Diagnostický případ

Opravené vozidlo

Fleischhans

Jazyk případu:

Jeep – Erratic idle with irrelevant DTCs

23.10.2004 | aktualizováno 18.03.2005 0:00:00 0 8654x

Informace o vozidle

VIN:
Výrobce:	Jeep
Model:	Grand Cherokee
Rok výroby:	2000
Kód motoru:	4,7L V8
Typ motoru:
Výkon (kW):	0 kW
Převodovka:	Automatická
Palivo:	Benzín
Najeto:	0 km

R-CODE

paměť závad nečtena
nelze se spojit / asi chyba auta

během jízdy
[P0202]

trvalá závada
sporadická závada

Závěr

VOZIDLO JSEM NEOPRAVOVAL

Fault description:
The idle rpm are erratic and surge between 700 and 1 500 rpm without accelerator pedal input. The fault is intermittent, but occurs quite often. Sometimes under partial load and constant speed the engine misfires. After longer periods of driving the ECU reports fault codes related to injectors 2, 4, 6, 8, 3, and 5! Only the cylinder #1 injector according to OBD is not deffective. During idle the engine is ocassionally not smooth. The authorised Jeep dealer technicians are aware of this and it is considered as normal on all 4.7L engines.

Fault code description:

1= Fuel injection, cylinder #2, malfunction

Repair:

Replace all spark plugs

Summary:

The DTC descriptions are different to the actual fault. The O2 sensor signals were surprisingly interpreted as clear faults on multiple cylinder injectors. While the cause could have been a defective fuel pump, fuel filter or in our case burned spark plugs. This is a typical case and clear proof that the workshop has to verify the OBD reports with an oscilloscope.

Obrázky, fotografie a soubory

DTC's (367/1)

The long term adaptives of both engine banks are -19.5%.

O2S idle signals before repair (367/2)

The BLUE trace shows oxygen shocks - incomplete combustion in one of the cylinders. Shortly after that engine speed increases without any input.

High idle before repair (367/3)

Increasing the engine speed to high idle caused the O2 sensor signals to drop to 0V.

Seven seconds of high idle before repair (367/4)

For 7 seven seconds the O2 sensors didn't want to regulate. Only after the accelerator pedal is released the O2 sensors return to the closed loop mode.

Ignition signal at idle before repair (367/5)

The burn time at idle is within specs - 1.2ms.

Ignition signal during acceleration before repair (367/6)

During acceleration the burn time on all spark plugs drops to 0.2 - 0.4ms. Critical burn time during acceleration. This is on the edge where the whole mixture will burn. This is typical for "dual spark ignitions", (two sparks during one combustion), or for an excessive gap between spark plug electrodes.

Spark plug (367/7)

This spark plug is finished. The spark plug gaps on all plugs were between 1.6 to 2 mm! Too big! The specified gap is 1.1 mm.

Idle O2S waveforms after repair (367/8)

After the spark plugs were replaced the waveforms showed no signs of former oxygen shocks.

High idle O2S waveforms after repair (367/9)

At high idle the O2S waveforms after repair have a good shape and the O2 sensors are now working in closed loop mode. We can also notice, how both cylinder banks have independant regulation. While the amplitudes are synchronised at the beginning, at the end of this recording they are in the opposite position.

Intermittent problems during idle (367/10)

These engines are known to have intermittent erratic idle that can be recognised by listening to the engine and is also noticeable listening at the exhuast tailpipe. This, according to authorised dealer technicians is quite common on these engines. It appears after longer periods of idling.