I'm just curious, how can I check if my fuel injectors are leaking? Is it possible to narrow it down to which one or ones? I have an L98 motor with stock injectors and I have a fuel pressure gauge. Also does the test get done with the car on/off vacuum line to regulator on/off. I would really like to check this, thanks.

 

turn the key to "ON", let the pump prime the fuel rail, turn the key "OFF", pinch the return line and watch your fuel pressure gauge. If it start to drop rapidly, (like 5psi in a minute or so) then your injector(s) are leaking.

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Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, MSD 6AL, Aluminum Driveshaft, Wonderbar, TB Coolant Bypass, Ported Plenum, Modified MAF, Syclone Fuel Pump, JET Airfoil

15.556 @ 86.65mph, Nov 10, 2000.... I know it sucks.. but it will get better!

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You should also pinch off the supply line because the fuel pump may have a leaky check valve Pinch off the hoses with two pair of vice grips or something similar, but not too tight cause you don't want to cut the rubber fuel lines.

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Rob
High Performance & Party page
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95 Trans Am Conv.- LT1

 

Just don't pinch them off at the same time... that accomplishes nothing. But you are right, pinching off the supply line will tell you if the check valve in the pump is bad. I think mine is and instead of pulling the pump which is only about 1 1/2 years old, I'm thinking about installing a 40# relief valve in the return line.

 

Kevin,

That's what the pressure regulator is supposed to do. If you lose fuel pressure after the pump is turned off, pinch the fuel return line. If the pressure drop is still occurring, the injectors are probably leaking. If the pressure remains steady, the regulator valve seat and disc are probably damaged.

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Later,
Vader
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"I'm'a do Things My Way - It's My way or the Highway."
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Why not pinch both at the same time. By doing this, the fuel has no where to go but through the injectors. If you loose pressure, bad injectors, if pressure stays, injectors don't leak. Correct?

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Rob
'86 TA 305 TPI
Gutted MAF, Ported Plenum
TB Bypass, Home made Cold Air Intake,
Edelbrock T.E.S.

 

Vader,

I am losing pressure with either line pinched, I just sent off my injectors to Rich at cruzin performance to have them done so that should take care of the injector side of things....

Also, as per our e-mail conversation of about a week ago, I went ahead and built the AFPR like you said to do. But I thought that there was a relief valve back in the pump that kept fuel pressure from bleeding off?? It's the regulator?? Should what I have done to it help or should I go ahead and replace the internals too?

 

You DO want to pinch both lines at the same time to check for leaky injectors! But only after you have turned on the key and energized the pump and built up pressure.
Then quickly jump under the car and pinch off BOTH lines.
If pressure drops still, then leaky injector.
If pressure holds, then release the supply line.
If pressure drops then, then you have a bad check valve in pump.
If pressure still holds, release return line,
If pressure drops, then you have a bad regulator.
*
If injectors are holding pressure, be sure to do the same thing again, but releasing the return line first, just to make sure you don't have both a bad check valve and regulator!
*
Oh yea, if your injectors drop just 5# in a few minutes, thats normal and will not cause problems. If you can go for 10-15 minutes and still have any pressure at all, then everything is OK. For an injector to cause problems you would need to drop all 30-40# in less than 10 minutes.

[This message has been edited by 2QUIK6 (edited April 10, 2001).]

 

Thanks for the input guys but I have a little question where and how do I pinch these lines. I bought a pair of hose pinchers which are basically a pair of fancy vice grips that are totally flat and have no teeth on them. However, I see someone mentioned under the car, but my lines are all steel I believe. There are the two lines that go up inside to the rail that are rubber for about 1 foot when they arc over the steering stuff, can I pinch them there? And how do I know which one is which? Thanks.

 

Yes, pinch them off right by the Brake Master Cylinder where they are rubber. You will need to follow the lines up as they go towards the fuel rails. The feed line will go directly into the fuel rail (on the passenger side I think) and the return will be coming from the regulator housing. I'm not sure but I think the feed line is the one closer to the front of the car.....can't remember off hand. Just look at where the lines go to and you'll be able to tell.

[This message has been edited by Matt87GTA (edited April 11, 2001).]