Hesitation/stumbling during acceleration

[HateThisCar]

Hey, guys... question:

I have a 2000 Civic EX with a y7 motor that was swapped into it by a prior owner. The car runs and drives out fine for the first fifteen minutes, but then it bucks and stumbles through all the gears between about 2K and 3K RPM. I figured it was some kind of spark problem, so I changed out the cap, rotor, plugs, and wires. No good. Removed, cleaned, and reinstalled the IACV (2 wire connector). No good. The computer and harness are from the EX and whatever motor came with that (y8?). I have the DX computer (P2E-A12) sitting here, but am hesitant to install it for fear that it will make something go haywire. I've been up and down forums for the last two weeks searching for a solution, but can't seem to find one. Could the ECU be the issue? I would check CELs, but, apparently the last owner also dismantled the check engine light, also.

Any help or advice would be greatly appreciated, so thanks in advance.

-J

 

[XpL0d3r]

I'm guessing o2 sensor... I had the EXACT same issue...

Car was fine when cold, but when it warmed it bogged terribly. Didn't throw me any codes, and voltage was fine because I always checked it when the car was sitting / cold.

I believe it was my primary o2 sensor but I'm not 100% positive.. either way definitely look into that!

 

[HateThisCar]

I was leaning in that direction, as well as reading up on a dash fuse issue to check first.... something about fuse 15 (7.5a). Does that sound like a related issue to check?

 

[HateThisCar]

So, maybe I'm missing somethng obvious, but I'm expecting the upstream o2 sensor somewhere in the header, but there are absolutely no wires or sensors coming from the header at all. Assuming that this is where the o2 sensor originates from and the wires are tucked somewhere, is there a good reference I can use to track the wires for the o2 sensor backward to find where they might be? And if they're cut somewhere, can someone let me know what color wires i'd be looking for in the harness?

BTW, checked fuse 15... all good.

 

[203CT]

The o2 sensor is very visible if you have a stock header. If you don't see it you might not have one.

 

[TokyoSkies]

If it's been converted to a y8/EX exhaust/02 system, the 02 will be post-cat, and there will be nothing on the exhaust manifold. Check there. Pull it (when the car is cool, obviously ), if it has white residue on the end of the sensor, replace it. My car was doing the same thing for a while. Re-timed it, new plugs, wires, rebuilt dizzy. It ran decent after that, but after replacing the 02, it was 10x better.

 

[HateThisCar]

If it's been converted to a y8/EX exhaust/02 system, the 02 will be post-cat,

Only one O2 on that system?

 

[203CT]

Only one O2 on that system?

I have a 98 ex and I have two O2 sensors. One in the header and another under the car that goes to my cat.

 

[Hendo]

Try the DX computer. You want the same computer to the same motor generally speaking. One is VTEC and the other isn't. I'm guessing maybe it's not an issue since nobody else has said anything, but you could probably sell the VTEC one for a few bucks if you don't need it.

 

[XpL0d3r]

I was leaning in that direction, as well as reading up on a dash fuse issue to check first.... something about fuse 15 (7.5a). Does that sound like a related issue to check?

Not the fuse.. Fuse 15 if blown won't power the alternator, and eventually the car would die out / not start. I had this issue too lol when it kept blowing because of a faulty ELD.

So, maybe I'm missing somethng obvious, but I'm expecting the upstream o2 sensor somewhere in the header, but there are absolutely no wires or sensors coming from the header at all. Assuming that this is where the o2 sensor originates from and the wires are tucked somewhere, is there a good reference I can use to track the wires for the o2 sensor backward to find where they might be? And if they're cut somewhere, can someone let me know what color wires i'd be looking for in the harness?

BTW, checked fuse 15... all good.

You should have two o2 senors... one before the cat, the other after. The job of the o2 sensors are to make sure that the cat is working properly. The o2 sensors both take in readings... if the second o2 sensor (the one behind the cat) reads identical to the primary it will throw a CEL at you because the cat isn't functioning like it should. The reason I think the primary o2 sensor is defective is because the car will get the "faulty" reading, but the secondary o2 sensor (which is presumably good) will have a cleaner reading, thus no CEL will be thrown. Again I'm not 100% sure it's the primary sensor, but I have a pretty strong feeling that it's one of the sensors on your car. If you have the y7 header the primary o2 is just before the cat, and the secondary is actually ON the cat.