PMP-LED lights up, no rpm

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Re: PMP-LED lights up, no rpm

Postby Matt Cramer » Mon Aug 24, 2015 5:42 am

The ground looks OK. At this point, I would check for an issue with the module or pick-up coil.
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Re: PMP-LED lights up, no rpm

Postby flowbench » Mon Aug 31, 2015 2:43 am

I already did replace the module and pick-up. No change. I'll have someone here this week with an oscilloscope checking everything .
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Re: PMP-LED lights up, no rpm

Postby flowbench » Mon Sep 07, 2015 11:49 am

O.K, had a guy here with an ocilloscope to check whats going on:

Measurement 1: Open harness (ECU disconnected), measured at pin #24 - 0V (with little noise), independent from ignition (TEK0024.BMP)
- with ignition on and cranking there is Square wave with 6V amplitude (TEK0025.BMP)

Measurement 2: Harness connected to ECU, measured at pin #24
- 0V when ignition is switched off
- 1V when ignition is switched on (!!!)

- No wave can be measured and seen on the scope when starter is turning. The ECU seems to force the 1V level on the pin and overlay the input from the tach input .

Any ideas ? THANKS !!!
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Re: PMP-LED lights up, no rpm

Postby Matt Cramer » Tue Sep 08, 2015 7:09 am

Try redoing the board for VR input - it sounds like the opto circuit is drawing too much current for that sensor type.
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Re: PMP-LED lights up, no rpm

Postby flowbench » Fri Oct 16, 2015 4:46 am

Well, I got results now: the guy working on this thing now changed tho polarity of the opto-circuit, did the modification with the transistor in order to enhance the signal.- all with no success. As soon as the wiring harness is connected, the signal from the HEI-module dissapears on the board. Now he made an interesting test: he disconnected pin 6 , 36 and ground, one at a time to see if one of this wires have an impact,- pin 24 stayed connected all the time. When we disconnected wire on pin 6 (override cranking signal) we DO GET AN RPM-SIGNAL !!!! When we connect it, it'll kill the signal again. A test with the oscilloscope revealed that the 5V coming from the ECU on pin 6 seem to kill the signal in the module. Whats wrong- the new hei module or a setup on the board ? ANY IDEAS HERE ?
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Re: PMP-LED lights up, no rpm

Postby Matt Cramer » Fri Oct 16, 2015 6:05 am

Make sure the board is only sending 5V on pin 6 when the RPM is over cranking RPM using a Stimulator.
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Re: PMP-LED lights up, no rpm

Postby flowbench » Wed Oct 21, 2015 1:56 pm

Matt, the opposite is happening: Ignition on,- got 5V on pin 6, if I raise the rpm through the stimulator the voltage drops to zero at around 670 rpm.
The engine runs and I took the car for a testride today,- everything smooth and flawless, but all this with pin 6 disconnected (!) and: I do have the correct ignition advance as well !!
When I connect pin 6 while engine running, engine keeps on running. With engine shut down and pin 6 connected it wont start again, since the 5volts on that pin is somehow killing the signal from the ignition-module.
So something here seems to be reversed completely.If we got this right:

-5 Volts on pin 6 are there to engage timing advance. The opposite is happening on my setup: with no voltage I do get advance.
- The voltage on pin 6 kills the rpm-signal from the ignition-module instead of switching the signal from the HEI module through the ECU as its supposed to do.

Did I get that correct ?

I could just leave pin 6 off and drive the car, but I would always be concerned I am covering something up that would give me a headache in the future....
any ideas ? Thanks again for your time !!!!
flowbench
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Re: PMP-LED lights up, no rpm

Postby Matt Cramer » Thu Oct 22, 2015 5:19 am

If it's behaving backwards, you will need to make sure:

1. You are using LEDs for both outputs and not using JS10.
2. Spark output is set to Going Low.
3. You are on the latest firmware.
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Re: PMP-LED lights up, no rpm

Postby flowbench » Tue Nov 24, 2015 2:50 pm

Hi folks,hi Matt - thanks so far for all the inputs and help ! In the meantime I had to disassembly the engine due to a blown headgasket.
I will continue with the last remaining small problem in springtime, when the car is back on the road. But I am happy so far that the car drives fine .
I would like to leave some thoughts and a resumee so others may benefit from my problems so far:
a) My first problem was due to a wrong firmware. b) Second:If I would have used a oscilloscope in first place while searching for the missing rpm-signal I would have found
the problem much, much faster. This is a point, that I feel should be pointed out in the MS- instructions. With an oscilloscope you know, what kind of signal you have, how strong it is, where it goes and where it dissapears on the board just right away...
And c) there seem to be two kinds of HEI modules on the market: ones that produce a voltage, as mine did, and the other ones that switch against ground, which seem to be the more common ones. If you don't know what module you have i.e. if the polarity on the board doesn't match it, all of the testing procedures with an voltmeter are worthless.
This is something that , to my taste, could get pointed out in the instruction a little bit better. During my hunt for the culprit of my missing rpm-signal I talked to two other people who had the same problem: they never solved the problem and had given up on Megasquirt.
Again,- THANKS !!!
flowbench
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