Glow plugs

Decidiver

New Member
Insufficient time for glow plugs to operate correctly despite new plugs, plug relay and temperature sensor.
 
Might be worth explaining the issue you have, what have you done, what are you trying to do? Any error codes?
 
Might be worth explaining the issue you have, what have you done, what are you trying to do? Any error codes?
I have two Audi a2 tdi’s, one 75 the other 90ps. When comparing the length of time that the glow plugs are in operation via the dash lamp, the 90’s light goes off just after one second, while the 75 takes up to five seconds. Consequently the 90 sometimes fails to start at the first attempt. I have had the battery capacity tested - 95% efficient.
Changed the glow plugs (being aware of the 75 and 90 difference).
Changed the temperature sensor.
Changed the glow plug relay.
Concentrated on having a good earth by additional earth leads from the new starter motor, and cleaning main earth point and connections at rear of nearside front headlamp with new earth bolt.
In addition the crank shaft and cam shaft sensors have also been changed.
Once started the difference between models is quite remarkable which is expected, the engine providing lots of smooth and rapid acceleration when required.
I have owned the car for over two years and the glow plug lamp has always been the same. Having owned three Audi a2’s, this fault has only shown on my 90 version.
 
Can't say I had noticed how long the glow plug lamp stayed on so I just checked. All three of ours were on around 1-1½ seconds. Our three TDIs cover the three engine variations (ATL-90 and AMF/BHC-75).
I'd suggest it's your 75 which is displaying unusual glow plug illumination timing. Regardless, I suspect the glow plug lamp timing is likely a red herring as the glow plugs are not required for starting much of the year (I'm sure someone will be here with the temperature soon).
Occasional slow starting is more likely to be fuel starvation (not uncommon) caused by an air leak allowing fuel to drain away from the tandem pump. This will not be displayed in a scan.
Have you noticed the behaviour is more likely the longer you leave the car?
 
Hope this isn't a stupid comment, but I vaguely recall that there are 2 different glowplugs (voltage related? but getting the wrong one is a big problem). Not sure if this refers to early models as against later ones, or the 75 as against the 90.
 
Hope this isn't a stupid comment, but I vaguely recall that there are 2 different glowplugs (voltage related? but getting the wrong one is a big problem). Not sure if this refers to early models as against later ones, or the 75 as against the 90.
Not stupid at all though OP noted different glow plugs so guessing they are aware. I believe ATL uses 5 volt plugs and really should know as I have one reported failed on my 90.
 
Yes I am aware of the different glow plugs specifications for the 75 and 90 versions. I continue to believe that there is a problem with the length of time that my glow plugs are powered on the 90. It’s the same throughout the year, but on the 75, the light goes out immediately during the summer months, but takes up to around five seconds during the winter. I have driven diesel cars since 1981 so am quite aware of glow plug importance for starting the engine, and the automatic variation of glow plug operation throughout the year.
My appreciation to those that have taken an interest in my problem. If I cannot establish what is causing the problem, I could send the car for fault diagnosis with my local Audi garage at a cost of around £100. If found I would certainly advise all!
 
Just out of curiosity, if you spray the outside air temperature sensor with a freezing spray then try the glow plugs does the light then stay on longer? Have all the parts that have been changed for the ATL engine specifically?
 
I have looked at the Audi Workshop Manual, and under the checks for the glow plug circuit, it lists the following - j179 Audi glow plug period control unit.
Tomorrow I will check the number of the relay that has been replaced but it could be the glow plug relay, which is quite small in size, either a J52 or 471. So it looks as though the j179 unit is the one that could be faulty. If it is, it does not indicate a fault code on my car. To be continued.
 
If the glow control unit is receiving the wrong information or faulty that could be the reason for the short glow period.
 
Making progress. The relay number that has been replaced with a new item was the 471 relay. Looking at the Audi Workshop Manual, I cannot identify where the j179 glow plug period control unit is. I would think that this is the faulty unit. The 179 would feed the 471 to supply voltage to the heater plugs. Any a2 enthusiasts aware of where the 179 is, and it’s part number?
 
I think you'll find that the glow plug relay is J52, not J179. There's no timer relay, the plugs are self-regulating. J52 is found in the footwell on the 3-point relay carrier, position 1, next to the terminal. Position 3 is empty.

RAB
 
There's a reference to J179 for the ATL engine in this video @ 1.07:
I assume this is located in the relay carrier under the footwell as suggested by RAB.
 
Have inspected the footwell today. There are two relays as detailed in the video, the first nearest the terminal has the number 614 on its top. The second relay has 461 on the top. As advised earlier in this topic, the first relay, relay 1 was the one that was changed. Now when I picked up the relay from my local Audi garage, it was not the number (on the top) that I had established that I ordered, and requested that they check to see if it was the correct item (the original relay had 471 printed on its top). After about ten minutes checking, I was advised that the 614 relay was the superceeded relay. So according to the video, the original 471/614 relay must be the j179 relay.
While I was inspecting the footwell area, I took the two large fuses out to check their continuity (ok) but didn’t see the small one in between them. Will check it tomorrow. Many thanks to all who are taking an interest........!
 
The other elephant in the room is the coolant temperature sensor. As it has 2 circuits, one for the dash gauge and the other for the ECU. If the ECU side is misreading then that could also be reducing the glow duration and fuel map.
 
According to Elsawin, the ATL's glow plug relay is still a J52 and is in the same position. The Automatic Glow Period CU (J179) is next to it.

RAB
Well that has surprised me - the j179 is further away from they’re terminal marked 461. Will get in touch with local Audi garage and advise of any progress. Checked small fuse between the two large fuses and found ok.
 
Be aware that the J numbers and the numbers on the relays almost certainly won't be the same. Letters followed by two or three digits are components on their wiring diagrams. So 461 could be J179!

RAB
 
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