fix

DeneOehme · Post by **DeneOehme** » Sun Aug 06, 2006 4:50 pm

MS 2.2 board running latest MSnS code, MSD6a

With my MS running fuel only I get one or two tach spikes at about 5 grand but otherwise all ok.

When running spark as well I get tack spikes all over the place and the thing's basically undrivable.

What is the common cause of tach spikes and what have people done in the past to get rid of the problem?

I've searched these forums - tried grounding to the same point and using shielded wire. No better. It seems like this is a common, frustrating problem that no-one knows definatively how to fix or prevent. Some things works for some people and not others. It also seems to be more prevelant in using MSnS than the standard fuel only code.

Dene

DeneOehme · Post by **DeneOehme** » Mon Aug 07, 2006 4:22 pm

I take it by the lack of replies that this is a quagmire that no-one really knows about.

Surely someone has fixed this who can help??

Dene

rebel2k4 · Post by **rebel2k4** » Wed Aug 09, 2006 3:55 pm

I had a huge issue with them on my 2.2 board (though now on the 3.0 board it has turned into a reset issue instead). I added a 4.7 uf (trust me, I tried TONS before I found that one to work) cap on the pullup resistor and the problem was almost eliminated.

What are you using for a tach sig? I had a hall sensor, seems that those are notorious for tach spikes

DeneOehme · Post by **DeneOehme** » Sun Aug 13, 2006 6:46 pm

When you say the pull-up resitor which one is that? Do you just add this cap in parallel with the resitor?

Using a VE sensor and 4 pin ignition module.

Dene

DeneOehme · Post by **DeneOehme** » Thu Aug 17, 2006 3:57 pm

Following is a jpeg of a datalog. Note the unevenness of the tach signal even whjen there are no actual spikes. Is this aproblem?

Dene

DeneOehme · Post by **DeneOehme** » Thu Aug 17, 2006 8:30 pm

Sorry - forgot to attached the jpeg

thechuckster · Post by **thechuckster** » Thu Aug 17, 2006 10:38 pm

to get rid of noise on my VR input i ran shielded cable right up to the sensor and connecting the shield to the (-) trace in the cabin where it enters an external box with the VR interface.

Ended up doing similar thing with the O2 signal from relay board to ECU (single wire with shield, earthed at ECU DB37 conenctor only) and TPS from engine to relay board (as it ran in the same tray as the injector wiring).

Most frustating part was locating shielded cable with three traces (for the TPS) - ended up recycling soem wiring out of an old Toyota Soarer wiring loom.

cheers,
Charles.

newtyres1 · Post by **newtyres1** » Fri Aug 18, 2006 1:05 am

Looks like 1 spike in the tach signal (which didn't affect the fuel - except for the smaller negative spike on the rhs) and 2 big spikes in the duty cycle to me. What's causing the duty cycle spikes, accel enrichment?

Ian.

DeneOehme · Post by **DeneOehme** » Fri Aug 18, 2006 4:49 pm

That's what I'd like to know. It shouldn't be accell enrichment because my foot was flat to the boards for a good five seconds or more before those spikes. Do you think the wavering/unevenness of the tach signal is normal though? It should just be a steady smooth increase in revs up to 6000 not all the little bumps and valleys all the way.

Dene