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240 Installed tach but it's reading wrong.

volvo 4 life

volvo 4 life

Active member
Joined
Aug 9, 2007
Location
Northwest Connecticut
I finished putting the tachometer into my car this weekend. It's the stock 240 kind for the old dash so no special wiring was needed except for the wire to the coil which I put through the fire wall. The problem is that it's only showing about half of the revs the engine's actually turning and I got a tach for a redblock and not a PRV as far as I know. What could be the problem? I have the wire to the coil connected to the negative terminal (#15) like I've heard it should be.
 
My tach only redlines at 6k so maybe it's a V6 tach. If anyone has a four cylinder tach that they'd like to trade for mine then let me know because it's kind of useless.
 
As I recall the back of the tach is stamped with something that indicates if it is a 4 or 6 cyl tach. But I can't remember exactly what the marking is. Anybody else know?

The problem with trading is finding somebody that needs a 6 cyl tach. Every 6 cyl Volvo that I've seen comes standard with a tach.
 
It's been awhile since I looked at one but, I think they do have adjustments on them, if so you might be able to recalibrate with a hand held tach.
 
Most tachs, whether they are VDO, Stewart, Autometer, whatever, have means to adjust, usually via a "screw" on the backside. But you need to make sure the readings are good throughout the RPM range, which can scare people.

We do this all the time with twin Volvo Penta TAM-D diesels on boats. Boat motors, whether they be gas or diesel, don't seem to mind WOT. Scares the hell out of car owners though!
 
Early in this thread you wrote that you connected the tach to terminal 15 on the coil. It's supposed to be connected to terminal 1 on the coil. Terminal 1 is the negative, terminal 15 is positive. It won't work correctly if it's on terminal 15.
 
moxy123 said:
Get the right one, much easier.
Click to expand...

Not much easier to find though. If anyone wants to sell me their's I would gladly buy it if I can't figure this one out. The problem with this one is that it almost seems inconsistant throughout the rpm range. When it idles it says it's around 700 or 800 rpm but when I rev it I can only get it to about 3250 rpm before it sounds like it's really revving to 6500. I don't know if these can be calibrated or not but maybe it's just set wrong.
 
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