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Old 10-26-2003, 03:21 PM   #1
B84RADR
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Default Fuel Pressure Leak Down

I've been searching the archives to find out what is normal for fuel pressure when the car is off. I know the rail should hold about 40PSI which mine does when it's on. Southern Comfort and a few others has threads on the subject.

After I turn the car off, it stays at 40. I let it sit overnight last night and it's down to 0. Is this indicative of a leaky fuel injector? The fuel injectors are brand new, made by Accel. Maybe that's my problem :crazy: :crazy:

I got the impression from that post it was OK for it to drop to 20PSI, but it should stay about there, not drop clear to 0 like mine. Could very well explain the hard starts.

So if mine is 0 (and I'll test how long it takes for it to get to 0 today) where do you start trying to narrow that down and fix it? What can I start checking first? Leaky fuel injectors even though they are new?
http://forums.corvetteforum.com/zerothread?id=676662

The fuel pump is an AC Delco (brand new) and the fuel filter is new too.
OH, and could it be my adjustable fuel pressure regulator? I just don't know how to test for that.

Thanks,
Shayne


[Modified by sspackman, 1:23 PM 10/26/2003]
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Old 10-26-2003, 03:29 PM   #2
JAKE
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Default Re: Fuel Pressure Leak Down (sspackman)

I use to be concerned about this too. My fuel pressure would drop to zero over-night. I did a lot of checking and pulled the pump a few times trying to figure out what was going on. I even did the pressure/return line tests to try to isolate which was causing the pressure to bleed off.

Finally I decided that it wasn't a problem, so I just ignore it and learned to live with it.

I get nary a whiff of smoke when I fire the engine, plugs always look great, no drivablilty concerns, so for me I'm guessing the pressure is venting to the tank.

Once less thing to worry about.

Jake
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Old 10-26-2003, 06:35 PM   #3
AGENT 86
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Default Re: Fuel Pressure Leak Down (JAKE)

My fuel pressure drops like a rock and is zero within the hour. I haven't tracked down why yet because my car always starts instantly and runs strong. When it becomes a problem i will track it down. :cheers:
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Old 10-26-2003, 07:25 PM   #4
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Default Re: Fuel Pressure Leak Down (AGENT 86)

It is not unusual for for the fp to drop to 0 overnite. Now if it dropped to 0 within 10 minutes of turning it off, that's another matter. That's why the pump is turned on for about 2 sec. ( when the key is turned "on ", engine not running) so the fuel rail can be pressurized.
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Old 10-26-2003, 07:34 PM   #5
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Default Re: Fuel Pressure Leak Down (ittlfly)

My fuel pressure drops after @ 2-3 hours and by morning it is "0"
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Old 10-26-2003, 10:38 PM   #6
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Default Re: Fuel Pressure Leak Down (ld85)

It's normal. I think it is not suppose to drop like more than 15PSI in a set time frame like 30 min or something. I found this in a book a few years ago. Really can't remember the time frame but it wasn't something you had to watch for al ong time I remember doing the test in a short period of time.
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Old 10-26-2003, 11:02 PM   #7
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Default Re: Fuel Pressure Leak Down (ittlfly)

Quote:
It is not unusual for for the fp to drop to 0 overnite. Now if it dropped to 0 within 10 minutes of turning it off, that's another matter. That's why the pump is turned on for about 2 sec. ( when the key is turned "on ", engine not running) so the fuel rail can be pressurized.
:iagree: I think its the first couple of hours that tells the tale. After that not a big deal
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Old 10-27-2003, 03:05 AM   #8
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Default Re: Fuel Pressure Leak Down (Southern Comfort)

OK, I took some measurements while working on the ball joints this evening.

I am at 42PSI when turning the car off.
Here goes:
5:16pm, 41PSI
5:28pm, 33PSI
5:34pm, 27PSI
5:41pm, 19PSI
5:49pm, 15PSI
6:11pm, 10PSI
6:28pm, 6PSI
6:45pm, 0PSI

There was another reading earlier in the day for comparison:
4:15pm, 42PSI
4:20pm, 41.5PSI
5:00pm 16PSI
5:13pm 10PSI

There's a little data. What do you make of it?
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Old 10-27-2003, 07:43 AM   #9
Da Wiz
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Default Re: Fuel Pressure Leak Down (sspackman)

I am curious as to what problems you are having? Hard starts in the morning, or after the car has set for several hours? I am having these problems. I am watching this thread with interest.

:cheers:
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Old 10-27-2003, 09:27 AM   #10
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Default Re: Fuel Pressure Leak Down (Da Wiz)

It's a matter of how fast the pressure bleeds off , not if it does at all. If the leakdown is due to leaking injectors , then you will get hard starting which sounds like the engine is flooded. If you are getting instant starts, don't worry about it.
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Old 10-27-2003, 09:50 AM   #11
JAKE
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Default Re: Fuel Pressure Leak Down (sspackman)

Quote:
OK, I took some measurements while working on the ball joints this evening.

I am at 42PSI when turning the car off.
Here goes:
5:16pm, 41PSI
5:28pm, 33PSI
5:34pm, 27PSI
5:41pm, 19PSI
5:49pm, 15PSI
6:11pm, 10PSI
6:28pm, 6PSI
6:45pm, 0PSI

There was another reading earlier in the day for comparison:
4:15pm, 42PSI
4:20pm, 41.5PSI
5:00pm 16PSI
5:13pm 10PSI

There's a little data. What do you make of it?
I did this exact same thing a few years ago, logged the drop on pressure and posted the results to this forum. That was when I was still concerned about the pressure dropping.

I came to these conclusions:

Since the system works in a closed loop, there are only a few areas that can cause the pressure to drop: The front of the engine, the fuel lines leading to and from the tank and in the tank itself.

Squeezing off the return line and then the feed line alternately can insolate which end of the system is the culprit. Mine was at the return end.

Since I never saw any sign of fuel coming from the lines, I excluded them.

I checked the fuel pressure regulator, injectors, cold start line and fuel rails and again zippo.

I then checked the fuel pump and installed a new rubber line with clamps this time in place of the sound isolator (I believe that's what it's called) thinking it was the return line in the tank that was allowing the pressure drop. Same result; pressure still drops overnight.

Since I never experienced any downside to the pressure dropping condition I just learned to accept it, even though others claim the pressure shouldn't drop that fast.

I read on another thread that there are 8 areas in the PROM specifically dedicated to the cold start fuel condition and that once any mod is made to the airflow of the engine, hard starting results. If I remember correctly, these 8 areas are left blank in the stock PROM and that adding a value to these areas increases fuel flow on cold start up and eliminates the problem. I believe after several tries, the author (sorry forgot his name) entered $8 in those fields, which worked to solve his cold start problem.

As I said, mine has been that way for a few years with no downside. I've made WOT blasts with a fuel pressure gauge taped to the windshield with no pressure drop, I get no error codes, no smoke and drivability is excellent. So I figure it's really a non-issue.

Now I can expend all my energy worrying about all the other stuff that can (and will) go wrong with a 17 year old car. LOL

Jake

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Old 10-27-2003, 09:50 AM
 
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