Help identifying this issue.

[Nsx_downunder]

Hello group, Just wondering if anyone can help me please.

Car has been running all good and fine, parked up and this morning when trying to start up it, it had abit of smoke coming from this area?

The smoke seems to come when I try to crank the engine. But when no cranking and is on accessories. Nothing. Only when I start cranking.

Here's a video of it.

And picture to show location

First time it's ever happened to me. Any ideas or has anyone encounted the same/simular situation?

 

[comtec]

It appears to be an electrical short in the wiring. Check the ground wires in that area, I believe there are two. Make sure they are securely fastened. Also look for visible damage to any wires in that area.

 

[Nsx_downunder]

Double checked the wiring and ground wires throughout the car. All still seems fine. Car is currently cranking now but no start? would anyone know what that area would be? any sensors?

at first I thought it would be the starter motor but from my understanding is starter motor wouldn't crank if it was at fault?

Any help is really appreciated

 

[Old Guy]

Your picture shows the back bank of the engine on what appears to be an NA1 (confirming model year of the car always helps) and about the only electrical thing that I can think of in that vicinity is the VTEC solenoid / oil pressure switch since you don't have a rear O2 sensor.

The starter motor circuit is completely unrelated to anything in that area and is pretty much an isolated system. The CCU can be stone cold dead and the starter motor will still crank.

The VTEC oil pressure switch probably gets power from the ECU at start up and if there is a solid short to ground I would expect that it is killing an internal supply bus in the ECU which could pretty much kill everything. Have you checked for any diagnostic trouble codes? I also don't hear the fuel pump whine during the fuel pump prime cycle. When you turn the ignition switch to the run position (not the start position) do you hear the fuel pump run as it goes through its 2 second prime cycle? If the fuel pump does not go through the prime cycle you have problems.


Do the following:
- check the rear bank oil pressure switch connector and wiring for damage
- does the CEL illuminate for a couple of seconds then go out when you turn the ignition switch to run (but not start). That is the power on self test (POST) for the ECU which says the ECU is OK. If the CEL does not POST then the ECU is dead which could be as simple as a blown fuse.
- check for stored error codes if the ECU passes the POST
- confirm whether the fuel pump is going through its prime cycle

Get back to us with test results and confirm what model year we are looking at so we are not guessing.

 

[Nsx_downunder]

Your picture shows the back bank of the engine on what appears to be an NA1 (confirming model year of the car always helps) and about the only electrical thing that I can think of in that vicinity is the VTEC solenoid / oil pressure switch since you don't have a rear O2 sensor.

The starter motor circuit is completely unrelated to anything in that area and is pretty much an isolated system. The CCU can be stone cold dead and the starter motor will still crank.

The VTEC oil pressure switch probably gets power from the ECU at start up and if there is a solid short to ground I would expect that it is killing an internal supply bus in the ECU which could pretty much kill everything. Have you checked for any diagnostic trouble codes? I also don't hear the fuel pump whine during the fuel pump prime cycle. When you turn the ignition switch to the run position (not the start position) do you hear the fuel pump run as it goes through its 2 second prime cycle? If the fuel pump does not go through the prime cycle you have problems.


Do the following:
- check the rear bank oil pressure switch connector and wiring for damage
- does the CEL illuminate for a couple of seconds then go out when you turn the ignition switch to run (but not start). That is the power on self test (POST) for the ECU which says the ECU is OK. If the CEL does not POST then the ECU is dead which could be as simple as a blown fuse.
- check for stored error codes if the ECU passes the POST
- confirm whether the fuel pump is going through its prime cycle

Get back to us with test results and confirm what model year we are looking at so we are not guessing.

Thank you for your reply, it is a 1991 NA1 Automatic model. Closer inspection it looks to be coming from the Speed Sensor. Think the speed sensor has thrown in the towel so I've ordered another one.

Car currently cranks but no start, I've read up on this forum and others that if the speed sensor is at fault, it could cause the vehicle not to start as it won't be able to send the ECU how much fuel the engine needs.

Fingers crossed it works. I will keep this post updated for future references.

 

[Kaz-kzukNA1]

If you are sure that you have short circuit at the VSS (Vehicle Speed Sensor), check the 15A fuse at the fuse box inside the cabin.
With the RHD, it’s located at the passenger side.
With the LHD, I think it’s at the driver side.
Fuse position #2.
It’s also the power source for the fuel pump.

Don’t know where you got the info but faulty or even disconnected VSS won’t prevent you from starting the engine.

Normally I won’t recommend the following without first solving the short circuit but since you’ve already done few times, the damages were already done.

Turn IGSW into P2 ON and wait for at least 2sec.
DO NOT crank the engine.
During this 2sec, listen to the sound of Fuel Pump.
It’s behind your seat.
If you can’t hear the fuel pump priming the fuel system for 2sec, check the #2 Fuse mentioned above.

Also, as Old Guy advised, check the CEL operation during this 2sec.

You seem to have some sort of extension cable inside the eng bay.
Looked like O2 sensor ext cable.
Please make sure it’s securely fixed away from header/exh system.
Any short circuit there would damage the ECU resulting in permanent CEL although it won’t stop you from running the engine.

Kaz

 

[Old Guy]

In the picture below C119 is the connector for the wiring pigtail on the VSS. You can see the actual VSS as that thing just below the VTEC pressure switch in the picture.



Un plug C119 and see if the smoke stops! If it does then perhaps your diagnosis is correct.

As Kaz notes the VSS gets +12v power from fuse #2. Unfortunately, fuse #2 is 15 amps which is rather oversized for just the VSS. Its oversized because fuse #2 also supplies other stuff. 15 amps would prevent a burn down; but, might not be sensitive enough to prevent damage to the VSS in the event of a high resistance short.

As Kaz notes a dead VSS will not prevent the engine from starting. However, if the +12v supply line to the VSS has shorted to the sense line that goes to the ECU which is normally looking for a 0-5 volt pulse, that could potentially damage the VSS input to the ECU; but, I would not expect it to be fatal to ECU operation in terms of starting the engine.

I am thinking something else is going on.

 

[Nsx_downunder]

@Old Guy @Kaz-kzukNA1

Just want to give a massive THANK YOU to you two and everyone who helped.

Followed your instructions and checked out Fuse #2 and it was blown. Changed the fuse and turned it on to hear the fuel pump priming, once started. It started up then shut off. Checked #2 fuse and it was blown again. Changed the fuse and unplugged the VSS. Fuel primed and started. Now it is running back as normal. Culprit was the VSS which I have ordered a new one already and currently checking all the wires for shortages.

Vehicle was imported from japan with a HKS Speed Limit Defencer installed. I think the SLD has decided to throw in the towel so I have unplugged that with the Vehicle Speed Sensor. Inspecting all the wiring harness to see if anywhere else is shorting but at the moment it is looking good. Will keep updated if any wiring gremlins are found.


I am simply amazed at this forum and Thank you again!!

 

[Old Guy]

Good that things are now working. Details such as this car being JDM and having aftermarket stuff on it matter.

VSS failures are not common; but, are not totally unknown. However, they usually just stop outputting the speed signal in which case the engine runs; but, you get a CEL, TCS and other error lights. I have never heard of the VSS failing catastrophically and affecting other stuff like yours did.

The ECU may still generate a CEL after you replace the VSS. The speed defencer intercepts the VSS signal before it hits the ECU and the speed defencer may now be damaged which may be blocking the VSS signal to the ECU. Or, a speed defencer failure might have been what caused this very unusual VSS failure. Removing the speed defencer before you install the new VSS to restore everything to stock might be a good idea, particularly if it is the speed defencer that caused the damage. It would at least allow you to examine the defencer for damage.

Post a picture of the dead VSS. It would be interesting to know where the damage is (inside the VSS or just a short in the wiring pigtail).