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So I own a 1999 Buick Regal GS and I recently I replaced my cylinder heads because my previous ones cracked in multiple places because i was running lean for so long with no knowledge (was dropping fuel pressure) now I replaced the fuel pump with a zzp350 in tank fuel pump and also went e85 with a smaller pulley and come to find out that I’m still dropping fuel pressure (replaced fuel regulator, replaced the fuel filter, replaced all injectors for e85) any ideas on why I’m still dropping fuel pressure?
 

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Well,, based on what you have mentioned, I'm wondering if the fuel pump isn't holding fuel pressure when the engine is off. If you haven't , I would ask ZZ about this issue to see what their opinion is for the pressure drop. On another note, if the fuel line going to the engine from the tank is vinyl, I would try pinching the line closed with a locking pliers and soft teeth(so you don't damage the fuel line) and see if the pressure drop is still present. If the pressure holds, there has to be a problem with the fuel pump allowing fuel pressure back flow to the tank. One more thing is to look inside the regulator nipple where the vaccum hose would connect on the regulator body. Using a flash light look inside that nipple with a flash light to see if there's any fuel to be seen in the tube to regulator body. I have done this in days gone by and saw fuel inside the regulator body. I also went as far as to pull the hose off the regulator body and shook the car and was able to see FUEL MOVEMENT inside the regulator looking into the vacuum nipple. THAT IS A DEFINITE FUEL LEAK FROM the regulator internal diaphram. Hope some of this helps, Mr Goodwrench(Jake)
 

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Well,, based on what you have mentioned, I'm wondering if the fuel pump isn't holding fuel pressure when the engine is off. If you haven't , I would ask ZZ about this issue to see what their opinion is for the pressure drop. On another note, if the fuel line going to the engine from the tank is vinyl, I would try pinching the line closed with a locking pliers and soft teeth(so you don't damage the fuel line) and see if the pressure drop is still present. If the pressure holds, there has to be a problem with the fuel pump allowing fuel pressure back flow to the tank. One more thing is to look inside the regulator nipple where the vaccum hose would connect on the regulator body. Using a flash light look inside that nipple with a flash light to see if there's any fuel to be seen in the tube to regulator body. I have done this in days gone by and saw fuel inside the regulator body. I also went as far as to pull the hose off the regulator body and shook the car and was able to see FUEL MOVEMENT inside the regulator looking into the vacuum nipple. THAT IS A DEFINITE FUEL LEAK FROM the regulator internal diaphram. Hope some of this helps, Mr Goodwrench(Jake)
Thanks Jake I’ll make sure to check that diaphragm on the regulator and I emailed zzp and they said that it was most likely an install issue, and I quote “probably a kinked line or something” I don’t know how true that is honestly. I don’t remember seeing any kinked lines during my install of the pump. Also would I pinch the feed or return fuel line?
 

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If you pinch off the return fuel line and the pressure drop stops, the fuel pressure must be going back to the tank/pump via the return line. This would indicate that the the fuel pump allowing fuel to go back into the tank. OR, there is an injector that is not holding fuel pressure.
 

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One other thing you can do is to pinch off the pressure line and the return line as soon as the fuel pump turns off. If pressure still drops after pinching off both the fuel lines, this would indicate a leaky regulator or an injector. When I have done this in days gone by, I used a SMOOTH TYPE LOCKING needle nose pliars so there's no major stress on the fuel line itself. One other thing one can do is to pull the fuel rail/injectors out of the lower intake to see if there's any fuel leaking at the injectors. Mind you the leaks of this type will show up as wet at the tips of the injector/injectors. You could also try pinching off the return and pressure lines off one at a time to see which one is leaking back to the tank or not. When you do this, pinch off the lines as soon as the pump turns off. I'm still wondering if the fuel pump itself has a faulty CHECK VALVE allowing fuel to return back into the tank. Best of luck, Jake (mr goodwrench). This may or may not help you, but I'm still using an OEM FUEL PUMP with no issues or lack of fuel supply the the injectors. When I installed the new OEM fuel pump I drilled several holes in the outer plastic pump assembly to allow PLENTY of fuel to go inside the OEM pump assembly so the fuel pump pick up would have plenty of fuel to pick up. This insures there will be plenty of fuel supply the the fuel pump assembly. By the way, I used a new OEM PUMP.
You may want to send BYNO BRIAN a message about this issue to get his take and expertise.
This process is working very good for me and It's been this way for several years now with NO PROBLEMS AT ALL.
ONE last thing to check is to see if there's any fuel leakage where the injectors connect to the fuel rail and all other fuel line connections. I have gone as far as pulling the fuel rail assembly out of the intake and the pressured it up(make sure all the injector locking clips are in place) !! The injector tips should be DRY(wipe off as needed before looking at the tips) and then re pressure and watch for any fuel at the injector tips. PS, I'm running 42 psi injectors with no problems.

ONE LAST THING I DID,(after frying some pistons),was to insure I was getting at least ONE PINT OF FUEL FLOW FROM THE PUMP. When I burned down a set of pistons, I checked fuel flow volumn to be sure I was getting ONE PINT OF FUEL IN 30 SECONDS....I think this is also another critical need for our hot rods AND OUR POCKET BOOKS!!
I hope some of this makes since and helps you out, Jake (mr goodwrench) OH BY THE WAY......are you sure your fuel filter is not restricted in any way!!!! ? OH, one last thought......have you ever scanned you car under hard acceleration to see what the O2 sensor is showing?????? Do this if you haven't! I personally run mine of the rich side to keep away from toasting pistons(I run lots of boost) When I have scanned mine under HARD THROTTLE, I see about 600 MV. This a bit on the rich side, but I prefer this over taking a chance of killing more pistons! The car will never run any spectacular ET'S at a local drag strip(ZERO TRACTION) but it will smoke the tires at 50+MPH....

BEST of luck, Jake (mr goodwrench) Sorry for long drawn out post.....
 
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