78 280z Severe Driving Problems

[Dave WM]

what I don't get is why the color of the plugs is so consistent. Did you try new plugs?

[rcb280z]

3 hours ago, Dave WM said:

what I don't get is why the color of the plugs is so consistent. Did you try new plugs?

I was just wondering the same thing Dave. And you would think #2 and #3 would show signs of burning lean or cleaner than the other plugs if the injector flow is off. I could be wrong. 

This is a challenging one for sure.

kinser86 is running some thorough diagnostics though. Don't give up on it. Plenty of knowledgeable members on this site to help ya

Edited September 3, 2018 by rcb280z

[kinser86]

Time for an update.

I ran a few test this morning. First thing I did was pop off the fuel rail to capture some video of the injectors. I made a quick ground interrupt switch to an old injector connector and tested the injectors. I sprayed all of them but focused the video on #1, #2, and #3. I disconnected the starter signal and would turn the key to prime the rail before each test. In my opinion, the spray pattern for #1 looks really good. #3 definitely looks suspect with defined spray trajectories columns rather than a large cloud seen in #1. #2 I think falls between the both in quality but I will let the video do the talking. The other injectors looked similar to #1.

Next thing I did was pull all plugs and blow out all the fuel that got in the cylinders. I figured now would be a good time to do another compression check but the vehicle was not warm. Fuel was blown out of all cylinders before performing the test. Numbers again are high but they are still within 10% of each other. 

I then hooked up the FPR to a vacuum pump and put my vacuum gauge between the two to record FPR with respect to vacuum. Again, I charged the rail before doing this and slowly pulled vacuum until the pump couldn't pull anymore. It looks like 23inHG vacuum is only yielding 28PSI on the gauge. Is this an acceptable range? 

Now I made this chart for referencing fuel pressure with respect to vacuum. I read the FPR is to maintain a pressure differential of 36 PSI with respect to vacuum so if this chart is wrong, let me know.

That is all I was able to do. I have a new set of plugs I will put in next time but the spray pattern on #3 is suspect to me right now. The rail is still loose on the car anticipating suggestions to replace the two. I did not check valve lash or fuel return due to some time constraints.

[Zed Head]

Measure the volume.  You can ground them all at once, the dropping resistors will keep the current down.

Here's the ones that came on my car.  They looked like new aftermarket.  They sprayed, the engine ran pretty well, but they weren't balanced at all.

[Zed Head]

What is the highest value that you see on the gauge when you run the fuel pump without the engine running, or if you run the engine but disconnect the vacuum reference entirely?  That should be the highest pressure reading.  Best to do it with the engine running because alternator voltage will run the pump faster.  One of the proposals is that the Walbro is overpowering the FPR or the return lines.  You need to test at the highest possible pressure, which would be with no reference vacuum and maximum pump voltage.  The engine will run rich but it's a short test.

Consider also that you might have a bad gauge, with a 2-3 psi offset.

Edit - zeeboost raises the point, below, that the Walbro can't be overpowering the fuel lines or FPR orifice if pressure is dropping.  Still need the unreferenced number though.

Edited September 3, 2018 by Zed Head

[zeeboost]

Fuel pressure is fine, pressure drops with higher vacuum and vice versa. Fuel pressures are more important with the engine loaded (close to 0" ). Did you run a fuel pressure test with the engine loaded or just at idle? 

Curious, have you replaced the little injector seals on the intake manifold? You could try getting a small bottle of propane, with the engine running open it and direct the gas around any vacuum lines, afm to tb boot, or where the manifold bolts up to the cylinder head to make sure you're completely sealed off. If the idle raises then you found a leak. 

And though a volume test would be better, the injectors look like they're spraying well enough to not cause a misfire under light loads.  Careful when you're grounding out the injectors, the computer does it in milliseconds, not seconds, and you could fry one if you keep current flowing through it for too long. 

You can also get a cheap spark tester from harbor freight to put inline with the plug and wire to see if ignition cuts out on these cylinders when the engine starts to misfire.

Edited September 3, 2018 by zeeboost

[Dave WM]

I just don't get how that compression test can be so high. I wonder if there has been something done to the head?

think I saw 30psi at about 17inhg, so that is looking good. Don't understand why you were getting 34 with the car running at about the same vacuum.

I would not worry about psi with more greater vacuum than that, its not likely the engine will ever be operating with more that 18inhg, it only jumps up that high with quick throttle closure, and besides if the BCDD is working it should not do that either.

Edited September 3, 2018 by Dave WM

[Zed Head]

8 minutes ago, zeeboost said:

 pressure drops with higher vacuum and vice versa.

You're right , the fact that it drops says that it's not the lines being overpowered by the Walbro.  I missed that.  But it's been proposed that it's too high, generally.  That question is still open.

The FPR could still be defective, giving generally high pressure over the vacuum corrected span.  Beside that, the first, most basic fuel pressure test is with no vacuum reference.  That number hasn't been seen yet.

Edit - in short... I just want to see a 36-37 value somewhere.  That's the FPR's starting point.

Edited September 3, 2018 by Zed Head

[Zed Head]

Found it.  It actually looks like about 33-34 psi.  Low.

Edited September 3, 2018 by Zed Head

[Dave WM]

that's very odd, I thought it was reading that at idle in one of the earlier test when the engine was running.

[Zed Head]

Either your FPR diaphragm is solid as a rock, which happens when they get old, or the gauge you're using is broken.  It seems like the needle might have been stuck, it moved but not smoothly.  It kind of jumped.  Check that gauge.

[Zed Head]

Just a followup.  That's a good test.  The fuel pressure should drop smoothly as vacuum is applied, just as shown in your chart.  My pressure will sit at about 27-28 psi and jump up with RPM.  Very smooth and very fast.

You have a nice setup showing that something is wrong.  Just not clear if it's your gauge or your FPR.  Does the hose to the vacuum gauge have any fuel in it?  That would be a cracked diaphragm.