vtec

[917]

Hi, guys!

Just wondering if anyone can tell me the actual effect of vtec not functioning.

For example on a JDM DC5 Type R, would you still be able to hit the rev limiter in each gear ? How much of a drop in maximum power would there be ?

Also, does anyone know the cam profiles for the low rpm lobes and the high rpm lobes ?

Thanks in advance for your help.

Chris

 

[MilanoChris]

Yes to rev limit. Power wise I'd say around 30 bhp possibly more, would have to check dyno graph.

Why on earth would you want to know?

 

[jostrom]

If the VTEC does not work and you rev it to the limiter you're risking the engine. It could lead to valve float and engine damage.

We had a VTEC-solenoid problem last Friday in a dyno. The effect of VTEC not engaging was over 60hp in a 220hp K20A2 engine.

JDM engines don't have a VTEC oil pressure switch so they let the engine rev to limiter even if the solenoid dóes not work. Euro-engines give an error code and don't let the engine rev over VTEC engagement point. Both engines can be revved to the limiter without VTEC when they are cold.

 

[917]

Thanks for the quick replies. That's interesting and helpful stuff...

Well, to tell you the truth, I think it's probably not functioning in my race car. I seldom get to see the car as it is looked up in a workshop on the other side of town, so I don't get to see it much except for at the track (long story...).

Anyway, since the first time I drove it I thought it was "nice" to drive, but very slow in the straights. Nobody will take me seriously when I try to tell them that. They just keep telling me how good everyone else is. It's really f**king frustrating, so I'd like to get it sorted out.

Thanks again and any additional info would be greatly appreciated.

Cheers guys !

 

[MilanoChris]

What spec is the engine/ECU? Modified in any way?

 

[917]

I ran in the last two races of the Integra One-make series here in Japan last year and now that they have replaced the DC5 with the new Civic, I've done two races in the Motegi Integra series this year, so the specs are the same (except for the tyres), ie : standard engine, compulsory Mugen racing ECU & exhaust system and standard airbox & intake.

I feel like I'm driving the guts out of the thing, but I'm still just floundering near the back of the field... I'm with them through the corners, but they ALL leave me behind everytime we hit a straight.

It may sound strange, but I've never driven a vtec anything before, so I've got no sense of comparison. I asked the Mugen guys what they thought and just got vague stares... I only know that the engine compression is good (tested) and it runs and revs nicely, but it's simply not competitive.

Both the car and myself are a little over weight compared with the others, but this difference is BIG !

 

[jostrom]

Check your VTEC solenoid function! You're risking the engine if VTEC does not engage. Valve float is a real problem when revving to over 7krpm without VTEC. You should feel the torque difference if VTEC engages. With JDM engines it's hard to troubleshoot though, because you don't get the VTEC oil pressure switch indication to the ECU (VTP signal)...

 

[LeeH]

Cannot you 'feel' it engage? If not then I guess you do have a problem.

Even if you have no experience with VTEC it is obvious when it does engage on a stock or modified engine.

 

[logik]

As mentioned above mate, you will feel the Vtec kicking in, torque wise but also you will hear a distinct sound difference when the Vtec is engaged.

If you are not feeling or hearing this then stop, something is wrong and you are risking the engine.

 

[917]

Thanks guys, for all of your helpful responses. Sorry, I had to leave the board earlier and head off to bed since it was after 2:00 AM here when I got this bee in my bonnet...

These are the kinds of answers I've needed for ages, but everyone here (in Japan), I'm sure, just seem to think that I'm making excuses, so they don't even listen to what I am saying.

In my last race, my (flying) race lap times had a maximum variation of only 1.1 seconds for the whole race (tyre degredation offset by reducing fuel load ?), which was only marinally off my qualifying time on a lighter fuel load, so if the performance difference was just "me", I don't think I could be that consistantly bad !...

Don't get me wrong. I like it here and I like the people, but at times like this, it is REALLY frustrating !

Anyway, now that I'm armed with some clearer information I'll get stuck in and see if this has been my problem all along.

It really seems to point to that since it just seems smooth, but fairly docile right through the rev-range. I don't detect any particular spot in the range where there is a discernible "kick" or audible change in the note.

Although, on a good smooth racetrack with the 6 speed box, it's always operating above 6,000RPM, so maybe apart from off the line when I'm a little busy, it is always in the higher end of the rev-range, so hard to detect the cross-over point.

But... I really don't think that's the case. I think you guys are right and there probably is a problem with the vtec.

Thanks again. It might take some time, but I'll keep you posted on what I find.

Cheers !

 

[logik]

Let us know how you get on.

 

[917]

Thanks. Will do.

 

[Project]

One thing I must add is that with the mugen ecu you dont get your normal kick at 6,00orpm, its more of a gradual pull, you can still hear a change but its not as obvious as the oem ecu, plus with a standard airbox, it will be even quieter, as i had mine with a gruppe m, another thing to add is that you also have the noise of the other cars, plus your helmet blocking out noise, so i would say first thing, swap your mugen ecu back for the oem one and listen for a kick with no helmets or other cars in your way, then replace it with the mugen one again and feel if theres a performance gain. Simplest, cheapest and easiest way imo.

 

[logik]

One thing I must add is that with the mugen ecu you dont get your normal kick at 6,00orpm, its more of a gradual pull, you can still hear a change but its not as obvious as the oem ecu, plus with a standard airbox, it will be even quieter, as i had mine with a gruppe m, another thing to add is that you also have the noise of the other cars, plus your helmet blocking out noise, so i would say first thing, swap your mugen ecu back for the oem one and listen for a kick with no helmets or other cars in your way, then replace it with the mugen one again and feel if theres a performance gain. Simplest, cheapest and easiest way imo.

Good advice.

 

[raz786]

There must be other DC5's racing with you, see if you can get a quick test drive in one and if that fails let one of the other DC5 drivers test yours, have you not had it dyno'd?

 

[917]

Sorry guys. I know it's taken me awhile to get back here to update you on my finds. It's been a long drawn out process due to the difficulty in getting easy access to my car...

Anyway, this is what I've found so far. We managed to put it on the rollers (unfortunately the dyno controller is broken...) and run it up to speed with the Mugen ECU. It was really "doughy", sounded flat and was difficult to define the Vtec cross-over point. Then we swapped it over to an OEM ECU and it seemed like it came alive! Much crisper and we could clearly detect the vtec operation.

Hooked up OBII checker and it only showed one error code (which is for the absent secondary O2 sensor).

Did a rough AFR check with a wideband O2 sensor hooked up to the tailpipe and found that the OEM unit is sitting around 14.7:1 Vs about 12.3:1 for the Mugen.

Mugen, "helpful" as ever, said they won't check their ECU without replacing the primary O2 sensor first because they have heard of problems with them...

Since OBII scan tools don't work with the Mugen ECU, we just had to reconnect the OEM ECU and tried to get a primary O2 sensor fault code, but to no avail.

I followed the Enlish version of the manual for the RSX with the K20A2 engine. If the troubleshooting specs are the same for the JDM Type R (does anyone know if they are?), then I had a problem.

It should read 2.5~3.0 Volts between terminal #6 (ECU output) & #24 and also between #16 (sensor output) & # 24. Mine was 2.3V (#6) & 0.2~0.3 (#16)... Advice = replace primary sensor.

Checked circuit wiring & connectors for shorts or open circuits and they all checked out OK. Also checked sensor heater circuit which was OK, but open circuit in the sensor. Replaced sensor.

Rechecked, but unfortunately #6 voltage is still low at 2.3V, however, sensor output #16 is much better at 1.8V.

The engine seems smoother while idling and after refitting the Mugen ECU and running it up on the rollers, it was quite easy to detect the Vtec point, so at least it seems to eliminate the Vtec as the culprit... Unfortunately, however, it still doesn't seem to be as crisp as the OEM and I'm still worried about the low voltage readings.

Another problem is that we can't access any realtime data with his scan tool, so I'm now wondering if anyone has any suggestions regarding the low voltage readings that I'm getting in my checks (battery/charging voltage seems fine) or another way of checking the sensor (is there a current amp reading that I could check?).

I'm still suspicious of either a Mugen ECU problem or perhaps something else like a coolant sensor making it run too rich.

We are going to try and mount the workshop's wideband O2 sensor better for a more accurate reading and I'll do some more checking with my trusty multimeter. I think we're getting there, but it's just not right yet...

Thanks everyone for your time and I'd be glad to hear any of your suggestions.

Chris

 

[logik]

Cheers for the update mate.

 

[917]

No worries! I'll keep you all posted as I dig deeper...

Cheers!