Printable Version of Topic

Posted by: nycchef Apr 24 2006, 02:05 PM

73 914 1.7 (the one that tops out at 4000 rpm) now is idling @ 2000 rpm and dies every 15 minutes. einstein the mechanic thinks its the fuel pump now. i can hear it running. if i wait 10 minutes its starts again. does anyone know more than einstein and me. thanks

Posted by: SirAndy Apr 24 2006, 02:36 PM

tell einstein to stop "guessing" and start using his brain ...

add a fuel pressure gauge and see if you got enough pressure. whatch and see if the pressure drops *before* your engine dies.

if not, it's not the pump ...
Andy

Posted by: nycchef Apr 24 2006, 03:03 PM

andy thanks for the reply do you know what the proper pressure is? so i can pass it on to einstein. also any one know a good 914 mechanic in nyc this one is about to have an accident just kidding maybe

Posted by: Mueller Apr 24 2006, 03:09 PM

i'm too lazy to look for it...but you'll find the proper fuel pressure plus valuable tips and information on the D-jet here: http://members.rennlist.com/pbanders/

Posted by: SirAndy Apr 24 2006, 03:13 PM

28psi is minimum, 34psi is normal operating pressure ...

here's a good article on the subject:
http://www.rennlist.com/techarticles/djetronicfuel.htm

Andy

Posted by: nycchef Apr 24 2006, 04:30 PM

andy thanks again will pass on to einstein you may well have kept him healthy for a few more days kidding rich

Posted by: Dave_Darling Apr 25 2006, 02:18 AM

For D-jet systems (e.g., 1.7 or 2.0), the spec pressure is 2.0 Bar--2 atmospheres, or 29 PSI. 34 PSI would be significantly over operating pressure, resulting in an overly-rich mixture.

The high idle is almost certainly from a good-sized vacuum leak.

--DD

Posted by: SirAndy Apr 25 2006, 10:00 AM

well, what do you know, my Haynes manual says 34 psi for 1.7L D-Jet ...
Andy

Posted by: drewvw Apr 25 2006, 10:48 AM

while we are on the subject:

Dave you said that too much fuel pressure will cause and overly rich mixture.

Besides that....are there any long term effects it can have on the fuel system if the pressure is too high for a long period of time? How much pressure can the system take before something catastrophic occurs?

Posted by: SirAndy Apr 25 2006, 11:01 PM

Haynes manual, page 39:

pre '75 D-Jet = 2.4 kg/cm2 (bar) = 34 lb/in2 (psi)

'75 D-Jet = 2.5 kg/cm2 (bar) = 35.7 lb/in2 (psi)

Andy

Posted by: SirAndy Apr 26 2006, 11:13 AM

i stand corrected! and dave was right ...

this is one of the times where the haynes manual can be "confusing".
usually, you have a table with all the important numbers at the beginning of a chapter and then detailed descriptions of how to tackle certain tasks.

but in case of the fuel pressure on the injectors, you actually have to read the fineprint in the article to get the right number ...

i usually use the haynes just for reference. i already know how to perform most of the tasks, so i mainly use it to look up torque values etc.

i went to the table on page 39, looked up the fuel pressure for a pre '75 D-Jet and *thought* i was set.
turns out, that value is only the pressure "at the pump", but not at the injectors.
that number is buried in the fineprint of the "how to" article on page 42.

28.4 - 29.6 psi (1.99 - 2.07 bar)

Andy

Posted by: porsche914blue Apr 26 2006, 01:03 PM

Too high of fuel pressure will cause a rich mixture that can wash the cylinder walls of oil resulting in increased wear. It can also blow-by your rings and end up diluting your oil; also resulting in increased wear. If you do determine that it's overly rich do an oil change as soon as possible.

Posted by: Dave_Darling Apr 26 2006, 07:59 PM

Too much for too long also increases the likelihood of leaks. The inejctors seem to not like high pressures for a long time. And I am told that the spray pattern starts to degrade over about 36 PSI.

--DD