over boosting and predetonation under boost. no codes

[steve07588]

Have a 2003 audi a4 with the 1.8t that is predetonation badly under boost. the engine is 100% stock but is spiking at 20 psi and holding at 14-18psi. no chip no codes. turbo is not oem. cheap ebay knock off. what would cause this? watse gate out of adjustment? bad n75 vlave bad diverter valve. someone point me in the right direction.


no overboost codes
no n75 short to ground codes
no codes at all.

[steve07588]

So I unplugged the n75 valve and took it for a drive only hitting 5psi now but it don't feel any slower then when I'm hitting 20psi. Any ideas

Sent from my SM-N920V using Audizine mobile app

[Kevin C]

FYI, it's going to hopefully be either pre-ignition or detonation. Predetonation would be really, really bad. https://en.wikipedia.org/wiki/Nuclea...#Predetonation

Predetonation

If two pieces of subcritical material are not brought together fast enough, nuclear predetonation can occur, whereby a smaller explosion than expected will blow the bulk of the material apart. See Fizzle (nuclear test)
Detonation of a nuclear weapon involves bringing fissile material into its optimal supercritical state very rapidly. During part of this process, the assembly is supercritical, but not yet in an optimal state for a chain reaction. Free neutrons, in particular from spontaneous fissions, can cause the device to undergo a preliminary chain reaction that destroys the fissile material before it is ready to produce a large explosion, which is known as predetonation.[13] To keep the probability of predetonation low, the duration of the non-optimal assembly period is minimized and fissile and other materials are used which have low spontaneous fission rates.

That's probably not going to happen in a 1.8T

It sounds like a stuck wastegate. Can you log the amount of ignition retard? Same with a boost request. I'm assuming that you're measuring the boost with a mechanical gauge?

[steve07588]

Ill havent logged anything yet but will today. and yes I'm using an mechanical gauge. if it were a stuck waste gate wouldn't it still over boost when I disconnected the n75 valve?

[steve07588]

Changed the n75 valve and still over boosting

Sent from my SM-N920V using Audizine mobile app

[old guy]

If I'm reading your first post correctly you are running a stock tune but spiking to 20 psi. If those are truly the conditions I would say you have a wastegate problem.

You can use an air nozzle and a pressure regulator to get an idea as to the cracking pressure of the wastegate. You can reach up behind the turbo and feel the wastegate actuator. Have someone slowly pressurize the wastegate hose and observe when you feel the actuator start to move. I suspect you are going to find it set way too tight.

[steve07588]

Thank you for the response "old guy" I will remove the turbo and set it to 3mm of preload and see what kind of boost I'm making then. I was thinking it could of been that but didn't want to waste the time of removing the turbo unless someone else also thought it was the problem. Thank you for the help

Sent from my SM-N920V using Audizine mobile app

[old guy]

Before you remove the turbo why don’t you check the cracking pressure? You can do it with the turbo in place. And then if/when you do have to adjust it I would recommend doing it by pressure rather than a preload distance measurement.

Good luck!

[steve07588]

Could you please explain how I would go about checking the cracking pressure and what it should be set at?

Sent from my SM-N920V using Audizine mobile app

[old guy]

You need a cold engine and you have to be a bit of a contortionist. Plus it helps to have a second pair of hands. Disconnect the boost signal line that connects the N75 to the wastegate from the N75 end of the line. You will need an air nozzle and a compressor with a decent air regulator.

Now comes the fun part. You have to reach behind the turbo and get your fingers on the wastgate actuator arm so you can feel when it begins to move. Using the air nozzle apply air to the wastegate hose as you slowly turn up the regulator. You should be able to feel movement between 5 and 6 psi for a stock OEM K03 turbo. If it takes significantly more to move the wastegate actuator you are going to have to pull the turbo.

The good part is that you can then adjust the wastegate on the bench before putting it back on.

Good luck!

[Kevin C]

So I unplugged the n75 valve and took it for a drive only hitting 5psi now but it don't feel any slower then when I'm hitting 20psi. Any ideas

Sent from my SM-N920V using Audizine mobile app

If he is is getting 5 PSI of boost with the N75 disconnected, it wold seem that his waste-gate is set correctly? Since the valve seems to do something, ( boost goes up when connected) the ecu would seem to be trying to do somthing. I'm also assuming that disconnecting the N75 he means that he unplugged the cable to it?

In my mind that leaves either its not getting the correct signal to modulate or that the control loop is so far off it cant. The control loop is the signal applied based on pressure readings vs the response from the system.

Things that could go wrong:

Bad pressure data (map sensor)
Bad programming (tuned ECU)
Leak in the control lines to the N75 and or the waste gate.
A leak in the waste gate that changes the response.
A sticking waste gate that changes the response.

Confusing is that the car feels the same at 20 psi and at 5 psi.

Comments?

[steve07588]

Yes I just unplugged the n75 with all the lines still in place. Lines were inspected and seem fine. Map sensor is brand new. Symptoms did not change with valve

Sent from my SM-N920V using Audizine mobile app

[old guy]

Oops! I missed the 5psi when unplugged.

[diagnosticator]

Someone got mixed up between Pre-ignition and Detonation both damaging combustion conditions in an engine. Detonation more so.

[old guy]

OK. Let me redeem myself from my previous crappy advice.

If you unplugged the N75 and boost held at 5psi that indicates two things. Your wastegate is set properly and the boost signal hoses from the high pressure port on the turbo to the N75 and from the N75 to the wastegate are intact. If they weren’t you would probably see a bit more than 5psi since the split in the hose would be dumping some of the boost signal to the wastegate. So now let’s figure out what is causing the over boost condition.

You mentioned that you can log ECM conditions. First at idle check the atmospheric pressure against the actual boost pressure reading. The actual boost reading should either match or be slightly less than the atmospheric reading. This will confirm that your MAP and BARO sensors are aligned.

Next log your N75 duty cycle along with the actual and requested boost. This will tell you if the N75 is calling for all that boost or if for some reason the turbo actual boost is overrunning the requested boost. Once you get that answer you will have narrowed down the possibilities.

And last but not least log the CF’s on all four cylinders to see if there is excessive timing pull.