psu_Crash Posted September 28, 2008 Report Share Posted September 28, 2008 (edited) So I set the base fuel pressure with the car off and jumped the fuel pump test to +12V. Pressure is smooth when not running, but as soon as I start it the needle shakes very rapidly over a range of about 5psi. The pressure still increases with boost but doesn't stop fluctuating. It didn't do this at first and I just noticed it last night so I am not sure how long it has been going on. When I hold the fuel line I can feel it pulsing pretty hard like the pump is rapidly turning on and off but it shouldn't be. Tested out the connection with my DMM and it is getting a steady +12V. Sounds to me like the pump is dying ?? Edited October 2, 2008 by psu_Crash Link to comment Share on other sites More sharing options...
TainterRacing Posted September 28, 2008 Report Share Posted September 28, 2008 I think that might be the fuel regulator. With the car not running there is no vac getting to it with the car running you are getting vac and psi there is a diaphragm in there it might have a hole or leaking I would test it see if it keeps a vac. put a clean hose on it and suck on it hard it should stay there and you should not get more air then a little and it should stop. Might even be the vac line as well look it over closely oo and what does your vac gauge show? Is it jumping around at idle if so it would just be that I bet. Link to comment Share on other sites More sharing options...
psu_Crash Posted September 28, 2008 Author Report Share Posted September 28, 2008 Vacuum line is new and solid. I am not sure about vacuum jumping around. I will put the mityvac on the FPR and see if it holds. It better it is new and has only been on a few days! Thanks! Link to comment Share on other sites More sharing options...
mikec Posted September 28, 2008 Report Share Posted September 28, 2008 Is this on a MPI intake with the FPR's vac hose connected after the throttle plates (i.e. to intake manifold vacuum)? If so, measure the intake manifold vacuum... I'll bet you find it's bouncing around too. The FPR is just regulating to that "noisy" vacuum signal. A sticking valve or something causing a cylinder misfire will lead to erratic manifold vacuum. Just unplugging the vac hose while the engine idles should "cure" the bouncing if the vac signal is the culprit. Of course you can't run this way for long - the engine will be rich while idling now that the FPR's reference signal is zero vacuum. If the source of the manifold vacuum is very close to one cylinder's valves it's also possible you're not seeing the "average" manifold vac; instead you're seeing pressures at the end of an intake runner where that one cylinder is affecting it too much. Try a port closer to the plenum or throttle body area. mike c. Link to comment Share on other sites More sharing options...
psu_Crash Posted September 28, 2008 Author Report Share Posted September 28, 2008 Yep it's on a magna after the thorttle plate. Vacuum in MS isn't bouncing around. Kinda odd because it just started out of the blue and the car is still running great. I will look into it further tomorrow. I noticed my boost gauge no longer reads vacuum either but it still reads boost correctly. . hmm ... i think something came unhooked or is leaking. Link to comment Share on other sites More sharing options...
psu_Crash Posted September 29, 2008 Author Report Share Posted September 29, 2008 Well ... chalk one up to experience. I was a vacuum issue. Apparently I was pushing just a tad more boost than a FPR vacuum line could handle ... without a clamp or zip tie This is also the line my HKS gauge T's off of (I know it isn't supposed to) I had to actually pull on it a bit to get it all the way off, but one corner of the line was open to the free world. Reconnected ... connected the HKS EVC for the first time since the new build ... and wow ... now I have to gloat a little ... that sum' complain will scream at even 12 psi ... can't wait to turn it up and get the meth injection all set-up Link to comment Share on other sites More sharing options...
Indiana Posted September 29, 2008 Report Share Posted September 29, 2008 Its bolted to the motor what do you expect even one that is liquid filled will not remain motionless. Link to comment Share on other sites More sharing options...
psu_Crash Posted September 29, 2008 Author Report Share Posted September 29, 2008 It was more of an oversight than a "I think these will stay Link to comment Share on other sites More sharing options...
psu_Crash Posted October 2, 2008 Author Report Share Posted October 2, 2008 Fuel pressure is still fluctuating rapidly and in sync with a very distinct ticking that increases with the RPM. I think my pump no longer is able to keep up (it's 10+ years old) and when the injectors fire the pressure drops momentarily. Voltage and current to the pump are steady and the regulator is working fine with the car off. Going to get a new Walbro on the way ASAP and hope that does it. Link to comment Share on other sites More sharing options...
83TechMaster Posted October 5, 2008 Report Share Posted October 5, 2008 What size injectors are you running? How many pounds of boost do you plan to run? Cause if you plan to run alot of boost your gunna need a bigger pump than a walbro 255! just an fyi. I reccomend an aromotive A1000 or an S/X pump. Fuel pressure is still fluctuating rapidly and in sync with a very distinct ticking that increases with the RPM. I think my pump no longer is able to keep up (it's 10+ years old) and when the injectors fire the pressure drops momentarily. Voltage and current to the pump are steady and the regulator is working fine with the car off. Going to get a new Walbro on the way ASAP and hope that does it. Link to comment Share on other sites More sharing options...
psu_Crash Posted October 6, 2008 Author Report Share Posted October 6, 2008 Running 75# Delphi injectors. Plan to run it up to 18 psi boost. Currently only running it to about 12 psi since I haven't tuned MS past that point yet. It is running fine and not leaning out right now. . but it does make me nervous. Link to comment Share on other sites More sharing options...
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