So first off this may be my first post under this name. Ive got no clue what my old username use to be. I just lurk, and have been doing so for years.

With that aside, I am a certified honda technician. Have been for 6 years now. The guys on my team, along with myself are totally stumped on my problem. 1995 Civic Si 160k on the original d16z6. Upon reaching 5500 rpms (range for vtec) my car begins to rev-limit, and throws one of two codes: Cylinder positioning sensor, or vtec pressure switch. New vtec pressure swith(check), vtec solenoid working(check), p28 ecu(check), oil pressure at 5500 rpms meeting factory specifications with loads on(check), timing; dead on(check). Distributor was taken apart and the cylinder positioning sensor was checked and cleaned. Still no fix! grrr...Whats my problem guys? (and dont tell me i need a swap, im riding this badboy out til it blows lol) Thanks for any and all input!

 

so the mystery is find out what your old username was? haha

 

I thought the P28 VTEC activation was in the range of 48-5200

 

What?? No...Read the entire post my man....?

 

You would be correct my friend. Thats why I said range for vtec not engaging point. This isnt so much a vtec problem for me as it is a "why the early rev-limit?"

 

Have you checked for a short in the two CYL sensor wires running between the dizzy and ECU or in the CYL sensor/wires inside the distributor? Have you tried swapping in another dizzy?

 

Presumably, the next step is to try a new dizzy. No short in the wires though. Volt meter gets readings. Thanks for the input man. Any other takers?

 

Shorts are detected by looking for unexpected continuity to ground not voltage. Are the codes also thrown while revving the engine with the transmission in neutral?

 

Im aware of that, im saying there is no change in voltage while trying to duplicate the problem or when the actual problem occurs. If there was a continuity in the ground then there would definitely be a change (this is in neutral btw) And only sometimes will the motor not rev past 5500 with loads off.

 

Just curious. What's spec voltage for the CYL sensor? Does it change with engine rpm? Is it possible that voltage measurements are not sensitive enough to detect an intermittent open or short in the CYL circuit? Why not test resistance/continuity to ground instead?

Another possibility is a problem with contact between the ECU and ECU connector terminals of the CYL sensor.