wont boost past 7 lbs

[Enano]

I have an 7mgte that was originally automatic and i would hit fuel cut at 13 psi with just 3 inch exhaust Walbro 255 and intake. Did a tranny swap and immediately it would only boost to 7 lbs. Checked for leaks have none, tried 2 different wastegate actuators, same problem.

With boost controller i can spike to 17-18 but it will go down gradually and its slow as shit.

*This problem was happening before mods and after.*

Current mods now:
550CC injectors
Lex afm
3 inch
Intake
Walbro
Stock IC

I was wondering since it started right after the swap, could it possibly be because i had to leave the auto gear selecter in neutral instead of park or vice versa?

 

[IndigoMKII]

Any check engine codes?

 

[Enano]

Code 51, but I just recently got this code. I never had it before and it would still only boost 7 lbs. Plus I don't think a bad tps could cause boost problems could it?

 

[IndigoMKII]

Have you changed anything else? Just changed the transmission? How did you check for boost leaks? Also can you define 'slow as shit'?

If you're pushing the stock CT26 up to 18 PSI, you're just blowing super heated air into the intake, causing the ECU to retard timing further to avoid detonation. I wouldn't push the stock CT much past 13-14 PSI unless you've got a CT26 57 trim or higher.

The reason the PSI slowly falls off is the turbine isn't big enough to flow all the way to redline, that's why most people just swap out the stock CT for a turbo that pulls all the way to redline.

 

[Enano]

Sorry I haven't answered... I've been trying to figure this out. I had a leak at one of the injector grommets and now its fixed. I have a question though, during checking for boost leaks, my system will not get pressurized at all.

Nothing around my intake or ANY of my intercooler pipes are leaking but its like all the air is leaving through the exhaust? How am I supposed to test for boost leaks if it all just escapes?

Now that I fixed the injector grommet, I put on the boost controller and it spikes to 15 and holds at 12 but the car starts holding at 12 and just doesn't feel fast at all. I think the car was faster at 12 lbs with the automatic than with the 5 speed now. Anyways I took off the boost controller to see how it would do with just the wastegate and it only stays at 7. How is it possible for it to hold at 12 with a boost controller set at 15 but only at 7 directly to wastegate?

The only things I've done besides the swap are:

Charcoal canister delete
EGR delete
Cruise control delete
Powersteering vac delete

 

[MKIIISupraGuy]

Thought you were supposed to change Ecu to match whatever tranny you have ?

 

[hvyman]

Can use an auto Ecu on a manual but cannot use a manual Ecu for an auto.

 

[MKIIISupraGuy]

As in 7mgte w/ auto tranny. When i had mine down with ecu trouble i borrowed a buddies spare ecu that was the auto trans version and my supra wouldnt go past 7 either

 

[hvyman]

The Ecu does not control boost.

The wastegate does.

 

[Enano]

I'm still using my auto ecu.

So in theory, all my boost problems could be coming from my wastegate? Why would it hold at 12 with a boost controller and only 7 without one?

And what are the chances of 2 different actuators having the SAME problem?

Wastegate would hold extremely fine at 12 with my auto tranny and now wiht 5 speed it wont hold anything over 7 without a boost controller. Whats the deal?

 

[hvyman]

If your using a ct the wastegate is set at 7 psi.

What you are seeing is normal. Even more so when upgraded. My 57trim on my 7m only went to 6psi.

 

[MKIIISupraGuy]

Wastegate does control boost, and yes I am well aware of it, just sharing my similar issue I experienced. Im also pretty sure I never touched my wastegate. I did have a Electronic bc, but I never touched the settings, like the spring pressure.

 

[Enano]

Okay but explain to me this... How is it possible that before when I had my auto tranny, it would hold at 12 and hit fuel cut every time the transmission shifted and boost spiked to ~13-14 if the wastegate spring is only set at 7?

 

[MKIIISupraGuy]

I dont know man, Im still baffled. The temp outside was warmer when i had the auto ecu, and boost recall only showed about a 2.4 psi max boost difference. Still, there was a difference. Warmer weather the culprit ?, possibly.. But that much?

 

[Enano]

Nah man it can't be its just not possible. So people that run 25+ psi have 25+ psi springs in their wastegates? I don't think thats how it works...

 

[MKIIISupraGuy]

My car. Stock wastegate (7psi), lex afm, 550's, emanage, hks fcd, 57 trim, walbro, and a few other goodies. I'm at 15 psi max boost if I plant my foot.

 

[Enano]

Exactly man you have a better turbo and your wastegate is still holding like a champ. Maybe my turbo is gone?

 

[MKIIISupraGuy]

I dont know if my turbo is better, I only hold boost for a few seconds because Im at felony speeds if I hold any longer lol. Seriously though, might be a good idea to check your turbo, shaft play, impeller blades, etc.

 

[Enano]

I'm going to rip off the downpipe tomorrow and check the flapper and blades. If all is ok.. I'm taking it to a shop cause I'm about to drive this pos into a lake

 

[MKIIISupraGuy]

You should be able to spin that impeller freely with your finger, any hesitation or resistance is not good. In case you didnt know.