Date: Fri, 5 May 2000 10:17:01 -0400
Reply-To: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Bulley <gmbulley@BULLEY-HEWLETT.COM>
Subject: Bosch fuel pump history, and: Fuel Primer?
There has never been a "fuel prime" button for any of the type2 Bosch FI
motors (that I know of).
The MPC injection (1968-1972) used a different system to trigger the fuel
pump. The fuel pump used to sit back by the motor so the pressurized
section of hose was smaller. The problem was, the system was prone to vapor
lock. The pump ran off a relay, the contact breaker points in the
distributor, and the ignition switch.
In the earliest version, the pump would continuously as long as the
ignition was in the on position. Not very safe. A small leak or a motor
crash would see fuel continuing to be fed to an open line.
The next version of MPC would run the pump for the first five second after
the ignition switch entered (or passed though) the ON position. A little
safer. Thus, the fuel rail was 'primed' prior to ignition. If you got vapor
lock, you could repeatedly turn the ignition key from off to on in five
second intervals, and eventually you could break the vapor lock.
Then VW/Porsche got smart, and repositioned the pump to under the fuel
tank. Cooler. No more vapor lock. The AFM FI system kicks the fuel pump on
when the ignition is in the on or start position, and when the air flow
meter registers air moving into the motor. Much smarter.
Sounds like your van went to the Spanky & Alfalfa School of Engineering,
and had some modifications to mask symptoms, rather than repairs to
eliminate problems. I would guess this guy had vapor lock a couple of
times, and bypassed the AFM safety by jumping some wires on the relay
board, and putting this switch on the dash. Here's what I'd do:
Take a look to make sure you have the correct fuel pump, and measure the
max pressure at the rail. Make sure the pump is where it belongs (under the
van, about 10" from the fuel tank. Put in a new fuel filter. I like the
California fuel filter, since it is roughly 10 times the size of the puny
federal filter.
If the van has been sitting for a few hours, (meaning the pressure in the
line has dropped), it should start after about 1.5 seconds of cranking. If
not, the fuel pressure regulator may be bad, but that would also cause poor
running as well.
Good luck,
G. Matthew Bulley
Bulley-Hewlett
Corporate Communications Counselors
www.bulley-hewlett.com
Mount Olive, NC USA
877.658.1278 tollfree
"I, the undersigned, shall forfeit all rights, privileges, and licenses
herein and herein contained, et cetera, et cetera . . . fax mentis
incendium gloria culpum, et cetera, et cetera . . . memo bis punitor
delicatum!" It's all there, black and white, clear as crystal! -Wonka
-----Original Message-----
From: David [SMTP:david@RENAISSANCE-DESIGN.COM]
Sent: Friday, May 05, 2000 9:21 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Fuel Primer?
A previous owner installed a 'fuel primer' button on the dash of my 82
vangon. You push it and hear the wine of the pump and then a bit of a
gurggle and then you let go of the button and start the engine and it
starts fine. If you don't push the button it takes a loooong time to get
it to start. So your asking, what's the problem?
The problem is, why does it now need a button to start the fuel pump to get
the fuel up to pressure and it didn't when the vehicle was new? BTW it has
a GD000861 engine, or an early 2.0L found in the 76-78 BUS. Perhaps they
had fuel pump prime buttons in 76???
My purpose is to find and fix the original problem that caused someone to
install a fuel priming switch.
Thanks,
David
