checking fuel pump

914nate73 · 07-20-2003, 09:06 PM

I have a 2.0 73 and suspect that under a full load I'm running out of fuel. Shifting from red line in first to second and hammering the throttle down all the way the car dies, then bucks, then back fires, and it's ok. Testing fuel pressure reads 40psi. I'm autocrossing and have two questions
1. what is the max PSI you can safely push it to?
2. is there anyway to test the fuel pump with and w/o a load on it?
Thanks everyone for your past help on this site.
Nathan

Tidybuoy · 07-29-2003, 05:00 PM

Nathan,

It's possible that your fuel pump is fine but the fuel screen or filter is clogged.

I had similar problems & when I replaced the fuel screen (in the tank) all my problems went away.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Over about 36 PSI the injector spray pattern becomes more of a stream pattern. The lifetime of the injectors is evidently somewhat shortened above that level as well; they will tend to leak after running that way for a while.

Specified fuel pressure is 29 PSI. 40 is way high--and would lead to a very rich mixture. That can cause all manner of driveability problems.

The pump has a delivery spec for open-loop operation, i.e. pumping fuel into a bucket. I don't recall the spec offhand, but I'm sure you can find it somewhere in http://members.rennlist.com/pbanders .

--DD

chrisreale · 07-29-2003, 09:32 PM

Shifting at red line is a waste of time and power. max torque is around 4000 I believe, then it drops off like a cliff. Try shifting at 5000, and keep the rpm's in the 4000 to 5000 range

Dave at Pelican Parts · Dave at Pelican Parts's Garage

"Optimal" shift points are different depending on your gearing. It is almost always best to shift out of first gear at redline, or maybe even a bit over. (!!) Second to third, I believe that redline is pretty close to correct. Third to fourth is probably just over 5000, and fourth to fifth.... Well, it doesn't really matter IMHO. My car pretty much wouldn't accelerate in either gear over 100 MPH...

For a neat page with some good graphs, check http://members.rennlist.com/944sandmore/shiftingpoints.htm

The graphs show thrust vs. road speed in each gear. Thrust being the amount of push the drive wheels are making. (Engine torque multiplied through the transmission gears, the ring and pinion gears, and then applied through tires of a given diameter. The result is lbs of "push".) Note that the car is a 944 or 944 turbo, so the torque curve and gearing is different from ours. But still, the general concepts will apply.

--DD

chrisreale · 11:45 AM

Assuming gearing is stock, how can shifting at redline, where your torque and HP drop drastically be optimal

Look about six replies down...
http://www.914club.com/bbs2/index.php?act=ST&f=2&t=1696&hl=dyno+chart&

M. Hendrix · 12:26 PM

It works like this:

The cliff in a 2.0 is about 4700, so you rev to 5500, and by the time 2nd is engaged, you are sitting right at the 4500-4700 area, rinse, repeat. same to 3rd... and 4th, and 5th, gotta ride that powerband. Like Dave says though, makes less sense higher up, although I disagree on gaining speed above 100.. I say above 115.

YMWV, and I don't fully depress the clutch, I shift it like a dragster.

M

-damn edits won't stay!-

914nate73 · 07-30-2003, 09:27 PM

I checked the screen dirty but was not the problem. Upping the fuel pressure to 35 helped get the car out of it's nosing quicker but it still noses.
Would anyone recommend a rev limiter for autocrossing.
Also the problem I described above happens ONLY in 2nd gear and ONLY at 3500 to 4000. Weird! One theory possed to me is to check the breaker points, would this cause such a problem?
914 Nate