Lack of power and stuttering at high speed

[kieran_sly]

I bought a '98 Audi A3 a few months back. Although It ran alright the service history was vague so i decided to get it serviced and the cambelt changed.
All was good for a week but now when I pull away there is a severe lack of power and very big flat spot, then all of a sudden the car suddenly picks up. This happens mainly when cold but also when warm but not as severe. After the initial lack of power the car is fine.

Also on a dual carriageway it struggles to get above 55mph. stuttering and jerking and again lack of power. Under 50mph and around town the car is fine, just heavy on fuel.

I had the codes read and 00515 Hall sender - G40 open short circuit to positive came up. The Cam sensor has been changed but has made no difference. I havn't had the codes read since.

Any ideas?
Thanks

[Crasher]

You will have to get the codes read again to see what is stored.

[kieran_sly]

I took it to a local garage who changed the temp sensor and air flow sensor and this has seemed to fix the sysmptoms I mentioned, however a similar code (00515 hall sender G40 short circuit to earth) still comes up and the MPG is extremely poor at around 14mpg.

[Crasher]

What is your engine? I am guessing it is a 1.8 20v. If that code will not clear and the sensor is new, I suspect you have a wiring fault so the continuity of the wires needs to be checked for continuity

G40 plug pin 1 lilac/red to pin 62 of the ECU
G40 plug pin 2 lilac/yellow to pin 76 of the ECU
G40 plug pin 3 brown/blue to pin 67 of the ECU

Checking the Hall sensor

The Hall sensor indicates the ignition position for cylinder 1. If the Hall sensor fails to function, the knock control is switched off and the ignition timing is retarded slightly because the signals can no longer be assigned to the cylinders. Even without a signal from the Hall sensor, the engine will continue to run and can also be re started. When a fault is detected, the engine control unit produces one spark for each cylinder on every crankshaft revolution. The fact that the control unit is out of phase by one engine revolution does not have any noticeable effect on the injection system. If this happens, the fuel is injected "upstream" (before the closed inlet valve) instead of while the inlet valve is open. This has only a negligible influence on the quality of the air/fuel mixture.

Note on signal testing with an oscilloscope:

The centre point of the window of the Hall sensor must lie on the third trailing edge of the engine speed signal after the reference mark gap. Push back the rubber sleeve on the Hall sensor connector. Connect the V.A.G 1527 diode test lamp to contacts 1 and 2 on the Hall sensor connector from behind (the connector remains attached to the Hall sensor).

Note:
The connector contacts are numbered on the back of the connector.

Operate the starter for a few seconds. The diode test lamp must flash briefly on each second engine revolution. If the diode test lamp does not flash,
check the power supply for the Hall sensor.
Unplug the connector from the Hall sensor.
Switch on the ignition.

Connect the V.A.G 1526 hand held multimeter for voltage measurement contact

1 on the connector and the engine earth.
Specified value: 4,5 ... 5.5 V.

Checking the signal wire for Hall sensor
Connect the V.A.G 1526 hand held multimeter between contact 2 on the connector and the engine earth.
Specified value: approx battery voltage.

Checking the earth wire for the Hall sensor
Connect the V.A.G 1526 hand held multimeter for resistance measurement between contact 3 on the connector and the engine earth. Specified value: Continuity
If the specified values are all achieved and the diode test lamp does not flash (measured between contacts 1 and 2 with starter connector attached),
replace the Hall sensor. If the specified values are not achieved: Check the wiring between the Hall sensor and engine control unit

Connect the V.A.G 1598/22 test box to the wiring harness for the engine control unit

Check the wiring from the Hall sensor to the engine control unit for an open circuit and short to positive or earth.

3-pin connector on the wiring harness contact
Test box V.A.G 1598/22 contact
1 (positive)
62
2 (signal)
76
3 (earth)
67


If necessary, rectify open circuit or short circuit.
If a trial erasure of the fault memory is followed by the renewed indication of a fault relating to the camshaft sensor (Hall sensor) although all previous tests were OK, the following faults are possible:
Rotor ring for Hall sensor misaligned.
Unbolt the Hall sensor, then check to ensure that the rotor ring is
correctly aligned on the camshaft.(if it is incorrectly installed, the catch will be pressed flat

When the securing screw is tightened).
If the position of rotor ring is OK, check the position of the camshaft in relation to the cr

Note on signal testing with an oscilloscope:
The centre point of the window of the Hall sensor must lie on the third trailing edge of the engine speed signal after the reference mark gap crankshaft.