78 280z Severe Driving Problems

[Captain Obvious]

1 hour ago, kinser86 said:

It stays up, I don't have a number to support this but it does not drop to zero immediately. Give it 24 hours, it'll drop to zero. When working on the car, I could go away 30 min at a time and glance over the gauge and see its not at zero when going back to start it.

I think you should add more detail about what the pressure settles at when you stop the fuel pump. I understand that it'll droop overnight to zero, but the number I'm looking for is five seconds after you stop the pump.

Why? Because you said you have 42 psi engine off while the pump is spinning. That's too high.

But it's important to see what the pressure does right after the fuel pump stops spinning. If it stays at 42 even with the pump off, then you have a regulator issue.

If the pressure snaps down to 36 and holds there when the pump stops, then you're overwhelming the regulator. In other words, the regulator works, but can't handle the volume. It's trying to bleed excess pressure back to the tank, but it can only do that up to a certain volume. Above which, it's full open and can't bleed any more fast enough. That's the issue Chknman suggested.

Not sure I said any of that right... Does that make sense?

[kinser86]

9 minutes ago, Captain Obvious said:

I think you should add more detail about what the pressure settles at when you stop the fuel pump. I understand that it'll droop overnight to zero, but the number I'm looking for is five seconds after you stop the pump.

Why? Because you said you have 42 psi engine off while the pump is spinning. That's too high.

But it's important to see what the pressure does right after the fuel pump stops spinning. If it stays at 42 even with the pump off, then you have a regulator issue.

If the pressure snaps down to 36 and holds there when the pump stops, then you're overwhelming the regulator. In other words, the regulator works, but can't handle the volume. It's trying to bleed excess pressure back to the tank, but it can only do that up to a certain volume. Above which, it's full open and can't bleed any more fast enough. That's the issue Chknman suggested.

Not sure I said any of that right... Does that make sense?

Makes perfect since. The way I interpreted your statement was my volumetric flow rate of the pump is exceeding the capacity of the regulator, yielding in a higher pressure. Once the flow stops, system stabilizes and releases higher pressure down to 36psi. Is that right? I don't know if this is happening, but something I can definitely check. 

I do notice the gas tank pull in air when opening the cap. I have read that this is common with these cars though. The check valve is working on the gas cap though so its not clogged. This is stuff I evaluated before I got heavy in to the technical details.

Edited September 21, 2018 by kinser86
sentence phrasing

[Zed Head]

On 9/20/2018 at 4:13 PM, kinser86 said:

Test fuel gauge accuracy/precision

Lots of discussion about fuel pressure.

[Captain Obvious]

On ‎9‎/‎20‎/‎2018 at 8:46 PM, kinser86 said:

The way I interpreted your statement was...

Yes, that's a correct interpretation. It's just a suggestion for an easy method to determine the difference between 1) a faulty pressure regulator and 2) a regulator that works fine but simply cannot deal with the aftermarket pump is currently paired with (as chickenman suggested).

Of course the validity of any of this is dependent on the accuracy of your test equipment (as Zed Head suggested).

[kinser86]

Alright, I got the some parts off the car and brought them home. I evaluated the gauge first before I do anything else. I had 100PSI on the compressor supplying the line. I swept it to 80-PSI before the video and also did a couple of these sweeps before recording. 

 

[kinser86]

Update time. I had taken the injectors back to Fuel Injection Specialties and they agreed that two were flowing irregularly. They cleaned them again and got them back to flowing where they should have been. The discrepancy occurred because the cleaning solvent dried in the two injectors and clogged them back up. I took them back and did the same out of car test and got all of them to match volumes.

After this, I put the rail back on the car and put in new plugs on every cylinder. At this point I felt the fuel pump was too much for the car and we pulled it and replaced it with a Delphi stock replacement. We hooked everything up, set the timing again, and tried to drive it again.

From the video, the car is driving much better now. The resister between the coolant temperature sensor is turned all the way back as if it was never installed right now. With the stock pump replacement, the fuel pressure still seems a little high but not as high as with the previous pump. I pulled the plugs after we drove it around for a bit and took some pictures.

I need to put the AFM cover back on and clean up some of the engine bay before really driving it. Any thoughts on fuel pressure/vacuum reading?

[Zed Head]

26 minutes ago, kinser86 said:

Any thoughts on fuel pressure/vacuum reading?

Sounds pretty good.  Nice that the the fuel Injection guys owned up and fixed the injector problem.  Although, you'd think they would know better.

I see 32 psi on the fuel gauge, and 20 inches of mercury on the vacuum gauge.  That calculates to about 42 psi fuel pressure with no vacuum.  I think that you can borrow a gauge from the local auto parts store, for a cross-check.  They require a deposit but give it back afterward.  Looks like you're still working with a gauge of unknown quality.

Good luck.  Carry on.

[Patcon]

That's great progress! Sounds so much better!

[Dave WM]

sounds like its back firing? for the record my stock setup never backfires. Not sure what causes that, but was under the assumption that FI cars should not. I tried to find out by mr google, some said its a lean mix not igniting until got into the exhaust, some said its a rich mix not completely burning until the exhaust, others claimed all cars backfire unless they are de tuned, and a LOT of votes for it sounds cool. I remember it sounding cool when I would shut off the ignition with the key, wait a few seconds, then turn back on for a nice BOOM. real cool until I blew up my parents muffler, then not so cool. I am old now and prefer to not hear loud exhaust, at least not for extended trips. One last opinion was its the nature of the type of exhaust. I love google...

Edited September 30, 2018 by Dave WM

[Patcon]

2 hours ago, Dave WM said:

sounds like its back firing? for the record my stock setup never backfires. Not sure what causes that, but was under the assumption that FI cars should not. I tried to find out by mr google, some said its a lean mix not igniting until got into the exhaust, some said its a rich mix not completely burning until the exhaust, others claimed all cars backfire unless they are de tuned, and a LOT of votes for it sounds cool. I remember it sounding cool when I would shut off the ignition with the key, wait a few seconds, then turn back on for a nice BOOM. real cool until I blew up my parents muffler, then not so cool. I am old now and prefer to not hear loud exhaust, at least not for extended trips. One last opinion was its the nature of the type of exhaust. I love google...

I believe that may be the exhaust he is running

[kinser86]

On 9/30/2018 at 8:06 AM, Dave WM said:

sounds like its back firing? for the record my stock setup never backfires. Not sure what causes that, but was under the assumption that FI cars should not. I tried to find out by mr google, some said its a lean mix not igniting until got into the exhaust, some said its a rich mix not completely burning until the exhaust, others claimed all cars backfire unless they are de tuned, and a LOT of votes for it sounds cool. I remember it sounding cool when I would shut off the ignition with the key, wait a few seconds, then turn back on for a nice BOOM. real cool until I blew up my parents muffler, then not so cool. I am old now and prefer to not hear loud exhaust, at least not for extended trips. One last opinion was its the nature of the type of exhaust. I love google...

I think it might be the exhaust you hear. It does have a header and exhaust system. One way to check would be to let it engine brake and see if it makes any noticeable sounds but again it might be the exhaust. 

[Captain Obvious]

So what's the bottom line? It sounds much better. Are you calling this a success now?

The thread was about severe driving problems. Are you claiming victory? That would be sweet!