Diagnostický případ

Opravené vozidlo

Libor Fleischhans/jk

Jazyk případu:

Critical flashover voltage on engines with variable valve timing

24.09.2004 | aktualizováno 17.02.2005 0:00:00 0 7497x

Informace o vozidle

VIN:
Výrobce:	Acura
Model:	NSX
Rok výroby:	1995
Kód motoru:	3,0 V-TEC
Typ motoru:	181 CID
Výkon (kW):	187 kW
Převodovka:	Manuální
Palivo:	Benzín
Najeto:	0 km

R-CODE

paměť závad nečtena
nelze se spojit / asi chyba auta

během jízdy
[1]

trvalá závada
sporadická závada

Závěr

VOZIDLO JSEM NEOPRAVOVAL

Symptoms: Engine misfire above 3800 rpm, under
light throttle, that gradually becomes worse. The
first following major throttle application causes the engine to die and it cannot be restarted for about 10 minutes.

DTC: 1=Cylinder misfire...

This strange problem annoyed several Honda dealers
in the Czech Republic. No result, even after consulting
US colleagues who only recommended to use the specified spark
plugs. Finally we had to use common sense and principles of ignition
to find the problem, and we did. Follow the pictures in the detail
section.

Pic. 1: Engine compartment view

Pic. 2: Multi-channel scope recordings

Pic. 3: Shunt firing

Pic. 4: Both O2S waveforms are recorded

Fix: Readjustment of spark plug gaps
from 1,1mm to 0,6mm and replacement/cleaning of
ignition cables, cable boots and terminals.

Obrázky, fotografie a soubory

Pic.1: Engine compartment view (282/1)

Good access to the engine.

Pic.2: Multi-channel scope recordings (282/2)

We can see by looking at these waveforms, that under light acceleration the voltage at the transformers goes up. On one of the channels (2nd line from bottom) you can se a shuntover spark jumping from the end of the ignition cable to the spark plug isolator and then to the steel shell of the plug.

Pic.3: Spark flashover (282/3)

Under heavy load, when more fuel is injected the engine runs without any problems. During light acceleration (lower load) and at higher rpm, the variable valve timing system adjusts to increase the air intake amount and creates max. flashover voltage. The highvoltage insulation cannot handle that. At this point the spark finds the path with least resistance and this is between the plug insulator and rubber boot or through cracked insulator. Once the spark doesn't flash properly between the electrodes but between the cable boot and plug insulator, the O2 sensor signal for one side of the egine will register a lean A/F mixture.

Pic. 4: Both O2S waveforms are recorded (282/4)

Here you can see waveforms from both O2 sensors. While the left O2 sensor (red trace) shows only two misfires. The opposite O2 sensor (blue trace) is registering numerous misfires. If this was to occur on both engine banks (both exhausts contain higher levels of oxygen due to unburned fuel) the PCM rightfully increases injector pulsewidth and ads more fuel. The result is a rich mixture, wet plugs, hesitation and possible vehicle stalling.