Hey everyone, first time posting on this forum. I've seen a lot of forum threads similar to mine, but I think they have all resolved their issues yet I have not. I have a new problem with my car that I can't explain. I've done a fair amount of troubleshooting. I really need some advice because my car inspection is in a couple days and I apparently can't trust it to start when it's warm.
1) I've checked the error codes with a carsoft adapter.
1)A) There was an EWS error in german saying "key 1 not recognized" and I wasn't able to duplicate that with any of my three keys. I don't know which key is "key 1"
1)B) There was possibly an error for prefeed pressure to be too low. The problem is, the software didn't actually go out and tell me what that error was. I got DME/DDE error 4704, 256 and 4693 errors. None of which I could find information on. I don't know when these errors were logged. Maybe someone can point me in the right direction as to what these errors are. I found only one reference to 4704 being low pressure.
2) I checked the pressures and everything I could find on live data with the carsoft cable.
2)A) the prefeed pressure was between 3.6 and 3.8 bar depending on if it was full throttle at 3500 rpm or idle. Not much difference and the difference of 0.2 bar won't prevent it from starting. I found that by unplugging that pressure sensor (on the fuel filter) the computer reads 4.4 bar. Interesting that open circuit reads the maximum value it can read. So, I figured if I leave it unplugged it will always TRY to start even if it doesn't have sufficient fuel. The high pressure pump will pull a vacuum and then stall if there is something plugged or the electric fuel pump(s) aren't running. When it wasn't starting, the prefeed pressure was just fine with the key "on" and not running.
2)B) The high pressure rail was perfect. The requested versus actual pressure was within a couple percent even under transient conditions (sudden acceleration changes). It went up to 1380 bar and idle was something like 300 or something. All of the other live data values seemed normal.
3) I checked the fuel pump relays. I found there were 3 of the identical relays, so after popping open the covers I could see that they were all looking good. I swapped them all around in case there was a bad one somehow. No difference.
4) The battery is new. It is a very powerful Exide AGM battery and the charging system is good.
So, what it does is that it will just crank and not fire. It usually starts when it's cold but if I try to start it again later when it's warm, it might not. Several times, it cranked then instantly ran for 1-2 seconds then instantly stalled again with no stumbling or anything. It was as if I turned the key off.
I tried to verify if the cam position sensor works or not. Today, I tried unplugging it and it very strangely, it fired for several revolutions and then died again even without it plugged in. That doesn't make sense to me because it didn't do that even when plugged in. I ordered a new one to see if that will make any difference but I don't want to buy too many parts without knowing if they are bad or not.
The car has never stalled while running. I think that is an important point to make. Once it's running, it's not a problem.
Also, when I had the carsoft cable plugged in, I synchronized the EWS to the ECU computers thinking it might be a security/immobilizer problem but it made no difference.
Any help would be greatly appreciated! I have no idea what to check next or what to do. I've spent hours testing different theories and trying different things and I have no idea what the problem is.