Hi all,

I recently picked up a second Accord coupe. It's in need of a little tlc, but it's a nice little car. One odd thing, though, is that the tachometer reads low. The tach movement is smooth, and it doesn't ever jump around. It just reads much lower than it should. For example, at about 30 mph in first (according to the speedo) the tach is reading just over 4500 rpm, and it hits the rev limiter just over that.

The car runs well, and seems to have plenty of power, doesn't smoke, runs smoothly, etc. My first thought was that someone had replaced the cluster with one from a V6. That would cause the tach to read low. But there were no Accord V6/manual trans cars until much later, and this car does not have an automatic cluster, so that can't be it.

Any ideas?

Thanks,

 

Humm, can you tap into the tach test port - on right pass side by the strut tower and fuse box and verify the rpm's?

 

Weird results. Maybe my engine analyzer is acting up (it's really old, and designed to work with points). It read 2000 rpm at idle, when the tach read 500 rpm, and it read 15000 rpm at 3000 rpm on the tach.

I hooked up a voltmeter to the tach port and it read 13.3 volts at idle and 12.5 volts at 3000 rpm (indicated) on the tach.

 

Was it set for a four or eight cyl engine? 2000/4 = 500 .....15000/4 = 3750

Also note between 0 and 1K there are two marks. From zero the first is 500 rpm, the second 750.....then the 1k.

 

It has settings for 4, 6, and 8 cylinder engines. I had it set on 4. If it were set on 8, wouldn't the readings be half of that of a 4 cyl, not double? Or are you saying that the tach port is outputting one signal for each cylinder, hence it's four times higher than what the tach should read?

The car's tach reads 500 rpm at idle.

 

You said it was old, might only read point style ign systems....I was just trying to find a math answer to the situation....and dividing by four got me close.

For every 200 pulses of the ICM the tach reads 100 rpm.

At 60 mph in 5th gear, flat level ground and holding steady speed....what is the tach reading?

 

I drove the car today, but traffic was heavy. I did get it up to 50 mph, which worked out to 1250 rpm or so in 5th. One of the online gear/speed calculators says that it should be turning 1900 rpm at 50 mph.

 

Sounds like something is up in the "drive unit" on the tach.....strange for that to happen?

 

Yeah. It's weird, because the movement of the needle is really good, just inaccurate.