Hey all. car is a genuine EG6. Im running a H23 engine, with an aftermarket distributor, and a Hondata s300. The car runs great, and I get an excellent rpm reading through the ECU, which provides a shiftlight through the CEL at 7200 ppm. The tach itself doesnt read properly though. Sometimes it reads 5500 at redline. Sometimes 7000, sometimes whatever it chooses. I have tried 3 different oem tachs, and they all go goofy after about 3000 rpm. I have also soldered all connections inside the distributor, but still have the problem. Any suggestions?? Is it possible the cluster body could be bad? Thx.

 

bump

 

Might be a bad igniter unit, or a short or open in the blue wire.

 

Yeah, if your harness is like other EKs, the tach signal from the igniter doesn't go through the ECU (but I'm not sure how the ECU calculates it, in that case). Anyway, the book says the spec for a tach is - "Indicates 100 rpm at 200 pulses per minute of the ignition control module" which just means get the right tach, but you knew that.

Sooo, you could test at the under the hood test tach connector (blue wire), kinda like this DIY (even though it is for an Accord V6) - http://autorepair.about.com/library/a/1h/bl626h.htm Then redline with the external test tach, and see what it does. Could be the aftermarket dizzy (coil or igniter).

Just my .02 I'm far from an expert, but I can read the wiring diagrams in the manual...

 

The ECU gets its rpm signal from the CKP sensor in the distributor.

The ECU sends this rpm information to the igniter unit to determine spark timing.

The igniter unit passes its rpm information on to the tachometer in the cluster.

 

Oh yeah, I think you said that before, lol. Now the diagram makes perfect sense;


ECU has it's input (CKP), and output YEL/GRN wire signal to igniter.

Does the igniter need to modify the signal before sending it out on the BLUE wire for the tachometer? Just curious.
Since the cluster tach multiplies the pulses from the blue wire by 2, then would you need to do that when viewing a test tach? When I get a test tach I will have to try it on my '97 LX that has a cluster tach and compare readings....

 

thanks for this very valuable information. Im understanding now why the the ecu and tach can read differently. I will try replacing the coil and igniter, and will test at the blue test wire, and report findings.

 

You can move the tach into the engine bay and connect it to the tach test connect and try that way probably. If you are using a test tach make sure it goes that high 'cause some are only for idle adjust (low rpm). i.e. check the range. But I would test before and after replacing each part. And like Ron said make sure that blue wire isn't grounded out at all.

 

well, I did replace the coil and igniter as recommended with Hitachi junkyard finds. Issue remained. I then replaced the entire cluster. It took me a while to figure out how to get the cluster lights to work (non-dimmer car). Anyway, that solved the issue. Perhaps the problem was weak solder connections, or corrosion somewhere on the on the old board. Thanks for the help everyone.

 

Our stock tach's are known for not being accurate. I had this problem with my stock cluster.

 

I can understand 200-300 rpm. but 2000 rpm? thats too much for me.

 

Mine was 1000 rpms and I went through 3 more before I got one close to being accurate. I spent a couple hundred trying to chase a problem that wasn't there. Installed a autometer tach and it has been on the money ever since.