Jump to content
SAU Community

Recommended Posts

Morning lads!

I noticed recrntly when I'm WOT my car has a noticeable flat spot in power up around 5500-7000rpm.. I checked my power fc and it normally has injector duty at around 84-90% max at rev limit of 7500rpm and 25psi but now it's going strait to 100% before rev limit is reached...

Wile testing this I noticed it only does it in 3rd gear and the power drop seems to be coming from the fact it won't make target boost (25psi) in that gear... Hovers between 22-24psi. I use an eboost 2 ... Could it just be the tune?

I'll also say my fuel pump relay had been wired wrong and was like this nearly the whole time I've had the car.. It's been on the dyno around 7 times for multiple tunes without a problem also... but now it's fixed and has since been using a fair bit more fuel... Would a bump up voltage cause a bump up in fuel pressure causing the injectors to max?

I've done multiple boost leak tests now and found a couple of minuscule little leaks. Fixed them, car still does it. Swapped my z32 afm out for a brand new one... Still does it..

Assuming you have a normal airflow meter PowerFC setup? The duty cycle will only go that high randomly if the airflow meter THINKS it is moving more air than normal, a dodgy fuel pump or fuel pressure won't change the injector duty cycle - ONLY the ECU will decide to do that in response to how much load it thinks its under etc as it won't know what is happening to the fuel pump, etc.

To me it sounds a lot like you still have a boost leak as because you duty cycle has increased it indicates the airflow meter is metering more air than normal - which means the turbo is working harder than normal, which indicates that it has to spin harder to make your normal target boost but given you aren't reaching target boost the air the turbo is pushing must be escaping somewhere.

That seems like the most obvious and cleanest possible explanation to me.

 

Assuming you have a normal airflow meter PowerFC setup? The duty cycle will only go that high randomly if the airflow meter THINKS it is moving more air than normal, a dodgy fuel pump or fuel pressure won't change the injector duty cycle - ONLY the ECU will decide to do that in response to how much load it thinks its under etc as it won't know what is happening to the fuel pump, etc.

To me it sounds a lot like you still have a boost leak as because you duty cycle has increased it indicates the airflow meter is metering more air than normal - which means the turbo is working harder than normal, which indicates that it has to spin harder to make your normal target boost but given you aren't reaching target boost the air the turbo is pushing must be escaping somewhere.

That seems like the most obvious and cleanest possible explanation to me.

 

Boost leak was my first thought and as I said I've done multiple tests on the last two days.. I pressurised the whole system from the turbo inlet to 30-35 psi and fixed any leaks however small... Now I'm at a loss

I'll also say that in second gear boost builds no worries at all and even spikes to 26-27psi then drops to 24-25psi which is target...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • 😂 thanks guys. The diagram i had did not have the breather on it at all. Much appreciated.  
    • Geez, engineers fees have definitely gone up. Mine back 2007 cost me all of $300. Mind you, I had to go back to him a few times to get him to write the correct things on the report after he'd inspected it. Things like wrong exhaust size, wrong wheel sizes, etc etc.
    • Can we see a scan of the original quote? The problem with engineers (and by this, I mean, all engineers across all engineering industries) is that there are "engineers" and there are "engineers" (you'll have to imagine the two different vocal emphases on those two versions of the same word. Engineering is a mindset - your farm kid who spent his life rebuilding the tractor will likely make a good engineer. The farm kid who spent his life taking photos of butterflies.. perhaps not. But on top of that mindset, the modern engineer has to learn how to write so that there is absolutely no way of being misunderstood. Proposals/budget estimates/quotations are one place where this is absolutely vital. You have to delineate your scope of supply with extremely hard boundaries, and anywhere where there is any possibility of not being able to have such a hard boundary, you need to write language that will cover you from scope creep, cost overruns, the inevitable interference of the client or their "engineer", etc etc. Now, if your clients are the BHPs and the Rio Tintos of the world, and similar, then you get good at this. If you are an automotive engineer, pitching work to the great unwashed masses, your skills in this area might not be well developed, because you're only dealing with knuckle draggers trying to get a big block legal in a Torana. And when I say "might not"....I'd suggest there's a better than even chance that any such skills might be completely absent. So, we might be able to look at your quote and see what the opportunities are for rebuttal.
    • It’s an rb25 so a gtst and I’ll get that valve
×
×
  • Create New...