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Discussion Starter · #1 ·
Hey what's up guys, so I'm a little stumped with my 95 civic ex.
I was driving it and tried to stretch the gears out a bit to over take and noticed its rev limiting at 6000rpm. It also doesn't really sound or feel like vtec is engaging.

Things I have already checked and noticed are:
The car rev limits to 6k in both nuetral and in all gears
There is no cel or pending codes, and the light turns on then off on start up like it should.
I've verified the ecu is indeed a p28.
Ive also swapped a tachometer from my other civic and it read 6200-6300 at rev limit so it's not the tach.
I did put a spare d15b7 manual transmission I had laying around on the car because the bearings were bad on the original one if that would affect anything.

My d15beast7 with p28 ecu rev limits to 6800ish while throwing the cel for no vtec so this confuses me even more. Why would the p28 with the d16z6 rev limit lower while throwing no cel?

Would a bad vtec solenoid or pressure switch not throw a cel and lower the rev limit/disable vtec?
My brother has a spare vtec solenoid and pressure switch assembly for a z6 but he lives out of town. So I wouldn't want to drive awhile and not have it fix the problem.

Any insight on how to fix this would be greatly appreciated thanks!
 

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Discussion Starter · #3 ·
Thanks for the suggestion, I'll remove it and clean it out with some brake cleaner when I get off work.

I'll get back to you with the results and let you know if it helped.
 

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2005 Legacy GT
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Replacing the gaskets while you have it off wouldn't be a terrible idea. Also ... it's really hard to feel VTEC kick in on a single cam. Even when turbo'd, tuned, and with a slightly bigger cam ... I couldn't always feel it. If it doesn't fall on it's face at higher RPM ... chances are VTEC is engaging ... it's supposed to be a fairly smooth transition.
 

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Are ur harness connections correct?
 

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Discussion Starter · #7 ·
So yesterday I went over to my buddy's house and got to mess with two other z6 powered civics. the first civic a 92 hatchback with a z6 swap rev limited to 7500rpm every time in gear and I could slightly hear the vtec engage unlike my car. I didn't get to rev limit it in nuetral as the owner didn't want me to.
Next I tested a 94 auto ex and to my amazement it does EXACTLY what my car is doing, it rev limits to 6k in gear and in neutral and has no vtec engagement in gear.
Both cars had a p28 ecu
 

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Discussion Starter · #8 ·
Verify if the ecu is chipped, it might have a low revlimit and disengaged vtec
The Ecu is stock I checked, although when I bought the car the sun roof drain was clogged and there was a puddle building below the ecu on the passenger floor so it very well could have gotten wet.
 

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Discussion Starter · #9 ·
So I tried doing a little research and here's what I've gathered so far

If you have no cel and aren't rev limiting to 3500rpm your not in limp mode.
No cel and a 6000rpm rev limit indicates that one of the requirements for vtec engagement is not being met.

The requirements for vtec to engage are: engine coolant temp signal to ecu, oil pressure or dirty pressure switch/solenoid, vehicle speed, and load/throttle position.

I'd like to say the most likely causes would be an oil pressure or switch issue. Or the ecu is not getting ect signal and thinks the motor is cold.

Does this seem about right to anyone or am I off?

How would I go about testing ect signal to the ecu? Do I need to buy the ecu testing harness Honda has?
 

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Vibe GT
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The FSM can tell you how to test these sensors with an OHM meter, you test the temp sensor both cold and hot and at both the sensor and the ECU pinout for the sensor (this makes sure there isn't a break in the harness somewhere).
 

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So I tried doing a little research and here's what I've gathered so far

If you have no cel and aren't rev limiting to 3500rpm your not in limp mode.
No cel and a 6000rpm rev limit indicates that one of the requirements for vtec engagement is not being met.

The requirements for vtec to engage are: engine coolant temp signal to ecu, oil pressure or dirty pressure switch/solenoid, vehicle speed, and load/throttle position.

I'd like to say the most likely causes would be an oil pressure or switch issue. Or the ecu is not getting ect signal and thinks the motor is cold.

Does this seem about right to anyone or am I off?

How would I go about testing ect signal to the ecu? Do I need to buy the ecu testing harness Honda has?
Hook up a light in your vtec pin to ensure your vtec is working, i believe if the requirements are not met check engine light will turn on after your engagement point thus will lower your revlimit.

Also, are you sure your cel is hooked up correctly? Try unplugging a sensor and see if it will lit up
 
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