1998 jetta tdi glow plugs not working

[Becar]

Hey i have a 1998 jetta tdi,,,glow plugs didnt work at all the light would come on for a second or two but there was no power going to them,,,first i replaced the glow plugs after testing them two of them were bad so i replaced all 4,,,second i replaced the coolant temp sensor,,,then i replaced both realeys,,,not i get the maximum time 20 sec plus with the coolant temp sensor unpluged before i wasnt getting that...NOW THE FUN PART: Here in mass its been in the 20s in the morning i go out turn the key on the light comes on for 5 to 8 seconds (with the temp sensor pluged in) the car starts just like it should,,, if the car warms up to operating temp after that it starts right up ( light comes on for a sec or two) NOW IF I LET THE CAR SIT FOR 2 TO 3 HOURS IN THIS TEMPERATURE AND THE GAUGE IS SHOWING THAT THE ENGINE IS COLD,,MY GLOW PLUGS COME ON FOR A SEC OR TWO AND THE CAR STARTS HARD,,Sometimes i have to unplug the temp sensor to start it,,, please help i dont know what could be,,, i said this was fun... thank you and if anyone knows a good tdi tech in western mass please let me know

 

[Alchemist]

It seems as if the glow plug system is working normally. It does come on and the car starts easily when it is cold. The trouble seems to be limited to cold weather when the engine is not completely cooled off. My suspicion is it is at the borderline temperature for glow plug operation, and something else is making it difficult to start. The most common cause of this sort of problem is injection timing being a bit retarded. If you can locate someone with VCDS, have them check the timing. I am pretty sure this will tell the tale.

Paul

 

[k_harley]

Both relay's? There should only be one, labelled "180"
Secondly, you didn't say anything about the fuse, its on top the fuse box, really big one, 80 amp iirc.

 

[KLXD]

Odd, if the CTS is still warm the block should be even warmer. Do as Paul suggests.

In this situation have you tried cycling the key after the plug light goes out for a little more preglow?

 

[98tdicolo]

It shouldn't need glow plugs to start if it is partly warmed up. You have another problem.

 

[Becar]

Both relay's? There should only be one, labelled "180"
Secondly, you didn't say anything about the fuse, its on top the fuse box, really big one, 80 amp iirc.

yes #180 and also the one on the firewall whatever you wanna call that... fuse is good since they work fine when the engine is cold,,,

 

[Becar]

Odd, if the CTS is still warm the block should be even warmer. Do as Paul suggests.

In this situation have you tried cycling the key after the plug light goes out for a little more preglow?

i have tried cycling the key and i belive that the GP dont even come on if the light comes on for a sec...but i have tryed that

 

[Alchemist]

The relay on the firewall is for the coolant glow plugs. They are used to help the engine warm up quicker after it is running, but have nothing to do with starting.

Paul

 

[Bearer]

I have similar issue with my 98 but opposite. Light comes on for a second when cold and damn near drain batty before it starts. Even unplugging the temp sensor, the light still only comes on for a millisecond. Replaced relay, glow plugs and temp sensor. Gave it to the shop and they think it's the brain. Ever hear of that?

 

[Lug_Nut]

(Gosh, I didn't recognize how old this thread originization was!)

Have you reviewed the A3/B4 glow plug sticky thread to see if the answers to your respective issues are there?

A3 / B4 glow plug relay and fuse location

The question of which fuse or relay is the one for the glow plugs won't go away. Perhaps this one thread will eliminate the 40 or 50 each year that ask the same question over and over. The fuse for the four cylinder glow plugs is located inside the cabin above the fuse and relay mounting block...

forums.tdiclub.com

Please post if there are differences between what your car has as electrical / relay equipment and its symptoms to what has been previously identified.
You might, after 25 years, have found previously unknown issues.

There's also a means of modifying (raising) the temperature at which glow plug operation becomes effective.

How To extend glow time with Vag-com - ALH

First and foremost....Big thanks to member Fred (samfisher) who did the experimenting to find this info out. This mod will help a lot of folks with cold start problems who cannot rectify them with a timing adjustment. Now as we all now, some cars have a difficult time starting when it is just...

forums.tdiclub.com

Low compression (normal engine ring wear after 25 years) can drop compression produced heat enough to necessitate more glow plug assist to ignite the fuel. The adaptation process described has been proven on the ALH, like in your Jetta.
Some of the TDI have two separate modules as coolant temperature sensors. Be sure that you are unplugging the sensor to the ECU and not disconnecting just the sensor to the dash temperature gauge.

 

[Bearer]

(Gosh, I didn't recognize how old this thread originization was!)

Have you reviewed the A3/B4 glow plug sticky thread to see if the answers to your respective issues are there?

A3 / B4 glow plug relay and fuse location

The question of which fuse or relay is the one for the glow plugs won't go away. Perhaps this one thread will eliminate the 40 or 50 each year that ask the same question over and over. The fuse for the four cylinder glow plugs is located inside the cabin above the fuse and relay mounting block...

forums.tdiclub.com

Please post if there are differences between what your car has as electrical / relay equipment and its symptoms to what has been previously identified.
You might, after 25 years, have found previously unknown issues.

There's also a means of modifying (raising) the temperature at which glow plug operation becomes effective.

How To extend glow time with Vag-com - ALH

First and foremost....Big thanks to member Fred (samfisher) who did the experimenting to find this info out. This mod will help a lot of folks with cold start problems who cannot rectify them with a timing adjustment. Now as we all now, some cars have a difficult time starting when it is just...

forums.tdiclub.com

Low compression (normal engine ring wear after 25 years) can drop compression produced heat enough to necessitate more glow plug assist to ignite the fuel. The adaptation process described has been proven on the ALH, like in your Jetta.
Some of the TDI have two separate modules as coolant temperature sensors. Be sure that you are unplugging the sensor to the ECU and not disconnecting just the sensor to the dash temperature gauge.

I did notice 2 modules for temp. I unplugged both and it didn't change the glow plug light time on dash. My jetta has less than 100,000 miles on it so I don't think it's the rings. The one thing I saw in the thread you posted was the hidden fuses in fa ecu picture. It says it's for 97 but my 98 always uses 97 parts. 98 parts are always wrong. So I'll check that out.

 

[Lug_Nut]

Be very careful and be aware that the "FA" is a Passat with a completely different harness. Just because the 96-7 B4 Passat and 97~99 A3 Jetta used identical molded fuse and relay blocks does NOT mean the relays are necessarily compatible. They can not be freely mixed into any other ECU or wiring harness. The wiring harnesses, ECU pinouts, and relays are matched sets. Be absolutely sure that you use Jetta images to compare to your Jetta.

The fuse for the glow plugs is not hidden on the A3. It is positioned above the glow plug relay as shown in the A3 image in that other thread.
The wiring circuit is different (97 A3 has relay first, then fuse, then glow plugs, while the 98 and 99 A3 has fuse first, then relay, then glow plugs), but the fuse physical position is the same on all years A3.