STI fueling question

Re: STI fueling question

Postby 4th2ndgendennis » Fri Jul 27, 2012 6:55 am

The car is being tuned by a subaru tuner. The wideband obviously can not read all cylinders independently though. I did think about an egt for each header pipe, but keeping an eye on them is not realistic for my driving style. I would love a system to log each cylinder individually.

I seem to find no complaints about the Perrin system. If no obvious restriction is found on dissassembly I guess I will go that route. I am thinking I should also trace the wiring harness for that injector. Is it possible a bad ground or worn wire could effect pulsewidth without throwing a code?
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Re: STI fueling question

Postby 4th2ndgendennis » Fri Jul 27, 2012 6:59 am

Chief Geek wrote:Right, #98. #96 is a later generation Dennis.

Your best Sunday radar speed at Okemo was 2nd highest of all. The only one higher is Butch and I doubt his engine would fit in anything smaller than a truck.

Fuel pressure at the injector problems is where I'd look first too.

Will the fuel rail accept fittings near the injectors? If it's easy, I'll bet adding 4 fuel pressure gauges piped as close to the injectors as possible and videoing them would provide important clues. I don't know how you or our tech inspectors feel about extra pressurized fuel lines in the cockpit though.

Paul




Don't think gauge at the injector is possible---I will double check though.
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Re: STI fueling question

Postby agrabau » Tue Aug 07, 2012 10:24 pm

It shouldn't matter what rails you have at that power level. We've run standard rails up to 450whp on STIs with no problem. Assuming this tuner is doing a decent job you could have an intake leak on the manifold that's causing #3 to go lean. I would pressurize the manifold and check for leaks.

Next check the fuel pressure. The pump could be installed improperly and supplying inadequate pressure. There could be a post-maf leak causing the whole system to be lean and since cylinder 3 is by far the hottest (next to the up pipe) it is most prone to early failure.

Good luck guys. Let us know what you find.

Alex
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Re: STI fueling question

Postby 4th2ndgendennis » Thu Aug 09, 2012 7:14 am

agrabau wrote:It shouldn't matter what rails you have at that power level. We've run standard rails up to 450whp on STIs with no problem. Assuming this tuner is doing a decent job you could have an intake leak on the manifold that's causing #3 to go lean. I would pressurize the manifold and check for leaks.

Next check the fuel pressure. The pump could be installed improperly and supplying inadequate pressure. There could be a post-maf leak causing the whole system to be lean and since cylinder 3 is by far the hottest (next to the up pipe) it is most prone to early failure.

Good luck guys. Let us know what you find.

Alex


Thanks Alex,

Fuel pressure is good at the distribution block before splitting to go to the two rails. After the distribution block I don't know. Current pressure gauge indicates that it is OK throughout RPM band and rises with boost properly. The intake system has been checked for boost leaks(pressurized), but I don't know about the inlet pipe. The system as a whole is not running lean, and no signs of detonation at all on the other pistons---is the up-pipe heating the engine enough where that is possible? Both episodes were during the straights at Burke and Okemo--4th or 5th gear, long pulls. VP106 race gas, 1 step colder plugs, 850cc injectors, 25PSI tune.

Is it possible for the injector harness to have an issue and the injector may not be firing full pulse width? Or would it just not fire at all?

Any other thoughts? At this point I have not determined the cause, but will be installing 4 EGT monitors for each cylinder. Watching them is not going to be easy though.....

-Allan
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Re: STI fueling question

Postby sachilles » Thu Aug 09, 2012 9:27 am

are you data logging at all?
If not I have a netbook and obd2 cable that should work with your car if it is a 2005 or older subie you can use at the September Ascutney(sooner if we can figure out a way to get it in your hands).
The netbook has the Learning view utility installed as well as the Romraider software for data logging. You are welcome to use it as needed.
The software is free, so if you have your own laptop I can guide through getting it working on your computer, and you can borrow my obd2 cable or grab your own for around $25 if the car is 2005 or older, or closer to $100 if it's newer.
Sachilles
02 Subaru impreza (Donut) #66
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Re: STI fueling question

Postby 4th2ndgendennis » Sat Aug 25, 2012 2:19 pm

So I need a 2.5L case. Anybody have a good one to sell?
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Re: STI fueling question

Postby agrabau » Sat Sep 08, 2012 9:17 pm

I know we have an appt coming up but what I meant earlier was to pressure test the manifold not the fuel injection. There could be a vacuum leak on one runner or even after the MAF. The catch is that a vac leak becomes a boost leak so damage would be done at part throttle not W.O.T good to pressurize the throttle body with the intercooler off anyway to make sure that everything's sealed before tuning.

The car should run with an FPGreen with 750cc injectors with no problem, especially on race gas so with 1000+cc injectors you've got more than enough.

EGTs aren't going to do much for you aside from aiding tuning. They're so slow to react that the game will be over before you see it on the gauge.
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