"Noisy" RPM Signal?

[ShelGame]

I'm still getting a very noisy RPM signal in my datalogs. At times, it even affects the ignition timing. Has anyone else (with datalogs) noticed this? It's ~2-300rpm worth of noise, pretty constant. I would expect a certain amount of variation due to cylinder firing events, but not this much. I'm wondering if my distributor has slop at the oil pump, or if the shutter wheel is loose.

[Frank]

Still issues? That sucks!

[ShelGame]

Well, I never figured it out. And now it's giving me fits trying to devise a method to calculate wheelspin, gearshifts, HP, etc. :) with this noisy RPM data.

If it turns out that this is typical, and not a problem with my car, then I'll just have to filter the RPM data after reading it.

[glhs875]

What all have you tried to cure it?

[ShelGame]

What all have you tried to cure it?

Well, err, uh, nothing - yet.

So far, I've only pulled the dist cap to see how much rotor play there is. Seems to be quite a bit, but I'm not sure what's acceptable. Or, how to cure it. I have not checked the shutter wheel yet. But, when I assembled the engine last spring, it was solid.

If it's in the gear lash between the intermediate and the oil pump, there's really nothing I can do. If it's between the oil pump and the dist shaft, I guess I could try to take the play out with a shim, although that seems like it would be difficult to do. If the shutter wheel is loose, well, that seems straightforward enough.

Mostly, I was wanting to see if this is even a problem, or if it's just a typical RPM signal for our cars.

The data above is logged direct from the ECU. So that's the RPM that the SMEC is reading from the HEP pulses...

[glhs875]

Well, err, uh, nothing - yet.

So far, I've only pulled the dist cap to see how much rotor play there is. Seems to be quite a bit, but I'm not sure what's acceptable. Or, how to cure it. I have not checked the shutter wheel yet. But, when I assembled the engine last spring, it was solid.

If it's in the gear lash between the intermediate and the oil pump, there's really nothing I can do. If it's between the oil pump and the dist shaft, I guess I could try to take the play out with a shim, although that seems like it would be difficult to do. If the shutter wheel is loose, well, that seems straightforward enough.

Mostly, I was wanting to see if this is even a problem, or if it's just a typical RPM signal for our cars.

The data above is logged direct from the ECU. So that's the RPM that the SMEC is reading from the HEP pulses...

That's interesting. That's something similar to the problem I'm having. But I hope a capacitor on my neg coil lead will cure my problem. Haven't tried it yet though.

[contraption22]

Is your timing belt tight enough? That can cause this to happen.

[ShelGame]

I'm 100% sure the timing belt is right. I use the Miller tool to tension it, and I do the 90* twist test.

[ShelGame]

That's interesting. That's something similar to the problem I'm having. But I hope a capacitor on my neg coil lead will cure my problem. Haven't tried it yet though.

I've followed your thread, but this can't be the same issue. This is the RPM signal from the ECU itself. Not measured at the coil. The ECU measures the period (time) between the pulses on the shutter wheel to calculate the RPM. So, the only possibilities are: slop/play somewhere between the engine and the shutter wheel; or this is just the result of logging normal torsional vibrations - measured at odd intervals. You'd think the timing belt/oil pump would isolate the distributor from most of that, though. And, you'd still not expect the period (time) between any 2 cylinders to vary by that much.

I think I've convinced myself it has to be slop.

[glhs875]

I've followed your thread, but this can't be the same issue. This is the RPM signal from the ECU itself. Not measured at the coil. The ECU measures the period (time) between the pulses on the shutter wheel to calculate the RPM. So, the only possibilities are: slop/play somewhere between the engine and the shutter wheel; or this is just the result of logging normal torsional vibrations - measured at odd intervals. You'd think the timing belt/oil pump would isolate the distributor from most of that, though. And, you'd still not expect the period (time) between any 2 cylinders to vary by that much.

I think I've convinced myself it has to be slop.

I agree the problem sounds different than mine. The more innacuracies that continue to show up on the stock setup, is starting to make a crank triggered stand alone system look pretty good! I would think that would make things alot more accurate. But can be expensive as well, along with having to start all over with the tune up.

[ShelGame]

OK, so, the shutte wheel was kind of loose. I could move it with my fingers, but it wasn't loose enough to rattle around on it's own. There are, however, some whitness marks on the shutter wheel from where it struck the HEP. Probably not good, huh?

I got some hardware to re-secure the wheel. But, I'd still like to know what kind of RPM "noise" is typical (when datalogging direct from the ECU). If anyone has a datalog they could share, that would be great.

[Aries_Turbo]

what style of datalogging are you doing? minidash with serial code mod?

Brian

[ShelGame]

No, actually the datalog above was done with Jason's logging program and the hi-speed logger mod. But, I'm using that data to write my data analysis routines for MiniDash. It's also the sample data that comes with MiniDash :)

Did you ever get a chance to test the last .prc I sent you? With any luck, I'll get some time to work on MiniDash in the next 2 weeks while I'm home on vacation...

[Aries_Turbo]

no i didnt yet. I might be able to test it sometime within the next few days, maybe even tomorrow hopefully. i was busy making myself a 2.5L version of blueberry and doing some stuff around the house as the inlaws were coming over. hopefully i can test it tomorrow. gotta wash a little bit of salt that got on the car and park it back in the yard again. :)

Brian

[ShelGame]

No problem, just curious. Nice work on the 2.5 cal, BTW.

[Aries_Turbo]

thanks. i did an update on my thread. it wants a little more fuel when cold. I'll get'er ;)

Brian