My '95 150K Passat always used to start instantly from cold, as soon as glow plug light had gone out, Now suddenly turns over & over & over before kicking into life in cloud of white smoke, then runs fine, and always starts well when hot. Suspect the glow plugs, don't know when they were last changed, certainly 40K+. I can feel relay clicking when ignition on & off, and appear to have power at glow plug feed. I have removed one plug and appears in good order, lightly sooted but cleaned up easily. (Haven't tried the rest yet because they are awkward to get at!)
Presumably ALL the glow plugs must have failed to prevent it starting ? Have they been failing one at a time and I've only noticed when the last one went ? What tests can I do to check the plugs ? Presumably there should be continuity between the centre terminal and the threaded body ? If I connect one up to a spare battery (briefly!) presumably it should warm up if sound ?
Any advice or alternative suggestions appreciated.
Edited by Pugugly {P} on 12/01/2008 at 20:38
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someone will be along to ask you what the engine code is soon, such as afu, akn etc.
if you've got the plug out test it by putting a jump lead on the end of it and the other on the positive battery terminal. then touch the body of the plug on the negative terminal and the plug should quickly glow red.
but anyway id hazard a guess at a coolant temp sensor fault if the plugs are fine as i used to get a similer issue with my a4 tdi
chris
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It's an AAZ ! I did try connecting it to a battery & Zilch! So I suspect at least that one is duff. I'll check the sensor as well just in case. Many Thanks
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The temperature sensor simply allows the glow plug switch on time to be shortened when the engine is hot, as the glow plugs aren't required so much on a hot engine. Disconnecting the sensor should revert the system to thinking the engine's cold, and the glow plugs will stay on for longer when hot.
Although it is possible it's quite unlikely that the temp sensor has failed......
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Nearly all indirect injection diesels need glow plugs to start from cold. This is because diesel fuel does not vapourise at low temperature, and therefore the combustion chamber needs to be preheated to enable it to do so. The intake air needs to reach around 500 degrees Celsius for diesel fuel vapour to ignite.
One glow plug out and the engine will almost certainly misfire from cold. If all four have failed the engine will be very difficult to start at best.
Rather than remove the glow plugs, isolate them and using a multi-meter check the resistance of each of them in turn by connecting your red probe/clip to the glow plug terminal, and the black probe/clip to battery negative. They should each read somewhere around 2 ohms or less. If any are very high resistance or open circuit they need to be replaced, but it is usually good practice to replace them all in any case.....
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Also use a test lamp to make sure you have a feed to the glow plugs when the ignition is switched on. If you have no feed then the glow plug relay/fuse/wiring connectors may be the problem. To confirm try a test by placing a direct feed from battery positive to the glow plugs and see if it starts better. Be warned though that working glow plugs pull about 20 amps each, and so the jump wire you're using will get hot. If it does start easier then at least you know what you're looking for.......
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If you do put a live feed to the plugs count 4 seconds then take the wire off not to burn the end of the glow plug off!
As said if all are ok it will fire up.
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