I recently posted about a flat spot at 3500 rpm. As it's gotten worse, I did what any idiot would do, I went to dyno it for a laugh.

 

The healthy looking curve in the dyno plot is not my car. The unhealthy one is.

 

I did some data logging too, and everything looks fine from the cars point of view, until it gets to 3500 rpm then it dumps all the fuel it can and pulls timing, but it doesn't pull back on the throttle.

 

I might be wrong, but the car seems quite torquey pre 3500 rpm so perhaps a stuck wastegate? Are these electronic ones? The previous owner spent the first 48,000 miles mostly off boost.

I just noticed, over 400 nm of torque, and I am 100% sure this car isn't mapped. 

 

No wonder it feels punchy at low RPM.

It is an electronic waste gate but that wouldn't really explain the fuel dump, those AFRs are pretty bad. What are the knock sensors and fuel trims doing? How is fuel pressure, high and low, looking? Any codes showing up at all on the scanner?

No codes at all! I'll go out and check fuel trims, I'm not sure I can see knock in my app. 

 

I just threw new plugs in and I changed a coil pack that had melted to the Head but no change at all. 

 

It's coming on boost so strong, it shouldn't be that much torque that low down. 

Bad remap maybe?

 

Nope, car has definitely never been remapped, my dad owned it from new! 

 

7 hours ago, hobbes42 said:

Bad remap maybe?

 

 

What fuel do you use? Even on basic 95 octane it should be making 217bhp and quite a bit more on 99 octane Tesco Momentum. Torque is good though my 2017 Vrs245 running Shell V-Power produced 400nm standard at 2,600rpm, stage 1 map 467nm and stage 2 map 517nm for example.

The car had been run on 95 but it was on a second tank of vpower. Fuel alone wouldn't cause that massive drop in power / torque at 3500rpm

Cat converter blockage maybe? Just thinking out loud 🤪

Edited 29 September, 20205 yr by StealthRS245

Am I right in thinking the turbo has variable vanes? If they stuck in the low-rpm position. 

I don't think this turbo has variable geometry, and a blocked cat is a good idea but it wouldn't end up flowing ok at the end of the RPM.

 

My money is on wastegate. Maybe.

Bottom right graph..turbo psi all over the place......as been said before..wastegate sticky..VAG has had numerous problems across various engines of the pivot joint between the actuator rod & the turbo arm..& it either is too loose & rattles like crazy..or its too tight a fit & its sticks/seizes & cause the electronic servo actuator to FUBAR.....need to dismantle the joint/remove servo , then clean & grease using Loctite 1300C grease or VW "hot bolt paste"....

13 hours ago, fabdavrav said:

Bottom right graph..turbo psi all over the place......as been said before..wastegate sticky..VAG has had numerous problems across various engines of the pivot joint between the actuator rod & the turbo arm..& it either is too loose & rattles like crazy..or its too tight a fit & its sticks/seizes & cause the electronic servo actuator to FUBAR.....need to dismantle the joint/remove servo , then clean & grease using Loctite 1300C grease or VW "hot bolt paste"....

I agree with your theory but bottom left is boost pressure isn't it? I'm still not really sure what bottom right is 

1 hour ago, jon- said:

I agree with your theory but bottom left is boost pressure isn't it? I'm still not really sure what bottom right is 

 

one is boost called for the other is actual measured pressure I think.....anyway that bottom right one is up & down like mad... considering the bottom left one is fairly smooth....

It's titled turbo pressure control in the app so I was guessing maybe something to do with the waste gate control