svoets Posted June 5 Report Share Posted June 5 Hello, I am working on a Audi A1 1.4 TFSI with engine code CAXA that has a link g4+ force GDI. I'm having trouble with lambda fault code 28. Usally this means that the ECU needs te be checked by Link but I know in this case what te cause is. The switched voltage line has major interference (screenshot of scope measurement down below). This causes all sorts of problems and of them is the lambda controller not working. The interference only occurs when the engine is running and is rpm dependent. I unplugged everything that matches those symptoms while the engine was running with no improvement. The engine runs smoothly with this problem (altough way too rich). In red you can see the constant voltage on Pin +14V bat and blue is the switched voltage. Quote Link to comment Share on other sites More sharing options...
Adamw Posted June 5 Report Share Posted June 5 When you say "switched voltage", I guess you are talking about pin A5? This looks like ignition coil dwell period to me, approx 5ms pulse every 30ms would be ~1000RPM on a 4 cyl, and the curve matches a typical coil current curve. So, possibly two issues - 1) main supply to ign relay is too small or there is other resistance somewhere. 2) Possibly too much dwell, I havent tested these "short coils", but the common vag coils typically only use around 1.6ms dwell for 8A, by 3.0ms they are pulling something like 25A. Quote Link to comment Share on other sites More sharing options...
svoets Posted June 5 Author Report Share Posted June 5 36 minutes ago, Adamw said: When you say "switched voltage", I guess you are talking about pin A5? This looks like ignition coil dwell period to me, approx 5ms pulse every 30ms would be ~1000RPM on a 4 cyl, and the curve matches a typical coil current curve. So, possibly two issues - 1) main supply to ign relay is too small or there is other resistance somewhere. 2) Possibly too much dwell, I havent tested these "short coils", but the common vag coils typically only use around 1.6ms dwell for 8A, by 3.0ms they are pulling something like 25A. So the setup on the ECU might be wrong or I need increase the amount of power that can be delivered to the coils? and yes switched voltage is pin A5 or as we call it line 15 Quote Link to comment Share on other sites More sharing options...
Adamw Posted June 5 Report Share Posted June 5 25 minutes ago, svoets said: So the setup on the ECU might be wrong or I need increase the amount of power that can be delivered to the coils? Most likely both, but certainly dwell looks to be over 5ms in that scope if that dip is caused by the coils. So check the dwell setting would be the first step then see how voltage looks with normal dwell. Quote Link to comment Share on other sites More sharing options...
svoets Posted June 5 Author Report Share Posted June 5 28 minutes ago, Adamw said: Most likely both, but certainly dwell looks to be over 5ms in that scope if that dip is caused by the coils. So check the dwell setting would be the first step then see how voltage looks with normal dwell. You were right about the coils being the problem. When I do a coil test this signal immediatly appears. I did a current measurment te see how much current it draws and it measures to 8amps, so within spec (see screenshot). I've uploaded my file aswell for you to check. Don't be to harsh on how porely it is configured because this is my first time doing this and I am working with someone elses mess. aangepaste versie.pclr Quote Link to comment Share on other sites More sharing options...
Adamw Posted June 5 Report Share Posted June 5 8A shouldnt cause this much voltage drop if the wiring is adequate. General wiring rules in efi wiring is to aim for <3% voltage drop, so this should be less than 0.5V. Not only will it upset other devices as you have found, but you will also have very weak ignition energy. Below is a scope trace of the 715 coil I found on the megasquirt forum from Jalai who is quite smart, I trust his test method. I think this is the same coil your engine would have, this one is pulling ~20A at 14V after 3ms dwell. It looks almost identical curve to the R8 coils I have tested, so I would start with about 1.6-1.8ms dwell and only increase if there is a misfire. But I would say there is a wiring issue that needs to be addressed first, I suspect voltage at the coil will be even lower than you see at ecu. Quote Link to comment Share on other sites More sharing options...
svoets Posted June 6 Author Report Share Posted June 6 9 hours ago, Adamw said: 8A shouldnt cause this much voltage drop if the wiring is adequate. General wiring rules in efi wiring is to aim for <3% voltage drop, so this should be less than 0.5V. Not only will it upset other devices as you have found, but you will also have very weak ignition energy. Below is a scope trace of the 715 coil I found on the megasquirt forum from Jalai who is quite smart, I trust his test method. I think this is the same coil your engine would have, this one is pulling ~20A at 14V after 3ms dwell. It looks almost identical curve to the R8 coils I have tested, so I would start with about 1.6-1.8ms dwell and only increase if there is a misfire. But I would say there is a wiring issue that needs to be addressed first, I suspect voltage at the coil will be even lower than you see at ecu. Dwell times were set at 8ms so I lowered these to the suggested value and this lowered the current to 8 amps while running. my first measurment I just had used the test button in link but now I started the car and it was drawing about 20 amps per coil. Second thing I found, the previous guy who worked on this car had placed a switch in the interior for what he tought was the main relay. But in reality it was the relay for the main power of the engine. So now with using this one and lowering dwell time the signal falls in this spec of <3% voltage drop. The only thing I need to fix is a sharp self indution spike. Quote Link to comment Share on other sites More sharing options...
Adamw Posted June 6 Report Share Posted June 6 3 hours ago, svoets said: The only thing I need to fix is a sharp self indution spike. The grounding of most VAG coils is quite unique. The metal "stalk" of the coil is designed to be the direct return path for the secondary voltage - so make sure the metal stalk touches the steel hex on the spark plug. I guess it should be ok since they are OEM coils in this case but something to confirm in case it has incorrect spark plugs fitted or something. Also make sure the 2 ground wires on each coil both go to the cylinder head, I have seen some documents incorrectly label one "ecu ground" so some users in the past have connected it to sensor ground or the main ECU ground. One is the high current ignitor ground and the other is the high voltage secondary ground (back up for the stalk). Quote Link to comment Share on other sites More sharing options...
svoets Posted June 6 Author Report Share Posted June 6 4 hours ago, Adamw said: The grounding of most VAG coils is quite unique. The metal "stalk" of the coil is designed to be the direct return path for the secondary voltage - so make sure the metal stalk touches the steel hex on the spark plug. I guess it should be ok since they are OEM coils in this case but something to confirm in case it has incorrect spark plugs fitted or something. Also make sure the 2 ground wires on each coil both go to the cylinder head, I have seen some documents incorrectly label one "ecu ground" so some users in the past have connected it to sensor ground or the main ECU ground. One is the high current ignitor ground and the other is the high voltage secondary ground (back up for the stalk). This all looks good on this car. I hooked up an Innovate LC-1 in the meantime en this one is not getting output either, but I am sure this is a different kind of problem Quote Link to comment Share on other sites More sharing options...
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