[T3] Why is it that when I got my 73 SB I never hadtoturnthekeysevera...

[William J]

----- Original Message ----- 
From: "Jim Adney" <jadney at vwtype3.org>
To: <type3 at vwtype3.org>
Sent: Thursday, August 10, 2017 3:17 PM
Subject: Re: [T3] Why is it that when I got my 73 SB I never 
hadtoturnthekeysevera...


> On 10 Aug 2017 at 13:04, William J wrote:
>
>> Jim. I've got a question . Today I connected my fuel pressure gauge to 
>> check
>> the pressure , I use the line that used to go to the cold start valve 
>> should
>> still be the same pressure . It read 32 PSI because I was told a while 
>> back
>> raising it might help with the ethonal fuel here. I adjusted it back to 
>> 28
>> PSI and watched after shutdown it dropped to 22 PSI then after 5 minutes 
>> it
>> rose to 23 PSI then got just under 28 PSI then after 10 minutes it was 
>> back
>> to 26 . I started it twice with the same result . I've never seen it 
>> raise
>> and each time I only ran the engine 5 minutes just long enough to adjust 
>> the
>> pressure the engine was not hot yet the fuel line to the gauge was warm. 
>> I
>> checked the gauge and it was 22 PSI engine off just keyed on/off to build
>> pressure before I started it . I can't imagine it's the gauge because it
>> read the 22 PSI priming and when adjusting the regulator it rose and fell
>> and held steady.
>
> It's interesting that you see the pressure drop, then rise, then drop 
> again.
>
> I'm only guessing, but I'd say that what's going on is that when you shut 
> off
> the engine, the valve is already open, so the pressure can drop right away 
> to
> the point where the valve can close (~22 psi.)
>
> Once it's closed, with a hot engine, the fuel in the line starts to heat 
> up and
> somewhere it begins to boil. This will raise the pressure, but if the 
> valve is
> the slightest bit sticky it takes a bit more pressure (~28 psi) to open it 
> again,
> but it only opens a tiny bit, letting gas leak back to the tank slowly.
>
> Eventually all the gas that can get hot enough to boil has done so, and 
> all
> the gas that needs to be pushed back to the tank has done so. At that 
> point,
> the pressure falls to the point (~22 psi) where the valve can close 
> completely
> again. This is the point where the engine temp has fallen below the 
> boiling
> point of the gas.

 Are you talking about the fuel pump valve?
>
> Now the boiling has stopped but you still have hot fuel vapor in the line. 
> As
> the engine cools the vapor also cools, allowing the pressure to fall more. 
> If
> there are ANY leaks in the lines, valves, pressure regulator, or 
> injectors, this
> will cause more rapid falling of the pressure.
>
> Note also that when you attach a gauge to the system, that hose is 
> initially
> filled with air. That air does not go away, because it's higher than the 
> fuel
> ring, so it sits there, acting like a compressed spring on the fuel. This 
> will
> distort the pressure readings you get over time. The steady state pressure
> you read, with the pump and engine running will be accurate, but the air
> bubble will keep the gauge reading from falling as fast as it would 
> without
> the bubble.
>
> You can fix this to some extent by bleeding the hose and the gauge, to
> eliminate as much of the air as possible, but this can be messy, and
> dangerous.
>
> Here are the takeaways:
>
> The factory pressure for your '73 should be 30 psi; 28 psi was for '68-9. 
> I
> would leave your pressure at 30.

 I set the pressure back to 30PSI . I shut it down and it dropped to 20PSI 
then again slowly rose to 22 PSI . Before I did this I checked and after 3 
1/2 hours the pressure was still 18 PSI . I didn't wait to see it it rose 
any higher. At the 18 PSI it fired right up. I'll see what it is in the 
morning. Also before I said it dropped to 22 PSI after shutdown it was 20 
PSI.
>
> What you're experiencing with your car is all perfectly normal for one of 
> our
> cars. You've said that you tend to overthink things. This is an example of
> that.
>
> Add the primer switch and stop worrying about it.
>
> One more thing: If your pump relief valve is starting to get sticky, it 
> MAY be a
> sign that your check valve is about to fail. It's a common problem at this 
> age.
> If it fails, it will probably not fail while you're driving; it will fail 
> when you've
> stopped and shut down the engine and then it won't want to start again. 
> You
> can take your chances and live with this, or you can bite the bullet and 
> send
> it to me to be rebuilt before it causes you a problem.

 Right now I have no other choice other than to live with it beside that I 
have no other transport to send the pump out or the funds to do so , wish 
things were different. It's been acting like this for quite a few years now 
yet I do realize there will come a day when it won't start . Hopefully after 
I shut it down in the garage my ins covers towing if needed and most of the 
time I'm just a mile from home if it's not sitting in the garage. The AAR 
seems to be working proper I did check that . I realized I do not need to 
remove the oil bath to adjust the fuel pressure regulator as the Bentley 
states.
>
>
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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