Draven8795

I just picked up a honda civic hatch with an h22a swap. This will be designated for track/auto x. I'm working through some bugs now for it to be ready in the winter.

1. I has an autometer tach in it. It used to work before I bought it but now doesn't. It has a good 12v source and ground. I traced the green wire from the tach and it is hooked to the blue wire just on the other side of the firewall. Based on my research this should be correct. My question is the blue wire coming off the distriburtor. Is that used by the ECM? To trouble shoot I'd like to tap directly into that wire.

2. I should be able to use a multi meter with the car on to make sure there isn't a short circuit to that blue wire correct?

grumblemarc

iTrader: (4)

So this is actually a "My aftermarket tach is not working any more" thread. You have signal. power and ground. That's it. The green wire is the rpm signal wire to the ecu.
https://www.google.com/search?q=civi...ient=firefox-a

Draven8795

You are quite correct. My autometer tach doesn't work anymore.

All wires hooked up. Question is does the blue wire from the distributor go all way to the ECM. i.e. can I tap into the wire right off the distributor to trouble shoot this. Right now the tach (green wire) is tied into the blue wire right next to the fire wall clutch master.

I'm trouble shooting if there is a short somewhere on the blue wire or if for some reason the tach just died.

It looks like I can tap into A21 on the ECU. But I should splice into that wire and keep the connection correct as the ECU uses this information.

Does someone have a more elaborate answer?

Former User

What car? What ECU?

Draven8795

p72 ECM. 1992 civic hatch. Can't remember the exact model.

Former User

There are OBD1 and OBD2 P72 ECUs. Is yours OBD1? In this case, the ECU gets the rpm signal from the CKP sensor inside the distributor, not from the blue wire attached to the igniter unit.

Draven8795

It is an odb1 ecu. So the blue wire coming off the ignitor is not what I should tap into as another source to test the tach then?

If not where should I tap it into. From my research right now i believe it is plugged into the diagnostic port blue wire coming out of the firewall. Which isn't working at this point.

Former User

This was your original question:

The answer to this question is no.

Your current question is different:

Answer -- Use the blue wire in the test tach connector on the firewall to hook up a test tach. If it doesn't work, check whether you are installing it correctly and whether the blue wire is broken somewhere between the igniter unit and test tach connector.

Draven8795

You basically answered my questions. I'm going to check the continuity of that blue wire next to the firewall. But just wanted to know if A. I could just tie directly into the wire coming off the distributor for the tach incase there is a break in the test wire. and B. wanted to know if that blue wire was actually used by the ECM just incase it caused some issue tapping into it. Or C. if it made more sense to come off a wire from the ECM instead. The car is totally gutted so I can pretty much run wire anywhere i need to to make this thing work correctly.

Former User

Yes sir.

Draven8795

Cool thanks for the confirmation.

I do have another question. Like I said the whole interior is gutted including the dash and panels.

I'm not sure if this was removed when that was done or the new ecu was put in but the diagnostic port that needs to be jumped to check the CEL is gone. Is there a way to readd this or check the CEL somehow?

Former User

Are you sure the service connector is gone? It may be inserted into another connector atop the main wire harness above the ECU.

Draven8795

Yea pretty sure. There is nothing in the footwell on the passenger side except the ecu (everything is down to the sheet metal). I felt around the ecu to see if was tucked someplace else but nothing that I could find that looked like the diagnostic port.

Draven8795

I created new post but it looks like I can ground D4 on the ECU to get the CEL to flash?


Also I talked to the previous owner and he said the the same time the tach quit working is when the CEL came on. So I'll have to check that before I do anything more with the tach. SOmething wrong with the distributor maybe?