1978 280z will not start without ether

[crash131313]

Hello everyone.   my name is crash and i am having an issue with my z.    i recently did a ton of work to my car and now it will not start without a shot of ether down the hole.   it starts, runs and idles perfectly with a shot of ether but it just cranks and cranks without.    it is a factory fuel injected 1978 280z 2+2 with lots of aftermarket external parts. nothing internal has been changed.   it has great fuel pressure and amazing spark but will not start without a shot of juice.    i have thoroughly cleaned all the injectors and the cold start valve ensuring great flow.   i replace all the fuel lines and vacuum hoses.   i have troubleshot everything i can think of and im sure its something stupid that i missed.   please help!!!!!

[Dave WM]

does it have fuel pressure during the cranking cycle?

[KSRosser]

The ECM needs to know the engine is turning to fire the injectors. You may have a loose connection at the distributor.


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[siteunseen]

Thermotine connection and the others at the themostat housing could be loose or need cleaned brass. How old is the metal fuel filter? Cold start valve has a good connection? Oil pressure sending unit is tightly connected?  It's a safety thing that cuts fuel when you have no oil pressure. Can you make the fuel pump run for sure? Sometimes the safety switches and relays keep it from running. You may could straight wire the pump bypassing all those safety switches? 

[Captain Obvious]

Crash,

Does it do the same thing even when the engine is warm and has only been off for a few seconds? In other words, give it a shot of ether and get it running. Take it for a ten minute drive. Shut if off for ten seconds, and what happens? Does it start then, or does it need another shot of ether?

If it needs another shot, it's not the thermotime or cold start system and more along the lines of the oil pressure stuff that siteunseen mentioned. Some kind of interlock problem or ignition switch issue.

 

 

Edited September 29, 2017 by Captain Obvious

[crash131313]

it has good fuel pressure during crank and run cycle dave. i dont think it has to do with the distributor because it runs great once it fires ksrosser it has a brand new fuel filter and all new gas lines siteunseen. it does the same thing when warm and cold captain obvious.   im going to try checking the oil pressure sending unit because it was doing something weird when i first got it back together and tried cranking it for the first time.   with the ignition on i could hear the fuel pump running but when i connected the oil sending unit in it would shut off.   but it seemed to fix itself.  maybe something is ****ocked there.   i really do not want to swallow my pride and take it to a shop for something that is probably a loose connection.  like i said  the car runs great but only with a small shot of ether.    all your advise is much appreciated guys and i will take all i can get.    thanks 

[Captain Obvious]

Well if it does the same thing when you just shut if off for a couple seconds, then there's something that is inhibiting either spark or fuel pump operation when the key is in the START position. Everything works fine when the key is in the ON position, but it doesn't work right in START. So if you can get it started, it's fine in ON, but getting it started is the issue.

With that in mind, I bet you could roll start it just fine. Without ether.

So I don't know the 78's like I know the 77's but it's either the fuel pump isn't running in START, or you aren't getting a spark in START.

Just as a quick way to narrow the field, when you are cranking and cranking it and it won't start... Do you get a good spark while you are cranking it?

 

[Dave WM]

don't forget to check out the start switch itself. you want to make sure the ON stays ON when the key is advanced to the start position, I had an intermittent ON that caused a lot of grief. You need to test it to be sure.

[KSRosser]

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[Zed Head]

10 hours ago, crash131313 said:

  with the ignition on i could hear the fuel pump running but when i connected the oil sending unit in it would shut off.   

This is normal.  It's an oddity of the fuel pump control system.  Actually a defect, safety-wise.

You said that you did a ton of work.  I'm going to guess that somehow you disconnected the blue wire to Pin #1, the one from the coil, to the ECU.  It's what the ECU counts to determine when to open the injectors.  If you added an MSD ignition or did some other igntion or tachometer mod, the EFI system might not work properly.  The tachometer is a branch off of that same circuit.

Make a list of the ton and maybe somebody will see something else.

 

[Captain Obvious]

It's not the blue wire off pin1. Once it starts, it runs fine. The ECU is getting the spark signal once the engine is running. It's something else.

One of the fuel pump interlock relays or something inhibiting the ignition only while cranking.

[Zed Head]

Alrighty.  I didn't really get a firm impression of that.

If that's the case, then a situation I had a while ago might apply.  I damaged my ignition module when I forgot to put two spark plug wires on and started the engine.  I shut it off right away but after that the spark was too weak to fire the gasoline.  It would only start with fluid.  And that was a warm engine.  I know he said amazing spark, but who knows.

Not sure how spark was measured either.  Maybe the Start ignition wire is disconnected, and it's catching on the one spark when the key is let go, using ether.

Maybe the fuel pump control is screwed up.  Test that by removing the oil pressure sensor wire.  The pump should run when the key is On.  Then you'll know you have fuel pressure.

Also, pull a spark plug after it doesn't start.  See if it's wet or dry.  Maybe you're flooding and the ether is enough to catch a wet spark.

Finally - when you say "won't start" do you mean it tries to go but won't catch and run or you get nothing at all?  Couldn't tell from cranks and cranks.

Finally #2 - describe the work you did.  Maybe, somehow, you've lowered the compression ratio so much that it won't fire a gas-air mixture at low RPM.  Maybe you have a vacuum leak.  Maybe your valves aren't closing completely (you run the risk of burning them if that's the case).  Measure cylinder pressure if you can.  It's a good clue.

Spitballing...