I just picked up a new car recently and when I purchased it the tach didn't like to work very well. The needle tends to wander up and down around the area that it would normally be at, and when you step on the gas it freaks out and just jumps up or down. The car is a 97 civic with an ls/vtec. It is equipped with a hondata s300 unit. I'm pretty sure the distributor is not the culprit here because, for those of you that are not familiar with hondata's Smanager, the display function shows RPM as perceived by the ecu and it's quite accurate, and working properly. I swapped out the tach for one of my known working ones and the problem persisted. This leads me to believe that the problem is not with the cluster, and is more then likely and issue with the wiring before it reaches the cluster.

I'm wondering if someone in here who is familiar with the wiring could point me in the right direction to diagnose this and fix it. What should I test that is affiliated with the tach signal, and what sort of signal should I be looking for with a multimeter (voltage scale??)? I'm familiar with the blue wire behind the cluster in the dash harness, but I don't really know where to trace it too and what to look for when I test it. Any help would be appreciated, thanks (we need a chassis wiring thread here...).

 

Anyone know where the wire for the tach signal coming from the ecu is located? Would it be one of the wires located within the A-C plugs at the ecu or would it be a wire that is part of the green chassis plug near the ecu? This is for a 96-98 obd2a vehicle, again. Thanks.

 

It's probably the ignitor inside the dizzy bro. But I know the green wire on the cannon pug by the dizzy is the tach wire. I have a LSV with hondata also. mine bounced around a little and got worse and worse till I bought a ignitor. Just pull off the dizzy cap and literally wiggle the wires going to the ignitor and it will prolly work fine for about a week. Mine did.
FF squad has all the wiring info you need BTW

Nick

 

I really didn't think it could have been the dizzy because hondata registers the tach signal perfectly in the display screen of smanager. Did you ever go inside the smanager to see if yours was accurate at all before you replaced the dizzy? This particular dizzy is quite new, about 20,000 miles on it, but that doesn't mean it's not going out prematurely. I just don't see how it could be fine in hondata when the ecu reads the same signal as the gauge cluster for the tach. Also, I checked on ffsquad for the ecu pin outs and there isn't a pin out listed as tach signal or anything of the like. It's more then likely the CKP pin, or something similar to that but there are a couple of those. Thanks for your help.

 

double check the ground on the thermostat housing.

 

I double checked the thermostat ground today and it was nice and tight. I even removed it, cleaned it (it was pretty clean already) and tightened it back on. There was no change. I haven't been able to figure out which pin is related to how the ecu recieves rpm signal for the tach. Any help regarding this would be appreciated. Thanks for your input.

 

Bump.

 

Bump. Still looking for a bit of help figuring out which whire the ecu gets engine speed info from on my obd2a civic. I searched and searched but couldn't come up with the info I'm looking for, including the in depth pin out info on cc squad. Any help would be appreciated, thanks.

 

Bump.

 

It is your ignitor...or you can keep fumbling around and ignore good advice again?

 

+1
The hondata gets the tach signal from a different source inside the dizzy.

 

I'm having this same issue.
However I have used 2 different distributors as well as a brand new ignitor.
After that I noticed the ignitor wire (yellow w/green) was loose in the distributor connector plug. Moved that to the extra pin location in the plug and thought it would have fixed it.
Test drove it last night and still the same problem, this time the PIN is connected tightly in the connector.

My only other guess is that the ignitor wire is broken somewhere in the insulation within the harness and keeps jiggling around.
I also didn't think to check the ground, will do that.

 

I wasn't ignoring good advice purposely, because it was good advice to check that and it's something that I would've advised to check right away as well; however, in my situation it is not the ignitor. Swapping to a known working distributor in a different car yielded the exact same results. I then traced through the wiring on the engine harness and it all checked out great. What I decided to do was rewire the tach using the tach signal test wire inside the engine bay. I brought it inside the cabin, tapped into it, and used that to wire into the back of the cluster. Problem solved for me. I'm guessing the wire that originally runs into the back of the cluster for the tach signal has a short somewhere or a weak pin. I didn't know how to test for this properly because I didn't know what sort of signal range I should test for with the tach, and I didn't know where the wire started before coming in at the back of the cluster. I don't really think my fix actually 'solved' my problem, because I still don't understand why the proper way for this to work inst working; I may of just caused it to work by simply getting the same signal from a different wire but it seems to be working well enough for now.

So, in my situation, it wasn't the ignitor, but it is in fact a common cause of the symptoms I described. I appreciate all the help and I don't ignore good advice, I value it very much when it's given to me because it's becoming harder and harder to come by. Thanks.

You should try swapping distributors. I kid. What kind of car is this too? If it's for your DA teg, they have a 2 piece engine harness as you probably know. You could try tracing the distributor wires to where they meet at the shock tower plug and double check that they are pinned good there. I would beep test them to be sure, staring before the shock plug on the ecu side, and then at the distributor. If they check out fine then maybe work your way back a bit more. I know it can be a pain trying to trace wires back like that but I would pick a wire at the dizzy, go to the shock tower plug (if this is a teg), look for that same colored wire and test it out. Also, you could go to ffsquad.net to get a detailed list of the ecu pin out's which might help give you some specific wires to look over at the ecu plugs to just make sure none of the pins are loose and making a bad connection. If all of that checks out then you've got a bit of a mystery on your hands like I did...well still kind of do.

If the wires are all good leading from the distributor, through the harness, and too the ecu plugs; then you have to assume that it's a bad connection after those plugs on the way to the cluster, or that the cluster itself is bad. If all else fails, then you could try my fix. I'm pretty sure that tegs have the same tach signal test wire. It's a blue wire coming out of the fire wall near the brake master. The wire just kind of leads off to nothing and is normally capped off on a bracket I believe. Now, I've read that this is less then ideal because supposedly the signal isn't as accurate but according to my findings it's definitely close enough to what my hondata is saying, so it's close enough for me. I hope some of what I said helps.

This thread also has a decent explanation of how RPM signal get's to the ecu, and how Tach signal gets to the...tach. It doesn't neccesarily tell you what wire to look at directly for ecu rpm signal, but it's a good explanation nonetheless.
https://honda-tech.com/forums/showth...est+wire+color

 

If you guys have an EMS and can datalog, check the RPM data. If it fluctuates, it's somewhere in the engine bay. However that would also cause bucking/etc issues, and probably some CEL's. If it's the cluster, you won't see anything abnormal since the cluster just displays info from that one tach wire.

I've seen someone with a bad TACH in the cluster, another with the spedo. The tach guy swapped to an EDM cluster, the spedo guy swapped out the spedo guts for the spedo inside a CX cluster. Sometimes it's not the drivetrain.

 

Very good advice, sometimes it's simpler then what it seems. I did check it in my Hondata and it didn't seem to fluctuate at all, it seemed quite accurate but at my tach it wasn't even close (with the needle just bouncing around, or doing nothing). In my case though it turned out not to be the cluster like I had assumed, but a wire short somewhere in the dash harness more then likely before it makes it's way to the cluster. I haven't pin pointed the point of the problem exactly yet but as I said, I've come up with a sorta solution for now that seems to be working fine; with the tach signal test wire jumped to the normal tach wire behind the cluster.

 

i got the hondata s300 and with my stock ecu my rpms work fine and now with hondata installed it no longer works. anyone have the same problem?