C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Hesitation/stumble When Accelerating

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Old Jul 14, 2008 | 05:53 PM
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Default Hesitation/stumble When Accelerating

I posted a few weeks ago about a huge stumble when accelerating. It turned out to be the fuel pump. The fuel pump, all screens and fuel filter were replaced. When driving the other day a small stumble started. It doesnt do it all the time, but its there the majority of the time. There are no codes. The wires and plugs are fine and I replaced the ignition coil a few weeks ago. The car idles at 40psi. The engine was rebuilt last year so everything is brand new.
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Old Jul 14, 2008 | 07:58 PM
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I'll take a stab.... Fuel pressure regulator. I'm told that could be your problem.When you floor it your pressure needs to drop so you get smooth power. Be nice fellow forumers if I'm wrong about this.
Check for vacuum leaks around the intake. All those hoses can develop pinhole leaks.
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Old Jul 14, 2008 | 08:03 PM
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I was thinking it could be the fuel pressure regulator, but wouldn't my fuel pressure be jumping all over the place. It stays at around 41psi. I can't tell if it drops when I'm driving though because I dont have the proper tools.

Last edited by jimmers; Jul 14, 2008 at 08:06 PM.
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Old Jul 14, 2008 | 08:54 PM
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Just for the heck of it....Does it stumble when taking off from a stop or all the time? And does your fuel gauge read 1/2 a tank or less? Try it with a full tank of gas.
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Old Jul 14, 2008 | 10:02 PM
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It stumbles all the time. Right now there is 1/2 tank of gas. I will fill it up tomorrow and see what happens.
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Old Jul 14, 2008 | 10:12 PM
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Originally Posted by jimmers
It stumbles all the time. Right now there is 1/2 tank of gas. I will fill it up tomorrow and see what happens.
Fuel pressure should be checked static (motor off), at idle with vacuum on FPR, at idle with vacuum off of FPR, and pedal down (get a longer hose, and tape it to the windshield).

I doubt too many folks have done the last test, but it IS recommended to rule out fuel problems...
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Old Jul 15, 2008 | 09:22 AM
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Originally Posted by jimmers
I posted a few weeks ago about a huge stumble when accelerating. It turned out to be the fuel pump. The fuel pump, all screens and fuel filter were replaced. When driving the other day a small stumble started. It doesnt do it all the time, but its there the majority of the time. There are no codes. The wires and plugs are fine and I replaced the ignition coil a few weeks ago. The car idles at 40psi. The engine was rebuilt last year so everything is brand new.
you said everything was new on the engine.. what injectors did you use? or, did you put back the orig. 90 Multecs
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Old Jul 15, 2008 | 09:54 AM
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A severe vacuum leak or a SP wire not on all the way, will cause a stumble. Don't just think fuel, check everything.
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Old Jul 15, 2008 | 06:54 PM
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Originally Posted by smoothbore
Fuel pressure and fuel flow are to differnt things. check fuel flow at fuel rail.
How do I check fuel flow?
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Old Jul 15, 2008 | 06:55 PM
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Originally Posted by FICINJECTORS
you said everything was new on the engine.. what injectors did you use? or, did you put back the orig. 90 Multecs
The injectors arent the Multecs. I believe they are Accel injectors.
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Old Jul 15, 2008 | 08:32 PM
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Originally Posted by jimmers
How do I check fuel flow?
Use to be disconnect the fuel line, crank the car, and feed the fuel that's pumped into a jug, while watchin' time.

With these cars, I think the 3 non-static pressure tests will tell you all you need to know about flow:
Fuel pressure should be checked static (motor off), at idle with vacuum on FPR, at idle with vacuum off of FPR, and pedal down (get a longer hose, and tape it to the windshield).

I doubt too many folks have done the last test, but it IS recommended to rule out any fuel problem...
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