New owner of '77 280z from Upstate SC

[Zed Head]

You're way ahead of many, you have a running engine.  Here's another thing that can cause rich running - a blown fuel pressure regulator (FPR).  Pull the vacuum hose from the bottom of the FPR and check for liquid fuel.

If you make a list of all of the suggestions being given you'll knock of the high probability stuff and might find a winner.  Many ways to get there.  Some people would just remove the engine and rebuild it because "it probably needs it".

[the_tool_man]

6 minutes ago, Zed Head said:

If you make a list of all of the suggestions being given you'll knock of the high probability stuff and might find a winner.  Many ways to get there.  Some people would just remove the engine and rebuild it because "it probably needs it".

Yep.  My 25 year Sunbeam project started out as "this car almost runs", and quickly became "the engine needs rebuilding", and then much more slowly became "I should just part this car out".  I will NOT do that again.  I probably won't live that long, anyway, lol.

[EuroDat]

What you are experiencing is normal. We have all sort of been through it.

My 280 was parked under a house in the owners workshop since 1993 and I own it since 2011. I have had blocked injectors where the PO adjustd the AFM to compensate, a TIU that played up awfully when the engine warmed up and after market injector connectors where the wires were badly soldered and intermittently causing and open circuit.

It sounds bad, but that was over a two year period. If you keep working through the system, you will find more problems, fix the problems and eventually it will become a reliable car.

I wrote a quick guide on Redwings thread on checking the fuel system for leaks. Ill can post my full step by step test with photo's tomorrow if you want it.

My post is on the first page about half way down.

 

[the_tool_man]

18 hours ago, EuroDat said:

...I wrote a quick guide on Redwings thread on checking the fuel system for leaks. Ill can post my full step by step test with photo's tomorrow if you want it.

My post is on the first page about half way down...

Got it.  Thanks.  I tried to find an inline fuel pressure gauge yesterday to facilitate testing.  But none of the local parts stores I tried had one.  I'm taking tomorrow afternoon off, and will go by the local pull-a-part to find a late model fuel rail with a built-in Schrader valve so I can use the gauge I have.  I also picked up a new fuel filter, even though the PO said he had just replaced it before I bought it.  Stay tuned.

[siteunseen]

You can get a gauge in the pool supply section at Lowes.  They sell them for the pool filters.

http://www.lowes.com/pd_199191-1003-PG550___?Ntt=pool+gauge&UserSearch=pool+gauge&productId=3151541

[Zed Head]

Here's a picture of the Schrader valve on a 1997 Honda Passport.  The same year Isuzu rodeo has one also.  Has a black cap, right in the middle of the red square.  Easy to remove.  You'll find many other valves on many fuel rails but they'll be difficult to apply to the Z.

[the_tool_man]

Update:

The visit to the pull-a-part yard was a bust.  So I bought some brass fittings and a pressure gauge and spliced it into the fuel line after the filter.  I put in a new filter, too, even though the one already installed looked brand new.

It was fun to test without a helper.  I had to lean in through the passenger side window to start it, and then try to watch the pressure gauge while manipulating the throttle linkage.  But I determined that when cranking, the fuel pressure would build to about 20psi.  Upon starting, it quickly (5-10 seconds) dropped to zero on the gauge.  I could keep it running by revving it.  But it sputtered, as you would expect.  So the fuel pump is running (eliminating electrical fault, contact in AFM, etc.), but it is either worn, or there is a blockage somewhere.

I'm not sure how this explains the symptoms of running rich.  But that seems to have been a red herring.

My next step is to run new fuel lines from the pump inlet and return line to a gas can in an attempt to isolate the issue to either a dirty tank/pickup or a weak fuel pump.  I was pleasantly surprised to see a drain plug in the fuel tank, BTW.  More to come.

 

Edited February 20, 2016 by the_tool_man

[EuroDat]

You don't need to run lines from the fuel pump to test its performace. Try doing a free flow test after the filter first. If the pump is in any condition, you should get 2 to 3 litres per minute.

After testing the flow pinch the hose shut with vice grips and two pieces of flat metal to prevent the vice grips from damging the hose. I have even used two euro coins to do the job. It should hit 55 to 60 psi before the internal valve in the pump starts regulating the pressure.

Remove the small spade terminal from the starter solenoid so you can use the key in start position the activate the pump.

I have some photo's of a test I did on mine. I used a small valve to block mine, but vice grips will do fine if the hose is in good condition and flexible.

Once you determine you have flow and pressure, you can move on. Keep ticking things off the list and you will get there.

[Zed Head]

13 hours ago, the_tool_man said:

But I determined that when cranking, the fuel pressure would build to about 20psi.  Upon starting, it quickly (5-10 seconds) dropped to zero on the gauge.  I could keep it running by revving it.  But it sputtered, as you would expect.  So the fuel pump is running (eliminating electrical fault, contact in AFM, etc.), but it is either worn, or there is a blockage somewhere.

Overall, it looks like you have the typical collection of problems and adjustments to the wrong parts to fix them.  It still looks like the fuel pump contact in the AFM is closing because of low air flow, or the AFM is still out of adjustment, causing the vane to stay closed.  You need to set the AFM back to where it was so that the vane can open and keep the pump running.  Or stick that wire back in there.

You can check the function of the fuel system by disconnecting the small wire from the starter solenoid and turning the key to Start.  The AFM contact is bypassed at Start and the pump will  get power.  I think what's happening now is the pump is getting power, then the engine starts and you're letting go of the key.  The AFM vane is closed so the power goes away because the Start bypass is gone.  When you rev it, the vane opens for a second, the pump gets a second of power, etc. 

You're about at the point where hot-wiring the pump just to be sure the power stays on, would be the thing to do.  I think you might be working on the wrong thing.  Get the pump powered permanently, either via hot-wire, or hard-wire in the AFM throat, and start the engine,  See what pressure does then.

 

Forgot to say - the old FPR's tend to leak down quickly. So if you try the solenoid wire disconnection test, you'll need to be able to see the gauge while you hold the key to Start.  It won't hurt anything, the pump stays on for hours while you're driving.

Edited February 20, 2016 by Zed Head

[the_tool_man]

Zed, I've confirmed that the contact in the AFM is working properly.  I can see, with its cover off, that the flap stays open while the engine is running.  I can hold the engine at 3000 rpm, and it runs.  But it misfires, I now believe, due to fuel starvation.

And for the record, I haven't changed the adjustment of the AFM spring from how I received it.  All I've done so far is check and clean electrical connections.

You and EuroDat have both suggested disconnecting the start solenoid to further test the fuel pump.  I will do that next.  I can at least determine if its building enough pressure.

[Zed Head]

My point was that without enough air flowing through the AFM to open the vane the contact will stay open.  No vane movement, no fuel pump power.  The contact can be perfect, just not closing to actuate the fuel pump relay.  Maybe you meant that the vane can be seen moving at idle?

If it will stay running at higher RPM, even though it's missing, you could open the idle speed screw to let it run by itself.while you watch the pressure gauge and fiddle with hoses and wires.  Or put a brick on the throttle pedal.  It shouldn't take 3000 RPM though to open the AFM vane.

And the reason I suggest these things is because you can't have zero fuel pressure AND 3000 RPM.  So there's a disconnect there.  There must be fuel pressure, either too high or too low,  One way that you can have low pressure but rich air/fuel ratio is if the FPR diaphragm has a hole in it.  The vacuum hose to the FPR will pull fuel straight through the FPR in to the manifold.  It's not uncommon.

Just suggestions.  

[Driver_X]

Forgive me if you've already done this, but have cheked & cleaned the injector connections?   Mine were in such bad shape I just replaced them.