Little background quickly. 1997 Civic EX. Got it wrecked with no engine... Put in a D16Y5 I had sitting in the garage mated with a Y8 tranny. I made the engine harness from a DX harness. Everything works. Throws a CEL for the catalyst efficiency. Not a big deal. I get 38mpg out of it in city with the A/C on. Averages 47 on the highway if I keep the rpms under 3k. Got 53 once. Ok, thats out of the way, now the real issue...

ECU is a federal ECU, NOT a California ECU. I want the federal ECU, it gets better mileage. Passes emissions too. That being said, the problem is the car "bucks" on acceleration... Its not horrible, but its pretty annoying. It seems to not have an issue when its cold. Gets worse in higher elevations also. The problem goes away as soon as Vtec activates at approx 3,200rpms (according to the stock tach). Information is very limited on these engines and there is a LOT of false information that I see on the internet. I know it enters lean burn mode below Vtec which I am assuming is around 3,200rpms. It also runs as a 12 valve engine until Vtec when it changes to a 16 valve operation. I can feel the car entering lean burn between 2-3k rpms... so it seems that is working correctly.

I am running the correct Civic HX distributor. Not sure WHY the distributor for the HX is unique, but it is. Cap and rotor appear in good shape. Plug wires are OEM Honda from 98 if memory serves me right. They are older, I know that. Plugs are brand new and the correct ones for the HX engine. I don't think the problem is ignition related since it seems to have no issues at higher rpm where the system is under more load.

EGR valve is brand new and I have verified is wired correctly. The EGR plate has been removed and all passages have been cleaned. I don't hear/find any vac leaks.

The 5 wire O2 is older. I saved it from way back in the day when I built a DIY-WB kit. Its from a 92-95 Civic VX. Perhaps its getting weak/slow in response causing the bucking issues. It not throwing any codes for the the O2, but I know that doesn't mean its fine.


If anyone with an HX has any information they would like to share it would be greatly appreciated. Doesn't seem to be much interest in these engines, most people just swap for something quick. Gas prices are horrible and I like to save miles on my Type R, so this car is great to me. The gas mileage has been great, so I am assuming the wideband O2 is working correctly, but this bucking issue has me considering it as a cause. Hard to commit to though when they want $200+ for a new one.

 

My old VX did the same thing. Replaced the o2 sensor (no CEL for it) and the problem went away. This is after the previous owner bought a brand new distributor, had the motor re-timed etc etc etc.

 

Ignition timing set to spec?

If you unplug the primary O2 sensor, does the bucking stop?

 

Are you running the Y5 5 wire wideband O2 sensor and a ECU for a Y5???