Check Engine Light codes

[Trident]

Help required please. Today is my last chance to get the car ready for Japfest and having passed the MOT (don't know how!) the engine has decided to misbehave. I connected a jumper wire to the Service Check-Connector to try and read the codes, but all I get is a constant short blink every 2 seconds with no variation.
Any ideas?
Trident

[Sudesh]

This is on prime, not sure if there much if any differences in US and other regions.

http://www.nsxprime.com/FAQ/DIY/trouble_codes.htm

[Kaz-kzukNA1]

Hi, Trident.

It would be nice if you can post bit more detail of your NSX.
From your signature, I believe it is the 91 model and possibly the UK spec.
Mileage?
AT/MT?
Any modifications to the engine/Gbox?

Bit more detail on the ‘misbehave’ of the engine would be helpful.
At what rpm/speed did you notice the issue?
Is it continuous misbehaviour (i.e., the engine is still not running smoothly) or it misbehaved just once at that point and since then, it seemed to be running fine even with the CEL (Check Engine Light or sometimes called as MIL, Malfunction Indicator Light) on the dash?


It would be nice if you can take video but sounds like you are getting CEL/MIL #1 or #10.

#1 is Front bank O2 sensor signal.
It is triggered by the abnormal reading of the A/F ratio and it has to be detected twice before the ECU decides to switch on the CEL.
Therefore, it could be triggered not just by the O2 sensor failure but also by misfire caused by the spark plug, fuel pressure, etc issue so needs to be bit careful with the diagnosis.

If your engine is running fine with the CEL ON (but with no other warning lights or other error code on the CEL) at the moment, then it is very likely to be the O2 sensor failure.

Under this condition, ECU will keep the system in Open loop control so your fuel economy would be worse and very likely the engine won’t respond as fast as it used to be.
Please note that the CAT won’t be working efficiently as it needs both the rich and lean cycle (Closed loop) to re-generate itself so not good for the CAT (and environment) from this point of view.


If the engine is not running smoothly even with the CEL (keep misfiring over any rpm range or below/above a certain rpm), you have other issues.


#10 is Intake Air temperature sensor failure but if this was the case, you will notice the change in idle rpm (rough or higher).

Enough as a starter.....

Kaz

[Trident]

Hi Kaz, Thank you for responding so quickly.
Yes, my NSX is a 1991 UK spec MT. 129960 miles.
Idle speed is high and variable. Car runs reasonably well for only half a mile then loses power. High fuel consumption and you can smell the unburnt fuel. O2 sensor has probably failed on the front manifold as you said but other issues as well. Did a temporary repair on the front flexible exhaust to get through the MOT. Spent the afternnon checking the plugs and coils which all seem fine although two of the rear coils are quite rusty as one seal was missing. Oil, oil filter and air filter were changed last week. The car has been idle for a few months although it has been run occasionally. Pete

[Sudesh]

Hi Kaz, Thank you for responding so quickly.
Yes, my NSX is a 1991 UK spec MT. 129960 miles.
Idle speed is high and variable. Car runs reasonably well for only half a mile then loses power. High fuel consumption and you can smell the unburnt fuel. O2 sensor has probably failed on the front manifold as you said but other issues as well. Did a temporary repair on the front flexible exhaust to get through the MOT. Spent the afternnon checking the plugs and coils which all seem fine although two of the rear coils are quite rusty as one seal was missing. Oil, oil filter and air filter were changed last week. The car has been idle for a few months although it has been run occasionally. Pete

Rust on the rear bank of coils seems to be a common enough thing. Mainly due to water coming in the rear vent and dripping down over the cover, plus old/perished seals. I managed to clean down and save some coils in the past, but some others had to be replaced.

There is only one seal on each of the coil covers, and obviously the seal should be at the top.

[Trident]

I will change the O2 sensors and front flexible exhaust pipe and then see how it goes. I will be coming to the show with Gary in his NSX so the tickets won't be wasted and there will still be the same number of cars. Kaz, when I'm ready I'll book in for a long overdue health check if that's ok with you? Pete

[Kaz-kzukNA1]

Hi, Trident.
Thank you for the additional info.
I presume you don’t have major modification on the engine/Gbox such as super/turbo charger, high lift camshaft, etc.
The biggest unknown factor for any low annual mileage NSX is the state of the fuel inside the tank.
Fuel is an organic compound and although there are several fuel stabiliser on the market, it will eventually decay.
Burning this bad fuel in the engine could result in intermittent phenomenon depending on the condition. One time it’s fine and the other time, not, making the diagnosis difficult.


With your mileage, if both of your O2 sensors were never replaced in the last 60K miles, I would recommend replacing both at the same time on OBD-1 cars.

You can get NGK/NTK or Denso O2 sensors from US (no cutting, no splicing required) at very good price from sparkplugs.com.
For your NSX spec, NGK/NTK parts #24172 is the one for both the front and the rear ones.
US$54 each plus the delivery (I think it was about US$50 but not sure, same for just one or two sensors), import VAT (20%), clearance fee.
There are several models available on ebay UK but never used them so not sure about the quality.

O2 sensor output can shift or even produce wrong output but not enough to trigger the CEL resulting in hesitation/sluggishness even without the CEL on the dash.

For this type of issue, I normally recommend the owner to disconnect both front and rear O2 sensors to force the ECU into Open loop mode to see how the engine runs using the base map with minimum correction factors.


From what you wrote, it is very likely that you have multiple issues so I think this is a good starting point.

You can’t really check the state of IG coil by the looks of it.
Also, using the multimeter will only allow you to check the primary side and not the secondary side.


OEM spark plug has maintenance interval of about 60K miles but most of the time, I had to replace them at earlier stage around 40K miles.
If you see dark brown marking (light brown is not perfect but acceptable) at the white insulator body near the metal HEX, replace all of them at the same time.
You can get the OEM ones at about GBP50 for all six.
NGK PFR6G-11 for your NSX spec if no major modification on the engine.


Fuel pressure can be checked through the service hole at the fuel filter.

Compression check will provide you with the state of your valve timing and health of your engine.


There are many other things to be checked with known failure items such as main relay, IG sw cable, fuel pump resistor, ignitor module, etc but best to start with the easy bits.

Kaz