90 fuel pressure issues
Thread Starter
Safety Car
Joined: Oct 2008
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From: Yucaipa CA
90 fuel pressure issues
OK I am running currently 19lb per hour new bosche injectors. I did this because of old gas in the car and I had them and decided to run the car through a lot of tanks a gas while this project is being done so that when I do put the correct ones in no contaminents will get to them ......
Alright just out of curiousity I decided to run a fuel pressure test on the car today. I know it should be at about 43.5lbs or thats what I have read.
Key on no start my car is at 74psi .... So I thought maybe bad gauge and went and bought a new one. Again 74psi ..... So I disconnect the vacuum line to the regulator and start the car. It has no constant reading on the gauge and the gauge flutters between 70 & 80psi very rapidly.
again I thought maybe another bad gauge ... however put it on my 97 camaro and the pressure was where it is supposed to be.
So what could be causing this? The car seems to idle ok like this. I'm fairly certain there is no adjustable regulator on it (I see no adjustable screw in the cap)
Any of you ever seen a TPI do this?
Another interesting thing .... when pressure is at 74psi and key shut off it falls fairly fast to 40psi then from 40psi down to say 37psi it takes well over like 15-20 minutes.
Alright just out of curiousity I decided to run a fuel pressure test on the car today. I know it should be at about 43.5lbs or thats what I have read.
Key on no start my car is at 74psi .... So I thought maybe bad gauge and went and bought a new one. Again 74psi ..... So I disconnect the vacuum line to the regulator and start the car. It has no constant reading on the gauge and the gauge flutters between 70 & 80psi very rapidly.
again I thought maybe another bad gauge ... however put it on my 97 camaro and the pressure was where it is supposed to be.
So what could be causing this? The car seems to idle ok like this. I'm fairly certain there is no adjustable regulator on it (I see no adjustable screw in the cap)
Any of you ever seen a TPI do this?
Another interesting thing .... when pressure is at 74psi and key shut off it falls fairly fast to 40psi then from 40psi down to say 37psi it takes well over like 15-20 minutes.
Last edited by jeffp1167; Nov 21, 2010 at 08:22 PM.
Burning Brakes
Joined: Oct 2009
Posts: 773
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From: Minneapolis MN
With vehicle running,disconnect vacuum line to fuel pressure regulator.Fuel pressure should increase about 10psi.After this test,reconnect vacuum line then rev engine up & see fuel pressure increases each time you give it gas.Is the fuel pressure regulator leaking when the vacuum hose is disconnected while engine is not running?Is the fuel pressure steady while engine is running?Let me know the results of this test
Last edited by 94vettelover2; Nov 21, 2010 at 08:21 PM.
Thread Starter
Safety Car
Joined: Oct 2008
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From: Yucaipa CA
With vehicle running,disconnect vacuum line to fuel pressure regulator.Fuel pressure should increase about 10psi.After this test,reconnect vacuum line then rev engine up & see fuel pressure increases each time you give it gas.Is the fuel pressure regulator leaking when the vacuum hose is disconnected while engine is not running?Is the fuel pressure steady while engine is running?Let me know the results of this test
rev up line connected (70-80 psi and fluttering)
only time gauge does not flutter is when motor isn't running but even so it still hits 74psi
The gauge has to be correct because it works correctly on my 97 camaro and does nothing like what it is doing on this corvette.
no fuel out of the vacuum line at all
weren't bosch injectors designed to shut down after like 50psi anyways? These were brand new 19lb per hr. injectors (not rebuilt) so it is highly doubtful they could be the cause. I installed a new fuel pump in the car few months back so doubtful it is that.
Last edited by jeffp1167; Nov 21, 2010 at 08:34 PM.
Le Mans Master
Joined: Feb 2005
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From: Clearwater Florida
........ There is blockage in the return line ... some of these things have a filter on the return just above the pressure side filter ... or road or jacking damage has kinked the hard line somewhere 'tween the engine and tank ...
Thread Starter
Safety Car
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From: Yucaipa CA
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Thread Starter
Safety Car
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From: Yucaipa CA
In the event the return line is kinked, why would it still be so high at an initial prime of the fuel pump? I would think maybe if it were running yes but not just priming the fuel system.
After shut off it drops from 74psi to 38psi pretty quik so the fuel has to be going somewhere yet I never see any leaks.
anyone have a diagram of how the fuel lines are routed on this car so I can check them all out?
After shut off it drops from 74psi to 38psi pretty quik so the fuel has to be going somewhere yet I never see any leaks.
anyone have a diagram of how the fuel lines are routed on this car so I can check them all out?
Le Mans Master
Joined: Oct 2008
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From: Houston Texas
Someone put an adjustbale regulator on it. What other mods do you have? Do you know? Did you replace the injectors with like injectors. I would do a datalog if i were you.
Thread Starter
Safety Car
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From: Yucaipa CA
everything is stock. really doubt it needs to be datalogged. It has 19lb per hr injectors in it for the time being till I am ready to put it on the road. I might just crank the fuel pressure up a bit to compensate for the smaller injectors. Figure if I run these at 50psi that should get me to around 22lbs per hr.
Safety Car
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everything is stock. really doubt it needs to be datalogged. It has 19lb per hr injectors in it for the time being till I am ready to put it on the road. I might just crank the fuel pressure up a bit to compensate for the smaller injectors. Figure if I run these at 50psi that should get me to around 22lbs per hr.
