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Discussion Starter #1
I was having some troubles with glow plug lights coming on and would have to cycle the car a bit until they came on so i decided put new glow plugs in. I just installed new bosch glow plugs and the ones i took out were burnt so i thought that was the culprit, I tried to start it after i put them in and nothing! not one time did the glow plugs go on. Am i missing something? Please Help
 

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Before the replacement, was the light coming on? Any other symptoms? What year is the car?
 

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Discussion Starter #3
It is a 2000 jetta tdi. The symptoms were that it was stuck in limp mode when the glow plug light wouldn't come on when you turned the key on the first time and once i cycled the key again the check engine light would go one and it was stuck in limp mode until a bit of driving , then it just got worse and the check engine light would never come off and sometime i would have to cycle the key 20-30 times before my glow plug light would come on.
 

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Did you ever scan the car for codes?
 

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Discussion Starter #5
i have but i cant remember what they were, I just cleaned out the harness a bit and after a couple cycles the car fired up. So it must be the harness then, Right? it still runs really rough like its miss firing, then it would make sense if harness failure correct?
 

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Yup. Get it scanned. And no, a harness failure shouldn't make it run rough. The glow plugs are off once the car is running. They aren't like spark plugs. Whatever is causing your car to run rough is probably the cause of the limp mode issue, which should be revealed by a code scan. Autozone, etc. can scan for free. Bring us back the code numbers (P####) not the descriptions, as those generic readers can interpret them wrong. The code numbers will help us help you figure out the root of the problem.
 

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The glow plugs aren't needed in warmer weather. On my 2003, the light would come on for less than 2 seconds for a cold start when the air temperature is above 60 degrees.

For a full 22 second glow plug warming, remove the coolant temp connector.

The ECM will think its −40 degrees. This will light the glow plugs for a full cycle.

This is a good way to test for power at each harness connector for each glow plug.
 

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As for your "No start" condition, do you have fuel? Did you remove the piping between the pump and injectors to replace the glow plugs?

To check for fuel, loosen the union and each injector 1/2 turn, then crank the motor. You should see fuel leaking from the loosened connection.

If not, could be a bad fuel cutoff switch on the injector pump, air in the lines, clogged filter, or possibly no fuel in the tank.

Diesels run on compression and fuel injected at the right time. The compression pressures are so high, that if there is air in the fuel lines, the fuel will not come out of the injectors, its held back by the high compression pressure generated by the engine.
 

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if you run out of fuel in a diesel, they really hate that. run some fuel through the injectors,bleed out all the air.the fuel lubricates the pump too.
 
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