TCS/ABS tach mystery

[bngl3rt]

So now that my fuel leak is fixed (check your injector o-rings people!! A $12 part could be all that stands between you and an engine fire!), my car is having another strange problem...

Under hard acceleration, the tach momentarily drops to 0 and the ABS light flashes (even though I'm accelerating, not braking). This is sometimes but not always accompanied by an actual lurch in the car (meaning the RPMs actually changed) but invariably the engine is still running after this occurs. No CEL.

Took a drive with the ODB2 scanner connected - no code before or after.

Theorized that maybe the TCS computer was starting to go, so I shut it off before driving ~40 miles to work. Initially I thought this fixed the problem, but then the strangest thing happened - the pavement underneath me changed from smooth asphalt to pretty rough old road with grooves, the ABS light flashed, and the TCS light turned *off* (meaning TCS was back on). This was cruising and not under hard accel.

Turned the TCS back on as I was under 4k RPM and did not have another "tach bounce" the rest of the way.

Could it be the TCS computer? Wheel sensors? Some other sensor in the transmission that drives the tach?

Any and all input is appreciated!

 

[bngl3rt]

Let me start with a simpler question: Under what conditions would TCS turn itself back on while driving if I had turned it off?

I wonder if power to the TCS/ECU/something else is getting momentarily interrupted and causing things to reset.

 

[Sportsmind4me]

Others chime in and correct me if I'm wrong, but I believe the it's the other way around with TCS. To my knowledge the TCS is always on when the car is started as a safety feature (green light when on) and has to be turned off (yellow light when off) if the driver wants the function disabled. Sounds to me like TCS was on and activated itself when the car detected an uneven surface just like it was designed to do, hence throwing the light. Not sure about your other issue though.:frown:

 

[bngl3rt]

Others chime in and correct me if I'm wrong, but I believe the it's the other way around with TCS. To my knowledge the TCS is always on when the car is started as a safety feature (green light when on) and has to be turned off (yellow light when off) if the driver wants the function disabled. Sounds to me like TCS was on and activated itself when the car detected an uneven surface just like it was designed to do, hence throwing the light. Not sure about your other issue though.:frown:

Yes, the thing with the lights can get very confusing.

I turned TCS OFF (yellow light ON) and drove for a while. Then the pavement changed, the ABS light flashed on, and the TCS turned ON (yellow light OFF). Since ABS and TCS don't share anything except sensors, I suspect a wheel sensor.

Interesting thing is I can't make the jerk happen with TCS off.

 

[bngl3rt]

Dropped the car off at Acura Authorized Service in Sunnyvale yesterday to see if their techs can reproduce the issue.

An NSX that you can only drive slow isn't really an NSX, is it... 6k RPM is a must have.

I'm reading that the tach is driven by a pulse signal from the ECU... so either the connection between the tach and the ECU is getting interrupted, or power to the ECU is getting interrupted, or the ECU is on the fritz. I haven't looked up the price for a new ECU yet but I might as well do so to prepare myself.

 

[bngl3rt]

Oh boy...

http://www.acuraautomotiveparts.org... / NSX-T&trans=5 Speed - Manual&view=normal

If ECU and TCS are toast, it's going to be expensive.

 

[Sportsmind4me]

Wow...I really hope it doesn't end up being a worst case scenario for you on this one. Please keep us posted on what the dealer determines.

 

[bngl3rt]

Wow...I really hope it doesn't end up being a worst case scenario for you on this one. Please keep us posted on what the dealer determines.

It's gotta be something electronic. Why would the ECU stop sending the pulse signal to the tach unless it was losing power/resetting spuriously/something else

 

[comtec]

Worst thing you can do is to start throwing money at it. Try fixing the tach problem first because a faulty rpm reading can effect the TCS and ABS.

I believe the ECM uses a pulse from the igniter unit to calculate the engine RPM. Check the connectors for the igniter and the coils first and then maybe do the manual test for it.

Mike

 

[99 rs]

It's gotta be something electronic. Why would the ECU stop sending the pulse signal to the tach unless it was losing power/resetting spuriously/something else

Losing electrical power sporadically sounds like the main relay is starting to let go. Might be worth it to try a "cheap" fix first (even trying someone's known good one).

 

[bngl3rt]

Losing electrical power sporadically sounds like the main relay is starting to let go. Might be worth it to try a "cheap" fix first (even trying someone's known good one).

Hmm... but why only under hard accel? Vibrations maybe?

 

[bngl3rt]

Two NSX techs put their heads together yesterday and still couldn't figure out what's going on... She was never meant to be a garage queen but now she is becoming a shop queen.

If they can't fix it I'll capture a video once I have the car back.

 

[Zishan]

Losing electrical power sporadically sounds like the main relay is starting to let go. Might be worth it to try a "cheap" fix first (even trying someone's known good one).

I had similar symptoms. Speedo would drop to zero while driving, it would hesitate, and then normal, all within a second. One of the lights flashed on the dash too, can't recall if it was the ABS or TSC. It was my main relay.

 

[bngl3rt]

I had similar symptoms. Speedo would drop to zero while driving, it would hesitate, and then normal, all within a second. One of the lights flashed on the dash too, can't recall if it was the ABS or TSC. It was my main relay.

Thanks, I will ask them to check that.

 

[Zishan]

The main relay is pretty cheap......and you might be able to repair yours. I believe there was a thread discussed a while back that showed a DIY repair. It required soldering the broken/deteriorated connections.

Good luck,

 

[bngl3rt]

I am pretty handy with a soldering iron but my car is already at the shop so I will just ask them to order and install a new one.

 

[bngl3rt]

So, it turns out VTEC was never kicking in. At all. Whatsoever.

I suppose it's a tribute to the car that I found it sufficiently enjoyable without VTEC to ever suspect that something was wrong, but...

A damaged pin was also found in the ECU wire harness, and apparently the resistor box for the fuel pump is also missing - but they said this would just cause a higher idle. I have no particular complaints about the way the car idles.

Anyway, the saga continues...

 

[bngl3rt]

Main relay is fine. ECU wire harness apparently in bad shape. Testing with a 95 ECU today...

 

[comtec]

Was your car sc in the past?

Mike

 

[bngl3rt]

Was your car sc in the past?

Mike

Yep. Voltage booster removed, fuel pump resistor panel apparently missing.

 

[EdinKali]

Main relay is fine. ECU wire harness apparently in bad shape. Testing with a 95 ECU today...

How was the main relay tested? The problem arises due to cold solder joints which can't always be seen with the naked eye. Better to replace or re-solder all the joints.

On my old relay, the bad solder joints could only be seen under magnification(at least with my middle aged eyes).

 

[bngl3rt]

Car is fixed. Extended alternator wire left over from CTSC install got stuck under the intake manifold, wore out, and started shorting under heavy vibration.

 

[comtec]

Yep. Voltage booster removed, fuel pump resistor panel apparently missing.

Thought it was from what you have said. With the stuff you have found i was kinda thinking it might be related to a sc removal.

Great news that it's fixed! :smile:

Mike

 

[bngl3rt]

Great news that it's fixed! :smile:

Mike

Indeed! The feeling of being back in an NSX after driving something else for a while is pretty indescribable.

Huge props to Justin, John, and of course Jim R at Acura Authorized Service in Sunnyvale for cracking the case. :smile:

 

[comtec]

Indeed! The feeling of being back in an NSX after driving something else for a while is pretty indescribable.

Waiting for that feeling since i haven't even seen mine in two months :frown:

Enjoy
Mike