MPG difference for Fed vs Cal ECU in VX
 

I really looked. I searched the forums for this and have not found it. THere is a lot of talk of the fed computer increasing milage compared to Cal, but i have not yet seen by how much.
Anyone have estimates on how much different the gas mileage is using a fed computer vs a cal computer? Seems the prices of the ecu's has gone up. I dont want to spend more on one then it would be worth in milage difference.
Thanks

From the official EPA Window Sticker, about 3-4 MPG depending on the year Civic. I did the swap, but also started changing my driving habits also, so hard to say. You can check out my gaslog.

Thanks.
I had seen your gaslog earlier. Unfortunately for me, I also saw you only had ~2 fill ups before switching and lots of other changes as you mentioned. Thanks for the window sticker info, this should serve as a baseline.

3 to 4 my ***!!!
when i did the federal ecu change over it jumped from the low 4os to the high 40s low 50s. i say 10 mpg minimum

I'm already at mid to high 40s with a CAL ecu. I'm hoping to switch over this summer to see how much I can squeeze out of the d15z1.

I was away for a while; sorry I didn't have a chance to respond sooner.

My situation is similar to Rancho. I did the switchover, but it was soon after I got the car. So I don't have much basis for a comparison.

I think the effect will depend very much on your driving environment and style. The Fed ECU provides lean burn. Lean burn happens at low throttle settings. If you have a strong P&G practice, you are generally avoiding low throttle settings. So you might not see a lot of improvement with the new ECU.

Another reference is this very interesting pdf (https://enduse.lbl.gov/INFO/Honda.pdf). Tell Adobe Reader to go to p. 23. You'll see an analysis which indicates that lean burn provides an improvement of 5-10%. I think those numbers are probably a pretty realistic guideline, for most drivers.

Judging from my own experience, and also from staring at a bunch of gaslogs here, I think it should not be hard to attain 50 mpg with a Federal VX. This assumes that the car is properly maintained (e.g., proper tire pressure, healthy ignition system). This also assumes that you're not driving in severe conditions (e.g., lots of short trips, heavy traffic, 2-3 passengers, very high speeds).

I sometimes see results that are only 45-50 mpg, but it's always because of those severe conditions. My worst fill ever was 34.2 mpg, but I was averaging a true 85-90 mph for the entire fill. And that was with the CA ECU.

Does one also need to replace the o2 sensor from the 4 to the 5 wire version? If so, how do you wire the last 5th wire to make it work property? Any directions? thanks and new to the boards.

Welcome!

It sounds like you have a CA VX and you want to convert it to Federal. The '92 CA VX already has a 5-wire sensor. But if your CA VX is another year, then I guess you have the 4-wire sensor. Yes, if you want to get the benefits of lean burn (which was found only in the Federal version), then you need the 5-wire sensor. You'll also need a Federal ECU. I recently saw one on eBay: https://www.gassavers.org/showpost.ph...11&postcount=2

If you intend to drive the car in CA, then you also should think about if it will pass smog. There are certain potential issues, which I described here: https://www.gassavers.org/showpost.ph...71&postcount=6

As far as how to do the wiring, I posted very detailed instructions here: https://www.gassavers.org/showpost.ph...3&postcount=27

Scroll up and down to see other relevant posts in that thread. It's not as simple as just hooking up one extra wire. But it's also not terribly complicated to accomplish, once you understand what you're doing.

And if you post more questions right here, I'd be glad to try to help.

yeah, 92 vx CA.

I've figured out that the 92 vx has the five wires 02 sensor. So, in my case all I need is to plug in the fed ECU and go, correct? Or do I need a different style o2 sensor connector even though I have the 5 wire?

Thanks monroe for the links.