Engine Starting Issue - HK

[EK4 hatchback]

[Kaz-kzukNA1: 20/Feb/25 12:18pm
Originally posted in 'Kaz's not so build thread' under the 'NSX Builds (1st Gen)' Forum.
To keep the subject related to the build of specific car, moved to this thread under the 'Technical' Forum.]

Hi Kaz,

Sorry to hijack your thread here. I am having starting issues with my NSX and it is a common issues for many local NSX in Hong Kong. I suspected it is the wiring harness that connect from battery positive terminal to the starting motor. It usually happen after driving in hot summer after shut off the engine for a few minutes. When try to restart the car with the key, all the light on the cluster is normal light up but when turn the key the cluster light would dim and starter not move (starter not turning / not hearing the start turn). If that happen, i open the glass hatch and wait maybe 30-60 minutes for the engine bay to cool down and it usually can start the engine again. I went to one of the NSX garage locally they said to me there is not enough electric to the under dash and i don't understand it. May i know from your experience is that harness the issues? I read the Facebook on T3TEC when they rebuild customer NSX engine, they always replace the engine harness and it is very un-common thing out side of Japan. Is engine harness consider consumable item that need to be replace with the age of the NSX? Thanks

FYI, i had replaced the following 6 years ago due to this very issues starter, ignition switch, fuel pump relay, factory start relay under dash (manual NSX has one), battery terminal ground wire to body but it came back again now.

[Kaz-kzukNA1]

HI, EK4 hatchback.

The starter circuit is fairly simple and it seems that you can re-create the same issue easily once it happened.
If it’s common among HK based NSX, then should be able to diagnose the cause.

Although you suggested that it was heat related, never heard from owners in Japan.

As you are in HK, you can probably guess what the weather like in Japan these days.
Used to have four distinctive seasons.
Now, it’s like having just scorching hot 40degC summer for months and straight into freezing cold winter without spring or autumn.

Part of Japan just had 5m (yes, 500cm) of snow but from today, many part of the country are expecting 20degC mild weather but in a few days, back to single figure.

Some people are tracking their NSX during hot summer with no cranking issue after each session.

There are thousands of NSX in Japan and from time to time, heard the 'no cranking' issue but nothing like common failure of Main Relay on many Honda models.
Majority was caused by the poor battery health or the starter itself.
Very rare but starter cut relay failed on few of them.

Your gauge got dimmed while IGSW in P3 START because the supply voltage to the gauge cluster was significantly lower than usual.
The battery power was consumed by excessive current draw.
Most likely within the starter but no cranking.

T3TEC replaces the eng loom for several reasons but not because of common failure.
The outer insulator can get harden and eventually crack, moisture can get inside if pressure washed and cause retina corrosion making the wire stiff, etc.

Majority of the NSX in the world are still using the original Eng & Cabin loom without any issues.

Mine is the original and don’t even use the Eng bay cover so even worse than standard condition against the UV ray.
Already 31 years old and covered over 284K km (178K miles) but still going strong and no plan of replacing the Eng or Cabin loom for any reasons.

As mentioned at the top, starter circuit is simple.

Honda didn’t change the material of wires just because of the different country spec.

No common cranking issue due to OEM parts - unlike the well-known 'cranking but no engine start' due to the Main Relay.

If many HK based NSX are suffering from the same cranking issue, I would say it is very likely to be something installed/modified at the dealer after leaving the factory.
For example, the Acura/Honda branded security system.
They are dealer fitted and not from the factory.
For the clarification, I'm not talking about the OEM immobiliser.

If I remember correctly, HK NSX was the only RHD NSX model under the Acura brand.

I recommend the following.

Make it as your habit to keep eye on the volt meter whenever you start the engine.
IGSW P2 ON and wait for 2sec to let the fuel pump to prime at max speed.
You should see about/above 12.0V.
IGSW P3 START and while cranking, should be above 10V with the healthy battery.
If less than 8.5V, you would really struggle starting the engine but at least, it’s cranking.
This will catch the first sign of battery health issue.

Next time if you experience the cranking issue, put jump starter pack at the jump start terminal in the engine bay.
Turn IGSW to P2 and then try P3 Start.
Try it several times.
Since you are only testing the cranking and no need starting the engine, you can disable the ECU or INJ in many ways.

Carry short cable with spade terminal at one end.
No need using the IG key at the IGSW.
Just apply 12V at the S terminal of the starter.
It’s hidden behind the single wire tiny black conical sleeve.
This will crank the engine but won’t start it without the IGSW in P2.

If replaced the starter with the original Denso or the Denso remanufactured one, no questions there.
I trust them for the classic parts.
If you just refurbished the starter using certain parts, you may need revisiting it.

Depending on the result, you will need to review the IGSW, starter cut relay, CL inhibit sw (Acura MT NSX and only on several later spec Honda MT NSX) or AT shift pos sw, factory fitted immobiliser on the later models.


Kaz

[Old guy]

Kaz has covered everything you need to do.

Given that you have already replaced a lot of the likely problem areas, I might fast track to checking the battery post positive terminal clamp (since you have already replaced the negative terminal clamp). The terminal clamp is easily damaged by overtightening. Shortly after I got my car back in 2011 it developed the same problem as yours and it was intermittent. Sometimes fine, sometimes no start. Even though the bolt on the clamp was tight you could pull the clamp right off the battery post by hand. This is my damaged terminal clamp after I cut it off the cable.

15001

The picture shows that the bolt was fully tight when I pulled it off. The area circled in red is where the metal was stretching and starting to tear. Honda battery clamps work fine if you do not over tighten them. I had the same clamps on my 2003 Honda Pilot for
18 years without problem; but, a lot of people seem to believe that you should tighten the clamp and then tighten it a little more just for good measure.

If you check the US based NSX Prime website, every year it seems like there are 3 or 4 owners asking about starting problems which are related to failed battery post clamps. Failed ignition switches are also common as the cars get older; but, you have already dealt with that.