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Discussion Starter · #1 ·
Hi, I’ve been searching a bunch of forums and have not found any answers that solve my problems.

So the motor is a D16Y8 with a P72 ecu. I don’t have a CEL as the motor is in a classic mini. I have hooked up a light to pin 13 on plug A to ecu (Malfunction Indicator Light) according to things I’ve found on forums. I have also tested solenoid and it clicks, I’ve hooked up a light to the vtec solenoid and it doesn’t turn on.

Last winter I changed the intake manifold to allow for better fitment. (Again it’s stuffed into a classic mini) since then I don’t think vtec has been engaging. There are no other issues with drivability or any weird behaviour.

I also have validated it gets oil pressure at the solenoid (forgot to re install vtec solenoid before starting the car... it was quite the fountain of oil!) and my oil level is good.

Any help would be appreciated. Thank you
 

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P72 ecu is supposed to be running a 1.8 vtec with intake butterflies (b18c1 Integra GSR)

While it technically will run the civic engine, it will be far from efficient at doing anything.

Check that the ecu is getting proper coolant temp data, and can see throttle position and MAP sensor data properly.

Bridging the service wires of the harness (if you are using a stock civic harness) and reading the check engine light blinks will tell you if there is any error codes.


You are under $200 from having a fully live tunable setup, so you can certainly find a stock basemap and tweak it.
 

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Discussion Starter · #3 ·
P72 ecu is supposed to be running a 1.8 vtec with intake butterflies (b18c1 Integra GSR)

While it technically will run the civic engine, it will be far from efficient at doing anything.

Check that the ecu is getting proper coolant temp data, and can see throttle position and MAP sensor data properly.

Bridging the service wires of the harness (if you are using a stock civic harness) and reading the check engine light blinks will tell you if there is any error codes.


You are under $200 from having a fully live tunable setup, so you can certainly find a stock basemap and tweak it.
Okay, good to know.

How do I validate its getting proper data? Do I need to get a S300 or something like it in order to do that?

I'll try bridging the service wires, It is not a factory civic harness so I'll have to do some digging to find which pins to bridge on the plugs.

Thank you for your help!
 

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If it is not a factory civic harness, likely it will not have the wires exposed. You will need to dig out a wiring diagram for the 92-95 civics if it is an OBD1 setup.

If it is a OBD2 setup (unlikely) you simply need to find 3 or 4 wires and grab a OBD2 port from any junkyard honda and wire it up.

You can verify coolant temp by reading resistance at the sensor, then reading the voltage for coolant temp at the ecu plug.

Same with MAP and TPS. Matter of finding the sensor value versus voltage tables in the troubleshooting sections of a civic technical manual.

The one in my signature I beleive is for EK 96-00 civics, so should work fine if you are on OBD2 P72.

If you are on an OBD1 P72 from a 94-95 Integra GSR, search for 92-95 civics wiring

Hopefully something of this garbled mess of mine can help!
 

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Discussion Starter · #5 ·
If it is not a factory civic harness, likely it will not have the wires exposed. You will need to dig out a wiring diagram for the 92-95 civics if it is an OBD1 setup.

If it is a OBD2 setup (unlikely) you simply need to find 3 or 4 wires and grab a OBD2 port from any junkyard honda and wire it up.

You can verify coolant temp by reading resistance at the sensor, then reading the voltage for coolant temp at the ecu plug.

Same with MAP and TPS. Matter of finding the sensor value versus voltage tables in the troubleshooting sections of a civic technical manual.

The one in my signature I beleive is for EK 96-00 civics, so should work fine if you are on OBD2 P72.

If you are on an OBD1 P72 from a 94-95 Integra GSR, search for 92-95 civics wiring

Hopefully something of this garbled mess of mine can help!
It is an OBD1 ECU
From what I've found I need to bridge the SRS Service Check Signal with ground. So connector "D" pin 4 to ground.
Here's some of the images I'm using to get to that conclusion incase others have this issue.
I'll let you know when I go back to looking at it in the morning!
Rectangle Font Parallel Slope Number

Font Screenshot Number Parallel Electric blue
 

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Are you checking A-13 at the Ecu plug for lights?

One way to verify it is working, have a small lightbulb like 5watt 168 or 194, wire tap one side to ecu plug and pin A13, ground the other side of the bulb. When you key on, it should come on briefly, then go away, or go away when the engine is running for a few seconds.
 

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Discussion Starter · #8 ·
Are you checking A-13 at the Ecu plug for lights?

One way to verify it is working, have a small lightbulb like 5watt 168 or 194, wire tap one side to ecu plug and pin A13, ground the other side of the bulb. When you key on, it should come on briefly, then go away, or go away when the engine is running for a few seconds.
I did that, and it doesn’t come on at all. I’ve tested the bulb before and after and I’ve even hooked a meter up to it and there is zero volts on that pin at all times. Is it possible to tune an ecu to not show a CEL or MIL at all? If not then maybe there is something wrong with the ecu?
 

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Check the inside of the ecu for a removable chip socket. If the ecu looks untouched, there is no way for it to be off.

Yes, you can program/tune and somewhere in there tell it to never use that light.

Very strange regardless.

What were you using for the ground? a ground via the harness? or a chassis/engine ground?
 

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What car do you have?

That first picture is an OBD2 connector (so 1996+ chassis) yet at the same time state you are running an OBD1 ECU, and show OBD1 ECU pinouts below the OBD2 connector picture.

If the car is indeed an OBD2 chassis but the ECU is OBD1, then the OBD2 port is dead on purpose. It doesn't work the same way when using an OBD1 ECU.

Post pics of said ECU, chassis, wiring harnesses, etc. so we can have a better idea of whats going on.
 

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Discussion Starter · #11 ·
Check the inside of the ecu for a removable chip socket. If the ecu looks untouched, there is no way for it to be off.

Yes, you can program/tune and somewhere in there tell it to never use that light.

Very strange regardless.

What were you using for the ground? a ground via the harness? or a chassis/engine ground?
I was using the chassis ground, same one I used to test the light bulb. I’ll get some pics of the ecu.

What car do you have?

That first picture is an OBD2 connector (so 1996+ chassis) yet at the same time state you are running an OBD1 ECU, and show OBD1 ECU pinouts below the OBD2 connector picture.

If the car is indeed an OBD2 chassis but the ECU is OBD1, then the OBD2 port is dead on purpose. It doesn't work the same way when using an OBD1 ECU.

Post pics of said ECU, chassis, wiring harnesses, etc. so we can have a better idea of whats going on.
I’ll take some photos, but I have an OBD 1 ecu I was only using the obd2 bridging the plug photo for reference as to what the names and wire colours of the pins are to correspond it to the OBD1 pin out.

Hères the images you requested, the green/orange wire I rang out to be pin 13 on Connector “A” (MIL) and the brown and white wire I rang out to be Pin 4 on Connector “D” (Service Check Signal).
In terms of the internals of the ecu I have no idea what I’m looking at...
Did notice no signs or smells of burnt electronics (Yay)
Hand Finger Automotive lighting Engineering Computer hardware

Green Font Audio equipment Electronic instrument Technology

Passive circuit component Circuit component Green Hardware programmer Electronic engineering

Passive circuit component Circuit component Hardware programmer Resistor Microcontroller

Electrical wiring Gas Cable Electronic device Electrical supply

Grille Automotive tire Hood Bumper Automotive exterior
 

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So yup, that is a true P72 with the daughterboard.

And you are running an OBD2 to OBD1 conversion harness.

Its also socketted and chipped with an aftermarket SST, so its likely running custom software. It is highly likely the tuner could have disabled the CEL/MIL.

If the MIL output doesn't activate/drive at all (cant remember if the MIL/CEL output pulls down to ground or pushes up to power, pretty sure its a ground controlled output), even when backprobing the ECU with a test light appropriately configured to test either output configuration, then you definitely need to get into the tune to see if MIL control has been disabled.

I did that, and it doesn’t come on at all. I’ve tested the bulb before and after and I’ve even hooked a meter up to it and there is zero volts on that pin at all times. Is it possible to tune an ecu to not show a CEL or MIL at all? If not then maybe there is something wrong with the ecu?
Just verified the ECU provides ground to the MIL lamp.

You need to touch one side of the bulb to POWER/12V, not ground, then run the other lead to the MIL/CEL pin to provide it ground.

Also, not knocking diag skills at all, just have to throw this out there, you have to use the vehicle power source as your references to power and ground. Can't tell you how many times I've seen guys say "I am giving it 12v! Or, I am giving it ground!" but they're using a damn Dewalt battery isolated from the circuit entirely lol.

The ECU will provide a MIL lamp path back to the vehicle battery ground, therefore you have to give your lightbulb vehicle battery power on the other lead, to complete the circuit correctly and allow the ECU to act as the switch.
 

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Discussion Starter · #13 ·
Okay. So I assumed the ECU would provide the 12V for the MIL. I didn't realize it was switching the common. So great news I have a CEL! lol Obviously not a good thing but I'm just happy I can the read codes now and troubleshoot from there and not blindly trying to diagnose. So when I put the Service check signal to common or (Chassis ground) I get 6 short blinks, no long blinks. So from what I've researched that would be Coolant temp sensor. From link below:


First things first I'm going to run permanent wires to this light for CEL not the current alligator clips I'm using. Then a switch to connect the service wire to the common/ground. Then I'm going to look into the coolant sensor/wiring.

Thank you guys so much for your help! I really appreciate it!
 

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That hand writing looks a lot like my chicken shit scratch, I read it as Mod, no VTEC. But I've never had a P72 ECU.
 

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Coolant temp definitely is one of the most important parameters for vtec engagement.

You can test with a 5k poteniometer, after looking up the resistance tables for coolant temp to ohms in any 88-2000 civic manual. The sensors are all extreemly close to their ranges. THe newer cars have a bit bigger range, thats all.
 

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Discussion Starter · #16 ·
I had a chance to look into it last night and found the pins on the plug for ECT sensor looked flat, bent them a little bit to make better contact with the sensor and I’ve got VTEC again! I even went and unplugged my IACV plug to test my new CEL and button to display fault code and they both worked without issue! So I’m a very happy camper right now lol. Thank you again to all that chipped in with info.

That hand writing looks a lot like my chicken shit scratch, I read it as Mod, no VTEC. But I've never had a P72 ECU.
The photo makes it look that way but it’s just dirty.
 

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Good deal.


The fact it has a replacement chip, still might be worth building an emulator for the 4pin on the ecu board, and at least seeing if anything can be made of it.

ectune, neptune, crome, etc... are possibilities.

Hondata needs a daughterboard of its own, so it is not hondata.
 
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