Looking for Help with an SBD 500 Kit that Keeps Overboosting
 

So I'm having some issues with a SBD 500X kit that I got a while back. I paid a local shop who is pretty well known for 86 tuning to have it and a Delicious tuning E85 kit installed and tuned and after a month of it being fiddled with and tweaked they couldn't figure it out. It runs fine below 5500 RPM, but around or above that it lurches and throws a check engine light from the MAP sensor. For some reason it's reading 24 lbs of boost even though the thing is only tuned for between 4 and 7 lbs. It doesn't feel like 24lbs of boost either. The guy at the shop said the MAP should max at 19 lbs, so it's weird that it's even able to read up to 24 lbs. They've swapped MAP sensors, MAF sensors, taken the boost controller out, supposedly swapped the waste gate, and every time it's still reading overboost. They brought Ecutek in and even they have no idea so far.

It's still tuned for 91 octane if that helps anything.

Thanks guys

What map sensor are you using? Are they scaling the map sensor correctly?

What injectors are you running? You are running E85 exclusively, right? You aren’t running 91 with 24psi, right? Post a log on Datazap and post here.

Did you try installing a boost gauge to independently confirm the boost?

Overboosting could happen if the wastegate never opens, but most tuners initiate a fuel/throttle cut slightly above target boost, just in case overboost or boostcreep happens, so I think it is odd that you are overboosting.

They swapped the fuel pump and injectors when I first brought it to them. To what exactly I'm not sure, I've since moved across the country. The MAP is stock. Don't have a boost gauge yet, but one is on order. It's supposed to be setup on 7lbs with 91. The e85 kit was installed as future proofing for when I get better internals later. Currently I think they said it's only down at 4lbs since they weren't able to tune it up to 7lbs.

Still trying to figure out how to get the data logs now lol

The stock MAP sensor can’t read past like 5-6psi of boost. If your tuner is tuning off the stock MAP sensor then that is a problem. Most likely they are tuning off the MAF sensor. If the tune is a hybrid tune that switches to the MAP sensor at high rpms or is purely off the MAP then that is likely the problem.

The stock MAP sensor is rated to read 1.67bar, which in absolute terms is 24psi, but that isn’t 24psi of boost because 1bar of that is atmosphere. It would be like 9psi of boost, but the sensor really can’t function well at the limits, so I believe it tops out around 5psi of boost or at 1.37bar (19.87 absolute psi) before it breaks up.

https://ecutek.zendesk.com/hc/en-gb/...sor-Re-scaling

You could be boost spiking past 7psi to the limit of the MAP sensor of 9psi, but breaking up past 5400rpms because the MAP sensor is being pushed beyond 5psi of boost that is too close to its limits to read well.

Either you are confused, or they don’t have much experience tuning this platform. Make sure they do know what they are doing, and buy a 3-4bar MAP sensor. I don’t know what you plan to make for power or plan to raise your boost to, but you always want to leave room away from the limit of the MAP sensor. You could buy a 1bar MAP sensor that reads up to 2bar absolute or 14.7psi of boost, but it really shouldn’t be pushed past 11psi, boost spikes considering, so just get a big MAP sensor and have them scale appropriately. That should fix your problems.

Yeah I'm new to boost so I'm just going off what they're telling me. I'm taking it to a new tuner sometime this week so hopefully they'll have some better insight into what's happening there. The guys I took it to before were recommended as the best Subie guys in the area, but :iono:

Copy and paste or screen capture what I said in an email to them, and see what they say.

Hmm seems unusual a tune shop tuning a turbo capable of 12psi boost or more would be using a stock map sensor that can only read 5 psi boost.


means no overboost and you dint know boost and it they are using speed density that wont work either


also no idea how they could runn boost controller unless its external and has its own boost reference

FA20's don't tune like any other Subie.

Hey sorry to necro this, but I got in touch with the tuner directly and made some progress, but we still have kinda the same problem. We swapped the MAP for a 3 bar omni sensor that seemed like it would work well and it did okay at first. I'm able to rev past 5500 RPM without throwing a check engine light and the car seeming to go in to limp mode like it did previously. Now, the check engine light comes on after revving to around 7k for a P0068 MAP/MAF Throttle Position Correlation. Last I heard from the tuner a couple hours ago was that the car seems to think that I'm putting out 21 lbs of boost somehow and that's causing all sorts of funky stuff to happen. Haven't heard anything from him since and it seems like we're out of ideas again.

Was this a new sensor? Maybe this link would help. If you have a ECUTEK and can do a log and upload it on DataZap and post it then that could help. Who is your tuner? A reputable e-tuner? Make sure the scaling is correct. Maybe disable the code? I don't know about the boost reading wrong. Post a log.

https://www.ft86club.com/forums/show....php?p=3171961

https://www.ft86club.com/forums/show....php?p=2927612

https://datazap.me/u/hellhat/brz-sbd...?log=0&data=30


He seems pretty reputable to me. Also yeah it's a brand new sensor

:popcorn:

Is it your friend Joe? Is it the guy down the street giving you a discount? Or is it a reputable place like Zach at CSG, Bill at DT, etc? I’m not trying to throw anyone under the bus and blaming the tuner, but I have to ask to rule it out.

Your absolute manifold pressure is 1.5 bar, which is 22psi, but that isn’t your boost; you have to subtract atmospheric psi, which is 1 bar or 14.7psi, so you are only making 7.5psi of boost. Did your tuner say you are making 22psi?

https://www.goosetuned.com/
He's the guy the shop I went to before I moved has been using for their stuff. R35s, STIs, G35/37s. After I moved I scouted the area out and every reputable tuner has a two month waiting list get looked at or they just don't get back to me. So I just stuck with him. The words from him were "The car thinks you are making 21psi out of nowhere"