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Discussion Starter · #1 ·
I pulled them today to check and regap them. They don't look quite right - the ceramic is totaly white, there is carbon soot between the ceramic and thread (which falls out when you tap them). The ground and center electrode have light grey deposits and they were around 1.1mm gap after 4k miles. They are the stock NGKBCPR7ES. Directing a small flashlight into the plug holes I could see a few flakey black carbon deposits on the piston tops. My economy is good and I'm not burning oil and recently I've been driving quite conservativley. One thing that does slightly concern me is that the rad fan seems to be very active - has been since I had it. This would also indicate the engine is running hot although the needle never goes over 1/2 and I'm not loosing coolant.
 

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All seems to be quite normal, IMO.

How long is your warm-up time ( should be 4 to 6 minutes) ??
 

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Discussion Starter · #3 ·
It's about that but depends on ambient temp. It seems much quicker than my old c900T16.
 

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Your engine may be running a little rich.

The temp gauge on the instrument panel is very misleading. It is NOT a direct indication of engine temperature, the ICE module is programmed to keep the needle at 9 o'clock when the temperature is in an acceptable range, and that range is very, very wide. It is little better than an on/off light. Temp gauge is at mid point (9 o'clock) from 85-115C.

If our cars were the old-style mechanical carb and distributor etc., you could say that 90% of them (the NG900 at least) need a tune-up. Most people get about 10% worse fuel economy than the car is capable of, because the ECU is no longer regulating fuel as well as it should.
 

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Is this the fault of the ECU or the components it regulates and it's various sensors?
 

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It is not the fault of the ECU. It is usually something else, which is preventing the ecu from regulating fuel properly. Sensors, most likely.

If you have traces or layers of dry flaky stuff on the plugs, then the plugs are becoming fouled with carbon. The most common term is "dry-fouling", to distinguish it from sticky-tarry stuff (wet-fouling). You can see extreme examples here:

http://www.ngk-sparkplugs.jp/english/techinfo/troubleshooting/03/index.html
(but the page talks mostly about the plugs, not what is doing it, it can vary by engine type)

The most common reason on a fuel-injected car is that the injectors are dirty, not so that the ECU will detect misfire, but enough that the fuel is not vaporized properly, and burns incompletely. Unfortunately, I am not really sure how frequent that is with our injectors, they are pretty good in general. They do need some injector cleaner once or twice per year.

Our intake air sensors are in the intake air stream, and get coated with the same crud as the IAC valve and the throttle body. The throttle position sensor gets a little worn and the feedback is off a bit, the vacuum line to the FPR may leak a little, the O2 sensor gets fouled with carbon in the exhaust, and "tired", meaning it responds too slowly to changes in exhaust oxygen...

Most of this can persist for years before you get a CEL and a fault.

The thermostat can work partially for quite a while before you notice that the needle is out of range, and there is no fault for thermostat failures.
 
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