1997 fuel system what's different
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From: Tampa FL
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1997 fuel system what's different
The 97 has two fuel lines.
Is one a return line?
Is this system better or worse than say the 98s or 99s
How about the fuel pump, is that any different?
Is one a return line?
Is this system better or worse than say the 98s or 99s
How about the fuel pump, is that any different?
Melting Slicks
Joined: Mar 2001
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From: New Jersey
Re: 1997 fuel system what's different (JMon)
The earlier C5 fuel system had a fuel pressure regulator located at the fuel rail, in the engine compartment. Fuel pressure was adjusted based on intake manifold vacum. The excess fuel was returned to the tank, hence the 2nd fuel line. Newer C5s have the fuel pressure regulator integrated with the fuel filter, located next to the tranny, and only one fuel line goes forward to the engine. The new regulator is a fixed pressure design. Why GM changed this is curious. That is why the later fuel filters cost so much more than the early ones.
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Re: 1997 fuel system what's different (ersatz928)
Which system is capable of delivering more fuel for say a N2O system? I assume the way it works is that as intake pressure drops, fuel pressure increases. Now the next question is how do modification to say the air box change the operation of the system. It may land up reporting a higher air pressure because of a less restrictive flow, thus not allowing as much fuel to flow.
Burning Brakes
Joined: Oct 1999
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From: Rogers, AR, USA
Re: 1997 fuel system what's different (JMon)
Actually' it's just the opposite on pressure.
I was told that the noisy fuel pumps originally put on the 97's, which many people had changed, were noisy because they were a higher power, higher volume pump. I don't have any verification on this statement.
The pressure on my 97 is 60# with no vacuum applied to the regulator. With 10" of vacuum, the pressure drops to 55#, and with 20" of vacuum, the pressure drops to 50#. The more throttle you apply, the greater the vacuum applied to the regulator, and the less fuel pressure you have. The fuel trim tabs are set to compensate for this decrease in fuel pressure.
I was told that the noisy fuel pumps originally put on the 97's, which many people had changed, were noisy because they were a higher power, higher volume pump. I don't have any verification on this statement.
The pressure on my 97 is 60# with no vacuum applied to the regulator. With 10" of vacuum, the pressure drops to 55#, and with 20" of vacuum, the pressure drops to 50#. The more throttle you apply, the greater the vacuum applied to the regulator, and the less fuel pressure you have. The fuel trim tabs are set to compensate for this decrease in fuel pressure.
Melting Slicks
Joined: Mar 2001
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From: New Jersey
Re: 1997 fuel system what's different (alanh)
Not exactly. As the throttle is opened, intake manifold pressure increases (less vacum), and the fuel pressure increases. This causes a constant differential pressure across the fuel injector (fuel pressure on one side, intake manifold pressure on the other side). This constant differential pressure allows the amount of fuel injected to be linear versus the injector duty cycle. Thats why most cars use a vacum referenced fuel pressure regulator. In later C5s, where the fuel pressure is constant (does not compensate for intake manifold pressure), the fuel map in the ECU must compensate the duty cycle of the injector, which is done from info from the MAP (Manifold absolute pressure) sensor.
Burning Brakes
Joined: Oct 1999
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From: Rogers, AR, USA
Re: 1997 fuel system what's different (ersatz928)
Don't want to start a flame here but look at where the regulator vacuum line is connected. It's connected in the accordian tube ahead of the throttle body where there is no vacuum at a closed throttle position. With no vacuum applied to the regulator, the fuel pressure is 60#. Put a guage on your fuel rail if you don't believe me, then remove the vacuum line from the accordian tube, the pressure won't change. Then pump a vacuum on the regulator line, or suck on the vacuum line and watch the fuel pressure decrease. As the throttle body is opened, the pressure inside the accordian tube will decrease (more vacuum) and the regulator will decrease the fuel pressure. Your theory sounds good, but it isn't what the guages show that actually happens. You can also leave the fuel pressure guage on the car, tape it to your windshield, take it out for a drive and watch it decrease when you hit the throttle. If you have an aftermarket free flowing intake filter which greatly reduces the low pressure area ahead of the throttle boby, the fuel pressure regulator will have little effect on fuel pressure.
