fuel pressure problem part 2: cold=no fuel pressure, warm=pressure!?!

Obin Robinson · 10-06-2002, 03:41 PM

ok, here's what we have found with the hard starting problem in our 944. we haven't driven the car in about 3 weeks, it's just sat still.

today, when it was about 70 degrees out, i went to check the fuel pressure gauge and it read 30psi. we fired up the car and it was absolutely fine. started instantly with no problems. idled rock solid, no indication of any troubles

i took the vacuum tubes out of the dampener and pressure regulator and i thought i smelled a little bit of gas, but nothing that bad. no gas was leaking out of the lines. we let the car run for about 3 minutes like that.

then, we had to go do some shopping so we left for a few hours.

when we got back, the outside air temperature was 50 degrees, and i checked the fuel pressure... ZERO!!! flatline all the way down. i didn't even try to start the car because i already knew it would be a really hard cold start (i've done it before a hundred times and i don't feel like cranking on the starter any more!)

what's unusual is that the last time i turned the car off a few weeks ago, the pressure was at ZERO again. so here's what is happening:

cold out- zero fuel pressure
warm out- pressure returns to normal

i don't think it's a check valve, sounds more like a pressure regulator?!? could something be sticking when it gets cold? when i took the vacuum hoses out of the dampener i thought i smelled a bit of gas, but none leaked out.

any ideas?

thanks!

obin

todwic · todwic's Garage

Next time you start it (or it's 70&deg out) take a pair of vice grips and pinch the fuel lines shut. (both ther out and the return) then wait for it to get cold. As So Cal about the years that had the chitty hose fittings. There's a group of 944's that the fittings leaked...a small leak would answere the 0 pressure, but I have to admit that the 0 when cold then 30lbs when warm and no start in between puzzles me. of course, daylight savings confuses me, too.

Obin Robinson · 10-06-2002, 05:53 PM

hmmm,

i'll try that, thanks! i'm wondering though... wouldn't a leaky fitting have gas leaking on the engine? or are they just bad enough to lose pressure but not leak fuel on the engine?

thanks!

obin

Mike B · 10-06-2002, 05:57 PM

When was the last time you drained your gas tank...Perhaps corrosion has built up in the tank and is clogging the fuel pump / lines...Just a thought...

drew1 · 10-07-2002, 04:40 PM

Something I've noticed is that liquid, such as water, in a plastic bottle or jug closed on a hot day will contract when cooled over night & kind of pull the jug in. Maybe this is what is happening to the fuel in the lines, cooling & contracting so that you get no pressure. The strainer in the tank or fuel filter could be partialy clogged causing low flow & slow build up of pressure.

drew1

do an OT & tell us about the GTI

Obin Robinson · 10-12-2002, 04:22 PM

well, here's an update:

i installed a new fuel pressure regulator and damper today and started the car no problem! it was about 70 degrees outside too. after everything was installed and checked for tightness, we left the car sitting for 6 hours. now the temperature is 55 and i just went to check it and the pressure was back to zero

.

it's as if when it got cold, the pressure went back to zero again. i tried to start the car and the pressure shot up back to 35 psi. but the car will not start. the system is pressurized but the car won't start. i don't want to crank it forever because i'll kill the battery.

so i've done the:

spark plugs
DME
reference sensors
fuel pressure regulator
fuel damper
battery
battery cables
fuel filter

the ONLY thing left is the fuel pump. i checked the lines and there are no leaks in the fuel lines. where the heck is the pressure bleeding off? or is this stilleven a fuel pressure problem.

i tested the temperature switch and it looks like it's operating correctly. luckily i've been busy so i don't need to worry about it too much, but if it keeps happening i'm just oging to give up and send it to the garage. are there any last minute things i can check? did i not check something right?

thanks!

as for the GTI, i:

stripped ALL the interior out, including the headliner
installed coilove shocks, and a strut tower brace
installed air-fuel ratio meter
and gutted all extraneous electrical wiring.

i got a battery relocation kit and the battery will be going behind the passenger seat soon. i'm also installing an oil cooler. the car is fast and handles very well! i will be finishing it next year and right now i'm on target to compete in the grassroots motorsports challenge! more info to come as i work on the car.

obin