Cullen,
Is the problem really related directly to engine temperature or does it act
the same way when restarting a warm engine?
I've had a situation with a piece of the tank coating that was partially
attached. It would get sucked down and cover the tank outlet, then float up
after the engine was shut off and the suction was gone, so everything was OK
again. Could also be something in the line that gets sucked in tighter and
then eases back when the engine is shut off.
If you have bypassed the regulator, it would seem that the pump would
produce the full 8psi and you would be even less likely to see a drop in
pressure. That really makes it sound to me like a blockage of some sort.
On the other hand, have you examined the fuel line from the tank forward
closely. Any kinks, cracks or barely loose fittings? Since the pump is
pulling to the engine rather than pushing from the tank, is there any chance
of outside air being sucked into the line through an opening that is too
small to show a visible leak when the engine is not running?
This is one of those problems where everyone will want to know the eventual
solution.
Good luck,
A. C. Tynes
> -----Original Message-----
> From: tigers-bounces@autox.team.net
> [mailto:tigers-bounces@autox.team.net] On Behalf Of Cullen McCann
> Sent: Friday, September 18, 2009 9:32 AM
> To: tigers@autox.team.net
> Subject: [Tigers] (Non-Tiger) Fuel pressure falls off with temp?
>
> All,
>
> I try not to bomb the list with Non Tiger stuff, but we are a
> bit desperate, and you all can be so helpful.... I guess it
> could apply to a Tiger...the dynamics of the system aren't
> any different that I can think of. ...and we really need some
> good advice...
>
> Here is the situation, my good friend and I have built an
> early 70's full size ford truck 4x4...The fuel pressure falls
> off slowly from 6.5 psi on the gauge to about 3 or so....and
> eventually even lower until it tries to die as the engine
> warms up...over the course of a few miles driving or several
> minutes of engine at full operating temp.
>
> Here is what we have tried:
>
> 1. considered a bad fuel pump, replaced it with new and it
> didn't change 2. considered a bad regulator, replaced it with
> a brand new one from summit, didn't change 3. considered a
> bad gauge, replaced it with no change
> 4 considered a problem with venting in the tank or not enough
> vent...checked the cap and vent line and its fine, no change
> 5. considered vapor lock....if this is true, what causes it
> and how do you fix it? the fuel line is routed in nearly the
> exact same format as the factory...cant imagine what would
> cause it....
> 6. re-routed the fuel system with soft line to by pass
> regulator and remove line from near engine...no chance in the problem
>
> Any ideas would be appreciated....we are getting
> desperate....here is how its setup in case it matters:
>
> Engine and such:
> Ford 351 Windsor - roller conversion
> 9.3:1 compression, forged pistons
> Edelbrock aluminum heads
> comp cam (521/536 lift, 230-ish duration) Edelbrock 650cfm
> Thunder AVS carb Edelbrock Performer RPM intake Shorty
> headers with 2-1/2 mandrel bent exhaust
>
> Fuel system specifics:
> Stock tank
> Stock 3/8-inch lines from tank to pump
> Summit Mechanical 'high volume' fuel pump - 110gph, 8 psi
> -6 AN braided hose from pump to regulator Adjustable
> regulator - set at 6.5psi
> -6 AN braided hose from regulator to filter In-line fuel
> filter right at carburetor Full tank of 91 octane fuel
>
>
> Thanks Friends!
>
> Cullen
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