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Jeep Grand Cherokee - Will the Automatic Transmission require repair?

08.11.2004 | aktualizováno 03.04.2005 0:00:00 0 5850x

Informace o vozidle

VIN:
Výrobce:	Jeep
Model:	Grand Cherokee
Rok výroby:	1995
Kód motoru:	4,0L
Typ motoru:	MX
Výkon (kW):	0 kW
Převodovka:	Automatická
Palivo:	Benzín
Najeto:	0 km

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Závěr

VOZIDLO JSEM NEOPRAVOVAL

Fault description:

The vehicle intermittently bucks/stumbles and in partial load the auto transmission shifts erratically. Driving over uneven surface at high speed or during fast acceleration from standstill bucking/stumbling can be felt without being able to identify if it's the engine misfiring or transmission problem. The fault slowly worsens. Before we remove the transmission for further repair we have to determine where the problem is. Is it in the transmission or in the engine management? The MIL light is not ON and no DTC is stored in memory.

Diagnostic steps/procedure:

To discover this kind of fault we have to measure several components at once. On petrol engines bucking/stumbling is mainly related to fuel supply (injectors, O2 sensors), primary and secondary ignition signals, also position and speed sensors (camshaft and crankshaft sensor).

Only after we have tested the correct function of the complete engine we need to concentrate on measuring all automatic transmission sensors, solenoids, actuators, etc.

Repair:

Repair of damaged crankshaft position sensor wiring.

Summary:

The forecasted automatic transmission overhaul would have been a costly mistake.........

Obrázky, fotografie a soubory

FCD task Force Car - Mercedes Sprinter 313 CDi Max. (363/1)

Customer service available directly in your workshop!!

Our Mercedes Sprinter in the longest version, will carry the beforehand the agreed scope of equipment. We can participate at any event, where we can diagnose - live, faults on vehicle systems. Our "Task Force Car", is equipped next to diagnostic tools, with a conference section and access to Internet and the FCD system.

Connecting accessible actuators (363/2)

The easiest connections are to the ignition and fuel injection system.

Connecting sensors (363/3)

The ECM is mounted behind the coolant tank. Here is the place where to easily connect to all sensors, in our case the CKP and CMP sensors.

Oscilloscope connection (363/4)

We route the scope wiring from the engine compartment, through the side window into the vehicle being careful not to cuase any damage to the them. This fault occurs intermittently and only while driving.

First sharp acceleration (363/5)

During the first sharp acceleration we could see on the primary ignition signal, increased resistance in the probably reduced wire gage. (BLUE trace "6" = connected directly to terminal #1 of the coil and the orange trace "3" = connected to the ECU pin #19). On the secondary ignition trace (RED trace "2" = kV) we can see one double ignition with a mild popback into intake. The green CMP signal "5" and yellow ignition coil voltage feed "4" show no fault.

Major vehicle buck (363/6)

We stopped the scope recording during the first erratic shifting to lower gear and a major buck. We could now see the problem quite clearly. The ignition signals dropped out as the result of another fault (they were not the primary cause). The cause was a CKP signal drop out (BROWN trace "1" at the top). From the voltage line we can judge, that there is a short to power either somewhere in the harness, or inside the Hall sensor itself. We are suspecting the wiring because when the vehicle is driven over bumps and the engine moves on its mounts the fault appears every fifth attempt.

No faults at idle (363/7)

After the vehicle stopped and the engine was at idle the fault didn't appear. On the 0 V line (the bottom line) we can see that the trace line is disturbed. This is typical for an insulation failure and a short to voltage. The voltage value between the group of 4 amplitudes and invidual amplitudes doesn't stay at 0 V but oscillates above this level. Browsing back through the scope memory to a recording under load we could reveal intermittent shorts to voltage (5 V).

CKP sensor fault (363/8)

CKP sensor fault (RED trace) influenced decisions about ignition firing. The ECM based on CKP sensor signal decided even to fire at the wrong time. The TCM shifted gears using the ECM information and thus the erratic shifting...