fuel presure problems

3tstarlet · Post by **3tstarlet** » Sat Jul 08, 2006 2:36 pm

my car starts and idles fine but if you rev it the fuel presure will go down and the engine leans out ....i have a walbro 255 fuel pump a paxton boost ref presure reg and venon 720cc injectors,,,an -8 line all the way around....for my understanding the presure should go up when i rev the engine do to the boost ref vac port on the regulator

PSIG · Post by **PSIG** » Sat Jul 08, 2006 5:00 pm

Be sure to take the manifold pressure reference from the manifold itself and not from the throttle body or elsewhere. Only a direct manifold port will work properly for the FPR. What engine combo are you running and how is the FPR refrence hooked up?

Eville140 · Post by **Eville140** » Sat Jul 08, 2006 5:10 pm

Everything is hooked up correctly.

The problem we where having is when the fuel pump comes on (new walbro inline 255) with the engine off it goes up to the 42# that we want, but then after about 4-5 seconds the pressure drops down to 20 or less and then bonces around about 10#.

It does the same thing with the car running(well hardly running) with or without the vacume refrence line connected.
And while running if you tap the gas the pressure will go all the way down to almost 0.

As of now I am betting it is a bad pump. It is slightly lounder than my 255 inline and he did run the tank dry here recently, but it does have a large inline filter before the pump also.

Also everybody...Tell him not to give up on this car. He is so close to having a damn quick little street car. It's a built bottom end (eagle rods, wisecos) He has a nice cam, about the best head you can get, a good size turbo and a EFI that is pretty much ready to go.
I even have an extra inline 255 and regulator that he can barrow!!

Here is the car in question

Car starts and idles with megasquirt and EDIS with 750cc injectors

It's just a few small glitches away from being done.

Idle video!!
http://www.eville140.com/3tstarlet/l.wmv

Later
Randy

PSIG · Post by **PSIG** » Sat Jul 08, 2006 7:58 pm

Now THAT looks like fun! I like the exaggerated temporary vacuum lines. Is that a 35? Yeah, there's waaay too much work in that to give up now for sure... I'd do a bypass volume flow test to measure the flow at your base pressure. Just disconnect the return line into a bucket and jumper the pump for 15 seconds for a volume test. Obviously it should bypass the equivalent of 3 liters of fuel a minute to feed four 720cc injectors 100% at base pressure - and that's without boost.

Keep an extinguisher nearby.

If it still acts the same, pull the fuel line before the rail to check free flow volume for the same dropoff. If it does drop volume after the 4-5 seconds, try pulling the Out line off the pre-filter and do a quick flow test by pressurizing the tank to a couple pounds (careful!) to test free pickup, screen, and filter flow that may be cavitating the pump. I just wrap a shop towel around the air nozzle and shove it in the filler neck and give it a squirt of air. Just enough to check for free flow - don't balloon the tank! It just beats sucking on the fuel line...

If you have the spare pump to drop in at any time then start there, but if it acts the same, the diagnostic flow tests may show you where the problem lies.

David

3tstarlet · Post by **3tstarlet** » Mon Jul 10, 2006 6:13 pm

i found the problem ...it was the filter ....and the turbo is an h1c holset

simonbos · Post by **simonbos** » Sun Jul 30, 2006 1:55 pm

Thanks for posting the resolution. I had the same problem and found your post. Checked my filter and sure enough, it was clogged.

Thanks,
Simon