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Discussion Starter #1
75 280z with fuel injection only runs for a second or two the first time trying to start it. Then won't even do that unless it's left alone for a while. Have power @ the fuel pump when starter is engaged but no power when ignition is in the on position. Is this normal? I'd think fuel pump would have to run with ignition in the on position after the car has started. ?? Have tested both fuel pump relays both test good. Any ideas on what to look into would be greatly appreciated!! Thank you
 

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Sounds like a fuel pump relay problem but would need more information to help.
Read this 280z fuel injection theory and troubleshooting. You find the problem of you read this and follow the steps. Page 23-25 talk about the relay. I know your mentioned testing that already but take a look at the guide.




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A good document to have, also make sure you put in a pressure gauge. Also recommended is to check spark when the car dies. Don't want to get too far down a rabbit hole and find its something else.
 

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Have tested both fuel pump relays both test good.
Check the fuel pump shut off switch contacts in the AFM. They are very small and the least little resistance when closed will cause issues. The contacts should close when the air flow "flapper" opens up a tiny bit. This tells the fuel pump that the engine is drawing air, therefore running.
afm1.jpg
 

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you need power to fuel pump when key is in on position. no pump, no run.
This statement is incorrect. The pump is only activated with the key in the start position or after the engine starts then the FP points in the afm connect like was already mentioned. If a fuel pump has power with the key in the on position that is a recipe for disaster. The only exception is the 80-83 280 zx with a fuel pump timer. You turn the key on and the pump runs but only for a few seconds if the engine hasn't been started. Putting a fuel pressure gauge on the engine is a big plus. It helps to have all the figures in an equation before you try to come to a conclusion. Checking to make sure that you still have spark is also a good one. Almost all the advice up above is good and could be related to your scenario. Also check your fusible link connections, especially the one going to the positive terminal on the battery. That's the one for the EFI.
Z man of Washington
 

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Discussion Starter #8
you need power to fuel pump when key is in on position. no pump, no run.
This statement is incorrect. The pump is only activated with the key in the start position or after the engine starts then the FP points in the afm connect like was already mentioned. If a fuel pump has power with the key in the on position that is a recipe for disaster. The only exception is the 80-83 280 zx with a fuel pump timer. You turn the key on and the pump runs but only for a few seconds if the engine hasn't been started. Putting a fuel pressure gauge on the engine is a big plus. It helps to have all the figures in an equation before you try to come to a conclusion. Checking to make sure that you still have spark is also a good one. Almost all the advice up above is good and could be related to your scenario. Also check your fusible link connections, especially the one going to the positive terminal on the battery. That's the one for the EFI.
Z man of Washington
Check the fuel pump shut off switch contacts in the AFM. They are very small and the least little resistance when closed will cause issues. The contacts should close when the air flow "flapper" opens up a tiny bit. This tells the fuel pump that the engine is drawing air, therefore running. View attachment 107074
My AFM is slightly different than the one you have pictured. Also I have a fuel pump pressure gauge ordered. Hopefully have it by the end of the week. Thanks
107080
 

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I wouldn’t mess around with the AFM until you have isolated the problem. The best approach to mechanical problems is a methodical approach that you can validate before pulling things apart and guessing. It will save you $$ on the long run. I used to run a fighter squadron and my Marines would always do this crap. They’d guess and then cannibalize parts to try and fix problems or order parts they hadn’t confirmed wet bad. Some of the parts would exceed $200,000 and I’d lose my mind when I found out.


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Try moving the Air Flow Meter (AFM) flap with the key in the run position you should hear the fuel pump run. When the AFM flap moves the contracts for the fuel pump will close and you should hear the fuel pump. This is the same idea Crayzlair brought up earlier but doesn’t require you to chance bending the contracts. Your hand should fit in the mouth of the AFM, I’ve put a screw driver in there to hold it open while I was checking the circuit at the ECU.

Download the 280z Fuel Injection Manual.
 

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Runs a couple of seconds? Did you check plugs to verify if flooded?
My cold start injection went faulty this week.... unplugged it.
 

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Discussion Starter #14
Sorry for the slow update. Doing daycare etc don't leave alot of play time for me. Lol. I put a fuel pressure gage in the line just after the fuel filter and before going into the fuel rail. It reads 28-30 psi. I have spark. So from there I gave it a small shot of starting fluid in the air intake and she fired right up for a second or two. Repeated this another time same result. So it appears either something with the fuel regulator or the injectors aren't working/ getting power. ? Is there anyway to test the regulator? Injectors? Thank you Ed
 

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Discussion Starter #16
Ok I had time to look at the Z again. As I said before I checked the pressure after the filter and have 28-30 psi. so I move the gauge to the inlet side of the fuel filter and have the same 28-30 psi. I should have 36+psi there correct? To me this is looking like the fuel pump. ?? Any other tests for checking the fuel pump? Thanks
 

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Have you ever seen it run properly with this pump or has it always been this way? Electric fuel pumps either work at the full pressure they're designed to output or they don't work at all.

It's possible that the PO put the wrong pump in which is why it isn't running properly. Maybe go look at the pump and see if you can find the pump's model number and see what psi it's rated at.
 

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Discussion Starter #18
I have owned the car for 5-6yr. It has always ran great. This issue started when I pulled it out of storage from last winter. The car is stock with 77,000 miles on it. "Electric fuel pumps either work at the full pressure they're designed to output or they don't work at all". That's kinda what I was thinking also. Thanks
 

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I'd tend to leave the fuel pump along for now. 30 PSI is enough that you should be getting fuel to the vehicle. I know it says a few more PSI on the top end, but what you are seeing seems sufficient to me. If nothing else, it ought to be plenty to keep the car running at low to moderate RPM; if it were a problem i'd expect it to be at full throttle when the demand for fuel is greater.
 
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