78 280z Severe Driving Problems

[Captain Obvious]

kinser, Thanks for the gauge details. I had found the datasheet, but didn't see that gauge mechanics document.

It looks identical in theory of operation to the one I have. If it works as well as mine, you're gonna love it.

So it sounds like the car is running well enough to drive it now? That's a great improvement from when you started!     Your next task... Clean some electrical connections and double/triple check for vacuum leaks. It's likely you have several small leaks throughout the system.

[Zed Head]

17 minutes ago, Captain Obvious said:

Oh.  I was going from the text above when the OP said "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." and "With the stock pump replacement, the fuel pressure still seems a little high but not as high as with the previous pump."

Kinser86 seems a bit like a fresh engineer itching to use new knowledge to solve problems as fast as possible.  Very detailed work but he has skipped the basics of calibration and verification.  

No offense kinser.  Everybody jumps ahead to what "must be" occasionally only to find that what must be, wasn't.  Some people spend much time and money doing that.

[kinser86]

On 10/4/2018 at 9:16 AM, Captain Obvious said:

And you paid for an injector cleaning that had to be done twice because the first time didn't work out as intended.

Just for future reference, Fuel Injection Specialties did not charge me the second time and were extremely diligent and supportive of my concerns towards correcting them. I don't want people to be discouraged from using them nor do I want to tarnish their name. In the end, I got the injectors flowing evenly. It could have been my fault letting the injectors sit to long before reinstalling them.

11 hours ago, Zed Head said:

Kinser86 seems a bit like a fresh engineer itching to use new knowledge to solve problems as fast as possible.  Very detailed work but he has skipped the basics of calibration and verification.  

No offense kinser.  Everybody jumps ahead to what "must be" occasionally only to find that what must be, wasn't.  Some people spend much time and money doing that.

None taken. Quality and cost go hand in hand which is why I keep opting to spend money on better testing equipment rather than throwing it at the car. Like you mentioned, I am more interested in the measuring than driving the actual car ?. There doesn't seem to be any higher quality 1/4" NPT fuel pressure gauges readily out there. I am keeping my fingers crossed that the ΔP gauge will read better. Who knows, maybe the OTC vacuum gauge is incorrect and I don't really have 20inHg and I do have a vacuum leak somewhere which is why my fuel gauge is reading what it is. Time will tell, just have to wait for the gauge to come in.

[rcb280z]

16 minutes ago, kinser86 said:

maybe the OTC vacuum gauge is incorrect and I don't really have 20inHg and I do have a vacuum leak somewhere

This is what I have thought about a couple of times. I've never seen a stock L engine run at 20inHg. Not that it isn't possible? IDK. I just haven't seen it myself. But I have thought you should check it with a different gauge just to eliminate it.

[Captain Obvious]

Well I've kinda lost the pea on where the vacuum measurements are being taken at this point, but I've easily seen 20inHG when measuring on the port vacuum source at the throttle body. You get the throttle plate in the right position and that vacuum really spikes. Depending on how it's running and if you need the throttle open far enough just to keep it running...

Interestingly enough, I don't remember if I ever measured a non-ported source on the main intake manifold log on my car. Not sure I ever needed to.

[kinser86]

Well the new gauge gives the same numbers, 42-PSI. In the video, the first clip has the High and Low side hooked up to the gauge. The second short clip is just the high side. I haven't tried running the return off the rail into a bucket yet to see if the hard return line is causing the issue. I am running the Delphi FD0035 fuel pump now as I mentioned a few posts back. Right now this has to be isolated to a few things:

• Fuel Pressure Regulator
  • No fuel is leaking from the vacuum side
  • I don't know how this could fail and yield higher pressure
• Hard return line to tank
  • Dump fuel return from rail to bucket to see if pressure is still high or not

?

 

[Captain Obvious]

Gauge looks like it works great. Isn't it nice to see pretty much rock solid numbers there even when you goose the throttle?

So, as for the numbers... It's definitely looking like a faulty FPR. Running the return line into a bucket is a good idea, but I'd be surprised if a partial blockage there would result in such a constant deltaP on the gauge. Easy to check though.

However, like you, I'm having a hard time coming up with a way the FPR would run high though. Anyone got theories on that?

[Zed Head]

Pretty sure I've read about crude pressure adjustment via hammer taps on the spring side.  Add some preload.  Not sure how sensitive it is, maybe the vacuum port got pressed in somehow.  It's just a pressure relief valve.

The simple "FPR or blockage" test is to remove/bypass the FPR.  A piece of hose will do it.  Put a loop in it to make it easy to fit.

[Captain Obvious]

Yeah, I was wondering about mechanical deformation as well. If you would crush in the end where the spring seats, you would increase the spring force, and hence, increase the operating pressure. But I think it would be an obvious significant deformation.

How about just plugged up with crud? I'd be hard pressed to be convinced that it would provide a constant offset, but crud could certainly raise the equilibrium pressure.

How about a 40 year old diaphragm that is stiff and doesn't flex as easily as it did when it was first produced? Now it takes more vacuum to pull the seat off the outlet orifice?

In any event, a six psi offset is something that should be taken care of.

[kinser86]

1 hour ago, Captain Obvious said:

How about just plugged up with crud? I'd be hard pressed to be convinced that it would provide a constant offset, but crud could certainly raise the equilibrium pressure.

How about a 40 year old diaphragm that is stiff and doesn't flex as easily as it did when it was first produced? Now it takes more vacuum to pull the seat off the outlet orifice?

In any event, a six psi offset is something that should be taken care of.

I have about the same two thoughts, rigid diaphragm or blockage. It definitely is not leaking but that would be an opposite symptom. I think it is worth replacing and seeing if it improves. If it does, I want to cut the old one apart and see the damage. That is a BIG if.

[Zed Head]

1 hour ago, kinser86 said:

I think it is worth replacing and seeing if it improves. 

Edit, summarized, too wordy - why don't you just bypass the FPR first?  You have a good gauge.  All you need is a piece of hose.

 

Edited October 8, 2018 by Zed Head

[kinser86]

1 hour ago, Zed Head said:

Edit, summarized, too wordy - why don't you just bypass the FPR first?  You have a good gauge.  All you need is a piece of hose.

I'll do that and get a video too.