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Discussion Starter #1
Hey Guys, I'm new to the forum, I'm an older Honda tech now retired. Just reaching out regarding a head swap I did on my wife's car. Its a 99EX Manual. Sent the head off to machine shop to discover it had a crack. I picked up another used head thinking hey all 96-00 D16Y8's are the same well...….

So I put the 97 head on her car and first fire has a high idle, I can hear a vac leak but cant find it.

Came on this forum and went wth is air injection haha. Here begins my problem haha.

So its a manual 99 EX I used all the OE equipment from the car minus the head is a 97. What should I do about going forward?

Pull intake off and plug us the 5 air injection holes on the 99 intake. Re-use the 99 IM gasket, not sure what else I would need to plug.

Or should I just get a 97 intake manifold?

I don't think the car will pass CA emissions in Comifornia but that's whatever.

I guess my question is what should I do as far as repair goes: It would be nice to not have CEL as well.

What's the most factory replacement program using the wrong year head lol.

Thanks for your Help!
 

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BATSLOMAN GIVES NO FUCKS.
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tap the holes and put in some threaded plugs with sealant. should be the easiest thing to do
 

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Discussion Starter #3
Thanks for the response. You think that if I pull mani and only plug up those 4 small holes, and the one larger one in the middle (probably just cap it on the top of the flange) everything should run as normal? No CEL's etc?

I should be running the same 99-00 Intake manifold gasket I'm guessing as well.

Thanks Again!
 

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BATSLOMAN GIVES NO FUCKS.
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if the 99 doesn't have the holes in it, use it. that will do the same thing with the gasket.
 

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Discussion Starter #5
Hey Guys, quick update. The runs and drives fine no CEL's I'm going to update check the DTC's here soon once reset see if it will pass CA smog with the 5 ports plugged. Having one more issue though. I cant get the cooling fan to kick on. I've swapped sensors, jumped the (coolant temp sensor) connector the fan does kick on, but it wont kick on normal driving conditions: Fuses are good, relays are good, don't know what else to check, any ideas? Thanks Again!
 

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93 Civic HB SI
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Which sensor are you jumping?

Are you jumping the one that is threaded into the thermostat housing, or the one on the cylinder head?

If you are jumping the thermostat housing sensor/switch connector and the cooling fan operates normally when its jumpered, then replace that switch. This device is actually a switch, not a sensor, and is the main control mechanism designed to turn the fan on and off. This circuit has no path for feedback to the ECU, and only operates the cooling fan relay.

The ECU temp sensor is the 2 wire connector on the distributor side of the head, and is a thermistor feedback style sensor. This sensor reports the resistance/temperature relationship to the ECU. If you jump this connector, it either means -40 degrees or +255 degrees to the ECU, I can't remember. If you jumping this one, and the cooling fan starts, then it's the +255 degree range limit lol. The ECU CAN take control of the cooling fan relay, but is not the primary cooling fan control mechanism. The ECU only takes control of the cooling fan relay if the ECU temp sensor detects coolant temp is in overheat range, where it will supplies the cooling fan relay a ground via a transistor inside the ECU itself.

Depending on which one you are jumping can mean a different path in terms of fan control circuit diagnostics and sensor/switch diagnostics.
 

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Discussion Starter #7
Hello Drtalon, wow I couldn't have asked for a better response, thanks! I basically just put and new OE temp switch sensor in the car swapped the ECT sensor under the dizzy with another one I had. Run about 3/4 fan kicked on brought it back down to regular temp the fan cycled on and a off a few times which was odd almost like it was learning or calibrating? Went for a test drive and seems fine. Weird I wasn't sure what was going on. I'll report back findings. Thank You Again!
 

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There are different variants of that thermo switch, in terms of how they work internally and each one can have quirks in terms of how they operate the fan. The cheap ones are typically the bi-metallic strip types, whereas the more expensive ones are the thermostat-type spring or glycol versions. They all basically function the same way, with the end goal of closing a switch.

It's hard to tell which version you've got without cracking them open though, they all look exactly the same in terms of the body.

The thermostat type spring version is the most accurate and repeatable variant, next to the glycol type.

The cheapest ones are flimsy bi-metallic strips that flex when heated and operate a switch, like an old school turn signal flasher does. If you buy one of these, and your fan clicks on then stays on but your engine isnt overheating, but the fan only turns off after letting the engine turn off and cool for a long time, this is the bi-metallic strip hanging the switch closed until it flexes back to normal/open position after the temperature has dropped considerably below thermostat control temp. This is why they are cheap, they click the fan on, but don't always expect them to turn it off like normal in conjunction with the coolant thermostat operation.

The coolest version I've seen is an expanding glycol version, where there is actually a bit of water/glycol inside a chamber of the sensor body sealed off from the outside that expands when hot and the pressure pushes a small spring loaded diaphragm that activates a switch. If you unplug the connector from this type and there is coolant/liquid inside the connector cavity with no other coolant leaks or water intrusion possible or present in that area, and your fan has stopped working, you have a water/glycol type sensor lol. Chances are your sensor connector pins will also be corroded and the pigtail needs to be replaced.
 
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