78 280z Starts then dies (Have searched forum)

[Zed Head]

The charge light should go off as soon as the engine starts.  Could be part of your problem.  

There are several "GM" "upgrades".  Not all are upgrades though.  An there are many "online" instructions.  And don't forget that people like us are the ones putting those "instructions" about "upgrades" online.  Air quotes galore...

[kutukutu1]

Lol, you all seem trust worthy.

 

I think I found the issue. The car had an aftermarket alarm and there is a mess under the steering column. There is an aftermarket installed relay that when unplugged the starter won't crank and I can replicate the issue or keep it running by wiggling the wires that go to the relay.

I'll get the fsm and fix the mess the previous owner left behind.

 

Thank you all for the help. I'll post back once I fix the wires and confirm the fix.

 

[kutukutu1]

OK, i put the ignition switch back to original and it still had the same issue. 

I tested point 1 and i got 12V constant even when the engine was stumbling and the fuel pressure was dropping.

Tested point 2 and you could see the voltage 12.4V when the engine ran fine, but you could see it cut out and loose voltage.

With this test, that tells me that the fuel pump control relay is faulty and sometimes it fails to keep the WB and WB latched together, which is why i loose voltage.

Correct?

[Zed Head]

Seems reasonable.  You could remove the plug and jump those pins to see if the rest of the system behaves normally.  You would be "unsafe" for a short while, but aware of the condition.

[kutukutu1]

Yep, I'll try that and jump it, see if it's all good.

I'll post back.

[kutukutu1]

Ok, so i looked at the relay and it looked ok, so i traced back to the blue alternator wire. Since my alternator dash light was always on, i swapped the 2 connection on the GM alternator and the light went off and now you can see the relay click and it all works great. I ask because the dash light now does not turn on, even when i put the key in "acc".

[Zed Head]

8 hours ago, kutukutu1 said:

Ok, so i looked at the relay and it looked ok, so i traced back to the blue alternator wire. Since my alternator dash light was always on, i swapped the 2 connection on the GM alternator and the light went off and now you can see the relay click and it all works great. I ask because the dash light now does not turn on, even when i put the key in "acc".

So you're saying that somebody had the L and the S wires crossed?  

You didn't really ask a question at the end.  The Charge and Brake dash lights should both be on when the key is at Run, but not Acc.  Then go off when the engine starts,

[kutukutu1]

I bought a connector for the GM alternator for the L and S. The connector only goes on one way so i wired it as it came. I took out the pins of the connector and swapped them and the car now stays on. I dont know if it runs because the connector came improperly pinned from the person i bought it from or because if the L wire is not connected or connected wrong, the relay will work and the car will turn on. I dont know if what i said makes sense.

[ramsesosirus]

I had a similar problem and had to have the gas tank boiled and cleaned.  Fixed my issue.  Common problem for these cars FYI.

[kutukutu1]

3 hours ago, ramsesosirus said:

I had a similar problem and had to have the gas tank boiled and cleaned.  Fixed my issue.  Common problem for these cars FYI.

Thanks. Tank is new, i swapped it, old one was shot.