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Fuel Pump and Pressure Regulator Questions

srpotter

New Member
Joined
Dec 29, 2014
Messages
6
Location
Houston TX
I have an 05 Av and am having the hard start issues I have read about in other posts. :E: When the key is turned to start the engine fails to start but always turns over the second time. lately I have been cycling the key to the on position several times and afterwords she starts every time leading me to believe I have a fuel issue.
So I used a cheap fuel gauge and tested the pressure, here is where my questions come in; when I turn the key to the on position the fuel pressure goes to about 60 then drops to zero, my guess is that this should not occur and the pressure should hold. When the vehicle is started the pressure reads around 60 and stays there. Anyway after looking into a few other posts I have found that the possible culprit is the pressure regulator and mine is attached to the pump itself inside the fuel tank. Anyways can just the pressure reg be replaced or should I just replace the whole pump entirely? Also plan on doing the floor cut method instead of dropping the tank. ???
 
I see over at rock auto they sell a fuel pressure sensor separate from the pump, how many miles do you have on it.
 
MS03 2500 said:
I see over at rock auto they sell a fuel pressure sensor separate from the pump, how many miles do you have on it.

Wouldn't the fuel pressure sensor be for the tank pressure for the EVAP system?
 
I'm not sure the manual does not tell me. But I'm thinking if they have over 100,000 miles on it they may as well change the whole pump since it's not easy to get to.
 
Also my Avy is a VIN code Z which means it is flex fuel capable as opposed to the T which is not. Not sure if this helps.
 
When you initially turn the key in your truck the fuel pump comes on for a few seconds to pressurize your fuel system then turns back off. I have not heard that a fuel pressure regulator will drop the fuel pressure, it is normally a fuel injector sticking open.

I have recently read that it is a good idea to change your fuel injectors every 100,000 miles because they do wear out just like plugs and o2 sensors. You can get yours rebuilt relatively cheaply compared to new ones but that is only an option if you have a backup vehicle because you send them out and wait 2 weeks to get them back. If you have fuel dumping into a cylinder it can cause it to start hard since one cylinder is flooded out.

Have you run E85 in your truck? E85 tends to be more corrosive than standard gasoline and maybe it prematurely wore one of your injectors?

I would think if it was a pressure regulator issue then the pressure when your pump was on would not be correct but I have no experience with that.

Rodney
 
 
The fuel pump has a check valve to keep fuel pressure in the system at shutoff. This valve can go bad and cause the hard start issue. I bet the issue is most apparent on a cold start? 

It's possible an injector is hanging open but you would have other symptoms like a lot of black smoke on startup, a rich condition code,mor a misfire code due to a fouled plug.

I think you'll find that a new fuel pump will solve the problem. 
 
Hey guys, got a fuel pressure issue... its always something. BTW I have an 05 1500 Z71 (Z VIN Flex Fuel) with 146000 miles

Just for background when I got the truck in June 2016 the dealer already replaced the fuel pump as it had hard start issues when I was looking at it. It worked great until about 2 months ago.

I had codes P0300, P0054, and P0141 and the hard start was back and decided its time to replace the O2 sensors(all 4), knock sensors & harness with red RTV seal, and intake gaskets and clean the throttle body & gasket. All done with that and all codes are gone but P0054 came back the next day, need to inspect to harness for the heater circuit.

I'm driving on the highway, punch it to get around someone and lose power at 70mph, engine light starts blinking so I pull over and turn the engine off and back on, engine light is not blinking any more. When I get home I'll check the freeze frame and the codes.

I am wondering if this is all fuel pressure related because I tested the fuel pressure at the rail on Saturday while replacing KSs and O2s, when turning the key to on the pressure goes to 10 then drops to 0, second time it goes up to 25 then drops to 0, third time it'll go to 35 then drops to 0. When running the pressure only gets to 35psi. I was going to check the pressure regulator, but the fuel rail doesn't have one, and I don't even see a return line hookup on the fuel rail. Its the stainless steel fuel rail as shown below.

of55cz.jpg


If I'm loosing pressure I can only think it's the fuel pump going bad (again), or the pressure regulator (does this even have one, and where???), or leaking fuel injector(s). I"m not getting black smoke in the exhaust, and since I cant find the pressure regulator I can't test that, and not having a return line is throwing me for a loop. Where do I start?
 
35 is waaay low I'm surprised it runs that low.

Another thing that may be wrong is dirty fuel injectors that are leaking. Try a fuel system cleaner like Techron or Lucas(not carb cleaner.)
 
MS03 2500 said:
35 is waaay low I'm surprised it runs that low.

Another thing that may be wrong is dirty fuel injectors that are leaking. Try a fuel system cleaner like Techron or Lucas(not carb cleaner.)

They wouldn't be just leaking, they'd have to be stuck open to bleed off 20+ psi at idle (or with it keyed on and not running).  Engine would be missing all over the place, exhaust would be pig-rich, set O2 codes because the fuel trims couldn't adjust, probably even hydro-lock the engine.

Most likely culprit is the regulator.  Maybe the fuel pump, but kind of doubt it.  With the low fuel pressure, the flow is reduced 25%, so the LTFTs are adding injector pulse width as much as possible to try and compensate (but the ECU is limited to how much it can add, so will still probably be 10-15% lean and set codes).  Engine will probably run fair at idle and cruise, but not great.  Throttle tip-in response will be poor.  Poor cold startability.
 
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