[Mk2] [Turbo] Over boosting after turbo rebuild

[benfacer]

I have just had my turbo rebuilt by Turbo Technics, to standard specifications (with a steel core) but am experiencing issues with over boosting. Car is a 1994 Rev 3 Turbo.

The car is exactly as per before the turbo was removed, but I have removed the boost controller to simply the system to help try and diagnose the problem.

The boost just keep rising until it hits fuel cut at 18psi by about 5250 rpm (checked on a dyno)
All pipes have been checked for leaks, the actuator has been confirmed to be operating correctly, isn't hitting the downpipe etc.

I have had the car checked over by a local Jap car specialist, and is currently back with Turbo Technics but we are all at a loss as to what the problem could be.

The car is fitted with a 3" decat downpipe and a 3" Fujitsibo exhaust which I have been running for some time without issue before the turbo rebuild.

The only current explanation is that the rebuild turbo is flowing so much more that due to the extra flow of the full 3" system it cannot control the boost. This seems difficult for me to accept as it is such a large increase in boost over actuator pressure, and the exhaust system has not changed.....

Does anyone have any experience of running a 3" de-cat and 3" system with a freshly rebuild standard CT20B turbo?

[SonicSW20]

So to confirm, you have a line going from boost reference port on the turbo directly to the actuator, and the 2nd port (assuming OEM) is blocked off, and you're still seing 18psi / fuel cut?

[benfacer]

Yes that's correct.

Before the turbo recon with the boost controller 'off' (creating the same situation) it ran about 10 psi.

The actuator is the same one (just tested and painted by Turbo Technics) and is defiantly opening correctly.

[SonicSW20]

OK, and with the actuator have you tested it with a regulated source so you can confirm it does open at the correct pressure?

A stock spec turbo should not creep like that, even with a 3inch downpipe. There must be an issue somewhere!

[shinny]

A stock spec turbo should not creep like that, even with a 3inch downpipe.

Some do, some don't. The stock wastegate can be inadequate on a free flowing stock setup (3" straight through exhaust with aftermarket decat) as my long-term battles with creep have shown. The key is the 3" decat... take a peak inside the stock cast DP and you'll see a massive restriction that keeps creep in check. A free flowing 3" pipe opens it up so much, you approach the capacity of the stock wastgate. In Ben's case, it may well be that the internal wastegate was just about good enough for the stock CHRA but with the Turbo Technics upgrade, it is no longer enough.

I feel your pain, Ben, but you're probably into the realm of increasing the size of your wastegate (difficult job!), adding exhaust restrictions (counter productive), or just accept 18psi is your new minimum so tune your EBC to give a stable 18psi ASAP.

[SonicSW20]

I have a 3 inch downpipe, a hybrid turbo (A Turbo Technics one, no less) and it holds actuator pressure just fine

I maintain that with a *stock* spec "CT20b", you should not be seeing 18psi or hitting fuel cut even if you had an open 3 inch downpipe. If you check the OP it's not an upgraded turbo, it's simply a steel turbine rebuild with standard compressor / turbine size / geometry. I accept that this can be a problem with some hybrid turbo / 3inch exhaust systems, but not with what is stock turbo as far as performance is concerned.

I note the OP has a Toyosport (same as Japspeed etc) decat pipe - these are notorious for not allowing the wastegate to open properly. I'd be checking that again very carefully and ensuring it allows for *full* actuation of the wastegate flap.

[benfacer]

Since posting this I have found your posts on boost creep Shinny. Certainly seems like that is the case....

I am disappointed I didn't search boost creep earlier as I have spent a month now trying to track down the problem myself, had a local Jap specialist check it over, and the car is currently at Turbo Technics having the turbo removed and checked (that I fear they are now going to charge me for....)
As part of the rebuild Turbo Technics fitted a new exhaust housing to the turbo, which made me convinced it must have been a problem with that hence sending it there for investigation but they have checked it over and all seems fine. I have asked them to re-fit my origional exhaust housing to put my mind at rest but it is looking like this won't fix the problem.

It would seem my original turbo was worn enough to not suffer from the creep, but with a nice new steel core it is overloading the wastegate.

To be clear the exhaust setup is exactly the same as before the turbo was removed and rebuilt (when it worked fine), and I have checked the wastegate defiantly isn't fowling the down-pipe.

I am toying with the idea of putting a restrictor on the bottom of the downpipe as I can get one made up quite easily, but not too happy about it.
Did you manage to get the boost under control with a restrictor Shinny?

Would a 2.5" downpipe help? I dug my CAT out of the shead last night but I would rather not refit that.... it is so heavy!!

[Ryan S]

Gut the cat and fit it, see how you get on. It splits in half remember so shouldn't be too bad to fit.

[shinny]

I have a 3 inch downpipe, a hybrid turbo (A Turbo Technics one, no less) and it holds actuator pressure just fine

Yup... some do, some don't. No idea what the difference is, because when I was battling boost creep I found others with identical sounding setups who weren't suffering issues. I've never found a decent reason why my engine would creep; I even went down to crank and cam timing to check things out.

[benfacer]

From the little reading I have done, and what i have learned though this process is it seems that it's how worn your turbo (Or possibly housing) is so maybe a good thing for you Shinny! As it is only some cars it must be so marginal!

The Turbo Technics hybrid runs a single scroll housing I believe so only has one wastegate port which must be big enough able to handle the free flowing of a full 3" system (I've seen other posts stating they handle it too)

[benfacer]

OK so I am making some progress and can actually drive the car now!

I refitted the CAT yesterday and that does seemed to have helped. It was hitting 15.6 psi (I think might have been 15.9 psi as was only a quick test and I can't remmeber) in 3rd.

I had a HKS intake pipe fitted so wondered if that could be contributing as it looks much less restrictive than the standard intake pipework (which is why I bought it) so I refitted the standard pipework with a HKS mushroom filter this morning.

This did help a little. I am now seeing 15 psi in thrid (it is leveling off), but strangly ony 12psi in 4th.
I have a Blitz SDC-ID so can record and view the boost as a graph.

https://drive.google.com/file/d/1eMX_Ot ... sp=sharing

I do have the boost controller connected now (as I am sick of taking my charge cooler off) but have it set to 0 so it isn't interfearing.

Going to try and speak to some specialists tomorrow see if I can get to the bottom of it. It is going to be very difficult to setup the boost controller with such a big difference between 3rd and 4th.

[shinny]

From the little reading I have done, and what i have learned though this process is it seems that it's how worn your turbo (Or possibly housing) is so maybe a good thing for you Shinny! As it is only some cars it must be so marginal!

I was re-reading part of my old project thread... back in 2015, just as I "solved" my creep issues, Jim posted this nugget which didn't really register in my head at that point:

boost creep can also be down to timing being pulled by the ecu (detecting knock/det).
also may explain high-ish EGTs.


i wasnt aware of this until recently, ATS racing:

Creep has more causes than just a turbo and wastegate.

We've had no problems with creep on any of the CT21's we have done here. Creep can be caused by cam timing, and even ignition timing. If the gen3 ECU is upset about detonation it will retard ignition timing back to about 3-4 degree (instead of 17-19 degrees). Running that low of timing means that some of the combustion process is still happening when the exhaust valves open. That puts a ton of heat into the exhaust and heat makes boost. Wastegates open up to bypass exhaust..but it's hard to bypass heat.

I never chased this up on my old car, but I suspect I might throw a fresh knock sensor on my rebuild just to rule it out.

[SonicSW20]

Resetting the ECU and running it should be enough to verify that. Pull the EFI fuse for a few minutes and reinstall, it takes a bit of time for the ECU to readjust for knock sensor feedback.

A bad knock sensor *should* trigger ECU codes, the OEM ones are very delicate and even a single bad case of knock is enough to kill it and trigger a code 52.

[2barGee]

Benfacer.........You either need to restrict the exhaust or the intake (i'd go exhaust as it's the cheapest option and works). Or get it mapped and it will level out at 1.3-1.4bar you'll find.

On every standard turbo set up with a free flowing exhaust + intake with a "healthy" turbo i've had boost creep.

[benfacer]

Thanks for all the info guys.

The car is all over the shop at the moment! I reset the ECU to get those stable boost figures in the image, but the next day the ECU seems to be dicking about with the timing a lot as it is holding back sometimes and not others. and the boost was very high again the other night....

I suspect there is something wrong, I am going to check the plug on my knock sensor (I fitted a new Toyota knock sensor when I bought the car, and got a new shielded wire installed by a pro, but with a basic connector sensor end).
Other than that I guess it must be something wrong with the ECU....

It was starting to have small hesitation issues before the turbo rebuild, I was investigating this, replacing plugs etc and through I had solved it as was a lot better then the turbo started making lots of noise!

Getting very frustrated!!

[SonicSW20]

So resetting the ECU initially sorted the boost creep issue? And yeah, it takes a bit of time for it to settle in after doing it.

Hope you get to the bottom of it, if resetting the ECU improved things temporarily at least thats a step closer to a solution.

[benfacer]

Resetting the ECU and fitting the CAT (done at the same time) definatly improved things.
The ECU has settled down now so running a lot smoother but still over bosting. Seeing about 17psi in 3rd, 12psi in 4th and 9.6psi in 5th...

I think I am going to fit the standard exhaust and see what that does. Not looking forward to it though as it hadn't been off before my time so the rear most flange is a bit worse for wear!

[SonicSW20]

You're seeing less boost in higher gears? That's unusual.

[2barGee]

Resetting the ECU and fitting the CAT (done at the same time) definatly improved things.
The ECU has settled down now so running a lot smoother but still over bosting. Seeing about 17psi in 3rd, 12psi in 4th and 9.6psi in 5th...

I think I am going to fit the standard exhaust and see what that does. Not looking forward to it though as it hadn't been off before my time so the rear most flange is a bit worse for wear!

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Yes putting the standard cat on will have helped as its more of a restriction.

Trust me.... just fit an exhaust restrictor! Simple and cheap!!!


Or continue to put it back to standard.

[shinny]

Trust me.... just fit an exhaust restrictor! Simple and cheap!!!

And a frustrating step backwards