Engine woes.

[gumball]

My bambino is not well at the moment, misfiring and smoking from the right exhaust pipe(front exit). I've checked the coils and they all measured the same on my ohms metre and the plugs look reasonably even. Also the cooling and oil look clean, but I guess a compression check would be the next thing, oh I did get caught short and had to put some regular fuel in last fill, maybe a bad batch has mucked an injector.
Not what I need with work so slow. :sadface:

[gumball]

Sounds headgaskety really, but I'm understandably very much in denial.
How much to do a front head gasket at Honda? :sadderface:

[Kaz-kzukNA1]

Hi, gumball.
Sorry to hear the news.

You can’t check the state of IG coil by following just the workshop manual.
You are measuring just the primary winding and not the secondary one.
When the coil head gets too corroded, it will crack the potting and cause intermittent/partial cut at the windings causing loss of energy resulting in misfire.

Therefore, even you have checked the primary side, you may still have faulty IG coil(s) due to the failure at the secondary side.


Spark plugs, if it is the OEM one, it’s good for 60K miles but quite often, I had to replace them well before that (about 40k miles) due to corrosion (dark brown) at the insulator body.


Not so common in Japan but there were several failure reports of the igniter unit in US.
If another NSX owner lives nearby, you may be able to borrow the known good one to try it on yours.
It’s the same one used on the previous LEGEND so you may be able to find it at the breaker yard.


I’m not sure what you mean by the ‘smoking from the right exhaust pipe (front exit)’.
The exhaust from the Front and Rear bank is mixed inside the exh box [Edit: on OEM Exh system] so smoke coming out from the right exhaust pipe doesn’t mean you have problem just at the front bank.
[Edit: If you have aftermarket system, then that's a different story.]


Not sure how it was diagnosed as the leaky head gasket but to start with, you can do engine block test.

However, unless you overheated the engine, had other issues, engine modified from OEM, etc, very unlikely to be the case.
The test fluid should stay blue for the duration of the test with no hint of yellow colour.
Otherwise, you have a problem.


Did you get this misfire all of a sudden or gradually?
Any work carried out recently?


Can’t remember whether you replaced your O2 sensor or not in the past but as a quick test, just disconnect them, reset the ECU (as long as you [Edit: didn't] see any warning lights [Edit: at the time of misfire issue]), start the engine and you should see the CEL immediately [Edit: because you disconnected the O2 sensors].

This will force the ECU into Open loop mode and if it is still misfiring in the same way, you will know that you have issue(s) other than the O2 sensor.

Please note that this method won’t gurantee you that your O2 sensor is 100% fine because you really need to monitor the raw signal on the ociloscope to check the sweeping frequency of lean/rich cycle to determine the reaction time of the O2 sensor.


There are other things to be checked such as main relay, fuel pressure, etc but hope you can find the cause of the issue.


Kaz

[gumball]

Hi Kaz, thanks for the reply, the exhaust is a Taitec GT lightweight and I think remains separate through the silencer, the 02 sensors and main relay are new.
The misfire has come gradually, late last year I notice occasional rough idle, is now worse. There was a little smoke I noticed late last year but I presumed that was the cold weather, again now worse.
I've never had any over heating problem at all, but she is old and under-used.

Thanks.

[gumball]

Regarding the 'smoking', just condensation in the front pipes, I should stop myself getting in a tizzy and thinking the worst. Running a pot down still, is at Honda at the mo.

Local Honda are getting their own back, picking apart work carried out by Letchworth. :hehe:

[gumball]

Update for my storm in a teacup, turns out it was just a faulty plug, the cheeky little thing could have helped me a bit by looking different from other five plugs. But running smoother than ever now, thanks Matt of Colchester.

I imagine there will be a little tweeking going on in the ecu? now that she is running properly.

[Kaz-kzukNA1]

Hi, gumball.
Glad to hear that your engine is happy now.

To learn from your experience, it would be nice if you can share the following info for other owners.

Which make of spark plug were you using? OEM NGK/Denso or aftermarket?

How many miles did you cover with this plug when you started notice the issue?

Any photo of the failed plug?

Thank you.

Kaz

[AR]

Glad all is well,, was it one of the rear bank?

[gumball]

They were NGK R double platinun PFR6G-11 , I have fitted the same(bought for around £50 on ebay, a little less than Honda.. ;)). The middle rear one had failed.

Idle had been a little rough late last year, (only a few hundred miles). when I lost the cylinder only about twenty miles on five cylinders.

The plugs were all fairly clean and even when checked(browned insulation though), Sorry I neglected to note which one was the failed one when they were removed.. :blush:

[Kaz-kzukNA1]

Thank you for sharing the info, gumball.

As AR suspected, it’s the one at rear bank, #2 cyl.


Seemed like little mileage covered with this failed spark plug??

Probably, your rubber seal at the IG coil covers were not replaced at the time of your last TB service.
If that was the case, best to replace them now and apply silicone grease once a year otherwise, same thing may happen with your new/existing plugs.
Very important if you drive/park in the wet condition or wash your NSX without protecting the rear valve covers.

Kaz

[gumball]

Thank you for sharing the info, gumball.

As AR suspected, it’s the one at rear bank, #2 cyl.


Seemed like little mileage covered with this failed spark plug??

Probably, your rubber seal at the IG coil covers were not replaced at the time of your last TB service.
If that was the case, best to replace them now and apply silicone grease once a year otherwise, same thing may happen with your new/existing plugs.
Very important if you drive/park in the wet condition or wash your NSX without protecting the rear valve covers.

Kaz


That was the mileage with the various symptoms. Looking back through my bills, the plugs were fitted at 42,000miles, she's done 70,000miles now. There was very light rust on the coil over that plug and no sign of damp, maybe the plug just wasn't up to standard, I'll look into the coil cover seals anyway.

Thank you.