1999 Civic Hx Mystery surge solved!

[Fletuitus]

OOOk, where to start. I suppose it is best to start with what I started with. I started with a stock 1999 Honda civic HX coupe. For those who do not know the major differences in this model Civic are as follows, it has an egr valve, it has roller rocker arms, it has a 5 wire primary or upstream O2 sensor, only 1 intake valve opens until vtech kicks in.

On my particular engine I have a zex light weight fly wheel with an act pressure plate and a stock clutch disk, Dc sport 4 to 1 headers, max speed exaust, Aem cold air intake, Aem adjustable fuel pressure regulator, skunk2 silica valve springs and titanium retainers, jackson racing underdrive pully's including the crankshaft pully, Aem highflow fuel filter, and finally the stock pistons have been replaced with PM6 pistons for an approximate compression ratio of 10.34 to 1.

Now for the problem. After doing a recent engine dress up including the piston swap the car developed an odd surge appearing mostly around 2500 rpms.

Keynote.. the primary oxygen sensor was replaced as part of the dress up.

An idle surge will be your Idle Air Contol Valve, or a Vacuum leak. No vac leak so that wasnt it. All the fuel injectors were ticking the same so most likely was not those. Compression was good and even across cylinders, not it. Ecu and distributor was swapped, not it. All sensors checked and no codes pending or otherwise, not it. No exhaust leak, not it. Timing all perfect, cam and ignition, not it. All sensors were throwing proper voltages with one anomaly, both the primary and secondary o2 sensors pulsed. The primary one is supposed to but the secondary should read flat.

It turned out that the primary o2 sensor had a bad resistor. As of now I am not sure if it is the one inside the connector (you have to remove the white insert inside the plug removed with needle nose pliers) or if it is the resistor inside the o2 sensor itself.

Best solution is to replace the o2 sensor.

Added note.. the iacv idle surge could be a clogged screen or an air pocket or clog in the coolant line that runs through it.

Added note on O2 sensors. I have run L1h1 o2 sensors and they have worked fine but I have read that L2h2 sensors come stock and both are listed as discontinued and dated. The newer o2 sensors are all LZA-** sensors. Though I believe mine were LZA-09 sensors. The next post will contain more info on this. Apparently the resistance should be around 6 OHMS, the new sensor I had installed read near infinite ohms. Not enough to cause a CEL apparently.

All info courtesy of "Kevin and Conners Shop" located in San ramon, 3211-A Fostoria way, 925-837-0554

[Fletuitus]

Update.. The bad resistor was INSIDE the o2 sensor.

[schlempfunkle]

well what kind of performance do you get now. hp/mpg

[Jakins]

Hey, sorry to bring thes back from the dead. How did you find out what resister it was? Did you fix it or buy a new sensor? My car threw a cel just recently and it is doing that surge you are describing. Out side of lean burn (a little below 2500) it is like hopping in and out of lean burn. So weird. I'm watching my mpg go 47-55-47-55-47-55 all down the highway. I don't get it. It's getting killer milage, but it just threw a code 61. I'm hoping I don't have to buy a new 300 dollar sensor. I'm going to try cleaning it first with sensor cleaner I guess.

[Rusty94cx]

It's always the sensor.

[Fletuitus]

Originally Posted by Jakins

Hey, sorry to bring thes back from the dead. How did you find out what resister it was? Did you fix it or buy a new sensor? My car threw a cel just recently and it is doing that surge you are describing. Out side of lean burn (a little below 2500) it is like hopping in and out of lean burn. So weird. I'm watching my mpg go 47-55-47-55-47-55 all down the highway. I don't get it. It's getting killer milage, but it just threw a code 61. I'm hoping I don't have to buy a new 300 dollar sensor. I'm going to try cleaning it first with sensor cleaner I guess.

Hey Jakins.. sorry for lag... They did a OHMS/continuity test with a multi meter (black to ground, red to sensor heater wires).. I bought another new one. The new one I had bought came from ebay, and came with a bad resistor which is why it was so hard to identify.. To speak directly to your problem.. make sure its none of the other potential probs.. dirty IAC or egr if you have an D16Y5, intake/vac leaks, timing, fuel filters, etc.. I also recommend getting the primary O2 sensor from honda if you have an HX as it is 5 wire O2. While you can find others that will work the one from honda is set up with specific resistances etc.. the stock ecu likes it. Also I live in California and they just recently tightened the tolerances on passing smog so it is important to have the proper one..

[hxman]

Can you please tell me what I should do next, I have cleaned the egr chamber, but I don't know what to do next (no CEL) I bought a NTK sensor off ebay but I haven't seen any CEL or mpg improvements.

I realize that o2 sensors are expensive guesses but I wonder if you guys can tell me what to do next. I have replaced, plugs, the distributor cap and wires. The car runs pretty well and I just had the timing belt job completed (valves adjusted too).

[California98Civic]

Give us some more detail. What are you driving (HX or VX)? And what else have you done to the car? Also, what are you doing "with" the car, in terms of driving technique?

[hxman]

Thanks for such a fast response. I have a 97 civic hx manual. I have good news guys. I refilled yesterday and drove 63miles per hour on the freeway for 287 miles and my mpg was around 40 (it appears like I used around 7 gallons but I haven't refuelled yet). It seems like the o2 sensor did it for me Now I think I didn't get good mpg (33) on my first tank on a new o2 sensor because I was driving 80 miles/hr the whole time. I tried to keep my RPM around 2500 this time around. Do you know what's the best range of RPM to keep my engine in lean burn without going so slow. It'd be nice to go 70 and not 62...

[cbaber]

The faster you go the less MPG you will get. 60 mph gives me a big improvement over 70 mph. And the kicker is that unless you are driving for multiple hours, the time savings by driving faster is not significant. I'm not sure of the exact number, but I believe the HX enters VTEC at 2500 or 2800 RPM. This is not good for fuel economy, so you want to make sure to keep it in 12 valve mode. If you still feel the need to go fast, swap out the transmission for the CX/VX to lower your cruising RPM's a little bit. You can also install taller tires to help too.