Need help troubleshooting VTEC activation with Hondaat ECU

Hondata installation questions / answers / issues.
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itr_hybrid
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Need help troubleshooting VTEC activation with Hondaat ECU

Post by itr_hybrid »

Hi folks,
I could really use some help on this one. I am stumped.
Vehicle is a 4g civic with a 2000 JDM type-r(b18c) motor. ECU is a P28 Hondata set-up. The problem we are having is that we cannot get the Hondata ECU to send the +12v VTEC activation signal.

What we know:
- JDM motor does not have an oil pressure switch. Wire from the ECU that would normally go to the switch is firmly grounded.
- If we substitute the stock JDM ITR ecu, VTEC engages normally. This would seem to confirm that the ECT switch and VTEC solenoid are working properly.
- The Hondata ECU works fine if it is used in another (USDM) car. This seems to indicate that there is a vehicle wiring issue, we just cannot determine what. There was a lot of customer wiring done in the engine / chassis harness so it is a possibility.
- We have tried anoher chipped p28 (Skunk2) ECU and it behaves the same way as the hondata.
- We have intermittently gotten a CEL code of 21 - VTEC spool.
Any and all thoughts would be appreciated.
G3-TEG
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Post by G3-TEG »

The problem is because you don't have the oil pressure sensor on the JDM head. You have to wire in a relay to trick the USDM ECU by using the VTS signal as the oil pressure signal.

Basically when the the VTS is activated (12v), the VTM signal needs to drop to 0 volts and when the VTS is 0v, the VTM needs to see 12v.. exact opposite of each other..

You'll need to add a wire to your harness to the VTM pin and run it to a relay using the VTS as the trigger.

I just wired one of these 2 weeks ago on a JDM motor using hondata.. works fine now.

Hope that helps.
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Hondata
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JDM VTEC pressure

Post by Hondata »

Wire a 1k resistor between the VTEC spool and VTEC pressure pins. You may need to also wire a 1k resistor between VTEC spool and ground.
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G3-TEG
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Post by G3-TEG »

Just an update.. I went over the wiring again, and I have it backwards in my previous post.. The VTP voltage follows the VTS, so just wire up a relay that will trigger 12v with the VTS and also send 12v to the VTP when VTEC engages. At idle and off-vtec, the VTP needs to see 0v.
itr_hybrid
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Post by itr_hybrid »

Hi folks,
I appreciate the input, yet the answer is not so clear just yet. Playing around with my buddies 1997 US-spec GSR (p72) - this is what we found:

With the ignition on (or engine runnning), the ECU is sending a +12v signal to the oil pressure switch. This switch is closed (has continuity) at any rpm as long as the vtec solenoid is not activated. The connector for the oil pressure switch has two wires going to it - the blu/blk +12 v signal from the ECU and ground.

The oil pressure switch opens (breaks continuity) after VTEC engages (when the solenoid is triggered by the ECU). I believe this is because the pressure switch is measuring oil pressure after the vtec solenoid. We confirmed this by varying the VTEC engagement point. The oil pressure switch always opens shortly after the VTEC spool solenoid is activated.

My interpretation: The ECU is sending a positive +12v signal to ground (through the vtec oil pressure switch) until VTEC engages. At that point, the oil pressure sender sees oil pressure and the switch "opens", breaking the circuit.

Based on this, your original recommendation (g3-teg) seems correct. It seems like you need to wire a relay that breaks the circuit for the oil pressure switch whenever VTEC is activated.

The only problem is that the Helm's manual states that you should see +12 at high rpm and 0 volts at low rpm.

Hondata, I would love to hear more about the resistors.

Please let me know your thoughts
-Phillip
G3-TEG
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Post by G3-TEG »

I'm pretty sure the i'm correct in my second post.. We did it the first way and the car still threw a code (from what i can remember) so we switched it.

I know for a FACT that one of the 2 is correct.. and i'm 99% sure its the 2nd post. So just wire it up to a relay, and try it one way, and if it doesn't, then switch 87 and 87a on the relay.. thats it!
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Post by QUICKSILVER RACING »

It would be hard to understand if we don't talk on the same language.

itr-hybrid,
Compare the VTEC solenoid of the OBD1 cars and OBD2 cars. You'll notice that there is no Vtec pressure switch output in the OBD2 solenoid. But OBD1 ECU's need this signal. Just follow either Derek or Cresent's instruction.
HONDATA official and sole Distributor in the Philippines.
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+639178954747
itr_hybrid
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Post by itr_hybrid »

G3-Teg & Hondata,

Thanks for all the help.
It sounds like the ECU needs to see +12v from the oil pressure switch when vtec spool activates.

Couldn't you just splice the oil pressure switch line from the ecu into the vtec solenoid signal? I think that is what Hondata is saying, only he also recommends using a resistor. Is this correct?

I guess the question is, why do you need to use the relay?

Thanks for all the help folkd, this is being very helpful.
doc
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Post by doc »

I did the simple way. I cut the VTM line (cause one end grounded) and spliced it into the VTS line. The frist few times i use a 1k resitor to ground. (as pull down resistor - to give the line a 0 Volt level when the VTec isn't activated) but in the meantime i left it, cause the vtec spool act as resistor to gound and the pull down isn't neccassary.

Christian
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