[T3] Why is it that when I got my 73 SB I never had to turn thekey several times to prime the system .

[William J]

Jim :
I realize you have much more experience than I on these FI systems I have 
only worked on and drove the one I have .

What's confusing to me is how I never had one issue with starting my car 
even if I drove it to work 7 miles one way in 100 degree heat let it sit 
many times for 14 hours since I started at 7 and didn't leave until 
sometimes 10pm and it fired right up every time without fail , just one turn 
of the key and it was running and stayed running. This was even before I 
rebuilt the engine in 97 and after. Why would VW make a system that would 
force the heated fuel back from the lines through the pump leaving you with 
just vapors. Mine never had any sort of covering over the fuel lines. What's 
the point of the check valve if it does not stop the fuel from going back 
through the pump. Some replace the pump with a 2 port pump from 85 to 
whatever foord rangers and need to prime the system I suppose because they 
have no check valve .

 Somewhere I  saw a photo of the newer three port bosch pump as mine is all 
3 ports on the same end and I can't find it , I think the check valve has a 
small spring under the cover and the check valve if I recall is part of an 
internal passage from the discharge port and the return port . Does the 
valve just regulate how much fuel is feed to the engine as in to reduce 
pressure on the pump so it does not work so hard?

 I never has the other issue I've read people talking about on samba when if 
you drive till hot then park for an hour or so the engine runs a bit rough 
because the head temp sensor banks heat and needs to cool down .

  Perhaps it's the unleaded ethanol  diluted fuel we have now yet we've had 
this garbage well before I had this issue the fuel didn't have quite the 
amount ethanol in 2006 or 2009 .

 Just one more bit . When I got this car in 85 it had a pressure sensor with 
the proper VW # according to Russ a chart he had , at that time I bought a 
trashed 72 Cailf auto trans car and stripped it and since it had a new 
pressure sensor I had one zip tied to the other so I could swap the plug 
because I could not pass smog and a new part seemed better than old . It was 
not even close to the same VW # yet both only had the one screw not like the 
early ones with 2 adjustments and with either the car ran perfect and had 
the same smog results on our shops dyno. It failed the idle test by a hair. 
I never looked at the numbers just that they looked exatly the same in every 
way. IN Calif we had leaded fuel until mid 91 the unleaded then the ethanol 
crap and the summer and winter blend gas. Guess summer has more oxygen 
something like that.who knows what they put in the gas or how they do it top 
secrete stuff man.


----- Original Message ----- 
From: "Jim Adney" <jadney at vwtype3.org>
To: <type3 at vwtype3.org>
Sent: Thursday, August 03, 2017 7:57 PM
Subject: Re: [T3] Why is it that when I got my 73 SB I never had to turn 
thekey several times to prime the system .


> On 3 Aug 2017 at 15:12, William J wrote:
>
>> I need to add a switch pretty easy. Yet up until 2011 even if I didn't 
>> drive it
>> everyday I never had to do this. Now if it sits for one day I need to 
>> cycle the
>> ign at least 6 to 7 times before it will start .
>
> It's impossible to be sure, but I don't think the cause of this is
> that the check valve has failed. This was a problem in some of our
> cars even when they were new.
>
> One difference that may be important is that, when new, all the fuel
> hoses in the engine compartment had grey vinyl oversleeves. These
> probably had a small effect as heat shields that kept the hoses from
> getting as hot in the heat soak after shutdown.
>
>" The problem you're experiencing is due to the gas boiling after
> shutdown, which forces all the gas back thru the pump, leaving the
> lines filled with vapor rather than fuel. The reason it flows
> backwards is that it takes 30 psi to flow forwards but only 20 psi to
> flow backwards. (The valve in the pump isn't really a true check
> valve; it allows reverse flow above 20 psi.)"
>
> An OE solution might be to replace the vinyl sleeves, but I haven't
> found anything I really like for this. My solution is to provide a
> switch to prime the system before trying to start the engine.
>
> You can provide your own switch or I sell complete DIY kits with
> instructions to add them to any FI Type 3. The cheap, $10, kit is
> just a simple pushbutton that you push to run the pump before
> starting. The $30 kit has a heavy duty 3-position (off, normal,
> prime) toggle switch that adds an OFF position that disables the pump
> in case of flooding and provides some extra theft protection.
>
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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