1992 Vx with 99 HX d16Y8
 

I just acquired this 1992 VX with a transplanted 99 HX d16Y8 motor. I am still in the process of dialing it in and learning about it. The intake, exhaust and all the sensors are from the VX motor only the block and the head appear to be the HX, I think the S20 transmission came from the 99 but I have no way of knowing.

When I got it was stumbling when at a constant throttle between 2K and 3K rpm if you gave it gas then it would run fine. I started by changing plugs, cap rotor and wires, and providing it with the missing air filter. After this it still ran the same. I took it to a tuner in Seattle and he adjusted the timing belt that was a bit loose, checked the compression and it still ran the same. He installed a test ECU and took it for a drive and it ran great. So he sold me a P28 ECU programed with the 99 HX Map and it runs great now and the Vtec kicks in if you want to rev it up to 4800 rpm.

I put my Mpguino in it last night and set it up with some basic info. Today on my commute to work and back about 40 miles total it was reading out at 43 mpg. It still needs to be calibrated but I think it is pretty close.

The car is fun and easy to drive and with a few tweaks I think I can get 50 mpg average with it.

You should average better than 50 mpg. I had a '98 HX and my ex-wife averaged 45 mpg without hypermiling. The VX weighs about 400 lbs less and with some light hypermiling should see over 50 mpg. A VX/CX transmission would be even more efficient than the HX tranny.

The D16Y8 is not a Vtec-e lean burn engine and did not come in a 1999 HX.

That is correct. The D16Y8 engine came on the 1996-2000 Civic EX and the 1996-1997 del Sol Si. It is the successor to the D16Z6.

The D16Y8 engine made 127 hp and is a regular VTEC engine, not a VTEC-E.

The HX Engine is the D16Y5. It made 115 hp was a VTEC-E engine.

... and for the record, 43 mpg is not bad at all for that particular engine, even in a light package like the VX shell, considering your gearing...

I think that the S20 transmission is from a 1992-1995 Civic EX, Civic Si, and del Sol Si. That has shorter gearing than the Civic LX/ del Sol S transmission. The Civic CX/Civic VX transmission is geared significantly taller than either of those. If you had a different transmission, it would help your mileage even more.

I messed that up the engine is a d16y5

That's actually good news, though. The D16Y5 is more efficient than the D16Y8. The P28 ECU is for the OBD1 engine, right? So they programmed an OBD1 engine with the OBD2 map to get the VTEC-E and lean burn systems working correctly?

I am still trying to figure it all out and by no means a Honda guru or expert. It seems to me they took out the VX block and head and put a 99 HX block and head using the exhaust, intake, dizzy, wideband 02 sensor, wiring, sensors and all controls from the 92 VX. When I picked it up the car would stutter, sputter buck and miss at any constant throttle rpm. It would Idle fine and run great under WOT. I replaced the cap, rotor, wires, plugs, air filter, cleaned the throttle body, set the timing, then took it to a tuner who checked the compression, tensioned the timing belt properly and then put p28 ecu in with what he told me was the 99 hx map on it. The car runs fantastic now through all rpm and load ranges, I am not sure if it is doing lean burn or not with the new ecu and map, it does kick the VTEC in at 4800 rpm and you can certainly tell when that happens.

Why are you at 4800 rpm. I hit that once when I was doing 100 in my vx. Lol.

running a p28 your not going to ever run in lean burn,unless they dyno tuned it to be close probably running hondata on the left side of the maps leaned out, but its still not a true lean burn only the vx, hx (manuals) ecus will allow you to do that since they have a wideband controller built into the ecu, running in closed loop when in lean burn monitering the o2readings and adjusting the o2 levels on the fly as you drive.

what ecu was it running before you switched to the p28? you should have ran the hx ecu with an odb2-1 adapter it probably would have ran better, use the ecu that was made for that motor, someone correct me if im wrong but the y5 head is differant then the z1 head better combustion chambers from what i understand