#117659, "General Overboosting Question (not for 420A)"
I test drove a 1.8t GTI today that had an aftermarket intake and diverter valve. The owner swore the car was not chipped, but if I got on the gas too much before 3500 rpm the car went into "soft limp mode" and limited boost. I had to cycle the key to reset the ecu to get full boost again.
The owner said this was normal, and had no problems when he demo'd how to do it right. He said I was overboosting and said it had something to do with the diverter valve.
The car seemed to pull harder than stock and I was totally impressed with the acceleration it had when his more experienced foot was on the throttle.....it never "overboosted" when he was driving.
My problem is, how does the car overboost with just a CAI and aftermarket diverter valve? Is he telling the truth, or is the boost pressure turned up somehow? If it is possible that it is just the DV and I buy the car and learn to drive it right, that somehow the setup is detrimental to the durability of the turbo/car?
Proud owner of a '95. Johnny Tran says the '95 VTEC just kicked in, yo.
RICE: AEM Short Ram, CI 55mm Throttle Body, GS-T Muffler, Self-Made Ground Wire Kit, Caulk, Duct Tape, and "Stage 1 Weight Reduction" aka screws and bolts always left over from working on car.
#117660, "RE: General Overboosting Question (not for 420A)" In response to Reply # 0
Problem solved. It was a boost controller or wastegate mod. Seller was lying.
Proud owner of a '95. Johnny Tran says the '95 VTEC just kicked in, yo.
RICE: AEM Short Ram, CI 55mm Throttle Body, GS-T Muffler, Self-Made Ground Wire Kit, Caulk, Duct Tape, and "Stage 1 Weight Reduction" aka screws and bolts always left over from working on car.
#117661, "RE: General Overboosting Question (not for 420A)" In response to Reply # 0
Originally posted by silverarrow My problem is, how does the car overboost with just a CAI and aftermarket diverter valve? Is he telling the truth, or is the boost pressure turned up somehow? If it is possible that it is just the DV and I buy the car and learn to drive it right, that somehow the setup is detrimental to the durability of the turbo/car?
ECUs these days are very smart. They have sensors to watch incoming air(pre-turbo MAP) in addition to metering air (MAS, MAF, or MAP for fuel calc) and then post-turbo air (MAP in the IC piping) and if any of them don't match what the ECU expects, it flags a code or panics. OEMs build them this way on purpose - change something, cause a problem, void your warranty. The SRT4 monitors vacuum at the turbo inlet and pressure in the IC piping post-turbo, plus a MAP for fuel metering. If they don't match, DTC. It's fooled easy enough, though. GM, on the other hand, watches all those same points but through their onstar program *can pull your codes remotely without your intervention*.
How does this apply to you? Well... he's driving it in such a way that he doesn't take it outside of what the ECU expects to see. You are, and so you're being hosed. His excuse of "Oh, well... it doesn't do that when I drive it" doesn't hold up because he's doing it on purpose whether he knows it or not.
There are most likely ECU tuners out there that can remedy the situation if you're willing to pay for them.
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'95 Eclipse TurboGS (garage deco) '95 TSi AWD (restoring a survivor) '97 Talon ESi-T (poor impulse control) '99 Eclipse RS-T (daily beater) '13 Evo X (mostly stock) '17 Sienna (Middle Aged Dad Mobile)
#117663, "RE: General Overboosting Question (not for 420A)" In response to Reply # 2 Nov-27-07 08:06 AM by slowmitsu
Originally posted by DarkOne ECUs these days are very smart. They have sensors to watch incoming air(pre-turbo MAP) in addition to metering air (MAS, MAF, or MAP for fuel calc) and then post-turbo air (MAP in the IC piping) and if any of them don't match what the ECU expects, it flags a code or panics. OEMs build them this way on purpose - change something, cause a problem, void your warranty. The SRT4 monitors vacuum at the turbo inlet and pressure in the IC piping post-turbo, plus a MAP for fuel metering. If they don't match, DTC. It's fooled easy enough, though. GM, on the other hand, watches all those same points but through their onstar program *can pull your codes remotely without your intervention*. How does this apply to you? Well... he's driving it in such a way that he doesn't take it outside of what the ECU expects to see. You are, and so you're being hosed. His excuse of "Oh, well... it doesn't do that when I drive it" doesn't hold up because he's doing it on purpose whether he knows it or not. There are most likely ECU tuners out there that can remedy the situation if you're willing to pay for them.
It's fairly easy to trip them if you don't know what you're doing especially since cars like the 1.8t and the SRT-4 have relatively small turbo's that are being managed by an ECU controlled boost solenoid. Part throttle boost will build quicker than the ECU expects when you start tinkering with the wastegate and take out the factory boost solenoids and that's when the ECU starts to freak out. The best ways around this are to avoid part throttle boost driving (e.g. Entirely in vacuum or WOT...nothing in between) or getting a bigger and slower spooling turbo.
It sounds to me like hew knew the condition of the car and drove it primarily in vacuum or with his gas pedal completely pressed. You get in, not used to the car and start driving the car not at 100%. Without the car being WOT the ECU is in a closed loop operation and ECU isn't used to seeing that kind of boost that early in the RPM range and would normally start limiting it via the boost solenoid that's probably been bypassed or tampered with.
ECU's in turbocharged cars may be a lot smarter these days but they have their advantages. You can usually mess with a lot more stuff before having to step up to an EMS.
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