Full Car Log Analysis Request - Need Help Identifying Potential Issues

[AceD909]

Hello everyone,

I’m reaching out for some help in analyzing my car's full log, specifically regarding an issue I’ve been facing. My car is running with the MAF unplugged, and when the MAF is connected, the boost is limited to around 0.5 bar. I don’t have access to diagnostics to check it with the MAF plugged in at the moment, but I did log it a couple of months ago and saw that the MAF is reading a max of 143 g/s.

Here’s what I’ve observed:

• The car runs fine with the MAF unplugged, but when I connect it, the boost doesn’t go above 0.5 bar.
• I’m concerned there might be a sensor issue, intake leak, or something else causing this behavior.

I’ve attached the full log in a zip file (since the site doesn’t allow me to post CSVs). I’d appreciate any suggestions or feedback from those who might have encountered similar issues. Could someone take a look and let me know if anything stands out or what areas might need further inspection?

Thank you in advance for your help!
The file is csv but t

Seat Leon Cupra R BAM 2004

 

[Battoussai]

Hi there.
Have you tried another genuine MAF (like Bosch) to see if the result is the same?

Regards.

 

[Alexis27]

If you unplug the N75 you also get the capped PSI. Had you had a look at that?

 

[mty12345]

Unplugging the MAF disables closed loop mode and forces the car to run open loop mode without the O2 sensors and fuel trims etc. You're removing a lot of the safety net that avoids damage to the engine!! There could be a boost leak or fuelling problem casuing the car to run lean etc, and without the O2 sensors working there is no way for the engine to protect itself. I wouldn't advise driving it hard until you get the codes read. Just a guessing game without them, but first thing i would do is check for boost leaks.

Nothing obviously stands out from the log, although it does look like it's pulling a fair bit of timing? Are you running it on 99octane?
143g/s does seem slightly low, usually it's horsepower x 0.8, so for 225 HP you;d normally expect around 180g/s, but that could be affected by throttle position or not reaching the rev limiter. I certainly wouldn't condem the MAF based on that reading alone,.

 

[AceD909]

Hi there,

I did try unplugging the N75, and I was getting a capped boost of 0.3 bar, which seems to confirm that unplugging it results in the same capped PSI.

Regarding the MAF, I understand that unplugging it forces the car into open-loop mode, disabling O2 sensors, fuel trims, and other safety measures. I definitely don’t plan on pushing the car hard without proper diagnostics. At this point, I don't suspect a major fuelling issue, but I’ll check for any potential problems.

As for boost leaks, I had previously resolved some a couple of months ago and checked again today. There are no leaks on any hoses based on both a smoke test and a pressure test. However, I did notice some smoke coming from the inlet pipe, possibly near the turbo clamp, so I’ll investigate that further.

I’ve also been consistently running 99-octane fuel. The MAF reading does seem slightly low at 143 g/s, but since that can be influenced by throttle position or not hitting the rev limiter, I wouldn’t rule it out just yet. I haven't tried another MAF, but I’ll consider testing with a genuine Bosch unit to compare results.

Let me know if you have any other suggestions.

Also here is vcds log from couple months ago with plugged maf.

1.8t Bam low boost problem

youtube.com

Regards.

 

[mty12345]

I did notice some smoke coming from the inlet pipe, possibly near the turbo clamp, so I’ll investigate that further.

If you have a leak there, that would explain your low MAF readings, and probably cause it to go into limp mode if it's a substantial leak too.

Would definitely start there and if not then get the codes read.

 

[AceD909]

If you have a leak there, that would explain your low MAF readings, and probably cause it to go into limp mode if it's a substantial leak too.

Would definitely start there and if not then get the codes read.

Yeah, just too hard to find an intake hose for BAM in my country.

I have VCDS and check for codes all the time, but nothing too special.

Here is the list:

17526/P1118/004376 - Oxygen (Lambda) Sensor Heating; B1 S2: Open Circuit.

And

17522/P1114 - Oxygen (Lambda) Sensor; B1 S2: Internal Resistance too High.

The cat was removed and I didn't disable it.

17863/P1455 - Exhaust Gas Temp Sensor 1 (G235): Implausible Signal.

When I did the turbo rebuild, there wasn't a hole in the housing for the EGT, and I left it unplugged.

17608/P1200/004608 - Boost Pressure Control Valve (N249): Mechanical Malfunction. This was bypassed.

17705/P1297/004759 - Pressure Drop between Turbo and Throttle Valve (check D.V.!). Only when MAF is connected, but it doesn’t appear always.

 

[mty12345]

The O2 sensor won't cause an issue other than a check engine light, as it is only the second sensor (S2)

Running without an Exhaust Gas Temp Sensor will definitely cause limp mode, that's probably the main issue. Unplugging the MAF probably disables it along with all the other stuff like fuel trims........ Boost without an EGT = high risk of engine damage, hence limp mode.

Code 17705 is usually set on mapped cars in the winter, causes limp mode but cycling ignition clears it.

 

[AceD909]

The O2 sensor won't cause an issue other than a check engine light, as it is only the second sensor (S2)

Running without an Exhaust Gas Temp Sensor will definitely cause limp mode, that's probably the main issue. Unplugging the MAF probably disables it along with all the other stuff like fuel trims........ Boost without an EGT = high risk of engine damage, hence limp mode.

Code 17705 is usually set on mapped cars in the winter, causes limp mode but cycling ignition clears it.

I have the car for more than 5 years and the EGT was not plugged even when i first got the car but i never had problems.
Is there way to install it near the turbo in the downpipe or somewhere close to get good readings

 

[mty12345]

I have the car for more than 5 years and the EGT was not plugged even when i first got the car but i never had problems.
Is there way to install it near the turbo in the downpipe or somewhere close to get good readings

Maybe someone has mapped it out, but if that's the case then i wouldn't expect to see a fault code? Doesn't really make much sense to me, but with modded stuff anything is possible.

Other than 17705 which only sets from cold start, EGT is the only thing in that list that would cause limp. Delete all codes and rescan it when it goes into limp. Maybe that will point you in the right direction.

No, the EGT needs to be in the turbo housing, most of the heat is lost by the time it reaches the downpipe, readings would be a mile off.

 

[AceD909]

Maybe someone has mapped it out, but if that's the case then i wouldn't expect to see a fault code? Doesn't really make much sense to me, but with modded stuff anything is possible.

Other than 17705 which only sets from cold start, EGT is the only thing in that list that would cause limp. Delete all codes and rescan it when it goes into limp. Maybe that will point you in the right direction.

No, the EGT needs to be in the turbo housing, most of the heat is lost by the time it reaches the downpipe, readings would be a mile off.

Yeah i will try to read codes after limp mode but even i with limp mode scan i haven't seen anything related before and this codes appear after couple of days driving and the egt is intermittent fault code.
I will go for drive, clear codes and if car goes to limp mode i will scan it and post the codes.
Also i will check if it possible to install the EGT back to the turbo but im pretty sure there wasn't hole for it.
If possible to install it back i hope it works still after more than 6 years left hanging

 

[mty12345]

If it's plugged in but it's just hanging, maybe the wire has become broken or melted and is shorting together and causing it to think the EGT is overheating? I would have expected to set a code if it wasn't within a certain temp range, but it's possible the ECU is only looking for high EGTs and otherwise doesn't care if it's stone cold. Given it's an old system that may well be the case. That's the only thing that makes any sense to me and would explain why you could drive it previously but not now.
Still be better with it in there for safety, but if there is no hole for it then not much else you can do.

 

[AceD909]

If it's plugged in but it's just hanging, maybe the wire has become broken or melted and is shorting together and causing it to think the EGT is overheating? I would have expected to set a code if it wasn't within a certain temp range, but it's possible the ECU is only looking for high EGTs and otherwise doesn't care if it's stone cold. Given it's an old system that may well be the case. That's the only thing that makes any sense to me and would explain why you could drive it previously but not now.
Still be better with it in there for safety, but if there is no hole for it then not much else you can do.

I will check the EGT wires for damages and see if possible to install it back.

If not i will drill the housing .. Just kidding i will talk to my turbo repair centar if they can sort it somehow.

I could try to do logs again with MAF connected and also i will check EGT readings in vcds.
Even when the car was perfect holding 0.9bar boost i didn't have any limp mode or anything.
But now it doesnt even peak boost more than 0.7bar which drops 0.5 or less all the time even after codes are cleared.

Thank you buddy for your time and trying to help me.. I will post logs late in the night so i hope we will found the cause.

 

[mty12345]

I will check the EGT wires for damages and see if possible to install it back.

If not i will drill the housing .. Just kidding i will talk to my turbo repair centar if they can sort it somehow.

I could try to do logs again with MAF connected and also i will check EGT readings in vcds.
Even when the car was perfect holding 0.9bar boost i didn't have any limp mode or anything.
But now it doesnt even peak boost more than 0.7bar which drops 0.5 or less all the time even after codes are cleared.

Thank you buddy for your time and trying to help me.. I will post logs late in the night so i hope we will found the cause.

No worries mate.

 

[AceD909]

No worries mate.

You were completely right about the EGT causing limp mode. On my first pull, it triggered limp mode, and when I checked the codes, there it was—the EGT-related fault.

I’ll see if it's possible to reinstall the EGT sensor, but if not, is there a software way to remove it properly, or would it be better to get a new housing and rebuild the turbo again?

Also, if anyone knows a good tuner who can handle this properly, let me know.

On top of that, I’ll be fixing the intake hose to stop the unmetered air from entering the turbo, which should help improve performance.

Here’s a log file with the MAF plugged in.

 

[mty12345]

Glad to hear that you have some data that's pointing you in the right direction mate.

Looking at your logs, the air/fuel mixture is going crazy rich under acceleration. If you look at columns J and K in your logs, you can see lambda requested vs the actual lambda. Because the ECU is seeing high EGTs, it's making the mixture richer and richer, trying hard to bring the temps back down. (HIgh EGTs are usually the result of a lean mixture)
Nomally you'd expect to see lambda in the high 0.7 range under wide open throttle, but your requested lambda is going way into the 6's. In fact it goes so rich that it seems your the lambda sensor maxes out and get pinned @0.750001. That's probably when the ECU sets the fault code. With a mixture that rich you aren't going to blow the engine up, but you will probably get misfires and possibly start fouling the spark plugs etc too.

Someone with the right tools and knowledge could probably map the EGT out, but I wouldn't recomend it. You may get away with it depending on the tune, but it would be far better to have it fitted if possible.

A machine shop maybe able to tap a hole for it to fit in your new turbo, but obviously it depends on the design and difficulty of doing it. You'd have to speak to a specialist turbo place really, see what they think. They may have dealt with similar issues before

 

[AceD909]

Glad to hear that you have some data that's pointing you in the right direction mate.

Looking at your logs, the air/fuel mixture is going crazy rich under acceleration. If you look at columns J and K in your logs, you can see lambda requested vs the actual lambda. Because the ECU is seeing high EGTs, it's making the mixture richer and richer, trying hard to bring the temps back down. (HIgh EGTs are usually the result of a lean mixture)
Nomally you'd expect to see lambda in the high 0.7 range under wide open throttle, but your requested lambda is going way into the 6's. In fact it goes so rich that it seems your the lambda sensor maxes out and get pinned @0.750001. That's probably when the ECU sets the fault code. With a mixture that rich you aren't going to blow the engine up, but you will probably get misfires and possibly start fouling the spark plugs etc too.

Someone with the right tools and knowledge could probably map the EGT out, but I wouldn't recomend it. You may get away with it depending on the tune, but it would be far better to have it fitted if possible.

A machine shop maybe able to tap a hole for it to fit in your new turbo, but obviously it depends on the design and difficulty of doing it. You'd have to speak to a specialist turbo place really, see what they think. They may have dealt with similar issues before

The best approach is to try fitting it back into place first.

I’ve already spoken with a reputable tuning company in Greece, and they confirmed that we can disable the EGT and O2 sensors. They also offered a Stage 1 map for 155 euros.

Before proceeding with that, I’ll first try to reinstall the EGT sensor and fix the intake hose.

Since I can't find the hose locally, my only option is to order from AliExpress. Getting one from Badger5 or another high-quality brand would be too expensive—£126 plus £70 for shipping, plus customs fees on top of that.

This one looks like decent quality:

I just found this on AliExpress: Fit Audi S3 A3 TT Leon Cupra R BAM AMK 225 1.8T Silicone Turbo Intake Inlet Hose

Fit Audi S3 A3 TT Leon Cupra R BAM AMK 225 1.8T Silicone Turbo Intake Inlet Hose - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

a.aliexpress.com

What do you think?

 

[mty12345]

Not sure on the hose mate. I've heard that some of the cheaper ones have poor fitment, hence why most people say to use the badger5 one, but i've never used either myself. Maybe start a new thread about it? Some of the other lads may have tried them.

 

[AceD909]

Not sure on the hose mate. I've heard that some of the cheaper ones have poor fitment, hence why most people say to use the badger5 one, but i've never used either myself. Maybe start a new thread about it? Some of the other lads may have tried them.

Ok mate thank you again i will see what i can do for the weekend.
I hope i will fit the EGT and fix a lot of problems

 

[mty12345]

Ok mate thank you again i will see what i can do for the weekend.
I hope i will fit the EGT and fix a lot of problems

No worries mate, good luck. Let me know how you get on.