[V8] Fuel pressure gauge

Tue Feb 13 17:37:14 EST 2007

You want the gauge to be after the fpr (on the rail) so you get the fpr 
reading at the injectors. Should be around 60psi or 4bar constant @any given 
rpm.anything more than 4bar is a ssymptom of bad fpr. less than 4bar =bad 
pump, or dirty filter.
----- Original Message ----- 
From: "Scott Phillips" <Scottp at ippe.com>
To: "V8" <v8 at audifans.com>
Sent: Tuesday, February 13, 2007 5:21 PM
Subject: Re: [V8] Fuel pressure gauge


> Fuel pressure would be fractionally higher on the line than the rail,
> depending on the placement of the gauge it is contending with the
> operation of the injectors. However it is the job of the pressure
> regulator, fuel pump and return circuit that maintains that pressure.
>
> Scott
>
> -----Original Message-----
> From: v8-bounces at audifans.com [mailto:v8-bounces at audifans.com] On Behalf
> Of Scott Simmons
> Sent: Tuesday, February 13, 2007 5:18 PM
> To: d saad
> Cc: v8 at audifans.com
> Subject: Re: [V8] Fuel pressure gauge
>
> Most that I've seen are on the rail.  How do pressure change compared to
>
> pressure in the rail and pressures on an input line?  Would not the
> input line be higher pressure than the rail?
>
> ~SS
>
> d saad wrote:
>
>>You have a few options -
>>
>>-> Buy a fuel pressure tester that
>>comes with the adapters. Expensive, but maybe worth it for the
>>convenience.
>>-> install a permanent test port - like most cars now
>>have
>>-> go to the junk yard and get some fittings and make your
>>own adapter.
>>
>>I did both the junkyard thing, and then put in a
>>permanent test port. Both were easy to do, but take time. To scavenge
>>junkyard parts, all I did was find some appropriate fittings, and
> attach
>>them to a brass tee which had a standard Ford style schrader valve in
> it.
>>
>>
>>I decided to do the permanent port when my flex line from the
>>right shock tower to the fuel rail started to leak. There is some risk
>>with this one - but mine has been there for many years now and I have
> had
>>no problems. Here is a short description on how to do it:
>>http://www.icehouse.net/dsaad/
>>This required me to have new hose
>>crimped on - because the soldering will destroy the old hose. It took
> the
>>guy at the hose shop a few tries to get it right, but it was cheap.
>>
>>
>>Dave
>>
>>
>>
>>><snip>Has anyone installed a
>>>
>>>
>>valve on the fuel rail to measure fuel
>>
>>
>>>pressure? I thought I
>>>
>>>
>>read about it somewhere.  The AF TWiki has one for
>>
>>
>>>S4/S6 cars.
>>>
>>>
>>It was an incredibly valuable tool on my previous cars and
>>
>>
>>I'd
>>
>>
>>>like to have one to check numbers. <unsnip>
>>>
>>>
>>>
>>
>>
>>
>>>Yes, I've installed a fitting on my S6.  I've also seen folks
>>>
>>>
>>who have
>>
>>
>>>modified their V8 fuel rail for the fitting.  I cut a
>>>
>>>
>>rubber section of
>>
>>
>>>the
>>>fuel line near the fuel filter,
>>>
>>>
>>installed a brass tee with two
>>
>>
>>>hose-to-pipe-thread fittings. The
>>>
>>>
>>third leg of the tee to a brass Schrader
>>
>>
>>>valve.  You have to use
>>>
>>>
>>FI hose clamps on the hoses and a metal valve cap
>>
>>
>>>on
>>>
>>>
>>>
>>the Schrader valve. The valve has a 1/4" flare fitting that's the
>>
>>
>>>most-common standard for EFI pressure gauges. The magic part is the
>>>
>>>
>>valve
>>
>>
>>>and it's NAPA # 209459 and I paid $3.74, (jobber price).
>>>
>>>
>>FI clamps are
>>
>>
>>>705-1226 or 1227 depending on hose diameter (14 mm
>>>
>>>
>>and 15 mm).  I've often
>>
>>
>>>wondered why so many guys on the list
>>>
>>>
>>just replace the FPR without
>>
>>
>>>checking
>>>the pressure.
>>>
>>>
>>FI pressure is critical, the ECM accepts it as a given
>>
>>
>>>pressure
>>>
>>>
>>and if it's off open-loop will be fat or lean and closed loop may
>>
>>
>>>not be able to squeeze the injectors enough to keep the engine
>>>
>>>
>>from
>>
>>
>>>running
>>>fat.
>>>Craig N.
>>>90 V8
>>>
>>>
>>Q
>>
>>
>>>95 S6 Avant
>>>
>>>
>>>
>>>
>>_______________________________________________
>>
>>
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>>>
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>>
>>
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