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Discussion Starter #1
How much fuel pressure should you see at the fuel rail with the car off and it has been sitting a while? I know the pumps have check valves in them and assuming no leaks it should hold most of the pressure correct?

Having a long crank cycle after sitting a while since installing my pump, flex and injectors? Could just need a tuning tweak but started doing this a few days later, that I noticed anyway. Switched back from E85 to 93 and it does the same thing. Today I turned the key on and gave the pump plenty of time to prime and it seemed to help. Was going to put a mechanical gauge on the rail just to see what the pressure is after sitting and before cranking, but wasn't sure what to expect after sitting for say 12 hours.

Thanks for any help.
 
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Sounds like a tune thing to me...

I run flex 100% of the time, it is only slow to crank if it has been sitting for say, a week (and I mean maybe an extra 2 seconds). Otherwise it starts right up. The fact that this is happening with 93 as well is interesting.

I believe the prime cycle is set at a certain length of time, not indefinite with accessory on.

Perhaps ask your tuner what they think?

If given 5 seconds to prime, fuel pressure should be a moot point IMO.
 

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+1

Agree with Adam - the fuel rail won't hold pressure indefinitely, BUT should hold pressure for a while. Running pressure with the pumps on is usually around 45-50psi from what I recollect, so I would expect static pressure in the rail to remain around that right after the pumps stop....

BUT, that pressure will bleed off for several reasons: are the injectors leaking? Is there a leak in the lines (ie where your ethanol sensor is), is there a leak at the factory pump fittings in the tank (known to start leaking over time), or are the pumps installed properly with the correct o-rings, etc?

So if your fuel rail pressure is bleeding off within a few hours I'd suspect a substantial leak somewhere. Otherwise I would expect the rails to be at least partially pressurized for days.
 

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Discussion Starter #4
Thanks for the info. I've only experienced if I go from ign off directly to start. Adam you are correct the pump only primes for a second or two. If I let it prime it starts normally. I added the DMX Flex kit, ID1050X injectors and DMX Aux pump so it could be just the way everything works together now. Just never noticed it before and want to make sure I don't have any issues. I checked all connections today and have zero leaks anywhere. So I can only be leaking thru an injector or bleeding off pressure back to the tank. $1K for injectors so I'd hope not. I'll put a gauge on the rail just to make sure I'm not loosing too much pressure quickly and call it good. My tuner wants to overlook everything as well just my crazy ass work schedule makes that a little tough.
 

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Thanks for the info. I've only experienced if I go from ign off directly to start. Adam you are correct the pump only primes for a second or two. If I let it prime it starts normally. I added the DMX Flex kit, ID1050X injectors and DMX Aux pump so it could be just the way everything works together now. Just never noticed it before and want to make sure I don't have any issues. I checked all connections today and have zero leaks anywhere. So I can only be leaking thru an injector or bleeding off pressure back to the tank. $1K for injectors so I'd hope not. I'll put a gauge on the rail just to make sure I'm not loosing too much pressure quickly and call it good. My tuner wants to overlook everything as well just my crazy ass work schedule makes that a little tough.
I had starting problems after going to E85. My first shop just said E85 was "harder to light off". But then I had two other VERY reputable remote tuners work on my car. I did like you - I put a gauge directly on the rail. Turns out I did actually have fluctuating fuel pressure - but NOT actually at start up! It was after the car got running, and this later turned out to be bad tuning. Won't go into details but I will say that after LONG hours of comparing tunes I discovered that in addition to some kind of fuel system fault (had a shop totally rebuild my setup - checking every fitting and every line, putting the stock FPCM back onto the bus so I could log fuel pressure), I also had some tuning problems.

What I learned from this huge pain in the ass was that more often than not, characteristics and behaviors like yours are likely tune related, and can be dealt with by a qualified "calibrator".

JMHO - I am not a tuning expert. But I've been a tuning victim enough times, so I feel qualified to post!
 
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I had starting problems after going to E85. My first shop just said E85 was "harder to light off". But then I had two other VERY reputable remote tuners work on my car. I did like you - I put a gauge directly on the rail. Turns out I did actually have fluctuating fuel pressure - but NOT actually at start up! It was after the car got running, and this later turned out to be bad tuning. Won't go into details but I will say that after LONG hours of comparing tunes I discovered that in addition to some kind of fuel system fault (had a shop totally rebuild my setup - checking every fitting and every line, putting the stock FPCM back onto the bus so I could log fuel pressure), I also had some tuning problems.

What I learned from this huge pain in the ass was that more often than not, characteristics and behaviors like yours are likely tune related, and can be dealt with by a qualified "calibrator".

JMHO - I am not a tuning expert. But I've been a tuning victim enough times, so I feel qualified to post!
Car runs beautiful other then this. My turner wants to tweak on it to get it perfect though. I just want to check the pressure to satisfy my own curiosity. Heading back to Houston next week to find that damn Eco Mustang!! LOL
 

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Car runs beautiful other then this. My turner wants to tweak on it to get it perfect though. I just want to check the pressure to satisfy my own curiosity. Heading back to Houston next week to find that damn Eco Mustang!! LOL
Swing by...we'll grab a beer!
 

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Discussion Starter #9
FOUND LEAK!

The 135deg fitting at the pump was damp. It wasn't enough to drip but probably enough to bleed off pressure after sitting a while. Just tightened it up and seems good so I'll see if that corrects the issue. Installer error :(
 

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FOUND LEAK!

The 135deg fitting at the pump was damp. It wasn't enough to drip but probably enough to bleed off pressure after sitting a while. Just tightened it up and seems good so I'll see if that corrects the issue. Installer error :(
Not uncommon I don't think. Leaks around the tank and such seem to be something Ive read about lately.

Question is - is a tiny amount of fuel barely enough to wet but not enough to drip really the cause of the starting issues?
 

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Discussion Starter #11
Question is - is a tiny amount of fuel barely enough to wet but not enough to drip really the cause of the starting issues?
There was some staining around the frame area so the leak could be worse when that aux pump kicks on. Driving more will tell. Decided to take the shuttle to Lake Jackson yesterday instead of driving so the car is sitting at the hanger with a full tank of E85 so I'll see how it starts up tomorrow when I get back.



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Discussion Starter #12
Question is - is a tiny amount of fuel barely enough to wet but not enough to drip really the cause of the starting issues?
Car sat for 2 days and a perfect start up this morning. Keeping my fingers crossed.


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