Steve-T

RE: 1991 CIVIC HB, D15B1 Engine, MT

What does a "1 to 4 pulse ignition signal" mean in relation to connecting a handheld tach to the blue wire coming from the distributor?

Thanks,
Steve-o

welfarepc

You need to tell aftermarket tachs how many cylinders your engine has so its displays the correct RPM.

I have a feeling that is what you are getting at. Your question is a little strange and vague.

Steve-T

WelfarePC -
Sorry for the response delay, I only have library access to a computer.
I came across that phrase on the net while trying to figure out why I seem to be getting a very low rpm reading on a circa 1970's tach I was using to check my idle speed.
Specs are 625rpm +/- 25 with the 2-pin EACV disconnected, if my memory is correct.
My tach was reading 150rpm, which when doubled would be 300rpms.
When I set the idle to 600rpms, you can tell just by the sound that it was way too high.
After seeing that phrase on the net, I was hoping I would just have to multiply the tach reading by 4 to get the right results and avoid having to buy a new tach.
I posted hoping to get confirmation.
Any suggestions?

Steve-T

Problem resolved.
For an 8-cyl engine, my old tach recognizes 8 igniter/coil pulses per 1 rpm because it assumes 1 pulse coming from each cylinder.
For a 4-cyl engine putting out 1 pulse per cylinder, 8 pulses is actually 2 rpms. However, 8 pulses would display as 1 rpm on the tach, and would have to be multipled by 2 to give the correct results.So far this is what I expected.
However, my 4-cyl D15B1 engine puts out 2 pulses per rpm (as per page 23-94 of the 1991 service manual), not 4.
8 pulses is actually 4 rpms. However, my tach would still display 1 rpm for the 8 pulses, but this reading would have to be multiplied by 4 to give the correct results.

Steve-T