78 280z Severe Driving Problems

[kinser86]

2 hours ago, Zed Head said:

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

 

Thinking of a way to do this using an n channel mosfet and arduino.

2 hours ago, Zed Head said:

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.

When the pump is running, I have seen above 40PSI without the engine running. I saw it today when I would prime the rail before injector testing. Once the fuel pump shut off, it would drop below 40. I don't remember if its 38 or 36, I would have to capture that.

1 hour ago, zeeboost said:

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.

All injector seals were replaced within the past few weeks when I put the injectors back in the car. I have tested vacuum leaks with carb cleaner but was unable to find any leaks. I have not tried using propane.

I think I will create a test setup using a n-channel mosfet and an arduino to run the injectors at a reduced duty cycle rather than getting the wiring in the car involved.

I don't have a spark tester but that is a good idea.

1 hour ago, Zed Head said:

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.

I can do those test but I think first I will pull the rail completely and do some bench flow test.

1 hour ago, Zed Head said:

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.

When spraying the injectors, the fuel pressure gauge would sweep to 0 when spraying. That doesn't mean it can't get stuck though.

1 hour ago, Zed Head said:

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.

Fuel Pressure gauge of vacuum gauge? I don't smell or see fuel in the line connected to the FPR but I wouldn't rule out a stiff/rigid diaphragm. The vacuum advance diaphragm was cracked and damaged a while back which warranted a replacement distributor.

There has been a lot of good comments. As everyone mentioned, I need to measure volumes. I will develop a simple test circuit using an arduino and n-channel mosfet and run the injectors at a duty cycle that is yet to be determined. The test rig will require some work as to how I will have everything setup. Once I have those numbers, I will see where we go from there. I am hoping #2 and #3 are low.

[Zed Head]

40 minutes ago, kinser86 said:

Thinking of a way to do this using an n channel mosfet and arduino.

When the pump is running, I have seen above 40PSI without the engine running. I saw it today when I would prime the rail before injector testing. Once the fuel pump shut off, it would drop below 40. I don't remember if its 38 or 36, I would have to capture that.

Fuel Pressure gauge of vacuum gauge? I don't smell or see fuel in the line connected to the FPR but I wouldn't rule out a stiff/rigid diaphragm. The vacuum advance diaphragm was cracked and damaged a while back which warranted a replacement distributor.

In the picture I grabbed from your video, copied again below, if you've ever seen 40 psi then you should have seen it at zero vacuum, as shown in the picture.  Unless the extra 2 volts from alternator power pushed the Walbro up in to the excess volume zone.  Who knows.  Fire up the engine, remove the vacuum reference hose from the FPR, and see what the fuel pressure gauge says.  Give the engine some RPM to be sure you're at maximum alternator output.  The pump is just pushing against the FPR spring to get the seat open.  Maybe you've got some particles holding the FPR seat open and that's why pressure is low and doesn't respond to vacuum.  Ponder that FPR drawing that you posted earlier and you'll get some ideas.  The vacuum just relieves atmospheric pressure from the spring cavity.  You could probably blow on the reference port and get pressure to rise.  These EFI systems are just a collection of really simple concepts.

So, unless your helper was pulling vacuum in the picture below and it didn't show on the vacuum gauge I'd say your fuel pressure gauge is sticky.

Pulsing the injectors adds extra information, but if your inlet screens are clogged it won't show that, directly.  I filled those bottles at wide open injectors with my own tester.  Injectors wired in series.  The injector solenoids are cooled by the fuel passing over them and the current is low.  They'll be fine.

Pressure should be at maximum with no vacuum...

[Zed Head]

Just realized that you might have run your vacuum port FPR test using residual pressure.  Fuel pressure tests are generally done with the pump on. 

There are many ways to run the fuel pump without the engine running.  A simple one for 1978 is to remove the oil pressure sender wire.  Then turn the key to On.  The pump should run continuously.  It's a flaw in the system.  The pump will be fine also, it's cooled by fuel too.  It runs full time when the engine is running.

You can also remove the starter solenoid wire and turn the key to Start.  Or prop open the AFM vane and turn the key to On.

Edited September 4, 2018 by Zed Head
Run to On

[kinser86]

21 minutes ago, Zed Head said:

 Fire up the engine, remove the vacuum reference hose from the FPR, and see what the fuel pressure gauge says.  Give the engine some RPM to be sure you're at maximum alternator output.

So, unless your helper was pulling vacuum in the picture below and it didn't show on the vacuum gauge I'd say your fuel pressure gauge is sticky.

Pulsing the injectors adds extra information, but if your inlet screens are clogged it won't show that, directly.  I filled those bottles at wide open injectors with my own tester.  Injectors wired in series.  The injector solenoids are cooled by the fuel passing over them and the current is low.  They'll be fine.

Pressure should be at maximum with no vacuum...

Did you run the supply voltage through the dropping resistor? I was thinking of 80% duty with the mosfet. This will help keep the injectors cool and I could run them for a fixed time. I could be over thinking the test stand but I have always been advised to not run full 12VDC through the injector.

12 minutes ago, Zed Head said:

Just realized that you might have run your vacuum port FPR test using residual pressure.  Fuel pressure tests are generally done with the pump on. 

There are many ways to run the fuel pump without the engine running.  A simple one for 1978 is to remove the oil pressure sender wire.  Then turn the key to Run.  The pump should run continuously.  It's a flaw in the system.  The pump will be fine also, it's cooled by fuel too.  It runs full time when the engine is running.

You can also remove the starter solenoid wire and tunr the key to Start.  Or prop open the AFM vane and turn the key to Run.

I think this will be a better test. I was unsure if the test I performed would work as intended but I can run the pump like you said and manually pull vacuum again and see if it reacts the same. I will pull the oil pressure wire and run the pump that way.

[Zed Head]

I forgot that you had the rail out when I suggested just starting the engine.

In my test, I wired the injectors in series so total circuit resistance was 6 x 2.5 ohms...15 ohms.  I was more concerned that they might not open.  But the key is that it's not voltage that is the concern, it's current.  Overheating.  If you connect 12 volts to a dry injector I think that it might heat up enough to do some damage, over time.  Maybe.  But in your case with the dropping resistors in place, and fuel passing through, there shouldn't be any problem.  The injectors see 12 volts as soon as you turn on the key.  They're opened by grounding that voltage at the ECU.

[zeeboost]

You could just try swapping an injector around to see if your symptom follows it before building an elaborate test setup. If cylinder #3 has no change when you disconnect the injector for it, you could swap the injector to #1 to see if the problem follows. You already have the rail out.

[Zed Head]

He already did that and more.  It's described above.

[zeeboost]

I saw where he swapped the injector connectors and later talked about swapping the injectors as a test procedure, but didn't see where he actually went through with swapping them. 

[kinser86]

6 hours ago, zeeboost said:

I saw where he swapped the injector connectors and later talked about swapping the injectors as a test procedure, but didn't see where he actually went through with swapping them. 

I performed a test swapping connectors during idle but I have not tried swapping injectors and starting the car again to see if it followed the injector or stayed at the cylinder. I am going to measure the volume of the injectors as Zed Head recommended and go from there.

Edited September 4, 2018 by kinser86

[kinser86]

On 9/3/2018 at 9:12 PM, Zed Head said:

In my test, I wired the injectors in series so total circuit resistance was 6 x 2.5 ohms...15 ohms. 

For clarification purposes, when you say you wired the injectors in series, you literally meant in series? If yes, then this yields 833mA at each injector.

Wired in parallel yields 5A at each injector. ? 

I don't want to let the smoke out, then they won't work anymore..... ?

[Zed Head]

Yes, low amps = low heat.

If yours are still on the factory harness don't forget about the dropping resistors.  They're 6 ohm, so 8.4 ohms per injector, in use on the car.  1.4 A.  Or, considering alternator voltage...14/8.4 = 1.7 A.

[kinser86]

41 minutes ago, Zed Head said:

Yes, low amps = low heat.

If yours are still on the factory harness don't forget about the dropping resistors.  They're 6 ohm, so 8.4 ohms per injector, in use on the car.  1.4 A.  Or, considering alternator voltage...14/8.4 = 1.7 A.

Thanks for the clarification?. I have an extra set of injector connectors I will put together in series for the volumetric test out of the vehicle. The parallel circuit was an example outside of the car (excluding the dropping resistor) but you are correct, about 1.7A in the vehicle with the dropping resistor.