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I recently had my CEL check after having it flashing everytime I slow down in town after a continuous drive. The scanner said i had a bad egr, cylinders 1 and 3 misfire and a o2 heater malfunction which i think may have caused this issue by the car running too rich. From what I've read I believe it could be from an exhaust leak introducing exhaust fumes into the intake manifold but not sure.
1998 Civic HX
D16Y8(I believe it was swapped before I got it)

 
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Post the actual code numbers please

 
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I didn't get a print out from advance auto when they checked the codes and I don't have my own scanner yet. Any ideas of what it could be?

 
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....
go get the print out...

 
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I used the jumper connection method today and retrieved the following codes:
41: primary o2 heater
65: secondary o2 heater
71: random cylinder 1 misfire
73: random cylinder 3 misfire
8: TDC position (loose wiring)

 
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Makes me wonder if the ECM and harnesses are right for the engine now, or if it's for the HX engine (D16Y5?)

Did it have the O2 sensor heater codes stored all along, long before the misfire issue happened? (cel was on when you bought it?)

If you've solved this one, erase all the codes and give it a drive to see if it still sets misfire codes?

 
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The o2 codes came when I got the car which were assumed to be from the ebay exhaust system installed by the previous owner but I know believe that all of this is due to having a y5 ecu and harness running a y8 engine.

 
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Cat is located out in front of the engine?

The engine harness plug for the front (primary) O2 sensor....how many wires does it have? How many wires does the front O2 sensor have?

 
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I forgot...Manual trans? CVT? Automatic?

ECM part #?

 
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I have the y5 harness with the 4 wire o2 and 5 wire wideband connectors. Ive read that you can wire in another 4 wire connector in place of the wideband connector.

 
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manual trans
ecu- p2n-a31(HX ECU)

 
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Oh boy.....Still has the HX ECM and harness.....and stock HX sensors?
Looking in one of the diagrams it shows a 7 wire primary sensor, do you have that?

I wonder if the HX ECM tries to lean out the engine at steady speed and low loads and the Y8 engine doesn't run well like that?


For sensor fault codes I'd run thru the trouble tree and probably ohm check the sensors (heater circuits)

As long as you have the HX ECM and harness it won't like modding the sensors at all

 
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I believe you are right about it being a 7 wire and that would be why I have an issue with primary bc I dont have one. The secondary code is due to me removing the sensor for trouble shooting but at the time I assumed it was the primary.

 
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Ok if the O2 sensors are unplugged then fuel injection should be calculated from base tables or maps.....and should have no bearing on the misfire issue. And it probably can't go into lean burn mode at all without the sensor inputs.

First post said it had an EGR code, but not now?

What about this:

 
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I have also checked and see that i have the y5 intake manifold with EGR. I do however have another mani from an ex without egr that needs a little work that I will try along with the EX ECU.

 
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I have not been able to figure out the TDC code yet, not sure what it is.

 
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TDC sensor is inside the distributor.

If the ECM needs to see the EGR valve, don't swap in the other manifold sans egr.
If you want to swap in the ECM for a y8 version or whatever, you'll probably need all the matching harnesses too?

I have a feeling some problems may have been caused by an incorrect engine swap and have been there ever since. Hard to tell from here though. Maybe they only replaced the block and head?

 
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I feel like they may have swapped the block and left the rest the same bc the block says y8 but I'm not totally sure and i havent been able to identify the head yet. I also plan to use a p28 chipped ecu with moates demon which may help me get rid of these codes and fix things to get it back the way it should be. I also plan to swap in my p2p intake for y8 if this is a y8 head if not I may swap in both

 
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If I have to change a blown engine, it gets the block and head at a minimum because any lube related failure in the bottom end also contaminates lubrication stuff in the head/cam/valvetrain.

Reusing the original intake and exhaust manifolds is pretty routine when doing this work, especially if the ones on the replacement engine aren't exactly the same.

 
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Update: went back to advance and the code for her is p0401- insufficient egr flow

 
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That might be as easy as reaming out all of the EGR passages....they get clogged up with carbon buildup which becomes a flow restriction.

I think there's a long skinny cover plate about 1.5 inches wide and runs from manifold runners 1-4....it's below the injector rail. Maybe 5 bolts in it. Pull up the injectors, remove that plate, clean all the soot buildup out of that plate....and ream out the hole in each manifold runner with a poker of some sort.

You might even find the holes for cylinders 2 and 4 are completely blocked.....which may explain the misfire codes in cyls 1 and 3.

 
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After cleaning the egr plate my idle is much more stable and the cel hasn't been flashing anymore but haven't checked codes. I still assume I have o2 sensor codes but plan to convert the 7 wire o2 connector to a 4 wire connector to remove all the codes.

 
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I haven't read a DIY but I still wonder how you can fool the HX ECM

 
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I thought about rewiring the pho2s plug to be the same as a d16y8 harness and then swapping in the p2p ecu I have but for some reason with the p2p ecu the car has no acceleration power once I'm actually going could this be from the egr valve with an ecu that doesn't need one or different injectors?? So confused by this loss of power.

 
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Don't use that ECU then!
You're welcome LOL

If you think it's possible, unplug it so it can't operate and see if it makes a difference.