77 280Z Dropping Fuel Pressure once Warm

[Z-Heap77]

Hello All:

My father and I have own several Z's over the years, but we've had this 77 280Z for quite a while now. I've collecting some parts to lately to do a "intake clean up" project. I found a non-egr intake manifold and purchased a PALNET fuel rail. New injectors, o-rings, fuel filter, fuel pressure regulator, pvc valve, fuel hose and vacuum hose. We just completed all of the work and at initial start up the car was running fine. Fuel Pressure was a little low but seemed to idle fine and rev smooth. We took the car for a fine and about 2 miles down the road things went way down hill. Any throttle caused the power to break up horribly. Car would idle ok (fuel pressure gauge only reading 20 psi) but any power would totally screw it up. We had to limp it back to the house, but it was blowing blue smoke from the exhaust.

When I popped the hood i found see some fuel around one of the jnjectors so I pulled that one and replaced it with one of the old ones, buttoned it back up and tried again. Again it started right up and would idle fine and rev smoothly. We let the car run for a while for it to warm up and eventually the fuel pressure dropped and any throttle would cause it to break up.

While cleaning up the intake I removed the CSV, AAR and disconnected the Thermo Time Sensor. I removed the magnet valves and air tank associated with the AC. I did keep the charcoal canister in place and connected as it should be.

Just to be clear the car was running just fine before doing this so there weren't any issues that I was hoping to correct while doing the intake clean up project.

https://db.tt/SyCkTvNx

The link above will show you some photos that I took of the engine compartment and 3 videos that I took with the car running. I'll give you a summary of each below:

1st photo - fuel filter side of the engine compartment

2nd photo - fuel gauge showing 30 psi at initial startup

3rd photo - intake manifold side of the engine compartment

1st video - initial start up, you can see that no throttle change the fuel pressure

2nd video - engine idling w/about 30 psi of fuel with vacuum removed from FPR, you can see the change when I reconnect the vacuum, it drops to 20 PSI

3rd video - the car is warmed up enough that any throttle total bogs the motor down

I've done quite a bit of searching but thought it was time to create my own post and see what kind of responses I get. Any help or direction on what to check would be greatly appreciated.

Patrick

[Zed Head]

Any throttle caused the power to break up horribly. let the car run for a while for it to warm up and eventually the fuel pressure dropped and any throttle would cause it to break up.

2nd video - engine idling w/about 30 psi of fuel with vacuum removed from FPR, you can see the change when I reconnect the vacuum, it drops to 20 PSI

The power break-up is because the fuel mix is lean. You should be at ~28 with the hose connected and 36 without.

Did you get an adjustable regulator? It may have slipped adjustment or was never set right.

If you have the stock regulator, pinch the return hose when the pressure is at 20 and see if it rises to 36 or greater. this will tell you if the pump can supply the pressure. Be careful, the aftermarket pumps will hit 90 psi and can cause leakage.

If you think it might be the pump, you can prop the AFM door open with the key On, as Blue suggests in another thread, and just let the pump run while watching the gauge. Several people have had pumps that fail when warm. If the pump is bad, eventually it will start making funny noises and pressure will drop. I had one of those.

[Z-Heap77]

The power break-up is because the fuel mix is lean. You should be at ~28 with the hose connected and 36 without.

Did you get an adjustable regulator? It may have slipped adjustment or was never set right.

If you have the stock regulator, pinch the return hose when the pressure is at 20 and see if it rises to 36 or greater. this will tell you if the pump can supply the pressure. Be careful, the aftermarket pumps will hit 90 psi and can cause leakage.

If you think it might be the pump, you can prop the AFM door open with the key On, as Blue suggests in another thread, and just let the pump run while watching the gauge. Several people have had pumps that fail when warm. If the pump is bad, eventually it will start making funny noises and pressure will drop. I had one of those.

Zed: Thanks for the response. I did not purchase an adjustable FPR, I just purchased a replacement stock model. I started the car up just now and had about 30 PSI (that's where the pressure is when cool) and then pinched the return line and the pressure shot u to over 40 psi. So what does that mean? Is the FPR not working correctly? Does this rule out the pump as a problem?

[Zed Head]

30 psi at idle when cold is in the right range. Since your problem happens when warm you need to do the same thing when it's warm and you have 20 psi, which is not in the right range, it's too low. The cold test just shows that everything is working right when cold.

[FastWoman]

I had a fuel pump fail that way. My car would idle fine in the driveway, but when I drove it, the engine would eventually falter and then die. It turns out the fuel pump ran fine until it heated up. Then pressure and volume would fall off. You might be able to recreate this problem in the driveway, without even running your engine. Pull off your return line, and connect a long fuel hose that you can run back to the filler neck of your gas tank. Connect a fuel pressure gauge between your fuel filter and the fuel rail. Finally, hot-wire your pump, and run it with the ignition off. Pressure should read about 36 psi, and you should get a healthy rate of fuel flow from the end of the return hose into your gas tank. Let the pump crank for a while, and see if pressure starts to fall and return fuel flow starts to decline. If your pump is like mine was, pressure will fall quite low, and there will be no return fuel flow at all.

And BTW, I'm a bit concerned about "blue smoke from the exhaust." Perhaps you mean black or gray smoke? Blue smoke would suggest oil burning.

Also check that your coolant temp sensor has a good connection. If that circuit goes open, then you can enter an extremely rich condition that would have your exhaust belching black smoke.

[Z-Heap77]

I had a fuel pump fail that way. My car would idle fine in the driveway, but when I drove it, the engine would eventually falter and then die. It turns out the fuel pump ran fine until it heated up. Then pressure and volume would fall off. You might be able to recreate this problem in the driveway, without even running your engine. Pull off your return line, and connect a long fuel hose that you can run back to the filler neck of your gas tank. Connect a fuel pressure gauge between your fuel filter and the fuel rail. Finally, hot-wire your pump, and run it with the ignition off. Pressure should read about 36 psi, and you should get a healthy rate of fuel flow from the end of the return hose into your gas tank. Let the pump crank for a while, and see if pressure starts to fall and return fuel flow starts to decline. If your pump is like mine was, pressure will fall quite low, and there will be no return fuel flow at all.

And BTW, I'm a bit concerned about "blue smoke from the exhaust." Perhaps you mean black or gray smoke? Blue smoke would suggest oil burning.

Also check that your coolant temp sensor has a good connection. If that circuit goes open, then you can enter an extremely rich condition that would have your exhaust belching black smoke.

Thanks Fast. I will give this a shot today and see what results I get. I know I can recreate the hot running low fuel pressure in my driveway but that's with the car running. I'll need to head to the store for some fuel line to go from the engine to the fuel tank because I don't have enough line left over now.

One thing I forgot to mention in my original post was that when I shut the car off the fuel gauge goes immediately to zero. It's not holding any pressure. It used to hold pressure before. It would reduce over time, the car isn't a daily driver, but it always held something. Yesterday after driving it, I shut the car off and pulled the hose off the filter and had no pressure. Does that make any difference in what the issue might be or does that still point at the pump as the potential issue?

I'll post results later today. Thanks all.

[FastWoman]

Heap, you've probably got a bad check valve on your fuel pump. The Nissan part is NLA, but there are other alternatives available -- see recent thread. That said, the check valve is only important for preventing hot restart issues. It would in no way impact the ability of your engine to run correctly, once started.

[Z-Heap77]

Fast,

I'm not sure I follow why the check valve a your suggestion on the defective part. If you say this part affects hot restarts and not the running of engine, why would it be a potential problem? The car doesn't have a problem starting cold or hot. The car does have a big time problem of not having enough fuel after the car warms up.

I was thinking, and you guys correct me if this sounds absurd, but if the car isn't building up enough fuel pressure while running AND drops down to zero immediately after shutting off the car would it make sense for one of the new injectors to be faulty? Could one of the injectors always be wide open? Never allowing pressure to build and eliminating all pressure as soon as the engine shuts off? How can I test that? Aside from reinstalling all the old injectors, I'd rather rule out certain parts instead of guessing.

Be the way I did try punching off the return fuel line even when the car has warmed up and is only getting 20-22 psi. The pressure would rise to over 40 psi when pinched.

I couldn't complete the test of running the pump with the return line extended to the fuel tank filler tube because none of the part stores are open to get more hose.

[Zed Head]

Be the way I did try punching off the return fuel line even when the car has warmed up and is only getting 20-22 psi. The pressure would rise to over 40 psi when pinched.

This is a sign that the regulator is not regulating correctly, but the pump is okay. Pull the vacuum hose from the bottom of the regulator and see if it smells strongly of gasoline. It might smell faintly of gas but if there's any mositure in there or it reeks of gas you probably have a blown FPR. Also, when you get a chance, warm the engine up again and remove the vacuum hose. If pressure does not rise to 36 psi or better then you have a bad regulator. Should have added this step before to save you time. I've seen on another forum that a blown diaphragm can cause a cold spot on the intake manifold at the point where the FPR vacuum hose nipple on the manifold points. The cold fuel cools it off. Just another sign.

It might be that you have a hole or crack in the FPR diaphragm or the seal around the diaphragm, that gets worse when it warms up. This will give conflicting behavior, the intake will suck in extra fuel causing rich running, but the fuel pressure might read low, which would normally cause a lean mixture. The smoke from the exhaust might be signs of too much fuel.

I had a bad FPR that showed correct pressure but was dumping way too much fuel. My gas mileage dropped to 15 mpg from 19, and the people driving behind me were angry. I got screwed up even more because I had a gauge on the fuel rail that read high when it got warm.

[Z-Heap77]

Zed, Thanks. I have done that test already and I can tell you that it never gets more than 30 psi pressure no matter what I do. I'll have my dad order another fuel pressure regulator and we'll give that a shot. I picked up the one I got recently from a local advance auto. Any recommendations on purchasing locally or ordering online from more reliable Z parts source?

[siteunseen]

Could the filter up front be stopped up?

[Z-Heap77]

It is new, but then again, so is the fuel pressure regulator, so that isn't saying much!