(Over)Boost/ECU issues! Help!

[exigeracer]

Alright we were at the track the other night in a 240SX (SR20DET). Car/motor is mostly stock except FMIC and some little piping for more boost.

The third run, we made some changes to allow up to 25psi and tried to keep the temp down prior to launch. At around 4,800 rpm WOT in all gears, the engine cuts out.

Upon replacing original piping the car would run fine.

Is the ECU sensing overboosting and cutting out? Is there a simple way to have this fixed?

 

[IMADreamer]

Alright we were at the track the other night in a 240SX (SR20DET). Car/motor is mostly stock except FMIC and some little piping for more boost.

The third run, we made some changes to allow up to 25psi and tried to keep the temp down prior to launch. At around 4,800 rpm WOT in all gears, the engine cuts out.

Upon replacing original piping the car would run fine.

Is the ECU sensing overboosting and cutting out? Is there a simple way to have this fixed?

That is exactly what the ECU is doing. It is pulling timing or fuel or something to make sure the engine doesn't blow. The solution is to upgrade your fuel system and then do a stand alone management system. Your lucky it cut out or you would be telling a different story this morning.

 

[Duke]

I'm not a turbo expert, but that sounds exactly like what is happening.

The Shelby turbo folks do a little thing called the Grainger Valve trick to make sure that the senosor is never subjected to overboost. Try a Google search for it and see if you turn anything up.

25psi sounds like a hell of a lot of boost for a basically stock engine, however, even for a sainted SR20DET which is widely believed to be as indestructible as Superman.

 

[Jay]

Is the ECU sensing overboosting and cutting out? Is there a simple way to have this fixed?

Yes that would be what is happening, well I know for a fact standard RB20/25/26 ECU's cut off when boosting that high, and I'm certain SR20 ECU's do the same.

What SR20DET you got? Most stock SR20DET turbos have a cermaic exhaust wheel, your lucky it didn't break at that sort of boost. You should really have it tuned for that boost before trying, its a good thing the ECU cut out.


If you want to increase boost without cutout then you will need a fuel cut defender or a replacement/modified or piggybacked ECU.

 

[Holdenhsvgtsr]

does that engine come with a maf?

sounds like that.

 

[exigeracer]

Alright thanks for the replies. I've heard stories about SR20s handling such high boost, but I do not know the specifics or the reliability of these claims.

The exhaust is stock S13 Silvia exhaust replacing the 240SX setup.

We were worried that a blowout would occur, this was the second time he had tried the pressure so high, and I wasn't there the first time to see what had happened.

My friend will take a look at the ECU at work, he has access to all sorts of machinery suitable for that kind of work.

Thanks for the replies, I think we'll only be trying the high boost under better mechanical and electrical circumstances.

GTSR, what would be the optimal boost level for this kind of motor? It seemed to be able to take around 18psi fairly well. Is this good?

 

[Holdenhsvgtsr]

not to sure
to me it sounds like the maf sensor(Mass Air Flow),friend had a problem with it on his leon when he upgraded from a ko4 to a GTRS turbo,kept putting it into limp mode(which sounds like your problem) and to solve it he just took it out

did you try turning the engine off fully and take out the key and then wait for 1 minute and start the engine again and if you did how did it respond?

 

[exigeracer]

I do not recall the exact procedure, this all happened a week ago. I do know that once the engine cut out down the strip, we sailed to the turnaround point, tried again, same cutoff. We switched back to the stock piping and went for another run, the same problem. We then quit and headed back home, but the problem was gone when we were on the street with stock pressure.

 

[Jay]

GTSR, what would be the optimal boost level for this kind of motor? It seemed to be able to take around 18psi fairly well. Is this good?

Boost level isn't really a problem for the SR20DET engine itself to an extent(Seen standard internal SR20DET's running 25-30psi daily). Its all about the fuel supply, engine management and turbo handling the increased load.

As far as I'm aware all but the late S15 SR20DET's (and maybe GTiR SR20) turbos have ceramic exhaust wheels, which are prone to cracking and breaking with loads around and exceeding 1bar (14-15psi). A S15 turbo is a good replacement as its Steel exhaust wheeled ball bearing turbo that bolts straight up, so you don't need to worry about it breaking when increasing the boost to 1bar+.

Really if you want to run these high boosts with standard turbo, you really should have the ECU tuned for these levels as leaning and fuel cut off can become a serious problem. From memory a SR20DET with modified/replaced ECU and standard injectors/afm and turbo should be able for around 200rwkw's (roughly 270rwhp) (can't remember the actual boost pressure is at with this power), I remember someone making 220rwkw(295rwhp) with a high pressure fuel pressure regulator but their injector cycle was pretty much maxed 100% which is not good at all. What ever you do if you ever hear any detonation when playing around with boost, stop it immediately and make sure it doesn't continue for extended periods, detonation is the main killer especially with standard pistons.

A aftermarket replacement ECU like the Apexi Power FC with hand controller really pays off, you can tune on the run and see what all the sensors are doing all the time, like the knock sensors and injector cycle. Plus it makes it easy to tune of the dyno (or street) with a lambda sensor hooked up so you can tune to keep your safe all the time.

But overall 18psi is fine on the engine itself, just make sure the engines sub systems can handle it.

 

[Holdenhsvgtsr]

could be the car going into limp mode as you are still being able to drive it,to me it sounds like a faulty sensor thats sending a message to the ecu to cause it to do it and not the ecu as such causing the problem

 

[Jay]

I do not recall the exact procedure, this all happened a week ago. I do know that once the engine cut out down the strip, we sailed to the turnaround point, tried again, same cutoff. We switched back to the stock piping and went for another run, the same problem. We then quit and headed back home, but the problem was gone when we were on the street with stock pressure.

If it ever gets stuck in safe mode with the boost lowered, easiest way to reset the computer is disconnect the Battery and hold the brake light on to discharge any power, when you start back up (with battery connected) your ECU will will be reset and the first while the ECU will re-learn and adjust its tune so dont trash too much initially. This will also reset the timing that the ECU may have automatically retarded due to and knocking it sensed when you had the boost up.

could be the car going into limp mode as you are still being able to drive it,to me it sounds like a faulty sensor thats sending a message to the ecu to cause it to do it and not the ecu as such causing the problem

The AFM (SR20DET's have mass airflow sensors/ air flow metres) is what tells the ECU how much air the engine is getting, if your running 25psi its not out of the ordinary for the ECU to cut fuel for saftey. When the AFM is faulty your most likely going to get improper a/f ratio, if it was fuel cutting at lower boost then maybe I would suspect the AFM but not a 20psi+.

That is why there are fuel cut defenders.

 

[exigeracer]

GTSR, I know that it isn't an S15 SR, and there is a little extra hissing right near peak pressure coming from the turbo. Baically, it sounds a little harsh at the higher ends of the spin cycle. My friend replaced the cold-end gasket thinking that was the problem of the leakage, but could it be the ceramic wheel already on its way out?

This could be the root of the problems. Any comment on this?

 

[Jay]

GTSR, I know that it isn't an S15 SR, and there is a little extra hissing right near peak pressure coming from the turbo. Baically, it sounds a little harsh at the higher ends of the spin cycle. My friend replaced the cold-end gasket thinking that was the problem of the leakage, but could it be the ceramic wheel already on its way out?

This could be the root of the problems. Any comment on this?

Well its hard to tell without listening myself but the ceramic wheel often just lets go without much warning. The sound you may hear could be caused from a over restrictive exhaust when you are at high boost levels, on non ball bearing turbos it can cause excess wear on the thrust bearing causing the sound. (excess exhaust backpressure pushing the turbine against the thrustbearing)