Strange fuel problem..
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Joined: Jun 2001
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From: Princeton NJ
Strange fuel problem..
Well, I went out and got a gauge to measure fuel pressure, and this is what I found:
When I turn my key most of the way, the fuel pressure pumps up to 41-42psi. It then, immediately dropps off to 10psi, and stays there. When I crank the key all the way, it pumps back up to 36-38psi, and the engine turns and turns, until after 10-15 turns it fires up. It then stays at around 38psi at idle. The car idles extremely rough, and this morning I had a couple misses. At first I thought it might be leaky injectors, but dropping from 41psi to 10psi in less then a second.. doesnt sound like just an injector! Anyone have any ideas? :cry
When I turn my key most of the way, the fuel pressure pumps up to 41-42psi. It then, immediately dropps off to 10psi, and stays there. When I crank the key all the way, it pumps back up to 36-38psi, and the engine turns and turns, until after 10-15 turns it fires up. It then stays at around 38psi at idle. The car idles extremely rough, and this morning I had a couple misses. At first I thought it might be leaky injectors, but dropping from 41psi to 10psi in less then a second.. doesnt sound like just an injector! Anyone have any ideas? :cry
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Re: Strange fuel problem.. (Mark92LT1)
It actually sounds like the same type thing that is happening to me. Do you notice that it will do the same thing if you run it for a while and shut it off and then try to start it again in the next 15 minutes or so? Mine does that, but not every time. That's why I think it could be an injector. I don't have a hand held fuel pressure guage, but I hope to get my permanant fuel pressure guage up and working tonight so I can take a look. I've also got a set of SVO 24# injectors on the way. I'm getting them tomorrow, brand new, $125
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Joined: Jun 2001
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From: Princeton NJ
Re: Strange fuel problem.. (Mark92LT1)
Nathan-
I just figured out what my problem is: my fuel pressure regulator. Try starting your car, then take out the vaccum line that plugs into the pressure regulator- if gas comes out of the vaccum line, then the membrane in the pressure regulator is broken (I had gas spraying out). The reason I dont suspect a leaky injector, is injectors typicaly leak slowly. With the pressure drop I am getting, I would practicaly be filling up the cylinders with gas, and wouldnt be able to get the car started at all.
-Mark
I just figured out what my problem is: my fuel pressure regulator. Try starting your car, then take out the vaccum line that plugs into the pressure regulator- if gas comes out of the vaccum line, then the membrane in the pressure regulator is broken (I had gas spraying out). The reason I dont suspect a leaky injector, is injectors typicaly leak slowly. With the pressure drop I am getting, I would practicaly be filling up the cylinders with gas, and wouldnt be able to get the car started at all.
-Mark
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Re: Strange fuel problem.. (Mark92LT1)
Thats good troubshooting Mark...gas should not be spitting out the regulator.When a engine has erratic fuel pressure it will run rough at times.
A good working fuel system will have pressure right away and hold for a while then slowly bleed off.
Just for reference, sometimes when the FPR is fine and isnt leaking internally, the check valve in the fuel pump can cause the pressure to drop off fast when turning the key off.
This only makes hard starts, doesnt affect the car when its running as far as I know.
The fix is to replace the pump...I had this problem for 5 years but waited until the pump started to go bad...I just had to crank the engine a little longer then normal between stop and go trips.
A good working fuel system will have pressure right away and hold for a while then slowly bleed off.
Just for reference, sometimes when the FPR is fine and isnt leaking internally, the check valve in the fuel pump can cause the pressure to drop off fast when turning the key off.
This only makes hard starts, doesnt affect the car when its running as far as I know.
The fix is to replace the pump...I had this problem for 5 years but waited until the pump started to go bad...I just had to crank the engine a little longer then normal between stop and go trips.
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From: Princeton NJ
Re: Strange fuel problem.. (Bill's86Coupe)
Thanks Bill-
Its been a long road to get here though! For a while I was convinced that my injectors were leaking. Almost ordered new ones. Then, early this morning, I was missing a bit at idle, and was terrified it was my Opti-spark (Which was just replaced 500 miles ago!!!). Now I am feeling much better, knowing what the culprit is (I hope!!!)
-Mark
Its been a long road to get here though! For a while I was convinced that my injectors were leaking. Almost ordered new ones. Then, early this morning, I was missing a bit at idle, and was terrified it was my Opti-spark (Which was just replaced 500 miles ago!!!). Now I am feeling much better, knowing what the culprit is (I hope!!!)
-Mark
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Re: Strange fuel problem.. (Mark92LT1)
Well I want the new injectors anyway, but gimmie a little more info. I have the stock fuel pressure regulator, where is it located. I thought it was the round thing in line with supply fuel line up near the fuel rail. But if memory serves that doesn't have vacuum line on it.
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From: Princeton NJ
Re: Strange fuel problem.. (Nathan Plemons)
Here is a picture for you Nathan- it shows my new adjustable pressure regulator, in place of the stock one. You can see the vaccum line coming down from it. On the stock regulator, the vaccum line comes out towards you (perpendicular to the picture). Pull that vaccum line out- if you get gas, its bad. After changing mine, my car runs like new! Perfect idle, and starts like a champ! :cool: :cool: :cool:
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