1995 NSX-T engine wont shut down

[Husri]

Happy New Year everybody!!

I've been in a dilemma for a year now so please help me revive my '95 nsx-t. The nsx was fine until i decided to do a precautionary measure to solder the Main Relay (did it once on my previous '93 nsx soldered by my cousin and it was successful). I am not an electrician nor an engineer so asked the same cousin to help me do it for me again. However, this time right after we solder the Main Relay, I could not shut down the engine. I have replaced the Main Relay with a new one but it still wont shut down. I have also replaced the ignition switch and it still wont shut down. I also tried to reset the ecm by pulling out the clock fuse but it doesn't work. Checked all fuses and they're all fine. The only way to shut it down is to disconnect the Main Relay. I live in Brunei (next to Malaysia) and we dont have any nsx expert mechanics here. I did manage to pull the codes and it came out A/T Fi Signal B. Yes my car is an A/T and we dont have any M/T nsx here in my country.

Any ideas contributed on how to solve my problem is highly appreciated. Thanks.

Please help.

Husri
A/T 1995 Nsx-T Midnight Pearl / Black

 

[Old Guy]

I have attached a screen grab of the wiring for the ignition system on the '91 NSX. Turning the key off should open the ignition switch contacts which should kill power to both the ignition system and the main FI relay. As you can see by the wiring diagram, if you pull fuse #13 (30 Amp) in the main fuse box, this should also cut power to the ignition system and the main relay.

With the ignition switched off, the key removed and the engine running, try pulling fuse #13. If the engine stops, then you likely have a problem with the ignition switch not breaking the circuit when you turn the key off. You say you have replaced the ignition switch so perhaps you have a short in the wiring associated with the ignition switch.

If you pull fuse #13 and the engine continues to run, purchase a large bottle of acetaminophen as you are in for a world of hurt! You have somehow managed to create a sneak circuit which is supplying power to the ignition system from the circuit associated with the main FI relay. My guess is that the Main FI relay has an internal short somewhere or that you somehow managed to bugger up the socket that the relay plugs into. I suspect that somehow you are shorting the supply from the #18 fuse to the main relay over to the supply for both the ignition and the fuel injection. The #18 fuse is constantly powered whether the ignition is on or off. With the ignition switched off, the key removed and the engine running, pull the #18 fuse and if the engine stops you have your answer.

I have attached a diagram of the internals of the main FI relay. If you cousin who did the soldering can use an electrical tester, he can check the operation of the relay. Is your replacement relay an OEM Honda part? Examine the relay socket and make sure that there are no internal shorts. Also, check to make sure that you have the correct relay. I seem to recall hearing that there was a change in the main FI relay during the production run. I don't know this for sure and if it did occur, what the year of changeover was.

 

[Husri]

Hi Old Guy..

I've pulled out fuse #13 and the engine died! Phew! I guess I will not be in a world of hurt...but on the other hand..I will be in a world of back pain! Because checking the wiring on the ignition switch will need me to crawl under the steering. I already peeked at the wiring..they look OK so that's the problem. I don't know where exactly to look at. But at least after taking your advise, i now know where to focus on.

I tried reading the service manual many times but I'm not an electrician..seems like i need to look at the starter cut relay? but my car is A/T so should i look at the transmission position switch? Nevertheless, I will try to read and understand the service manual more and update if i manage to fix the problem. Thanks.

 

[Hugh]

If you don't have the right tools to troubleshoot an electrical circuit, take it to a tech that knows what he's doing. The last thing you want to do is create a new short which could fry your wiring harness. Since you just replaced the ignition switch, I doubt that's the issue. Plus looking under the dash won't visually reveal anything. The ignition switch wires make a very short run to the multi pin connector next to the center tunnel. A visual inspection won't reveal anything. The circuits need to be properly checked. Do you at least have the service manual and electrical troubleshooting manual (ETM)?