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Old 06-11-2012, 12:24 PM   #1
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Lean issue

I was told after my dyno that I was running lean, guy told me to use a adjustable fuel pressure regulator to correct that well I have the regulator now, at what pressure should it be adjusted to without vacuum? 95 cobra with o/r h pipe, flowmaster cat backs, and a CNL cold air calibrated for 24lb injectors
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Old 06-11-2012, 12:36 PM   #2
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Subscribed. I'd like to know too.
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Old 06-11-2012, 03:18 PM   #3
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38 lbs
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Old 06-11-2012, 03:32 PM   #4
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Old 06-11-2012, 08:54 PM   #5
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Are those both at idle with no vacuum?
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Old 06-11-2012, 10:03 PM   #6
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Yes.

The range between both of our answers is good.
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Old 06-12-2012, 01:57 AM   #7
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Re: Lean issue

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Originally Posted by jwhayne0001 View Post
I was told after my dyno that I was running lean, guy told me to use a adjustable fuel pressure regulator to correct that well I have the regulator now, at what pressure should it be adjusted to without vacuum? 95 cobra with o/r h pipe, flowmaster cat backs, and a CNL cold air calibrated for 24lb injectors
The stock range is 38-40 psi. Try upping it a pound or two at a time until the lean condition is corrected.
Read your plugs (Yes, I know it will be a PITA, but without a Wideband or being on the Dyno there is no other way to tell.) to see if you are making a difference and to tell when to quit raising the pressure.


The best way is to have the engine warmed up (Mechanics gloves are going to be very beneficial for this.), make a WOT run, then shut the engine down, pull and check the plugs. You do not want to idle or run on slow speed for very long at all to read the plugs as it will give you false readings.


Are you using a C&L MAF that uses the calibration tubes?
If so, I have read that they are not very good at correcting your fuel mixture.
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Old 06-12-2012, 07:39 AM   #8
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Yes I am using the calibrated tubes for 24lbs, guess I check with the local dyno on how much 3 runs with wideband and fuel pressure tune would be I know my better half won't let go of 500 bucks for a full on tune
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Old 06-12-2012, 10:18 AM   #9
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I would suggest getting a wideband air fuel gauge. I plan on it myself as soon as I can get the $$. I am carbed so its gonna be an asset to my tuning. But you would still benifit from it very nicely.
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Old 06-12-2012, 03:47 PM   #10
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Re: Lean issue

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I would suggest getting a wideband air fuel gauge. I plan on it myself as soon as I can get the $$. I am carbed so its gonna be an asset to my tuning. But you would still benifit from it very nicely.
You would also have something tangible for your money spent.
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Old 06-16-2012, 11:36 PM   #11
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Ok I installed the regulator, set at 41 psi for now till I can get it tuned out right, I've noticed if it sets for over a hour it has an extended crank time to start, considerably longer than before, about 5 or so seconds
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Old 06-17-2012, 03:59 AM   #12
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Re: Lean issue

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Ok I installed the regulator, set at 41 psi for now till I can get it tuned out right, I've noticed if it sets for over a hour it has an extended crank time to start, considerably longer than before, about 5 or so seconds
I don't know why it would be worse, unless the regulator bleeds off faster or more than the old one.


Cycle the key on and off a couple of times. Give it long enough for the pump to get the pressure built up good then try it.


My 86, my wife's 2010 Milan and my 2002 Ranger will do the same thing if you don't wait long enough for the fuel pressure to build up.
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Old 06-17-2012, 09:02 AM   #13
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With fuel pressure gauge on I start it, 41 psi, shut it off it drops immediately
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Old 06-17-2012, 11:45 AM   #14
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Re: Lean issue

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Originally Posted by jwhayne0001 View Post
With fuel pressure gauge on I start it, 41 psi, shut it off it drops immediately
That's not right.
It should hold the pressure for a while then slowly drop off over time.
If this just since the new adjustable regulator installation?
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Old 06-17-2012, 03:16 PM   #15
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Quote:
Originally Posted by Trojan Horse

That's not right.
It should hold the pressure for a while then slowly drop off over time.
If this just since the new adjustable regulator installation?
Yes, started within 2 seconds of turning the key even after sitting for a week or 2

---------- Post added at 03:16 PM ---------- Previous post was at 03:15 PM ----------

Quote:
Originally Posted by jwhayne0001

Yes, started within 2 seconds of turning the key even after sitting for a week or 2
With the OEM regulator
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Old 06-17-2012, 07:32 PM   #16
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Re: Lean issue

Your new regulator must be defective.

IMO starting the EFI cars is a different procedure from the old carbureted cars.
I think you should always turn the key on and then wait a few seconds for the pump to pressurize the fuel system fully.
If you do not, then when you engage the starter it pulls power away from the fuel pump and it won't finish priming the system to full pressure properly as quick as it would have without engaging the starter. Thus it takes longer to start the engine because you are trying to do that with low fuel pressure.
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Old 06-17-2012, 07:35 PM   #17
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Quote:
Originally Posted by Trojan Horse
Your new regulator must be defective.
Yeah I just shot them an email
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Old 06-17-2012, 07:38 PM   #18
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i know my setup is way different. but my pressure leaks down as soon as i shut off to.i thought it was wierd but it doesnt really bother because it runs good, and stays at a steady 6psi.
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Old 06-17-2012, 07:56 PM   #19
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Quote:
Originally Posted by dreamstang
i know my setup is way different. but my pressure leaks down as soon as i shut off to.i thought it was wierd but it doesnt really bother because it runs good, and stays at a steady 6psi.
I dont think carb setups hold pressure anyways do they?..thats when the accelerator pump comes in handy...do you ever pump it before you start it or no need?...
I never timed my the bleed off on my stang but it does hold pressure for a bit..
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Old 06-17-2012, 08:06 PM   #20
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Re: Lean issue

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i know my setup is way different. but my pressure leaks down as soon as i shut off to.i thought it was wierd but it doesnt really bother because it runs good, and stays at a steady 6psi.
You have a reserve of gasoline in the carb for start up. The EFI has to have pressurized fuel on start up.
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Old 06-17-2012, 08:10 PM   #21
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Re: Lean issue

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Originally Posted by XXSTEVEO66 View Post
I dont think carb setups hold pressure anyways do they?..thats when the accelerator pump comes in handy...do you ever pump it before you start it or no need?...
I never timed my the bleed off on my stang but it does hold pressure for a bit..
I have never timed mine either, but it will still have some pressure the next day.
There doesn't seem to be a firm "rule" for bleed down times or at least I have never seen any specs on it.
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Old 06-17-2012, 08:12 PM   #22
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Quote:
Originally Posted by XXSTEVEO66

I dont think carb setups hold pressure anyways do they?..thats when the accelerator pump comes in handy...do you ever pump it before you start it or no need?...
I never timed my the bleed off on my stang but it does hold pressure for a bit..
well if i start it right back up it will fire right up, without even touching the pedal. but if its been sittingi usually let it prime for a few seconds.

---------- Post added at 08:12 PM ---------- Previous post was at 08:11 PM ----------

Quote:
Originally Posted by Trojan Horse

You have a reserve of gasoline in the carb for start up. The EFI has to have pressurized fuel on start up.
makes sense.
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Old 06-19-2012, 05:25 AM   #23
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Re: Lean issue

Ok, I'm an idiot. I completely forgot about the check valve in the electric fuel pumps.


If the check valve is bad or has been blocked open by debris that has gotten around the in tank filter, the fuel pressure will bleed off quickly.
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Old 06-19-2012, 05:37 AM   #24
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Quote:
Originally Posted by Trojan Horse
Ok, I'm an idiot. I completely forgot about the check valve in the electric fuel pumps.

If the check valve is bad or has been blocked open by debris that has gotten around the in tank filter, the fuel pressure will bleed off quickly.
Does it affect anything though? Cause I don't seem to have a problem.
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Old 06-19-2012, 06:01 AM   #25
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Re: Lean issue

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Does it affect anything though? Cause I don't seem to have a problem.
With a carb you won't notice anything because fuel is stored in the bowls of the carb and feeds into the engine from there.
EFI however has to have a certain amount of fuel pressure to start and run properly.
With low or no pressure it will take longer for the pump to start up and deliver the proper amount of fuel flow and pressure to get the engine started.
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