urdrwho Posted July 31, 2013 Share Posted July 31, 2013 Months ago when I first got the subbie and had the P304 I read about a guy that a new fuel pump solved his P304 problem. The reasoning was that #4 was at the end of the rail. I only got the P304 at idling, slowly taking off from a stop light and never, ever on the highway. After replacing the coil, plugs, plug wires, fuel filter I was down to two tests. A compression test and a fuel pressure test. I decided on the fuel pressure first because it was easiest and I had a feeling about the fuel pressure. The pressure read 30 and had a slight shake. Turn off the car and bam.....pressure went to zero. Did the test again and the same thing. I guess I don't have to watch the time on a leak down test because there isn't any pressure to leak. So I am confident that I am not keeping a constant fuel pressure and that would be the reason the car flies on the highway but has low pressure at idle. Not sure if the Subbie has a non-return valve outside of the fuel pump. The non-return valve is probably incorporated in the fuel pump. So is it time for a new pump????? Link to comment Share on other sites More sharing options...
Kennyfvholla Posted July 31, 2013 Share Posted July 31, 2013 I wish I knew more about the fuel system to give you some help. I've just never worked on it before... But, if it was a weak fuel pump causing the issue, I would think that all the cylinders would be miss firing. Or, at the very least, the cylinder that is furthest down the line of the fuel rail.. Idk. Have you checked to make sure that the fuel injector on that 4th cylinder is working correctly? Put the tip of a plastic handled screw driver on the injector body and listen to the noise it makes at idle. Have you looked for any vacuum leaks? Link to comment Share on other sites More sharing options...
spooln30 Posted July 31, 2013 Share Posted July 31, 2013 Yes the fuel pressure shouldn't drop down the moment you shut the engine off BUT it's not due to the pump. The pump already sent the fuel to the rails creating the psi. If it's dropping of then you either have a leaky fuel pressure tester or you have a fuel leak. A weak fuel pump would in most cases cause a multiple cylinder misfire not just one cylinder. I would look towards a vacuum leak or a dropped valve guide. Get a can of carb spray and while the engines running spray in the area of the intake manifold gaskets and other vacuum sources. On my old 96 L I had a misfire that I couldn't figure out till one day I hooked up a EVAP smoke machine to a vacuum line off the intake manifold and found smoke coming from the cylinder I had the misfire. Replace the gaskets and problem solved. Later I had another cylinder misfire on only 1 cylinder. So I did a little research and found the second gens can develop a dropped valve guide issue. What happens is the guide becomes loose and will work its way down and prevent the valve from fully closing this the misfire. The way to check this is to drop the exhaust header down and look into the ports to see if any of the guides dropped down further then 1/16". GL Link to comment Share on other sites More sharing options...
urdrwho Posted July 31, 2013 Author Share Posted July 31, 2013 From what I know from experiencing fueling issues on other cars over the years --- the pump has what is called a non-return valve, they work the same way a check valve works in a water supply. Without that non-return valve or a weak valve in the morning the car would need to be cranked more than normal for it to start. I once had a car that had two gas tanks and two non-return valves (one on each side of the car). When they didn't hold pressure they caused all kinds of problems. The injectors are not leaking, they have been changed out and were holding pressure when removed from donor car. No gas leaks in engine compartment. My Alldata account says that I should be getting 26-30 psi at idle and higher if the fuel regulator isn't working. Haynes says 26-32 psi at idle. Haynes manual says for leak down testing to wait 5 minutes and recheck the pressure on the gauge, compare to hold pressure listed in Specifications. Haynes says fuel pump hold pressure is to be 30 psi. Alldata -- When the engine and fuel pump stop, spring force acts on the check valve to close the discharge port so that fuel pressure remains in the fuel delivery line. This morning I'm off to the parts store to buy a bit of FI hose so it is easier to hook up the fuel pressure gauge Tee. I plan on pumping up the pressure, clamping the return fuel feed line and see if the pressure drops. If it drops it is a dead check valve in the fuel pump. Not a fan of in the tank fuel pumps. My past two daily drivers have been cars with external pumps. The one car had the pump in the trunk area. I could sit in the trunk, stay clean and comfortably sit to change the fuel pump and fuel filter. I understand all the theories of in the tank pumps staying cooler but when they do die the replacement cost is a lot more than an external pump replacement. Yep the valve guide is on the test list but I need to get the fuel system to hold pressure first and see how it runs. I could have several different issues going on at the same time. Yes the fuel pressure shouldn't drop down the moment you shut the engine off BUT it's not due to the pump. The pump already sent the fuel to the rails creating the psi. If it's dropping of then you either have a leaky fuel pressure tester or you have a fuel leak. A weak fuel pump would in most cases cause a multiple cylinder misfire not just one cylinder. I would look towards a vacuum leak or a dropped valve guide. Get a can of carb spray and while the engines running spray in the area of the intake manifold gaskets and other vacuum sources. On my old 96 L I had a misfire that I couldn't figure out till one day I hooked up a EVAP smoke machine to a vacuum line off the intake manifold and found smoke coming from the cylinder I had the misfire. Replace the gaskets and problem solved. Later I had another cylinder misfire on only 1 cylinder. So I did a little research and found the second gens can develop a dropped valve guide issue. What happens is the guide becomes loose and will work its way down and prevent the valve from fully closing this the misfire. The way to check this is to drop the exhaust header down and look into the ports to see if any of the guides dropped down further then 1/16". GL Link to comment Share on other sites More sharing options...
johnegg Posted July 31, 2013 Share Posted July 31, 2013 i'm really at a loos regarding your problem other than to think logically. butr the fuel pump is accessed by opening an access panel in the trunk / cargo area, under the carpet, near the back seat, passenger side. that reveals the top of the tank, the hoses, and the wire connections. and the access panel for the fuel pump. needless to say , none of these parts have been touched since the factory. Link to comment Share on other sites More sharing options...
urdrwho Posted July 31, 2013 Author Share Posted July 31, 2013 I was in there last Saturday putting penetrate on all the nuts....just in case I had to remove them. Now today. I did the test again and it held pressure. In fact it held pressure so well that I could not get it to release pressure. My protocol for lowering fuel pressure is to remove the electrical connector at the fuel pump, start engine and let engine die. Do it again until engine dies so on and so forth. The engine would not start anymore but the gauge read 12 pounds of pressure remaining. That is enough pressure to get a gas shower and I already had a shower. Kept trying to start engine and it was a no go but pressure was down to 9>10 psi. Ok I'm tired of this. I get my rags and go the old fashioned route, using a rag to catch the gas as I slowly take the FI hose on and off the hose bib....ever so slightly. Finally it was down to zero. What the heck? Do I have a haunted fuel system?????? Next step is to do the compression check and maybe the fuel pressure again. i'm really at a loos regarding your problem other than to think logically. butr the fuel pump is accessed by opening an access panel in the trunk / cargo area, under the carpet, near the back seat, passenger side. that reveals the top of the tank, the hoses, and the wire connections. and the access panel for the fuel pump. needless to say , none of these parts have been touched since the factory. Link to comment Share on other sites More sharing options...
johnegg Posted August 1, 2013 Share Posted August 1, 2013 i have heard of intermittent fuel pump problems, that that was usually associated with a no start situation. Link to comment Share on other sites More sharing options...
spooln30 Posted August 2, 2013 Share Posted August 2, 2013 Try another fuel gauge. Link to comment Share on other sites More sharing options...
the pizza Posted August 4, 2013 Share Posted August 4, 2013 Has anybody seen a tutorial on how to remove/install a fuel pump on a 4th gen leggy? I'm about to attempt that for the first time, and I have the factory manual on my computer, but pictures or a few pointers would be appreciated. Link to comment Share on other sites More sharing options...
monkeyposeur Posted August 5, 2013 Share Posted August 5, 2013 DIY for a first gen: http://legacygt.com/forums/showthread.php/walbro-255-lph-install-diy-198427.html Maybe a fourth gen is similar. Link to comment Share on other sites More sharing options...
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