MSefi.com read only forum (Jan.15,2018)

I am experiencing this exact problem. At any RPM I am seeing tach dropouts. Trigger+- seems to count up more than it counts down, and I am seeing tachcount reset that the dropout/miss.

On my scope the VR signal looks very clean, as well as the signal into the CPU from the vr circuit. However, probing with the scope at pin 14 of the CPU SEVERELY exacerbates the tach dropouts, to the point where the engine struggles to stay running.

Going to try the 2n2222 tomorrow, missed RS by half an hour.

Export from scope software to Excel and charted:



Is that tooth supposed to be there? If so, I reiterate that my signal looks clean to my eye. My ignition capture setting is Falling Edge, and I'm using VRout->TachSel.

what is the voltages of the high and low sides of the square wave sent to your CPU?

your question mark square wave looks fine. a good example of why you have to choose the proper phase of falling or rising. in your case, with falling edge, you are properly looking at every moment that the VR wave is rising through zere, and the square wave is dropping.

just remember though, when you put in the additional transistor, your VR and square wave will be back in phase, so swap your capture setting.

report back with results.

Low = 0V
High = 3.52V

interesting. sounds like a good candidate for the additional transistor. hope it works for you.

To understand what the processor sees, put a piece of paper with the edge along the horizontal axis and mark off the Falling edges of the red curve a few teeth before and after the gap. Then lay a cm ruler over the tics and write the cm between each tic, you will get something like 1.0, 2.7, 1.2, etc. Those are distances but they are directly proportion to the delta times, in microsecs, that the processor sees. Now repeat but use the Rising edges and you get a little more consistent numbers like 1.0, 3.0, 1.0. The latter would be perfect if you have two missing teeth. If you only have one missing tooth, then there is a problem, because then you should have 1.0, 2.0, 1.0, so in this case I would try flipping polarity of the VR sensor leads, changing nothing else in s/w or h/w and see if that helps. The processor looks for consistency in the times and it will allow a little slop, but no more than the PulseTolerances that you put in.

I am in fact running a 60-2 wheel. My distances are actually quite consistent, 0.9, 0.9, 0.9, 2.9, 0.9, 0.9 to my measurements.

I'll make the transistor mod this afternoon and post back with results.

Edit - I had to delete my latest update, if I admitted my mistake, it would be embarrass theater.

Signal appears to be rock solid, commencing 46deg test drive. Chilly.

BTW, TheMonkey, where are you? I'm in Brooklyn Park.

That made a huge difference. Whereas the car was almost un-driveable before with all the dropouts and resultant ignition misses before, it was smooth and revved strongly. I did however still have a few counts +/- on the trigger, and at least a couple spots where it I had a tachcount reset because of 2-3 "blips" of the trigger+-. But I didn't detect a misfire in driving.

Anything I could/should check to make that rock solid? I'll read through the rest of the thread again and do some searching as well.

Would the VR circuit adjustment clean that up?

You should try to clean it up electronically, but make sure you can go back to what you have now, since it is half way decent. What typically happens is that at some relatively high rpm that big gap in the missing teeth section pops up a tiny bit above 0. If it gets to be more than about .5 V above it, it can trigger an extra tooth and that will cause a problem. The tip off to this is that it starts at a specific rpm and keeps going. So look at when the trigger+/- counts up and see if it is consistent with what I said. Also make sure you are using 2.890 code as this compensates for the extra tooth (throws it out). If it is just random, then just try the usual remedies, make sure VR wires not near coil and spark cable lines, shielded, twisted pair, audio cap across battery, etc.

Great that you improved.

One thing that helped me quite a bit, was to record on the scope the signal coming out of VR circuit, into CPU, and compare that to ignition signal output. I was able to spot any ignition misses and compare it to what the CPU was seeing.

ddn wrote:...
BTW, TheMonkey, where are you? I'm in Brooklyn Park.

I'm in Plymouth.