Quote:
Originally Posted by aaguirre123
I had the same problem. I have the solutions for you.
For the 750-1300 rpm fluctuations:
1) install two check valves. one between the AOS and the intake manifold (located on top of the intake manifold). If elected not to have an AOS then check valve is installed between PCV and intake manifold. Make sure that the check valve flows in the right direction. Flow direction should be from the PVC to the AOS (again if you installed one) and to the top of the intake manifold.
2) the other check valve is between the EVAP solenoid and EVAP line. The EVAP solenoid is located under the intake manifold. EVAP line is near and behind the AC compressor. By memory I think the EVAP line is between the DI and PI line. Again make sure the check valve flows in the right direction. Flow should be from EVAP line to the EVAP solenoid.
3) install clamps between the EVAP solenoid and throttle body (located under intake manifold near the throttle body).
4) Install clamps between the EVAP solenoid and the EVAP line.
In my case, which I think it's the same with yours, the reason why it fluctuates is because the EVAP solenoid is defective. The EVAP solenoid is leaking fuel fumes (gasses) from the gas tank to the intake manifold or vice versa. Working order EVAP solenoid only do two things; Open or close. Nothing in between. When the EVAP is not completely closed it creates a leak (vacuum leak). When the ECU sees a low pressure signal from the MAP sensor, it corrects this by sending more fuel and open more throttle. Hence, rpm increases. When the ECU sees pressure within normal range is reached then fuel amount is reduced. Hence, rpm decreases. Fluctuating rpm during idle is an attempt by the ECU to correct low pressure created by the defective EVAP solenoid. The ECU does not throw a CEL because either the tuner tells the ECU to ignore a drop/increase in gas pressure in the fuel tank (tuners usually disable this feature because flex fuel was installed) or it does not throw a CEL because the leak created by the defective EVAP solenoid is too low (within normal range). A minor leaking EVAP solenoid during close operation is ok with a NA engine but in a FI engine it's a nightmare.
Hesitation when transmission is on 1st gear solution:
1) change or replace the OEM fuel pressure regulator installed in the fuel pump canister.
2) 2nd option is to install an after market fuel regulator inline with the PI (port injection) line. A second aftermarket fuel regulator will make sure proper fuel pressure and volume is met.
There's hesitation because there's not enough fuel being delivered by PI.
The problem with the OEM fuel pressure regulator is that when they manufacture these parts, the tolerances are too wide during manufacturing. They are not concern about it because FR-S/BRZ are NA cars.
There's no hesitation at higher rpm because DI is being utilized. DI has an independent mechanical fuel pump so fuel pressure and volume is being met.
Tuners can't see any problems via logs because I don't think there's a fuel volume sensor or a way of sensing how much fuel volume is being delivered. When I read the logs I don't see any information regarding fuel volume; Only fuel pressure. So if the fuel pressure is within normal range and everything else are within normal range then tuners will say "There's no problem with my tune so it's not my problem. My tune is the best and I've sold my tunes around the world so I conclude that it's definitely the stupid owner's fault and/or you have a stupid car". I will not name names but some tuners are not mechanics. Many are just tuners. One of the tuner that tuned my car thought that there's a return line from the engine bay to the fuel tank. He noticed that there were three fuel lines and therefore the third line must be a return line. It's an EVAP line you dumb ass tuner.
Well I hope this fixes your problem.
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So just to be 100% clear before I throw more money at this stupid car, you're saying that you had random hesitations/stumbles on partial throttle before, and you replaced the stock FPR and (without changing anything else), the problem disappeared? It's just strange to me that there's at least a handful of us in this thread, with this specific kit, having the same specific issue, while my tuner is telling me they've never seen anything like this before and it makes zero sense. I'm also $10k+ into my car and at this point I'm about ready to rip everything off and go back to NA.