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Old 12-01-2012, 08:29 PM
Gibbmodoll Gibbmodoll is offline
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Location: Madley in Herefordshire Uk.
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Unhappy Hyundri Lantra DOHC no start, only when hot.

Hyundri Lantra DOHC no start, only when hot.


Where to start, well with it running ok it's hard to say what is wrong, but the fault is heat related.

The car is old on 1999 plate, it has a 16 way port, but we found we could not read, the engine light has never been on when running.

First thing is to see the car in a no start, the car has a cam and crank sensor and i can tell you this car wont start on just the cam sensor.


The cam sensor however is of the hall effect type (voltage to ground giving a square wave trace), the crank sensor however is not, there is an AC trace made by the speed of the crank, the more the speed the bigger the trace, if the resis: of this sensor is changed by the heat of the block and the higher the resis: is the lower the trace and if it becomes to high the sig: will no longer be seen by the ECU.


So we have to put this high on the list of things to check when the motor wont start.

The Customer has not said that the car cuts when running, only ever when restarted from hot.

When the motor is stopped the temp will rise, there is no water pump and no fan or air threw the grall, this is where a crank sensor will if faulty will go high resis:, or go open circ:, the speed of the flywheel is low at crank 200 - 300 RPM., the AC waveform is at it's low point, this is where in this case we look first, (the crank sensor).

Checking with the Customer and finding out how the fault IS being set and thinking about it is a good starting point.

After a time of running the motor, we stopped the car, and sure thing just as the Customer said the car would crank but not start.

First we checked the sig: output of the sensor and sure enough there was no sig: cranking and a resis test said that the sensor was in fact open.

Removing the sensor and cooling it under a tap and checking it's resis: made it go from fully open to 8k, and as it got evern cooler the sensor could in fact be refitted and the motor would restart agan.

Chacking a sensor like this one, form hot to cold and seeing a big resis: change can find a fault, look for it being close to the resis: when cold, say within 100 ohms.
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