fatpride111

Recently purchased a 97 civic Hx with a d16y5. After doing some research and maintenance, I was expecting 35-40mpg, some people claiming up to 45mpg. I am currently struggling to get 30mpg with an average of 280 miles with a full tank, with the ac off.. I've owned b-series cars that got more than that. The only thing I can think of, would be code p1165 for the heated oxygen sensor, which I replaced already. I have done the following:
New NGK plugs
New wires, cap, rotor
New air filter
New fuel filter
New clutch
New timing belt
Clean egr ports and replaced egr valve
New heated oxygen sensor (almost $400 from oreilys)
Checked wires for shorts, and no bare wires, or cuts in harness.
I DID remove the stock exhaust manifold with the catalytic converter and replace it with a EX manifold and 02 sensor spacer for a cat delete. Still has stock ecu.

Now I'm not sure if the ex manifold without the cat is keeping the sensor from heating up to where it needs to be, and that's why it keeps throwing that code, or if I have a defective oxygen sensor, or bad ecu.

Would like some input if anyone has had this problem before, or has any tips on solving the issue. Thanks in advance.

TomCat39

I believe your car uses two o2 sensors an up stream and a down stream. Without the Cat, the 2nd o2 sensor is going to report a faulty cat.

There is some sort of sensor faker thing you can use so you can keep the cat delete. Don't recall exactly what it's called, saw NotARacist mention it one time.

fatpride111

It does use 2 sensors, and it's just a simple 02 sensor spacer that's used, which it have installed. I have no codes for a cat, just p1165 for my primary heated oxygen sensor.

tony_2018

Did you by chance had to extend any wires to use the ex manifold?

fatpride111

Nope, still reached. Not sure if the heated 02 sensor needs the cat to reach operating temp to work and maybe that's why it doesn't activate.

Thinking about getting a obd1 ecu, and getting a Hx basemap.

tony_2018

Check to make sure your spark plugs are snugged. For the o2 sensor check to make sure all sensor wires have continuity back to the ecu.

fatpride111

We did, my bro owns a shop and I had him go through the wires and said they are making good contact, but with his snap on scanner it showed the 02 sensor reacting slow, still worked but not like it should, which is weird cause it's a new sensor.

tony_2018

Defect probably, ask for an exchange. If your bro owns a shop than he can back up that claim for an exchange, no sweat.

NotARaCist

iTrader: (1)

It's just a plug defouler, but that's only for secondary O2 sensors.

Probably defective out of the box. It shouldn't need the cat reach proper operating temps. That code is caused by one of three things. Poor connection in the harness, a damaged wire, or a faulty O2 sensor. You said your brother checked the connection, but have him test for continuity from the wire at the plug all the way to the ECU - you may have a damaged wire hiding itself.

fatpride111

Yeah he was busy so he only checked it from the plug to the ecu. I'm not good with wiring so I didn't want to mess with it.

I assumed a loose wire somewhere. Even before I changed the 02 sensor it threw that code, I swapped it and problem persisted, just took longer to activate.

I'm also leaning towards bad ecu. I've never owned a Hx before this one, but they somehow wired it to where the "cruise control" light on the cluster lights up as a Vtec light as well. Sometimes it will work and kick on like normal around 2800-3200 rpm, and other times it won't kick on, then I hit a hard bump in the road, and it'll start working again. In case you can't tell, this car was hacked together by previous owner lol.

Former User

Was P1165 thrown before installing the new primary O2 sensor?

Is it a 7-wire O2 sensor?

fatpride111

It had a check engine light when I bought it (I got it cheap), ran the code which was 1165, ran over to oreillys and got another brand new 02 sensor and threw it on, drove it around after I did some Maintenance to it and it popped back on. Same code.

After I did the clutch swap about a month ago, the light stayed off the longest, about 800miles. Usually it'll pop back on between 20-100 miles. So I'm assuming if there's a loose wire, or a loose ground, I probably moved it while dropping the transmission and it slowly came loose, but I've nearly traced each wire back to the ecu, grounding points, and to the intake temp sensor where one wire ends up at. All are fine and no loose grounds.

fatpride111

And yeah it's a 5-wire sensor. I believe the plug to the vehicle harness is a 7 wire.

Former User

The primary O2 sensor for the D16Y5/manual should have 7 wires.

Former User

This^...if you have the correct O2 sensor.

tony_2018

Going by what the above has stated, OP you need to get the correct wideband.

edit: Whats the part # for the ngk o2 sensor?

Former User

OP probably does. The circuit diagram in the service manual shows the O2 sensor having 7 wires like the wire harness connector. However, the O2 sensor actually has 5 wires even though the wire harness has 7 wires.

fatpride111

Yeah correct oxygen sensor was purchased, Hx is the only 88-00 civic that has a 5-wire that runs well over $300. I learned that the hard way. I had a bunch of 4-wire sensors laying around that wouldn't connect to the harness. Sensor has 5 wires, however harness on the car has 7.

It's been about 200 miles since it's last popped on so I'm expecting it to kick on any minute now.

Another question I have is if I go obd1, and get an Hx basemap installed in said obd1 ecu, should it go back to getting 35+mpg's since it won't be relying on the reading from the primary 02 sensor? It's basically a daily driver that I bought specifically for fuel economy, but so far it's costing me more money than when I had my Gsr.

tony_2018

I don't think they have a basemap of the civic HX, also where you live do they do inspections that require them to plug there system up to the obd reader port near your fusebox? If so than a chipped ecu is out of the question.