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Boost Problems

artemk93

artemk93

Ready to race!
I have APR K04 kit with the latest tune. Recently I've noticed a problem with hitting specified boost levels before 4k rpm.
It feels and sounds as if the diverter valve constantly opens and closes so I can't hit the specified levels. On the boost gauge the needle tingles at the same position, but everything seems fine after 4k.
I've recently changed the diverter valve, so that can't be the problem.

I don't think it is a boost leak, since I see standard boost readings after 4k.
But I don't know what else could be causing the problem.

I've attached an excel file with the log, and highlighted the the 3rd gear pull.

Link for logs:
https://www.dropbox.com/s/whye87n6qnjcima/BoostLog.xlsx?dl=0

Link for screenshot of APR Mobile:
https://www.dropbox.com/s/0sx12sjn4oip2nl/unnamed.jpg?dl=0

Would appreciate any help or input
 
F

FriggenT1

Banned
artemk93 said:
No issues at idle. Checked the pcv using the dipstick method. Pulled it out and the idle became rough, thus the pcv should be fine
Click to expand...

Should be, you never know with those things sometimes though. I don't know if that is an absolute positive test for a pcv. Anyway though, so what happens on a 4th gear pull from say 2500-6500? Same type of problem?
 
artemk93

artemk93

Ready to race!
FriggenT said:
Should be, you never know with those things sometimes though. I don't know if that is an absolute positive test for a pcv. Anyway though, so what happens on a 4th gear pull from say 2500-6500? Same type of problem?
Click to expand...

same thing, logs for 4th gear vs 3rd gear look pretty much identical
 
F

FriggenT1

Banned
artemk93 said:
I guess it could be a faulty n75, but I assumed the car would run messed up at any revs
Click to expand...

I'm simply throwing ideas out there right now. I'm not sure how often the n75 goes bad honestly. I would check every connection though, especially at the turbo to top since oil can get on there and cause the hose to slip a bit. A small leak might be more pronounced at less psi anyway since the air at higher boost is moving faster and thus the ecu may compensate by upping the WGDC
 
artemk93

artemk93

Ready to race!
FriggenT said:
I'm simply throwing ideas out there right now. I'm not sure how often the n75 goes bad honestly. I would check every connection though, especially at the turbo to top since oil can get on there and cause the hose to slip a bit. A small leak might be more pronounced at less psi anyway since the air at higher boost is moving faster and thus the ecu may compensate by upping the WGDC
Click to expand...
Yeah, I'll try to check it out sometime this week.
 
L

lilfleck

Go Kart Champion
Can you elaborate a little more? Maybe take a video?

APR limits the boost below 4k RPM purposely to reduce air surging back into the turbo.
 
pashley

pashley

Ready to race!
This happened to my ko4 with latest tune as well. Sounds like exact same symptoms I had. Turned out to be a broken N75. I'm willing to bet this is the problem. From what I gather on the forums and from the guys at my shop this is not uncommon as the n75 is sort of cheaply made.
 
artemk93

artemk93

Ready to race!
lilfleck said:
Can you elaborate a little more? Maybe take a video?

APR limits the boost below 4k RPM purposely to reduce air surging back into the turbo.
Click to expand...

I'll try to take the video today. I know that APR limits the boost, and I had their 3.1 tune since it came out, and never had any problems until recently. I also have older logs and you can see a difference in boost behaviour from 2k-4k vs the log that I have posted.
 
artemk93

artemk93

Ready to race!
pashley said:
This happened to my ko4 with latest tune as well. Sounds like exact same symptoms I had. Turned out to be a broken N75. I'm willing to bet this is the problem. From what I gather on the forums and from the guys at my shop this is not uncommon as the n75 is sort of cheaply made.
Click to expand...

I just ordered one. Even if I find a boost leak, N75 is pretty cheap, and ECS has free shipping today.
 
F

FriggenT1

Banned
pashley said:
This happened to my ko4 with latest tune as well. Sounds like exact same symptoms I had. Turned out to be a broken N75. I'm willing to bet this is the problem. From what I gather on the forums and from the guys at my shop this is not uncommon as the n75 is sort of cheaply made.
Click to expand...

A vw part? Cheaply made? Noooo lol. Yes, the overall car is very well designed with a great engine, tranny, interior, but the small parts they skimp out on, which is why imo they are relatively inexpensive, but a pita to replace. An n75 isn't easy to get to to switch out, in my experience at least.
 
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