So, I have a 2003 C32 AMG that has been running into an overboosting issue recently. Everything was fine with the vehicle... then I blew out welds on my driver side cat and had to get it fix as it created a large exhaust leak. Took it to the exhaust shop, had cats gutted and added an xpipe. The same week prior and post, I was easy on the car and added fuel injection cleaner. Left the exhaust shop everything seemed fine... first time I got on it I was in 3rd and in the top of third 5000k+ I got P108 and random missfires. I have since changed the o2 sensors and added oil air seperator to no avail. I noticed all three breathers had cracks so I replaced 2 and added the separator to the large breather that goes to the intake ypipe. Also checked exhaust backpressure... all is good. Ordered new Map sensor, will get that replaced next week and check again.

Mods
Needswings DCAI
64mm clutched pully
SL55 Ypipe
NW pully saver kit + HD green belt
Colder plugs and blue spark plug wires(not sure brand)
larger Heat exchanger
Eurocharged headers? Not sure brand but not needswings.
​​​​​primary cat gut/
secondary cat delete/ added x pipe
res delete/stock muff
SAI delete
Tuned by unknown source

Also... the reason i changed both primary 02 sensors is O2 sensor 2(driver side?) Is locked at 99.2% in following photo. Voltage changes and is correct but the % never changes. O2 sensor 1 does fluctuate and seems normal. Codes thrown also listed. They are random missfires. Never same cylinders when code throws. I'm now not driving the car till I get this figured out. 29psi scared me seeing that. Talking with Vtech Gorgia hoping that he can help with a tune, but looking for help here first just in case

Codes
.



02 sensor stuck at 99.2%



29PSI

 

Really sounds like you have an exhaust back pressure problem with the timeline and fact that the only way to create more boost with this type of supercharger is to spin it faster.

 

That is exactly what I assumed... although I bought a boroscope and exhaust backpressure tester to ensure it wasnt not the issue. I check the exhaust and visually inspected with the boroscope and saw no clogging. So I went one step further and checked with an actual guage hooked up to the oxygen sensors(same places I boroscoped on both sides) and tested the backpressure. They didn't even hit 1psi. My exhaust only restriction is the stock muffler. Everything else is straight through.

Also... apparently that o2 sensor reading 99% on sensor 2 is normal? I will check my other 02 c32 and get its reading to verify.

 

I am at a loss then, i don’t think there is a way to control boost on these engines, so over boosting would just be some sort of restriction. I could be wrong, but it all seems fishy that you had a converter blow out and exhaust work done and nothing else.

 

that has been my thought the entire time.... I am going to open it up again today and check with boroscope. I am going to replace the map sensor incase it's bad or giving a false reading. But again.... everything happend right after exhaust work. Backpressure test on 2ndary o2 sensor showed 0 psi both sides. So that means it would have to be before the o2 sensors locations. Only thing before them is the cats that are gutted and headers. I will update in a few hours.

 

Update***
The 99.2% o2 reading is normal after verifying on my other C32. Still replaced the o2 sensors reguardless .




I went back and boroscoped a second time. Saw no restrictions and even went deep to the headers collector pipes (3 on each side) and could see them all right where they meet. I'm lost! Map sensor will be here this week. Once installed I will update again.

 

Vacuum leaks?

 

Update****

OK so a few things... I spoke with Rob at Needswings and he helped me a lot. He said its more than likely a leaking intercooler causing my symptoms.

Also... the second o2 sensor reading 99.2 is normal. i cerified on my other C32.

The overboosting # is also inaccurate. Probly normal as well as I used cheap obd program and it did not account for ambient and that's 14.9psi... so that's why it was reading so high. Actual was more like 15 and that's normal.

map sensor will have to be exact one and I'm not sure I got the right one... still need to verify as the map sensor is used when mapping and tuning so I can't just change it to a different one. I have to pull it and make sure I install the exact one, otherwise problems will occur. I will check what map sensor I have today or tomorrow and get it changed or order the one in need. I ordered a Bosch but Rob said I should get OEM at basically the same price.

I have since split the cooling system to see if the extra pressure from the main cooling system is encouraging the leak. Haven't gone full throttle yet but I might try it today and if I get the missfires...

going to verify I have zero vacuum leaks this week at my buddy's shop just as safe measure.

pretty sure Rob is correct. Still all seems very odd that I blew my cat, then had exhaust work, and now I have missfires. Bad timing I suppose.

pulled the things that say amg (peleniums?) Off and looked inside. Very little muck inside and it looks to me just to be oil from not having a catch can. Pulled them off both cars and my other stock c32 looked even worse but it has no issues. I expected a leaking intercooler to have more of a water oil mixture and it did not... was just sludge... wondering if I should have it tested to see if it has coolant in it?

I will update asap. Have a busy week at work so I will get to it when I can.