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I have low fuel pressure like under 20psi. And after diagnosing came to the conclusion I need a new fuel pump. So how can I even start my car and drive every morning with such low fuel pressure. Yet recently (today and yesterday) it's been stalling at stops have to put in neutral and rev up. So my question is how am I able to even drive at such low of fuel pressure. And mainly why does my car smell so look rich? If there is not enough fuel how can it be rich?
Pressure changes based on certain vacuum/engine conditions. 20psi at wide open throttle is WAY low. 20 psi at idle or low rpm cruising is....well....still low, LOL, but not AS bad. Also, while the pump pressure SHOULDN'T change based on RPMs, with older wiring/alternator/battery affecting voltage output...it could. So exactly what pressure you're getting at what RPMs, and under what kind of load conditions is tough to say, unless you've checked all these.
What have you done to determine the pump was bad? Possible leaking injectors?
I didn't mention that not only does it reach the 40psi key on engine off but it also bleeds off very fast and also after engine running and then shut down.This is what I'm using for diagnosis but i want to be sure im not dealing with leaking injectors or regulator before i go through the trouble of changing pump. I'll try to apply 12v to pump block return and pressure line then see if it bleeds off (injector leak down test?) After work. Thanks for the reply
After applying the 12 volts and blocking return line i still dont have any increase in pressure
Alternator seems okay after watching voltage (scantool) and turning everything on, brights, radio, accesories, and alternator seems to keep up voltage.
After using a better guage I get almost 40psi with engine running at idle. If I shut it off it bleeds down, if I apply 12 volts to the pump then block the pressure line it holds, if I block the return line it still bleeds down.
Well 12v at the alternator and 12v at the pump are different. I know these cars are prone to losing voltage through 80s era, barely adequate when new wiring. -but I don't think that's our issue. ...and again, I don't think this is our issue, but are you testing pressure with the regulator vacuum disconnected or not? Pulling it off simulates WOT vacuum conditions, to see max pressure. I think factory is 43.5 but its definitely in the low 40s. 42? Can't remember exactly. With connected, at idle....it'll be in the mid 30s "ish".
Also, it should NOT leak down quickly. This would lead me to lean towards injectors. I wonder if plugging the line is acting like a vacuum, not allowing the injectors to leak. Think putting your finger on top of the straw and holding in your drink!
I'm not one to throw money and parts at a problem, but replacing 30 year old Multec injectors wouldn't be a bad idea, regardless of what the problem ends up being.
Mid 30's at idle with vacuum connected was what I was seeing, so I'm thinking your right beings how I have a rich condition, sometimes little backfire on startup that changing injectors and probably regulator diaphragm while I'm in there might solve my issue makes the most sense so far. Do you know of any injectors people recommend for a stock untuned 305?
Absolutely. Check out our sponsor SouthBay Fuel Injectors. LOTS of us running various injectors including myself. He's great to deal with, although I find calling and talking to them was easier than getting all the info off the website.
After using a better guage I get almost 40psi with engine running at idle. If I shut it off it bleeds down, if I apply 12 volts to the pump then block the pressure line it holds, if I block the return line it still bleeds down.
Pinching the pressure line and the pressure holds would indicate that the leak down problem is in the tank.
Pinching the pressure line and the pressure holds would indicate that the leak down problem is in the tank.
I was wondering about that, I didn't want to believe it either because of the hassle in replacing the sending unit. If I makes a difference I did block pressure and return and it still leaked. But I'm guessing after all these years, and it did sit in a field the last couple,I may have multiple issues and should probably just replace the stock injectors, fpr diaphram, gaskets, that I just ordered and see what happens then move on to replacing the sending unit.
Do i replace the whole sending unit or just the pump? And what type/brand of pump is recommended.? Thanks for everything you guys are a big help, love this forum, maybe as much as I love my crappy z28.
Hopefully other members can suggest a good replacement stock pump. When I did my TPI conversion I bought a Bosch pump from Rock Auto, but pressure bleeds back thru the pump when I turn the engine off. So I would not recommend Bosch. I read somewhere on this forum that GM has an improved pump for this application. I think EP241 but don't quote me on the part number.
About to swap injectors but noticed the new ones from southbay are shorter and have the retaining clip slot in different location so that when I put it in the fuel rail it's loose and with it all the way in snug the retaining ring doesn't seem to fit in the other slot. What am I doing wrong
Well Im late but I was going to ask if you could turn the key a few times, let the pressure go down and check a few spark plugs or look inside with a scope to see if its actually leaking few before buying injectors.
Also you said that it's stalling out when driving. If its just an injector thats leaking, its just going to run rough not flat out stall out lol.
Well new injectors are in and it made a bid difference, I have extended crank times now but oh well it runs much smoother. I believe my stall at idle condition is either related to my irratic idle issue or maybe my fuel pump check valve going bad. Im going to replace fuel pump next weekend and see what that cures. Thanks for the reply.
Stalling seemed to have stopped so far. Believe it was maybe not running completely on all cyl. and at a stoplight rpms would eventually die down and engine would stall.
09-13-2017, 08:06 PM
