I have a 91 standard hatch, I am planning on putting a d15b vtec in and a five speed trans. On h-motors its an extra 135 for a PO8 ecu. I have a PM6 ecu laying around from a 90 si. Will this work with my new motor? Any help would be great, please excuse my newbieness, this is the first swap I am doing on my own.

 

No it wont work properly(NO VTACK YO!). Some people have done it with a switch controling when vtec engages, but IMO that's super ghetto. I'd say just get the p08 ecu (or a p28).

 

Thats what I figured, I appreciate the help!

 

On hmotors for availability its says years 96-98 only OBD2 3 stage vtec.. Which is contradicting to the P08 ecu which is OBD1, I am familiar with the three stage vtec d15b however I am not familiar with what ecu/ fuel control it uses.

 

for true 3 stage control you need the ecu that matches the engine, which would be the 96-98 ecu, and a lot more wiring work to make it all happen. if i was in your shoes i would go for an obd1 d16 or d15 that has normal vtec so you can use the p08/p28 and not deal with the headache of wiring an obd2 engine into an obd0 car.

 

There was a thread on a 3 stage VTEC engine... He was trying to get it to work wth the different stages... I am pretty sure it was abandoned.

 

The only "decent" way to control the three stage VTEC engines other than with the factory OBD2a ECU for the engine, is by using an OBD1 ECU with an additional programmable output. (ie: Neptune RTP or Hondata S300). You can use the optional additional output (for instance use and auto trans lockup output for the first VTEC solenoid engagement), then use the normal VTEC output (which also switches fuel/ign maps for the higher rpm VTEC solenoid engagement.

 

How do you deal with the fuel and ignition maps for vtec engagement using RPM switches?

I could understand with the S300 some tuning (or at least a basemap since it's a stock engine) could set it up properly .

 

You can't. All that would do is physically engage the solenoid. It won't switch maps, etc as intended.