a few drivibilty and other questions

[sierrap615]

just a few questions, some are in general, some relate to my 95 Buick Regal 3.8L

1. i know NOx emissions form under load due to high combustion chamber temps, and NOx levels peak at about 16:1 A/F. but does anyone know at what RPM range NOx levels are highest?

2. A vacuum controlled fuel pressure regulator increases fuel pressure during low engine vacuum/heavy load. my teacher says the increase is designed for a power boost on acceration, but my thinking says its to allow for proper atomizition of the fuel, as with out the increase in fuel pressure the relitive difference between fuel pressure and intake manifold absolute pressure decreases(hence worse fuel atomizition). am i making any sence? does anyone know for a fact the purpose the vacuum controller? and is there any extra steps taken on non-vacuum controlled FPRs to adjust for engine load(besides injectior pulse width)

3. higher fuel pressure allows better fuel atomizition right? better atomizition means better fuel economy right? if i was to increase my fuel pressure(by disconnecting and pluging the vacuum line, i check the numbers today, it would be a 10 PSI increase at idle, from 35 to 45 approx) at frist i know it would run rich due to extra fuel being injected, but after the PCM adjusted for it and tuned the injectior pulse width accordingly, would it seem possible to increase fuel economy in the long run?

4. my buick has a 4T60-E Hydromatic trans. the vacuum modulator is not used for shift timing, only for shift feel(firm or soft), the vacuum modulator normally controls whats known as throttle valve pressure inside the trans. on the 4T60-E is this stall consided throttle valve pressure or is there another name for it? also most automatic transmission the main line pressure increases as throttle valve pressure increase. is this also the case in the 4T60-E? i know increase main line pressure can increase the clamping force on the clutches, are there any other effects of increasing main line pressure? throttle valve pressure? do you think it would increase or decrease the life of the transmission?



i know, thats alot, thanks to anyone how can share a little knowlege with me.

[sierrap615]

answered one of my own questions, i found a hydraulic diagram of the 4T60-E. the pressure controlled by the modulator valve is refurred to as Modulator pressure, there is no throttle valve pressure in the 4T60-E. and I beleave it does affect main line pressure.

[benchtest]

#2: you are correct. The fuel pressure rises to maintain a constant pressure differential between the fuel and the intake pressures. Enrichment for acceleration is handled by the cpu. Atomization and flow are affected by the pressure differential.

[curtis73]

Originally Posted by sierrap615

just a few questions, some are in general, some relate to my 95 Buick Regal 3.8L

1. i know NOx emissions form under load due to high combustion chamber temps, and NOx levels peak at about 16:1 A/F. but does anyone know at what RPM range NOx levels are highest?

It depends on several things, but in general it will probably happen between the torque peak and where the HP starts to fall off (about redline). Peak torque is generated by peak VE and therefore it vaguely corresponds to peak cylinder pressures. The effectiveness of the EGR system is key as well.

Peak load is also a point of high NOx. You know that point where you are at 3/4 throttle and the tranny doesn't want to shift? Tons of NOx right at that point.

2. A vacuum controlled fuel pressure regulator increases fuel pressure during low engine vacuum/heavy load. my teacher says the increase is designed for a power boost on acceration, but my thinking says its to allow for proper atomizition of the fuel, as with out the increase in fuel pressure the relitive difference between fuel pressure and intake manifold absolute pressure decreases(hence worse fuel atomizition). am i making any sence? does anyone know for a fact the purpose the vacuum controller? and is there any extra steps taken on non-vacuum controlled FPRs to adjust for engine load(besides injectior pulse width)

The vacuum referenced regulator's main purpose is to keep the pressure differential equal at all times. If you supply 40 psi to an idling manifold that is drawing 3 psi of vacuum, it effectively injects fuel at 43 psi. At WOT with zero vacuum, its fighting higher pressure than it is at idle. Boosting pressure at lower vacuum just evens the playing field so the metering can be more effectively mapped with pulsewidth alone.

3. higher fuel pressure allows better fuel atomizition right? better atomizition means better fuel economy right? if i was to increase my fuel pressure(by disconnecting and pluging the vacuum line, i check the numbers today, it would be a 10 PSI increase at idle, from 35 to 45 approx) at frist i know it would run rich due to extra fuel being injected, but after the PCM adjusted for it and tuned the injectior pulse width accordingly, would it seem possible to increase fuel economy in the long run?

Not really. The injectors, the hot manifold, and nozzle of the injector do a very fine job of atomizing the fuel. It is by no means a limiting factor in the engine's efficiency. Maxing out the pressure may decrease idle quality and overall fuel economy. The higher pressure will force the pulsewidth to be much shorter everywhere but WOT. Injectors are most accurate at lower pressures where they can stay open longer. Injector pulsewidth is only accurate to a certain time. The shorter pulsewidth you ask it to meter, the less accurate it will be. If anything I would think that the opposite of your theory would be true to an extent. If you didn't allow pressure to rise it would force the pulsewidth to increase... which is good up to the point where RPM makes the injection window shorter than the pulsewidth required to deliver the fuel... if that makes sense Fuel requirements and injector function are opposite. The faster your RPMs, the less time you have to get fuel injected, but the faster the RPMs, the more fuel you need. Hence the secondary reason your fuel pressure rises; so you can get more fuel in less time.