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Diagram / breakdown of p28 ecu? (long)

Old 11-10-2004, 10:50 PM
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Default Diagram / breakdown of p28 ecu? (long)

I have an ODB I p28 ecu for my civic and have a question about it. I went to chip it and noticed when I opened the case that one of the capacitors / resistors / diodes something is burned in the upper left region of the ecu (if the board is oriented with the spot for a socket in the lower right). It doesn't appear to have ever been opened / chipped before. I went ahead and socketed it and chipped it anyways and it runs fine, no big deal. Thing is, my car is a 92 cx which uses a 1-wire o2 sensor. So when I first installed the un-chipped p28, I had a o2 sensor heater code. So I got a 4 wire o2 sensor and harness and I wired it up correctly per some hybrid-tech instructions (orange / black wire to the heater circuit wire on the ecu, yellow / black to another yellow / black, for switched 12v+, green / white to a shared ground for the coolant temp sensor, other sensors, and white wire remains the same, the o2 signal.) I was still throwing the code and I double checked all the connections with a meter, so I am thinking perhaps it could be a bad ecu. I don't have another p28 to test it. Currently I am running the same 4 wire, but with the heater circuit disabled in uberdata. It doesn't throw a code, but I think it's not going into closed loop or it isn't sending the same signal as the 1-wire would be because I think I have worse gas mileage.

Is there a breakdown of what chips are functioning for what on the p28 ecu available that you know of? If you would like me to take some pictures, let me know. Thanks in advance.
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Old 11-11-2004, 12:32 AM
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Default Re:Diagram / breakdown of p28 ecu? (long)

Your ECU will still go into closed loop with O2 heater disabled in Uber.

Is the transitor thing thats burned out happen to be Q31 or Q32? (cant remember excactly)
If so, you guessed right. Thats part of the O2 circuit.
Either way, no real big deal, you can still run in closed loop fine.
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Old 11-11-2004, 01:39 AM
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Default Re:Diagram / breakdown of p28 ecu? (long)

I'll take a look. And if it is, you think I can get one from digikey or some other place and replace it?

I am currently running the 4-wire with the heater circuit disabled, so I am thinking maybe it's not giving the same signal as a 1-wire sensor would, since the 4 wire is made to be heated and the 4 wire isn't. I'll try hooking up the 1 wire if I can't replace the (transistor) and enable the heater circuit.

Thanks.

Oh, btw leed, my great grandmother has a yeast infection, I'll tell her to give you a call
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Old 11-11-2004, 06:20 AM
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Default Re:Diagram / breakdown of p28 ecu? (long)

i believe q30 is the location and it requires an npn switching transistor. i have the components to repair your ecu. give me a pm if you're interested and i'll have a look at it. if that's the problem, i would repair it for change.
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Old 11-13-2004, 01:15 PM
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Default Re:Diagram / breakdown of p28 ecu? (long)

Well, q31 is the location of the chip that was fried, so I borrowed a transistor from q31 on a good p05 that I have, but I had trouble soldering it onto the p28 board. The board was also burnt and the solder wouldn't stick, I tried scraping some of the carbon off, I think one or more of the printed circuits have been severed. I tried my best to get the solder to stick to its respective printed circuit, but all in all it ended up still throwing a code when I enabled the o2 heater circuit. I guess I'll go back to a 1-wire sensor and disable the circuit. Thanks.
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Old 11-15-2004, 11:43 AM
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Default Re:Diagram / breakdown of p28 ecu? (long)

if you have a good p05, you should be able to use the parts from the p28 to convert it to vtec. what is the board number.
you do the vtec conversion projekt?
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Old 11-15-2004, 11:48 AM
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Default Re:Diagram / breakdown of p28 ecu? (long)

Originally Posted by whiterice
if you have a good p05, you should be able to use the parts from the p28 to convert it to vtec. what is the board number.
you do the vtec conversion projekt?
yeah, i can do vtec conversions on p05's and p06's. on the p05, it's not as simple as moving the vtec components over, you have to enable teh o2 circuitry as well
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