fuel delivery not constant

[mattszcar]

I have been trouble shooting my 78 280z for about 3 weeks now. I have replaced the fuel pump with a msd 2225, new air flow meter. new clear fram g3 fuel filter at the engine and the tank before the fuel pump. new thermostat. new temp sensor, cleaned the injectors and installed new o rings. new fuel pressure regulator new vacuum line to the regulator and distributor. new fuel line and clamps from the tank to the rail all new fuel line.I have done every last test on the ecu with my multimeter according to the fsm. I also have a fuel pressure gauge just after the filter at the engine. I can charge the fuel system by running the pump only. the filter at the engine fills up and the gauge reads a solid 40 psi when pumping. Start the car fuel pressure with the car running is 35-36 So Im good there. It will idle for quite a time like this or drive for about a mile. You can sit and watch the fuel slowly drain out of the filter at the engine. eventually draining almost completely out the pressure drops of course and the engine dies. If I disconnect the vacuum from the fpr the pressure surges right back to 36 and stays there. Fuel will come back into the filter, but after a few minutes it will just drain out again. although with the vacuum line disconnected from the fpr even though there is no fuel in the filter the pressure remains on the gauge. With the vacuum connected the fuel pressure drops with the loss of fuel from the filter. either way the car dies. As I said i have a clear filter at the fuel tank. There's not a spec of dust in the filter so it doesn't seem to be that anything is in the tank. I also have about 12 gallons of gas in the tank. When the pressure just starts to drop i can get under the car and hear the fuel pump running so i know its not shutting off. As a matter of fact when the engine sputters to a stop the pump runs a few seconds after the engine dies from no fuel. Please Help. I am at a complete loss. I have gone through all the trouble shooting and just can't figure it out. I am in the army up in Ft drum NY and i have called 10 different mechanics. No one will touch a car this old up here. I have read and read and read other peoples problems with fuel . Nothing matches this issue I can find. even if the ecu or fpr was malfunctioning. If the fuel pump is running. fuel should be in the filter should it not???

[mattszcar]

Some suggested to me if the timing was off that could cause this problem. I say again. If the fuel pump never stops running how is anything going to stop fuel from entering the filter.

[siteunseen]

Unhook the fuel line from the top of an injector at the rail and put another short piece of hose on the rail, secure it in a jar or bottle or something. Crank it over and see what comes out. Sounds like a vent line or something is clogged up.

Oh yeah! Could a fuel filter arrow be pointing the wrong way? I've done that before.

Edited April 5, 2014 by siteunseen

[mattszcar]

Yep ive done that and fuel comes out fine. the arrows are definately pointing the correct direction as it says flow with the arrow

[FastWoman]

Matt, what sort of filter are you using? The OEM design of filter is quite large, and I've not seen a clear one of that size. There are some clear, low-flow filters for carburetors. When running one of those on a carbureted 318, there were times the filter appeared to be empty, when in fact it just had an air pocket. It was still passing fuel just fine. That said, an OEM fuel filter is oriented in such a way that any air inside the filter should be purged. You would see nothing but fuel in the filter, if you could see through the metal can.

I'm guessing your issue is simply one of the fuel pump fading. As your pump is new, I'm guessing your electrical connections aren't in good shape. You should trace all your connectors from the fuel pump relay to the pump. Check that the connections are clean and solid (and haven't charred/arced). After cleaning, grease each connection with dielectric grease to preserve it.

First stop is the fuel pump relay connector, inside the big, black box on the passenger side of the engine compartment. The blue/green wire leads to the pump. Second stop is the big wiring tree connector (there are two of them) just inside the passenger firewall. This is where I had a melted, charred connector. I snipped out the blue/green wire and connected via a bullet connector. Last stop is the fuel pump.

Also check your ground, which runs from the pump, through a bushing in the floor, and to the interior of the cabin.

FAIW, 35-36 psi running pressure and 40 psi non-running pressure is a bit high. Non-running pressure (during cranking, or also with vacuum line disconnected) should be 36. Idling should be about 29 if your engine is running efficiently -- higher if it's not. The 4-5 psi differential you're getting between non-running and running should be more like 7 psi. This tells me your engine is either running rich or lean. If your fuel pressure gauge is accurate, your high pressure might have your engine running rich. That would indicate a fuel pressure regulator issue. It's more likely your gauge is off, though.

Edited April 6, 2014 by FastWoman

[Zed Head]

It may be that the things you listed are not all related.

Following FastWoman's logic, what happens if you just let the pump run alone for the same amount of time it would take the engine to die, but without the engine running. Is the behavior the same? That would separate any engine heat, injection issues from the general weirdness. Just let it run, it won't hurt it, that's what it does when you're driving.

And are you running a stock fuel rail and return line?

[mattszcar]

Thank you very much for the suggestions FastWoman. I will check these things first thing monday morning as I left the car at a shop for the weekend trying to decide what to do with the car. The fuel filter is a fram g3 as I have read many z owners using on there cars so i figured it was ok. I just wanted something clear to see if there was something in the line that was obvious. I still have the original filter which is new from the previous owner who could not make the car stay running. Also I cleaned up the connectors at the pump. with electrical cleaner and a brass brush but I will follow the line up on Monday as you suggest. The interesting thing I thought to is when i take off the vacuum from the fpr the gauge reads a perfect 36 and does not waver even when hitting the throttle and as the filter empties of gas it continues to read 36psi. Now if as Im whatching the fuel drain from the filter I connect the fpr back up the pressure drops with the emptying of fuel. Regardless the fuel runs out and the engine dies. Again I say though when the engine quits the fuel pump can be heard running. So monday i will check connections and put the original filter back on for starters. Again thankyou so much I have no way of getting this thing done except my self and I feel like its getting beyond my skill level. At least my ability to figure it out. As I have checked and replaced or cleaned everything i can see to do. Its not that I can't work on or replace something its just I have run out of ideas of what to do.

[mattszcar]

I do run the pump after the engine dies to get the engine started again. The fuel pressure reads around 40 and the filter refills only about one quarter the way and won't get any fuller than that. but the pressure remains at 36 when i release the key. It is a stock rail and return and all my rubber fuel lines are new with new clamps

[Zed Head]

I think that Fast Woman may be right and you have weak pump volume. But I wonder if the volume is low because you're pulling air in to the pump. There's enough gasoline getting in to keep a seal in the pump mechanism and let the pump work but it's pushing mostly air instead of fuel. Or the fuel is sitting at the bottom of the system, back-flowing in to the pump to let it hold pressure. Maybe. Check your fittings in to the pump and the filter and its fittings.

Or a quick test would be to disconnect the inlet hose to the pump and run a hose without a filter to a gas can. Make sure the hoses seal tightly.

[FastWoman]

If I were you, I would rule out the pump as Zed suggests. You can "hot-wire" it by running a wire from the battery's (+) post to the (+) post of the fuel pump (blue/green wire). You don't have to disconnect the existing wiring.

Before you fire up the pump, connect a long piece of rubber tubing to the "return" line of your fuel rail (coming from the outlet of the fuel pump regulator and sweeping around the front of the engine -- the tube other than the one connected to the fuel filter.

Now fire up the pump. Your pressure should be 36 psi, and you should have a steady flow of fuel coming out the end of the hose. You can pour it into a fuel can, or if your hose is long enough, you can dump it right into the filler neck of your gas tank. Just watch it for a while to see what happens. If you've got the same fuel flow and pressure after 15 min or so, then your pump and filters are probably fine, and we search for other issues (like electrical).

[mattszcar]

Ok Im on it first thing monday. I going to get my fuel line today. and do both. Run the pump from a can and run it directly to the return line at the fuel rail coming off the fpr.

[FastWoman]

BTW, I note that JRSGTS (on this list) is a pro mechanic specializing in classic cars, located in Greenwich, NY, about 3 hr from you. I realize that's a bit of a hike, and I suspect you can tackle this issue on your own. However, he's there if you need him. He's not a Z specialist, but he's currently working on a customer's Z and is coming up to speed quickly -- apparently eager to learn.

There may be other mechanics closer to you who would be willing/able to work on your Z. In fact you might find some old-timer mechanics at your local Nissan dealer. The PO of my Z lived in a fairly remote part of Virginia, but he was able to find expertise at the local dealership. There was one mechanic there who cut his teeth long ago on the Z and did all his work. I've had a few nice conversations with him, both before and after the sale.

I vaguely remember being at another Nissan dealer's service department inquiring about a fuel pump check valve. One older mechanic shouted over to another and asked, "What's the part number on those old Bosch check valves?" The other mechanic rattled off the number from memory!

I mention all this not because I don't think you're up to solving this fuel delivery problem. I think you are. Rather, I saw JR's post on another thread and remembered you -- both of you from the nether-regions of New York.