Vtec and brakes

[Supercar]

My car has the following symptoms

1) Vtec will only engage randomly
2) Spongy brake feel especially when stuck in a traffic jam. Also brakes will give out clutter sound occassionally especially right after start up.
3) Speedometer will only work once in a while. (odometer will only function if speedometer is working). Also, speedometer seems to be working only if aircon is on.

I did a search on this and found fragmented answers. However, after 'exercising' the brakes (as I found out in my search - braking hard at 80Km/hr), all of the sypmtoms are gone. Vtec will engage, brakes feel firm, speedometer and odometer will work.

I was informed by a mechanic that the Vtec is related to the ABS and that he needs to check the brake system. Is this true? I just need to get the expert opinion of Prime members before sending my X to the workshop.

I also bought a new sensor and is wondering if I should install it or have my brakes checked first.

And just recently a check engine light had come on. Your expert opinion on this is highly appreciated.

 

[TyraNSX]

Somebody is smoking some major crack if he thinks VTEC & ABS are related. What makes you think VTEC is working sporadically? How on earth would excercising the ABS fix VTEC (if it was ever broken) in totally separate & unrelated component of the car?

http://www.nsxprime.com/FAQ/Technical/VTEC.htm

 

[H-carWizKid]

When researching VTEC a few years back I discovered a very accurate description of the system engagement as it referred to the Integra B18C series. I am posting with the assumption that the system is similarly oriented in the NSX.

Here is a quote from Team-Integra.net -

In order for the ECU to initiate the VTEC system, 5 engine conditions must be met.

Temperature: The engine must have reached normal operating temperature.

Throttle Position: The throttle must be open far enough to allow for increased airflow in VTEC.

Vehicle Speed: The car must be in motion (wheels spinning).

RPM: Engine must spin to it's target value. The GS-R will send it's "GO" signal for VTEC at 4400 RPM while the Type R sends it's signal at 5700 RPM.

Oil Pressure: The engine must be operating with normal and safe levels of oil pressure determined by the VTEC pressure switch.

The ECU will send a signal for a spool valve to open. When this valve opens, oil is allowed into the pivot shaft inside the valve rockers and directed into the center rocker. Inside the center rocker, a set of pins are forced outward by the oil pressure and lock inside the rockers to both sides. This entire process occurs in 1/10 of a second.

Sooo... Number of possible diagnosis for sporatic engagement based upon the 5 conditions that need to be met for engagement...

Is the engine warm, or cold when you experience the "sporatic engagement"?

Oil pressure?

Bad ECU?

damaged, or worn spool valve?

The post doesn't say anything about brakes, but then the NSX has traction control while the Integra does not.

I am not sure if traction control is somehow related to the ECU, and if the ABS system might be somehow related via that avenue . This is a good question for a resident technition.

Hope that helps

Philip

 

[nsxtasy]

If the symptoms are gone, there's no need to send it to the shop.

For your check engine light, pull the codes and look up the meaning and diagnostic procedure in the service manual. You'll find it at the start of the "Fuel & Emissions" section of the manual. There's a description of how to jump the connector to pull the codes in the DIY area of the NSX FAQ.

 

[95gsrturbo]

I am probably mistaken but something tells me i have read somewhere that VTEC is partially vaccuum based, I know for a fact it is RPM and speed controlled..... but if there is a vaccuum component this would correlate to the brake issue...

Ill look for the article-----
---------------------------------
Found it and i was wrong.....here is the quote from Team-integra.net

"In order for the ECU to initiate the VTEC system, 5 engine conditions must be met.

Temperature: The engine must have reached normal operating temperature.

Throttle Position: The throttle must be open far enough to allow for increased airflow in VTEC.

Vehicle Speed: The car must be in motion (wheels spinning).

RPM: Engine must spin to it's target value. The GS-R will send it's "GO" signal for VTEC at 4400 RPM while the Type R sends it's signal at 5700 RPM.

Oil Pressure: The engine must be operating with normal and safe levels of oil pressure determined by the VTEC pressure switch.

The ECU will send a signal for a spool valve to open. When this valve opens, oil is allowed into the pivot shaft inside the valve rockers and directed into the center rocker. Inside the center rocker, a set of pins are forced outward by the oil pressure and lock inside the rockers to both sides. This entire process occurs in 1/10 of a second."

SurferX

 

[drew]

It appears you have a few issues.

I suspect your speed sensor either has bad connections or needs to be replaced. That should take care of your VTEC, Speedometer and probably the engine light.

The ABS "chatter" is either related to the modulator or the accumulator/pressure switch. Folks have had success in stopping the chatter by replacing the accumulator (I have no reasoning on why this works though)

The spongy brakes? Well, that is part of your "conventional brake system", I suspect your master cylinder needs to be replaced.

Drew

 

[H-carWizKid]

I am probably mistaken but something tells me i have read somewhere that VTEC is partially vaccuum based, I know for a fact it is RPM and speed controlled..... but if there is a vaccuum component this would correlate to the brake issue...

Ill look for the article-----
---------------------------------
Found it and i was wrong.....here is the quote from Team-integra.net

"In order for the ECU to initiate the VTEC system, 5 engine conditions must be met.

Temperature: The engine must have reached normal operating temperature.

Throttle Position: The throttle must be open far enough to allow for increased airflow in VTEC.

Vehicle Speed: The car must be in motion (wheels spinning).

RPM: Engine must spin to it's target value. The GS-R will send it's "GO" signal for VTEC at 4400 RPM while the Type R sends it's signal at 5700 RPM.

Oil Pressure: The engine must be operating with normal and safe levels of oil pressure determined by the VTEC pressure switch.

The ECU will send a signal for a spool valve to open. When this valve opens, oil is allowed into the pivot shaft inside the valve rockers and directed into the center rocker. Inside the center rocker, a set of pins are forced outward by the oil pressure and lock inside the rockers to both sides. This entire process occurs in 1/10 of a second."

SurferX

Lol- see my post two posts above yours...

Team-Integra is damn near tied for best Honda site on the Web...

Cheers!

Philip

 

[95gsrturbo]

you must have posted while i was searching

 

[nsxtasy]

The ABS "chatter" is either related to the modulator or the accumulator/pressure switch. Folks have had success in stopping the chatter by replacing the accumulator (I have no reasoning on why this works though)

The spongy brakes? Well, that is part of your "conventional brake system", I suspect your master cylinder needs to be replaced.

Actually, it sounds like the problem he had was that the solenoids were sticking, and he solved it by exercising the ABS...

 

[Daedalus]

VTEC on the NSX is similar, but differences exist:
* Oil pressure is not a requirement to engage the solenoids
* Vehicle must be moving at least 5km/h
* Engagement point is 5800-6000RPMs.

Why go to a 'teg site for NSX info?

 

[Larry Bastanza]

Oil pressure is not a requirement to engage the solenoids

Please explain this. Oil pressure feeds the spool valves to engage VTEC in the NSX engine just like all other HONDA VTEC engines.

Regards,
LarryB

 

[drew]

Oil pressure is not a requirement to engage the solenoids
Please explain this.

I think he means the ECU doesn't monitor the oil pressure and will send the VTEC command as long as the other conditions are met.

Kinda like having an empty fuel tank doesn't prevent you from depressing the the throttle.

You can do it: it just won't be very effective.


Drew

 

[Daedalus]

That's exactly what I meant. The solenoids will engage if all other conditions are met. Whether VTEC cams are actually engaged is another story, and that is where the pressure sensors come in--to tell the ECU if the solenoids are open AND if oil pressure is high enough to close both sensor loops.

 

[Larry Bastanza]

OK, seems a little wierd to me, but are you saying this is different then other Honda engines and the NSX is unique? Since the systems seem to operate and be construted indentically it just seems strange the ECU logic is different, and it does not check oil pressure the same way.

Thanks,
LarryB

 

[Daedalus]

Well, the caveat is I was assuming what was posted regarding VTEC on the Integra is correct (I'm not familiar with them). If that's the case, then there is indeed a difference, and I can see pros and cons with both approaches. If oil pressure is a deciding input, then the solenoids will only engage if oil pressure is sufficient (not sure if and how the CEL would be invoked). Also, only 1 sensor would be needed, and there would be flexibility in where it could be installed. But without adding even more sensors, the ECU would never know if the solenoids were actually opening, or if they were stuck open all the time. The NSX has the pressure sensors after the solenoids, so they test both oil pressure and solenoid actuation. If the ECU sends a signal but doesn't get a response from both sensors (or if the ECU doesn't send a signal but does get a response anyway), it trips the CEL. The downside (besides needing a pressure sensor in each head) is that if pressure is low, opening the solenoid would only make it worse, but at least the CEL would soon tell you.

 

[Supercar]

Thanks for the info guys. I am out of the country right now and wouldn't have a chance to check out all of the recommendations until the weekend (First I will try to pull the codes).

I did mentioned that the symptoms are gone after exercising the brakes. However, I do need to exercise the brakes everyday (CEL only lit up recently). So I am guessing that something needs to be replaced.

I forgot to mentioned that there are some oil stains on the bottom right hand corner of the engine bay (near the alternator). If it is an oil leak, which is the most common place for me to look at first?