Ok so I've replaced just about damn near everything on the fuel system on my car. Its a walbro 255 pump with a hot wire kit, new filter, -6 line from the filter to the fuel rails of the HSR, kirban billet regulator and a -6 return to the stock hard line. Also the injectors were replaced 3 times and the last set were a known good set that did hold pressure steady with another car. Now the problem is that the fp fluctuates arround 5 psi either way of the set psi (50psi w/o vac 43psi with vac) I tested all the wiring by ohming them out (zero ohms) and even went as far as making up a makeshift injector harness to bypass th factory stuff just for redundacy. The only thing that I havent replaced is the little rubber line in the tank that goes from the pump to the hard line. Sooo any ideas as why the FP fluctuates at all? Thanks!

What about voltage at the fuel pump? I have heard that that is a common place for voltage drops in our cars.

14.1v and no the voltage regulator doesn't fluctuate at all

How did you test this? Was the car running when you checked the voltage? I haven't tried getting to it with the car running, but I thought that the connector wasn't an easy thing to reach.

If your voltage it that high without the car running then you have something strange going on. I personally haven't seen that many volts right off the battery before.

Well according to tunerpro it says 14.1v and with the hot wire kit, it makes it kinda easy to get under the car and back probe the connector to verify the reading..

friend of mine has a walbro for like the 4th or 5th time they have been havin serious problems with them there's a post about them somewhere on here not sure where might just wanna take a peek at it

The fuel pressure can bounce around quite a bit. GM put an isolator (see Pic)in right at the fuel pump that most people take out when they do a pump swap as it's a cheesy push on deal that could be a potential problem with higher than stock pressures. Did you remove yours? There are aftermarket dampers that you can plumb in anywhere on the pressure side that will reduce the pulsations.

Another thing to look at is the gauge your using. Is it electric or mechanical? Mounted or just connected for testing? Some gauges are a little twitchy, meaning that a rapid pressure change of say 3 lbs will cause the gauge needle to move 5 because the inertia of the needle makes it continue past where it was supposed to read. Put a poorly dampened gauge like this on a pulsing source and the needle will be all over the place.

Try a liquid filled (usually glycerin) gauge up directly at the rail and it probably won't jump so much., It'll show you a closer representation of what the pressure is actually doing. If it still shows more variation than you care for put a damper in the system.

Yep the pulsator was removed when the pump was installed a while ago.

The fuel pressure guage is directly mounted to the rail with a liquid filled one. I thought that the non liquid filled one was on crack so thats why I got the filled one. The FP still bounces arround even with a Snap-On FP guage hooked up to it.

If I remember tomorrow I'll swing by where the car is at and take a quick video of the guage.

Thanks for the ideas!

edit:



You can see where the FP guage is on the fuel rail. right next to pass side of the throttle body.

Did you find the problem?

I am having about the same setup and the same kind of trouble and I can´t see what´s wrong.

Jumping fuel pressure when running engine, rock steady when running the fuel pump and engine off. No change with or without vacuum attached.
Any ideas are welcome.

Thanks
Jan

Bump also for updates.

Nope no progress at all in this problem.. Im thinking a magnafuel pump...