Need Help

[ElectroLost]

Hello everyone! I'm new to the forum and don't know much about electronics. I am hoping someone here may be able to help me with my problem...

I have purchased a 3-LED RPM shift light that works off of electrical noise via the cigarette lighter or a direct connection to the RPM signal going to the ECU. The LED's are individually adjustable for specific RPM setting, when max RPM is reached, all 3 start to flash.

The cigarette lighter connection works pretty good except at higher RPM's, when it gets erratic. So I tried connecting direct to my car's RPM signal wire to the ECU, but the unit does not work correctly with this connection.

All of the cars indicated on the instruction sheet for direct RPM signal connection appear to be Japanese-made (as is the manufacturer of the unit, I think), but my car is German made. I am wondering if there is a difference between my car's RPM signal and the signal that the unit is designed to receive (i.e., voltage, frequency, etc.), thus preventing correct operation.

Here are my questions:
1. If I can determine the specification (frequency,voltage) of the RPM signal coming from one of the cars the unit will work with, and then also the spec for the RPM signal coming from my car, is there a way to convert the signal coming from my car to the signal required for the unit?
2. If this is possible, what kind of tool or meter do I need to determine these signal specs and where can I get one?

Thanks in advance for any replies. All help will be most gratefully appreciated!

 

[akg]

An oscilloscope will enable you to quickly sort out the problem.

The cigeratte lighter may be getting an AC direct from the alternator, but the RPM signal to ECU will like pulses , that may be causing the problem.

 

[ElectroLost]

Thanks. I'll try to find someone locally with an oscilloscope that can check these signals out for me.

 

[mramos1]

If it is noise, you can possibly filter it out. In the old days, chokes and caps were used to stop alternator/generator noise from interferring with the radio.

Get a scope like akg said first and map it when working and when not working, hope you can see the noise. A storage scope would be nice if you can find one.

 

[ElectroLost]

Thanks mramos!. I am looking into all suggestions offered here. I appreciate the help.