Electronic revcounter which was working fine connected to my 283 now under reads by half now it's connected to LS1.Any ideas welcome,Thanks.

 

A tach thats connected to a SBC and set for 8 Cyc. when that tach is moved to an ls1 it must be set for 4 Cyc. to read properly, just a thing the ls1 does.

 

The Tachometer (assuming that is what you meant by a rev counter????????) needs to be set in the 4cyl mode. If you Tach does not have a 4cyl mode you can either-
-buy one that does
-adapt the signal using a tach adapter
-reprogram the PCM to support the Tach

 

all of the above.

 

Oh, one more thing, some of the aftermarket tachometers need a pull-up resistor when used with the output from the ECM. Just put an 1/8W resistor from the signal line to switched 12V. Somewhere between 2.7K and 10K should suffice. I believe the ouput may be an open collector (fairly likely) or perhaps a TTL device, and some aftermarket tachometers expect a TTL or CMOS type interface, while others are expecting a full 12V swing.

 

Rev counter(sorry tach!) is in a 61 vette,so although not original to car,is a few years old and with no apparrant way to switch it over to 4cyls.I guess the resistor trick won't work alone if the signal is not right?By the way what does TTL and CMOS type interface mean,in laymans terms please.Thanks for help so far.

 

I had to use efilive program and program the pcm to a value of 4 to get my autometer tach to read right in my 73vette ls1 swap,i was able to switch dipswitchs on my tach from4cyl,6cyl,8cyl,but still wouldnt read right.had to program the pcm to get it to work right.

 

TTl and CMOS are just logic formats, shouldn't really concern you, it just explains why some tach's read the computer fine, and other don't. I am thinking that the Dakota digital box is going to be your easiest solution. You can get it from Summit for $80.00. The part number is DAK-SGI-8 Tach Adapter. Pretty easy to set up.

If you look, you can see it mounted here in the middle of the pic...

 

Thanks for all the ideas,must be able to get the bl--dy thing to work somehow soon.kev.