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Sorry if this is a dunce question ;D My glow plug light only comes on if it's really cold (the weather I mean) and only on the first start of the day. In 'normal' temps and if the car has been run at all that day it doesn't come on. Consequently it has to turn over for ages before it catches (but then runs fine). This is tedious, but at least proves my battery & alternator are good  So, what tells the glow plugs they're needed? Is it the plugs themselves or is there a temp sensor somewhere? Or am I barking up completely the wrong tree (re. starting problem) anyway? It's an Audi 80 1.9 TDi by the way..  Thanks! |
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you can test to see if the plugs them selves are each working by just testing with a multimeter, they should be 12v when activated.
they do run off a temp sensor, that is in the plastic flange onto the head(normally on vw/audi's)
once the cars slightly warm they shudnt be needed.
my caddy was a pain to start when warm, without the glow plugs, my simple mod was get another sender plug that in instead and take it out of the way, so now they turn on everytime with the ignition and starts up instantly. bit of a bodge but works perfectly.
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12 volts only tells you if they're getting battery voltage. To test if they're working you need to measure the current draw. Most plugs will draw 16 to 18 amps from cold and drop down to around ten before the relay cuts out. And yes, most cars rely on coolant temp signal to activate glow plugs,
If your having to crank the engine loads to start it then the chances are its more likely fuel running back or air getting in the system.
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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Hang on, this sounds familiar. If I'm reading it right, your glowplug light comes on, and stays on while cranking (which can go on a while...) and goes out as the engine catches? Also, when it isn't lit the car starts on the button. I've had exactly this fault on a TDi octavia and it was nothing to do with the glowplugs. A customer of mine got the car cheap, because of the occasional starting problem - it had been to several auto-electrics places and had glowplugs changed and a bunch of other stuff looked at, everything seemed fine, no faults found. Except... it gradually got worse, some days it would not go at all (glowplug light lit) and others was fine all day (light off) until one time I had to recover it from a car park as a total non runner. A bit of multimeter action found that one of the fused "engine control" circuits was getting no power, so I traced it back to a relay under the dash. As I fumbled for the relay, the glowplug light went out..... Quick turn of the key, car is running. The relay had a dry joint inside, which was contracting in cold weather and breaking the circuit. VAG group "glow plug" lamps actually indicate an engine management fault  Might not be that, but next time the light is on, check for 12v both sides of the engine control fuses. |
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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Now that's well worth remembering.
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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bl1300
Posted a lot
Posts: 1,678
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Glow plug light is sometimes shared with the engine management light. When I test glow plugs I remove them and connect them direct to a battery with jump leads if they glow red they are ok if they don't there goosed. Provided of course the battery is charged.
How old is the Audi I think id plug in a code reader and see if it picks up any fault codes.
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Current fleet.
1967 DAF 44
1974 VW Beetle 1303s
1975 Triumph Spitfire MkIV
1988 VW LT45 Beavertail
1998 Volvo V70 2.5
1959 Fordson Dexta
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Scary, that (weird fault!) is kinda the other way around..! My glow plug light very rarely comes on at all, and only ever on the coldest of mornings. If the weather is mild (or just a bit cold) or the car has been used, then light doesn't come on at all.. It cranks for ages, then starts & drives fine. Weirdigans!
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Ah, I see what you mean. Never mind, it was an interesting fault! BL1300, that's a good way to set stuff on fire  |
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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If you start it then switch it off and try to start it again immediately does it still have to crank or will it fire straight away?
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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I can't recall a specific time where I have done that Rev., so shall try it when I leave work and report back! |
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bl1300
Posted a lot
Posts: 1,678
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Ah, I see what you mean. Never mind, it was an interesting fault! BL1300, that's a good way to set stuff on fire Only if your not carefull. Hold it in vicegrips to test and don't put it down till it stops glowing |
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Current fleet.
1967 DAF 44
1974 VW Beetle 1303s
1975 Triumph Spitfire MkIV
1988 VW LT45 Beavertail
1998 Volvo V70 2.5
1959 Fordson Dexta
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An interesting method but I can test a complete set if plugs with a multimeter in less time than it takes to remove one.
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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Ok, just leaving work, it's quite cold but not bitter, no glow plug light, turned over for a few seconds then fired up & ticked over fine. Turned it off, tried again, no glowplug light, turned over briefly (maybe once) then fired up.. No idea what all this means..  |
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Well we've just ruled out pump timing.
When the light does come on does it start easily or is it still a pig?
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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Well we've just ruled out pump timing. Oh really? Cool! When the light does come on does it start easily or is it still a pig? No noticable difference to be honest - it doesn't stay on for very long, but I'm not exactly sure what to expect..?  I've just driven home (45ish minutes) turned it off & back on again, it started up the same as it did when I left (the 2nd time I mean, after I turned it off & back on again) -basically 1 turn & vroom.. |
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I think you could have fuel running backp or a bit of air getting into the system from somewhere. These kind of faults can be an absolute  to find though. I'd start with a new fuel filter though, and get a decent one if you can. You wouldn't believe the amount of problems a cheap filter can cause on some diesel. |
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R.S. Autotech. Servicing/Repairs/Diagnostics.
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I agree. sounds more like a fuel leaking back problem. It's sometimes worth changing the filter to pump line with a piece of clear pipe while testing - you can see the bubbles! also +1 on cheap filters, with a side order of nipped o ring |
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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insig
Part of things
Posts: 32
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When I test glow plugs I remove them and connect them direct to a battery with jump leads if they glow red they are ok if they don't there goosed. Not a good way to test the glow plugs in some of the modern VW engines. They are designed to work fom a pulsed lower voltage, whacking 12 Volts across them make them melt. |
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it doesnt really sound like a air leak he says the glow plug light rarely comes on.
simple test, first thing when its cold if the glow plug light doesnt come on, get a piece of thick wire run from the +ve on the battery onto the glow plug rail(jump lead will do if you can get it on easily), leave it on for atleast 15 secs then try start the car, if it starts up straight away its the glow plugs not been turned on.
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Brilliant, thanks Gents, very much appreciated! I shall change the filter & investigate the pipes on Sunday & report back! ;D
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