civicgsr

I'm having issues with the tach in my '94 Si Hatchback with a GSR Swap.

Here's the story. Over the summer, I pulled my trans to do a rebuild and made the mistake of forgetting to unplug the VSS which lead to me ripping the VSS wires out of the plug. I repaired the mistake and the speedo is fine.

I do have an issue with my tach. It reads low, between 600-1000 rpms low at redline and as low as 2500 rpms (shows 6k while hitting the rev limiter).

I've pulled apart the wiring harness under the hood looking for a break in the wiring or something that would lead to the issues I'm facing. I do know that the tach signal comes from the Ignition Control Module. Using a Fluke meter that reads RPMS, I can get it to read 8300 reading from the back of the cluster and the test lead under the hood.

You would think it is a bad tach right? No. I bought a used tach and it reads incorrectly the same way the original tach reads.

I have a few more things I plan to try but any thoughts would be greatly appreciated.

Thanks,
Alex

civicgsr

Okay, I tried one more thing. I disconnected the VSS thinking that something in the wiring was wrong there. No speedo, still have the same problem with the tach. I checked voltage on the back of the instrument cluster and I'm seeing almost a volt less than voltage on the battery.

Tomorrow, I'm going to try and run power and a tach signal to the spare tach that I have to see if the difference in voltage has anything to do with my problem.

hoppin blox

any luck with this? mine is doing the same thing. @ 55mph in top gear its about 5-600 low...

civicgsr

Sadly, no. I've tried so many different things that I'm at a loss. I picked up some shielded cable to try and make a distributor harness that is completely isolated from the main harness. I also want to run power to the distributor directly from the batter at the same time as well as feed the tach directly from the batter. This all seems like a waste of time, but I want to try.

I have been looking at Rywire.com's budget B series harness http://www.rywire.com/catalog/budget...ess-p-160.html. It's a little pricey but when you consider what it would have cost to replace the harnesses through Honda, it is a bargain.

If money were no object, I'd love to replace all of the wiring, distributor, ECU, etc etc. But that's a bit silly considering the problem seems to only be impacting the tach. I'll update this thread if I find anything.

-Alex

speedjunkie_g35

There are two dials on the back of the tach gauge itself that allow adjustment. I documented the process in my build thread.

FairlyImprudent

I had this problem before and ended up replacing the cluster and it worked fine after that. It would red line around 4k. I didn't try to replace just the gauge so maybe it was something to do with the circuit on the back of the cluster. Not much help but just thought I'd let you know the possibility.

yungmulacrx

All i can say is oem tachs are not that accurate.. I had a cluster in my car that would be past 8.5k with my 7800 rev limit, i have switched clusters and the new one is only at 7k with my rev limit.. I have had an autometer tach that always seems to be reading correctly.. I would assume its something in the cluster but im not positive.. Good luck

civicgsr

It may very well be just a tach thing. However, it was fine for...16-17 years then all of a sudden not? Plus, it read just as incorrectly with the extra tach that I picked up. I'm not willing to buy a nice autometer tach just to experiment either.

I do want to take a look at adjustment that speedjunkie_g35 pointed out. Thing is, I really believe the problem is a little deeper. I know I'm not getting all 8300 rpms when I hit the rev limiter. Whatever is causing the tach to rear wrong is also faking the ECU as well.

hoppin blox

I found the adjustment at 12 o clock on the back of my tach. i drilled a small hole through the top of the cluster so i could adjust it with a jeweler's screwdriver while it was still screwed in. but alas,,, the adjuster was already bottomed out. i swapped in a 3 3/8" tach over the weekend. seems to be reading very close to spot on.