VX engine swap

[1992VX]

Hello everyone....

I'm trying to solve a problem with my 1992 VX. It racked up 556,000 KM on the original motor and finally the 11% grades on the Gaspe killed it.

I replace the engine with a D15B V-tec 1500cc (Japanese Domestic Market) that produces 130 HP and is downright scary in terms of power. (the old VX was a D15Z1, still a V-tec but the E version with 92 HP ) and back then Honda hadn't coined the term V-tec.
The catalytic converter was also repalced but they left the O2 Sensor from the original motor. It too was "cooked " a couple of years ago.

The motor ran rough at constant speed but fine at idle or acceleration or at high RPM( similar to the "bucking" thread I read on the forum), I too plugged the vacumm hose on the EGR valve but it didn't affect it. I unplugged the O2 sensor and it ran great....but the engine light is on. So I went through the expense of buying a NGK 5 wire wideband sensor ($ 300 aftermarket) because theVX ECU (P07) requires it.
Same problem! I unplugged it and it runs fantastic. But, even though I can get 620 KM of city driving on a tank, I think I can do better if the sensor functions properly; also I need this hooked up to pass an e-test and don't want to pollute.......did enough of that with the old motor.
I think my AF ratio my be too lean for the new engine?
Any comments?
Thanks

[88HF]

didn't you need to change the Engine Computer? I think using the VX computer is not right.

[1992VX]

Nope, still using the P07 ECU. I was told by my local honda dealer that it would be compatible, however I see many people with P28's and the d15b VTEC so I'm leaning towards getting one... anyone with a similar experience?

[GasSavers_bobski]

Well, the D15B and the D15Z1 have, as you said, different kinds of VTEC. Your ECU and oxygen sensor are meant for a VTEC-E motor. At low RPM, a VTEC-E motor pretty much only opens one intake valve. This creates a bunch of turbulence and swirl in the air/fuel mixture as it rushes into the cylinder during the intake stroke. That swirl helps evenly mix the air and fuel, and improve the quality of burn once the mixture is ignited. The super expensive 5 wire wide band oxygen sensor is used so the ECU can accurately adjust the air/fuel mixture to a leaner than normal ratio. Lean air/fuel mixtures tend to be difficult to ignite... This is where the swirl comes in handy.
The VTEC portion in a VTEC-E motor simply locks the first intake valve rocker to the second one, so both valves open and close like a normal 16-valve motor. This allows the motor to get the fuel economy of a 8 or 12 valve motor but still get the performance associated with 16 valves.
Your D15B has performance-oriented VTEC. With VTEC off, it opens and closes both intake valves like a normal 16 valve motor. When VTEC engages, it locks both of the intake valve rockers to a third middle rocker that rides on a higher performance camshaft lobe. This implementation allows the engine operate on a lumpy, high performance cam profile at high RPM, but avoid the poor idle issues associated with that kind of cam profile by switching to a normal profile at lower RPMs.
Point being, performance VTEC doesn't provide the air/fuel mixture swirl needed to operate in lean-burn mode. The D15Z1 ECU will assume the engine is in a high-swirl configuration unless it has activated the VTEC control solenoid. Your D15B doesn't even have a high-swirl configuration, but the ECU is clueless to this fact and tries to run in lean-burn anyway, resulting in poor performance, misfires, ect.

Get yourself a P28 ECU and a 4-wire oxygen sensor. The P28 is designed to operate a D16Z6 which is a 1.6 liter motor, but the Z6 is a performance VTEC motor very much like the D15B.

Your other option would be to bolt a D15Z1 head onto the D15B block. IIRC, the bottom end of the two engines is nearly identical. The down side being that you would be back to the old 92 hp performance of a D15Z1.

[1992VX]

Thanks........

What if just run the car with the O2 sensor unplugged? It seems to run great? I've already spent $300 on the wideband sensor.

[GasSavers_bobski]

You could try it, but your check engine light will be on all the time, and your FE will probably suck.
AFAIK, the P07 is only mapped to drive an engine at around ~92 peak HP. You might get a little more due to the D15B's wilder cam profiles, but not 130 HP. A P28 is mapped for ~125 HP... Not 130, but alot closer. You won't be using the engine's full potential if you stick with the P07.
Where did you get the D15B installed? If it came with an exhaust manifold, there should have been a 4-wire sensor installed on it. You could probably sell your current 5-wire sensor, and maybe even your old, assumed worn-out one to recoup the cost of a P28 and 4-wire sensor. Just be careful with them... Oxygen sensors are pretty fragile when they aren't screwed into a 20 lb chunk of cast iron.

[parasonic]

Originally Posted by bobski

You could try it, but your check engine light will be on all the time, and your FE will probably suck.
AFAIK, the P07 is only mapped to drive an engine at around ~92 peak HP. You might get a little more due to the D15B's wilder cam profiles, but not 130 HP. A P28 is mapped for ~125 HP... Not 130, but alot closer.

Or, if you got a P28, you could chip it and use Uberdata.

[GasSavers_Ryland]

I thought the D15B engine had the three stage V-tec, that is, at low speeds it acts like a v-tec-e at the very highest revs it opens the valves up all the way, thus the 8,000rpm red line.
how does the O2 sensor look? I had a new one that went bad right away, and it was covered under warenty.

[GasSavers_bobski]

Originally Posted by Ryland

I thought the D15B engine had the three stage V-tec, that is, at low speeds it acts like a v-tec-e at the very highest revs it opens the valves up all the way, thus the 8,000rpm red line.

Some D15Bs had two stage VTEC (I say two stage because only two of the engine's three operating modes use the VTEC mechanisim). "D15B" can refer to a number of motors... Its a bit like the ZC series of motors. There are single and dual over-head cam ZCs, some carburated, some fuel injected, some with cats, some without, but all of them are 1.6 liter D-series engines that simply have "ZC" stamped on the block as the engine model. "D15B" was used similarly, but for 1.5 liter D-series motors.
Unfortuantely, all of the two-stage VTEC D15Bs are OBD-2 engines. You could conceiveably run one as an OBD-1 VTEC-E motor, or an OBD-1 performance VTEC motor, but you won't find an OBD-1 ECU that will do both... They simply don't exist.
Two stage VTEC motors should be pretty easy to identify - The corner of the head between the distributor and intake manifold would have two VTEC solenoids (looks like a metal can, roughly the size of a C battery with a single wire) instead of one.

The highest stock redline (fuel cutoff that is) I've seen on a D-series ECU is 7,500 RPM. That can be raised with a chip, but you would have to do major engine work to make any power up there. The stock engine components just don't have the air flow capacity to keep up with demand. D motors generally start to taper off between 6.5k and 7k RPM. There are obvious exceptions to that like the 8-valve D15B6 with it's golfball-size throttle body and 5k redline.

[GasSavers_civicminded]

P08 is the ECU needed for "optimal" power. That is, unless this is the VTEC-E D15B. Look for the head code http://www.sohchonda.com/forums/index.php?showtopic=135

If the head is a P07, it's basically the same as the D15Z1.

If it's a P08, then you have the VTEC version.