AEM EPM - how to monitor cam signal

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fatcorvairman
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AEM EPM - how to monitor cam signal

Post by fatcorvairman »

Hello all,
Could anyone help me figure out how to log my crank and cam inputs to the MS3x 3.57? I'm not finding anything in the composite log to set up monitoring for those signals.
John
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jsmcortina
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Re: AEM EPM - how to monitor cam signal

Post by jsmcortina »

The MSQ looks ok. So that suggests an electrical issue preventing you from seeing those signals.
Do you need pullups on the inputs perhaps?

James
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billr
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Re: AEM EPM - how to monitor cam signal

Post by billr »

The engine sorta-kinda runs, doesn't it? Do you see any sync loss in the MSL file (post it, if in doubt). I think this question isn't about a lack of CKP/CMP signal; it is about how to log those.
Reverant
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Re: AEM EPM - how to monitor cam signal

Post by Reverant »

The AEM EPM doesn't need pullups, it has internal pullups to 12V. So it outputs 12V pulses as-is.

A word to the warning about the EPM - the pulses have a random delay between them, even when running at a constant speed from a battery-powered drill.

This makes the timing erratic and the engine RPM signal looks like a sawtooth in the logs, and makes tuning at high RPM almost impossible. For example at ~8500rpm, the RPM signal bounces back and forth by as much as 600rpm!

What is needed, is a filter that averages the RPM from the 8 last RPM measurements, like this, in ms3_ign.c:

ultmp = rpm + previous_rpm[0];
ultmp += previous_rpm[1];
ultmp += previous_rpm[2];
ultmp += previous_rpm[3];
ultmp += previous_rpm[4];
ultmp += previous_rpm[5];
ultmp += previous_rpm[6];
ultmp >>= 3;

outpc.rpm = ultmp;

This resolves the sawtooth effect, but obviously not the timing error/scatter that will show up when using a timing light. So one needs to tune conservatively with the EPM, as the scatter can be as high as 3-4*.
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Re: AEM EPM - how to monitor cam signal

Post by jsmcortina »

Wow, that's really hopeless.

Do you have an insight on why it is so bad?

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
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mrx79
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Re: AEM EPM - how to monitor cam signal

Post by mrx79 »

jsmcortina wrote:Do you have an insight on why it is so bad?
I have an EPM running as well, but can't experience these kind of issues.
But i have to agree, the EPM in it's stock configuration is not a good design.
When i first installed mine as it came from the factory, i had a LOT of trouble with noise on the CAM/CRK lines until i noticed that the output stage of the driver inside the EPM is VERY high impedance which makes even a twisted and shielded wire a pretty good antenna. After changing that, the noise issue was completely gone.

Maybe Reverant is picking up some high speed noise, which causes the rpm to be that errectic.

After solving the electrical noise issue i stumbled across another drawback of the design. As it is completely cam driven, you have alos all kind of drivetrain/valvedrain oscillations also on your cam/crk signal. I could improve these up to a point where they don't bother me any longer with running a bit tighter timing belt as stock.
But i guess a bit will always remain, but i't nearly as bad as i would get any ignition advance issues even at high rpm's. But i also run a stock valvetrain, i can imagine if you run some crazy cam's with valve springs the situation can get worse.

I fixed 60-2 CRK trigger on the crankshaft itself of course is a different deal, but on my engine much harder to mount, so i stick with my current solution which is fairly acceptable and not worse then stock.
Honda CRX B16A1 Turbo | MS3 running | pre1.5.1 beta7 Firmware | 24/1 Dual Wheel | COP ignition | 725cc ID injectors
Reverant
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Re: AEM EPM - how to monitor cam signal

Post by Reverant »

I literally put the EPM on the bench, and rotated it with a power drill. I put the outputs on the scope, and these are the results:

Image

These were measured by my scope, but manually. So noise is not a factor here.

So I marked a tooth as #1, then measured the time from tooth 1 to tooth 2, tooth 2 to tooth 3, etc.

As you can see there's a huge variance.

The problem is that these numbers are completely random; the next rotation would give completely different data for each specific tooth.

I have seen this issue in 4 EPMs so far.
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mrx79
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Re: AEM EPM - how to monitor cam signal

Post by mrx79 »

Looks interesting... i will check mine again when i have time.
Anyway in a few weeks i have to double check my timing, so i will check it in the car as well. But when i last checked it, it was rock solid up to 6000rpm without issues.
So at least from what a timing light might pick up, these was no jitter to be noticed.

But i also installed a new EPM on a friends car not long ago and noticed that AEM made some modifications inside the construction, may i ask which production year your model are? I haven't tested the newer ones, mine is quite old already, maybe there is a difference too.

PS: Sorry for the thread creator, to hijack your thread. I'am not sure if i understand your questions correctly, but i would assume that composite logger is able to log what you are looking for?!?
Honda CRX B16A1 Turbo | MS3 running | pre1.5.1 beta7 Firmware | 24/1 Dual Wheel | COP ignition | 725cc ID injectors
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