Throttle: Okay first off my car is a Chevy Prizm. It's a GM port of the corolla, 2002, 1zzge with vvti and 125hp. I noticed this, i hooked up my computer to my car, pushed full throttle, it only goes 75%, unlike my friends chevy that will go 100%. I look in the throttle body there is a little metal piece that will clip the body at 75%. But I can't just remove it because the metal piece holds the idle position as well. I figure this will make much more easy power I can use, as well as making the intake a lot more useful. Any ideas?
Exhaust: I am going to put a straight pipe cat on it, but my vehicle's o2 sensor is right behind the cat. I all ready have poor emission readings, so it doesn't matter. But I know the o2 sensor is used to tell the ecu if the engine is running lean or rich, these straight pipe replacements have a bung or whatever to install the o2 sensor in. If i put the sensor in the hole will everything work the same? Besides getting the emission readings?
Won't gain any power by forcing it open any further - you are still limited by how much flow will get past the throttle body itself. The number you get from WOT position is relative to a certain set point in software. Basically it means you are using a different metric between the various manufacturers. Some read 100% at WOT, some read a hair lower - doesn't necessarily mean it is only open a faction less.
Better approach is to replace the throttlebody with a larger one (have to run some engine management, as the ECM could be totally confused) or port the existing throttlebody (Maxbore or similar).
As for the exhaust, remember that you have two O2 sensors. The O2 sensor behind the catalytic converter is there to check for catalytic functionality and have some bearing on fuel trims. But the upstream O2 sensor is the one that determines air/fuel mixtures. Some people run "test" pipes, which basically replace the catalytic converter with a straight tube. You can get an O2 sensor bung welded on there, but the gases might be too hot, move too oddly for the O2 sensor to get meaningful readings. Best approach to this is to run an O2 simulator for the downstream O2 sensor, to keep the CEL off.
Also keep in mind that the difference between no cat and the OEM cat works out to about 1HP difference at the wheels. Not a lot of gain there. Not sure what you meant by poor emissions readings, but sounds like your car would benefit from a comprehensive tuneup than trying to use bolt-ons to get more power.
I all ready have a ram air and a IAT/MAF chip modder, helped milage and made the car a bit quicker.
And what you are saying seems pretty stupid.. You're saying another 25% more throttle won't do anything? The just sounds kind of dumb to me honestly. If the throttle isn't opening all the way the Ram air really isn't doing nearly as much as it could. But I'm surprised no one else has noticed this. I go all the way it's exactly 75%, this is what the computer says. It's an economy car so I could see them limiting it to 75% anyways. My theory is if the car would actually go wide open throttle, the bolt ons would actually make a difference.
ECU wise, what should I look at? Do they go cheap if I get an old used one or something? I'm really not putting any money into this car.
Without the sensor it'll just give poor emission readings so really I could just unplug it or something and it won't do anything to the car? My cat all ready quit working.
I don't think that's 75% you're reading. That number is a value going from the throttle position sensor to the ecu. If you notice, when the throttle is closed, it's still at 10 ish right? The metal piece is probably to keep the butterfly valve from actually going backwards, resulting in less throttle because it is not straight with the air flow.
Yeah it is 10% and you can actually adjust a screw to that. So I figure that controls the idle position.
So could I just remove the 2nd o2 sensor and just like hang it or something without any problems? Like it won't effect the car in any way besides the efficiency ready? I can do that straight pipe basically free. I all ready have poor efficiency readings.
Don't understand what you're saying, just saying it's not working? Becuase I all ready have like 4 Check Engine codes for emission leak and o2 efficiency. Other than that it will NOT affect my engine's performance or operation in anyway?
Don't go by the number the ECM tells you as the absolute amount that the throttle is open. On many cars, this is offset by a certain bias amount, as the sensor's output is not linear. Like I mentioned before, TPS sensors read differently from car to car, just because one says it is open 100% compared to the Corollas 75-80% open at WOT - doesn't mean that you have another 20-25% more to open. Induction systems are quite complex - there is more to it than stuffing a larger piping to the system. Just like exhaust systems, you have keep track of exhaust pulses and exhaust scavenging to maximize efficiency and power.
The second O2 sensor (downstream - post-cat) has nothing to do with the air/fuel feedback, that is all handled by the first O2 sensor (upstream - pre-cat). If you leave the downstream one disconnected, it will through a CEL (P0420) - Catalyst System Efficiency Below Threshold.
The downstream O2 sensor will have some bearing on your long term fuel trims, but should not be so much that it would affect daily operation of the car. O2 simulators or sensor defoulers are common fixes to deal with the downstream O2 sensor.
Okay, guess I would have to physically look at it to see if it's open and honestly it does feeling like it's lacking a bit when I go full throttle.
I all ready have that P0420 code reading along with another emission reading so my cat needs to be replaced anyways, but the exhaust is all welded and I don't have money for a new one so I can just put a straight on it and get even better milage.
The codes don't bother me, the car has 210k on it and I'm not gonna sell it. I AVERAGE 45mpg, so there is no reason to sell my car as it's still in great shape and I've done a lot of audio work.
Okay, guess I would have to physically look at it to see if it's open and honestly it does feeling like it's lacking a bit when I go full throttle.
I all ready have that P0420 code reading along with another emission reading so my cat needs to be replaced anyways, but the exhaust is all welded and I don't have money for a new one so I can just put a straight on it and get even better milage.
The codes don't bother me, the car has 210k on it and I'm not gonna sell it. I AVERAGE 45mpg, so there is no reason to sell my car as it's still in great shape and I've done a lot of audio work.
No worries - when I had my Scangauge hooked up and looked at TPS readings - I was thinking WTF, something is screwed up with the car!?
Which other codes were in there - did you get an EVAP related code like P0440, P0442, P0446? Those are all pretty common the 8th gen Corolla, especially with ones with lots of miles. All of them are only for emissions purposes, and generally will not hurt overall engine performance - just get that CEL staring back at you constantly. Unfortunately, those can be tough to diagnose and fix. I get them every couple of years, most from bad vacuum hoses, cracked plastic fittings, and stuck VSV solenoids.
Least costly method to fix a P0420 coupled with a test pipe (decat) is to get a sparkplug defouler, drill it out and use the resulting cavity to space the sensing element away from the majority of the exhaust stream. Lots of write up on how to do this, this example was from a BMW board.
By giving it that extra bit of space, it will trick the ECM in thinking the cat is still working. Might not be 100% effective for everyone, but only costing a couple of bucks, well worth a shot.
Oh thanks I don't really care about the codes honestly. Is the vacuum hose that tiny intake that's combined with your bigger intake? Is it to release the pressure when you drop off throttle?
And I have like 2 codes, i know one is P0440, the other one is for emission leak or something. I really don't care about them I don't think I'll get the light off and it really doesn't matter haha.
That is one of the vacuum hoses. You have them all over the car - most are around the induction system (including anything touching the throttle body, airbox and tubing, and intake manifold) - the rest are under the car by the vapor canister (charcoal canister).
The part you are thinking of is probably the PCV hose/valve - that should just be replaced from time to time. Even if the the PCV "rattles" when you shake it, the spring inside could be weakened or damaged. If the car is consuming oil between changes - might look into an oil catch can. Not only will you keep the oil vapors from fouling the TB and intake manifold, you also "clean" up the intake charge for more consistent combustion.
SOMEWHAT getting what you're saying lol but what is the hoses purpose? Am I losing some compression if it's broken? It has 210k miles on it but only a 2002.
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