Who knows about fuel pressure on a 1988 corvette?
03-22-2007, 06:28 PM
#1
Drifting
Thread Starter
Who knows about fuel pressure on a 1988 corvette?
Who knows about fuel pressure on a 1988 corvette?
Today I have different numbers than yesterday.
Yesterday the car may have been cold and it showed:
39 lb of pressure with the key on/engine off.
32 lb of pressure with the engine running.
Today I let the car warm up to operating temp and it showed:
Key On/Engine Off:
46 lb for approx 2 seconds, then it drops to 42 lb for a few seconds before it starts to build its way back up to 44 lb where it holds.
Engine running:
36 to 38 lb with the engine running at idle
When reving to wide open throttle dips to as low as 34 or 35 lb.
My 1988 corvette service manual shows on chart A7 fuel system diagnosis,
page 6E3-A-19
1. Ignition on, fuel pump will run for about 2 seconds, then turn off. Pressure should be 40.5 to 47 psi and hold steady when fuel pump turns off.
THIS IS THE PART I HAVE THE BIG QUESTION ABOUT
Mine is dropping from 46 to 42 immediately when the fuel pump stops, but then it holds steady for a few seconds before it starts to build back up to 44 lb.
Is this OK or NOT OK? It is still in tolerance. If it is OK, then my fuel system passes the next step in tolerance, and my problem is not with the fuel system.
My 1988 corvette service manual show on chart A7 fuel system diagnosis,
page 6E3-A-19
2. Start and idle engine at normal operating temperature. Fuel pressure should be
Lower by 3 – 10 psi.
Mine is within limits if you don't have a problem with it droping from 46 to 42 when the fuel pump shuts off in step 1.
Showing that there is no trouble found, review symptoms section B. Which pretty much is everything a computer can’t tell you to look for, like wire, caps, hoses…..etc.
But if you do count the drop in step 1; when the fuel pump shuts off, as a problem. Then I have a bad fuel pump, fuel regulator, or fuel injectors.
I am testing my fuel system because my corvette sputters, when I floor it most of the time, but not always.
It also dies when I idle sometimes, but not always.
It has always died at idle for the last 2 years, I have been living with it, But now the sputtering is very frequent at wide open throttle.
It did sputter every now and then for the last 2 years, but now it is much worse.
Today I have different numbers than yesterday.
Yesterday the car may have been cold and it showed:
39 lb of pressure with the key on/engine off.
32 lb of pressure with the engine running.
Today I let the car warm up to operating temp and it showed:
Key On/Engine Off:
46 lb for approx 2 seconds, then it drops to 42 lb for a few seconds before it starts to build its way back up to 44 lb where it holds.
Engine running:
36 to 38 lb with the engine running at idle
When reving to wide open throttle dips to as low as 34 or 35 lb.
My 1988 corvette service manual shows on chart A7 fuel system diagnosis,
page 6E3-A-19
1. Ignition on, fuel pump will run for about 2 seconds, then turn off. Pressure should be 40.5 to 47 psi and hold steady when fuel pump turns off.
THIS IS THE PART I HAVE THE BIG QUESTION ABOUT
Mine is dropping from 46 to 42 immediately when the fuel pump stops, but then it holds steady for a few seconds before it starts to build back up to 44 lb.
Is this OK or NOT OK? It is still in tolerance. If it is OK, then my fuel system passes the next step in tolerance, and my problem is not with the fuel system.
My 1988 corvette service manual show on chart A7 fuel system diagnosis,
page 6E3-A-19
2. Start and idle engine at normal operating temperature. Fuel pressure should be
Lower by 3 – 10 psi.
Mine is within limits if you don't have a problem with it droping from 46 to 42 when the fuel pump shuts off in step 1.
Showing that there is no trouble found, review symptoms section B. Which pretty much is everything a computer can’t tell you to look for, like wire, caps, hoses…..etc.
But if you do count the drop in step 1; when the fuel pump shuts off, as a problem. Then I have a bad fuel pump, fuel regulator, or fuel injectors.
I am testing my fuel system because my corvette sputters, when I floor it most of the time, but not always.
It also dies when I idle sometimes, but not always.
It has always died at idle for the last 2 years, I have been living with it, But now the sputtering is very frequent at wide open throttle.
It did sputter every now and then for the last 2 years, but now it is much worse.
Last edited by 5speedC4; 03-22-2007 at 06:37 PM.
03-22-2007, 06:59 PM
#2
Team Owner
Member Since: Dec 2000
Location: SE NY
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I'm not sure about the drop then back up again but doesn't sound right to me. But since it's holding at 44psi let this one go for a while.
When you check fuel pressure is it with engine at idle and with the vac line off and plugged at the plenum fitting? If should be.
If, after you take a reading in this mode, you nail the accelerator fuel pressure should remain rock solid.
To chase the idle problem I would:
-check manifold vacuum
-check for vacuum leak
-clean the TB & blades w/ TB cleaner
-service the IAC, i.e. clean it & it's bore and reset base idle per FSM
To check ignition clip a timing light in turn onto each plug wire and note if missed flashes correspond with engine misses.
It sounds like you may have several problems though they might be due to a common element.
If fuel pressure is behaving properly, check ignition, if ok check the "chase idle" items above.
When you check fuel pressure is it with engine at idle and with the vac line off and plugged at the plenum fitting? If should be.
If, after you take a reading in this mode, you nail the accelerator fuel pressure should remain rock solid.
To chase the idle problem I would:
-check manifold vacuum
-check for vacuum leak
-clean the TB & blades w/ TB cleaner
-service the IAC, i.e. clean it & it's bore and reset base idle per FSM
To check ignition clip a timing light in turn onto each plug wire and note if missed flashes correspond with engine misses.
It sounds like you may have several problems though they might be due to a common element.
If fuel pressure is behaving properly, check ignition, if ok check the "chase idle" items above.
03-22-2007, 10:19 PM
#3
Drifting
Thread Starter
I'm not sure about the drop then back up again but doesn't sound right to me. But since it's holding at 44psi let this one go for a while.
When you check fuel pressure is it with engine at idle and with the vac line off and plugged at the plenum fitting? If should be.
If, after you take a reading in this mode, you nail the accelerator fuel pressure should remain rock solid.
To chase the idle problem I would:
-check manifold vacuum
-check for vacuum leak
-clean the TB & blades w/ TB cleaner
-service the IAC, i.e. clean it & it's bore and reset base idle per FSM
To check ignition clip a timing light in turn onto each plug wire and note if missed flashes correspond with engine misses.
It sounds like you may have several problems though they might be due to a common element.
If fuel pressure is behaving properly, check ignition, if ok check the "chase idle" items above.
When you check fuel pressure is it with engine at idle and with the vac line off and plugged at the plenum fitting? If should be.
If, after you take a reading in this mode, you nail the accelerator fuel pressure should remain rock solid.
To chase the idle problem I would:
-check manifold vacuum
-check for vacuum leak
-clean the TB & blades w/ TB cleaner
-service the IAC, i.e. clean it & it's bore and reset base idle per FSM
To check ignition clip a timing light in turn onto each plug wire and note if missed flashes correspond with engine misses.
It sounds like you may have several problems though they might be due to a common element.
If fuel pressure is behaving properly, check ignition, if ok check the "chase idle" items above.
I didn't find anyplace in the service manual that said to disconnect the line, so I made sure it was put back on after I put the gauge on.
The engine only misses while going down the road/while the engine is under a load I guess.
It does not miss while in the driveway reving up the motor.
It is less of a miss under a load, and almost sounds like a motor bouncing up against a rev limiter. It is really more of a sputter than a miss. The motor is no where near the redline and does it at different rpms.
Last edited by 5speedC4; 03-22-2007 at 10:21 PM.
03-22-2007, 11:23 PM
#4
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Member Since: Dec 2000
Location: SE NY
Posts: 90,675
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I just finished a "search for lost power" that was finally traced to a clogged fuel line filter. My symptom was that fuel pressure dropped off when I hammered the accelerator with the vac line disconnected.
I suggest you unplug that vac line, plug it at the plenum fitting, lay the FP gauge on the windshield under the RH wiper blade and monitor fuel pressure when you experience the problem. Fuel pressure should be rock solid under such test conditions.
The reason for pulling the vac line is that fuel pressure will varry with manifold vacuum if the line is connected and we are checking fuel delivery for consistency.
You could pull the spark plugs to see if any is showing a problem.
Also you can lightly spray the wires with water at idle and in a darkened garage to see if any of the wires is "leaking".
Still, for your idle issue, I suggest you address the items mentioned above.
I suggest you unplug that vac line, plug it at the plenum fitting, lay the FP gauge on the windshield under the RH wiper blade and monitor fuel pressure when you experience the problem. Fuel pressure should be rock solid under such test conditions.
The reason for pulling the vac line is that fuel pressure will varry with manifold vacuum if the line is connected and we are checking fuel delivery for consistency.
You could pull the spark plugs to see if any is showing a problem.
Also you can lightly spray the wires with water at idle and in a darkened garage to see if any of the wires is "leaking".
Still, for your idle issue, I suggest you address the items mentioned above.
