280Z Difficulty starting

[Captain Obvious]

Mario, Yes, the wire colors came from the wiring diagram in the FSM. And remember that it's just a theory. I'd be happy to be proven wrong. I'd also be interested to hear if any other 78 owners have seen similar behavior. I guess unless they had a pressure gauge installed, they may never know.

 

After watching your last video, I don't see anything wrong with either the fuel pump or the fuel pressure regulator. They both appear to be working fine.

 

Yes. there is a check valve back at the fuel pump, but that's not what is causing your starting issues. It might be what is causing your eventual loss of fuel line pressure, but you showed that your starting stumble occurs even after you have primed the fuel lines. Your start stumble is not caused by low fuel pressure. So while it might be a good idea to chase your fuel line leak down at some point in the future, I don't think you need to do that now. It's not that big of an issue.

 

 

 

 

 

[Marios280Z]

Yes. there is a check valve back at the fuel pump, but that's not what is causing your starting issues. It might be what is causing your eventual loss of fuel line pressure, but you showed that your starting stumble occurs even after you have primed the fuel lines. Your start stumble is not caused by low fuel pressure. So while it might be a good idea to chase your fuel line leak down at some point in the future, I don't think you need to do that now. It's not that big of an issue.

 

I agree with what you said, and yes, the fuel pressure drop issue is secondary to my starting issue, at least in my books.

[Zed Head]

I'd measure voltage drop at the coil during starting.  Both the ECU and the ignition system don't like low voltage.  The ECU won't work right, and the ignition system will put out a weak spark.

 

I had a problem with an engine that would only start with starting fluid.  The spark was too weak to start the engine, with the voltage drop of the starter motor, but was fine once it started and the ignition system was at full voltage.

 

You've gone full-circle and are repeating things, with the removal of the FPR hose in the video.  Electrical is next.  It's not as hard as it seems, once you get in and start measuring you'll wonder why you waited so long.

[Zed Head]

I also recently had a battery go bad and do the same.  It would turn the engine over for a while, not starting, then slowly lose energy.  I put a meter on the battery and found that it was dropping to about 9 (if I remember right) during cranking, then 6 before it was done.  I think a reasonable reading during cranking is ~11 or better.

 

If you get a low voltage then there are a many things to look at for that problem.

[Zed Head]

Actually, a look at your dash voltmeter while starting might show something.  They're not super-accurate but a big needle move might be telling.

 

Might also explain why your starter solenoid seems to drop the contact when starting.

Edited August 9, 2015 by Zed Head

[Captain Obvious]

I don't know the current temps in IA, but here's something to try... Disconnect the electrical connector from your cold start valve. You might be flooding your engine while cranking which might be making it hard to start. And since it's temperature dependent, the times it starts OK might be a degree or two warmer. Warm enough to disable the cold start valve?

 

If your start stumble goes away with the CSV disconnected, that might be a clue. Or, on the other hand, if it now does it ALL the time, that might be a clue as well.

 

I know it's the shotgun approach, but it's free, easy and reversible.

[Marios280Z]

Might also explain why your starter solenoid seems to drop the contact when starting.

 

Zed Head, could you elaborate on this and explain a bit? How do you know it's doing it? What part of the rough starting video makes you conclude that? Sorry for ignorance, but I'm just not familiar with this.

 

I performed few voltage tests today as well as the fuel pressure discharge test.

 

2) Fuel pressure discharge test per AFM shows around 37 psi when ignition in START, which is up to spec.

 

The voltage of the battery when sitting is around 13V

The voltage of the battery when starting the engine is around 12V

The voltage of the batter when engine is runnig is aronund14V

 

The voltage at the ignition coil as measured at "-" and "+" teminal is 0V when igintion is in ON possitioin.

The voltage at the ignition coil as measured at "-" and "+" teminal is around 4.5V when igintion is in start and cranking.

The voltage at the ignition coil as measured at "-" and "+" teminal flactuates between 12-15V when engine is runing at idle.

 

The 4.5 volts seems low to me but I have performed several ignition in START tests, and all of them showed that , however only the first time around it gave me a bit hard time to start. After that it was easy starting. For curiosity, did anybody else tested ignition coil voltage this way and got different result?

[Marios280Z]

 

I don't know the current temps in IA, but here's something to try... Disconnect the electrical connector from your cold start valve. You might be flooding your engine while cranking which might be making it hard to start. And since it's temperature dependent, the times it starts OK might be a degree or two warmer. Warm enough to disable the cold start valve?

 

If your start stumble goes away with the CSV disconnected, that might be a clue. Or, on the other hand, if it now does it ALL the time, that might be a clue as well.

 

I know it's the shotgun approach, but it's free, easy and reversible.

 

Today I replaced the orignal electrical connector on CSV with the new design that allows for easy on/off with the new wire clip design. This will alow me to connect and dissconnect it on the fly.

[EuroDat]

Im not sure what to think of the 4.5 volts reading at the coil. The (-) side is an open and closed circuit which will be "pulsing" while the engjne is running. Some volt meters will average this out and say if it was 9 volts half the time, it would read 4.5volts. Low cranking speeds/low cranking voltage could influence this as well. Try measuring the voltage to the coil (+) and the ground or (-) battery terminal or ground.

What is your battery voltage while its cranking?

Testing for resistance: A simple way to check where voltage drop (resistance) occurs in a circuit is with a volt (multi) meter. An analoge meter works best, not as jumpy as a digital. Start with things like battery posts and starter solenoid terminals.

If you hold one probe on the centre of the battery post and the other on the outer terminal you will read 0 volts. If someone cranks the engine it should stay at 0 volts. A voltage reading means resistance.

The starter solenoid is a little different. It will read battery voltage across the two big (M8) terminals and while cranking it will go to 0 volts. High resistance here could be a reason for the rough starting issue Zed Head mentioned.

I have found bad fusable links and bad grounds this way.

[Hodgimus-maximus]

Did you measure the voltage at the starter when cranking?

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[Zed Head]

 The FSM says that you should see battery voltage at the coil with the key On.  You're seeing zero, although it's not clear how you're measuring.  There's a diagram in the FSM.  You should measure from coil negative to ground.  Actually, coil positive to ground would work also.

 

The  around 12 volts while cranking is a good number though.  

 

You could evaluate spark strength, and fuel injection.  Put some of FastWoman's Christmas tree lights on the injectors for injection evaluation.  Also described in the FSM.  Make sure they're flashing.  And check that the spark produced is thick and blue, not thin and weak.

 

There are many other basic meter measurements you can take, coil resistance, for example.  These things are all described in the Engine Fuel chapter, and Engine Electrical chapter, in detail.  Just saying, if you want to get ahead of the thread.  You might have a weak coil, or a weak pickup coil, or just a loose connection, or a dying ignition module.  You'll know what's right, what's wrong, and what's marginal.

Edited August 10, 2015 by Zed Head

[Marios280Z]

Im not sure what to think of the 4.5 volts reading at the coil. The (-) side is an open and closed circuit which will be "pulsing" while the engjne is running. Some volt meters will average this out and say if it was 9 volts half the time, it would read 4.5volts. Low cranking speeds/low cranking voltage could influence this as well. Try measuring the voltage to the coil (+) and the ground or (-) battery terminal or ground.

What is your battery voltage while its cranking?

 The 4.5V I think is a fault measurement. I was measuring between "-" and "+" on the coil itself, which showed me 0V when ignition key is ON. So as you said I measured between "-" terminal on the coil and a common ground. When I measured that way this morning it actually showed 12.9V when ignition was in ON position, which is per FSM spec. Measuring in the same way when my wife dressed in pajamas was cranking the engine was giving me some erratic measurements, voltmeter was bouncing all over the palace. 

 

 

Testing for resistance: A simple way to check where voltage drop (resistance) occurs in a circuit is with a volt (multi) meter. An analoge meter works best, not as jumpy as a digital. Start with things like battery posts and starter solenoid terminals.

If you hold one probe on the centre of the battery post and the other on the outer terminal you will read 0 volts. If someone cranks the engine it should stay at 0 volts. A voltage reading means resistance.

I'm a bit confused of what you really mean here. You want me to put one volt meter lead on the center post of the battery, say "-" terminal and the other lead of the volt meter on the outside (the cable clamp itself?) on the same "-" terminal of the battery?

 

 

The starter solenoid is a little different. It will read battery voltage across the two big (M8) terminals and while cranking it will go to 0 volts. High resistance here could be a reason for the rough starting issue Zed Head mentioned.

I have found bad fusable links and bad grounds this way.

Did you measure the voltage at the starter when cranking?

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When I measure the voltage across the starter at the two big terminals, it was reading 13V, as I would expect since they get direct connection from the battery. However, when measured in the same way but during my wife cranking the engine (still in pajamas), the voltage was reading around 6-7V.

 

 

 The FSM says that you should see battery voltage at the coil with the key On.  You're seeing zero, although it's not clear how you're measuring.  There's a diagram in the FSM.  You should measure from coil negative to ground.  Actually, coil positive to ground would work also.

 

The  around 12 volts while cranking is a good number though.   

Hed Zed when I measured this morning again per your and EuroDat recommendation it was actually showing 13V to the coil when ignition was in ON position. I'm assuming you are referring to the battery voltage of 12V when cranking, correct?

 

 You could evaluate spark strength, and fuel injection.  Put some of FastWoman's Christmas tree lights on the injectors for injection evaluation.  Also described in the FSM.  Make sure they're flashing.  And check that the spark produced is thick and blue, not thin and weak.

 

There are many other basic meter measurements you can take, coil resistance, for example.  These things are all described in the Engine Fuel chapter, and Engine Electrical chapter, in detail.  Just saying, if you want to get ahead of the thread.  You might have a weak coil, or a weak pickup coil, or just a loose connection, or a dying ignition module.  You'll know what's right, what's wrong, and what's marginal.

I can check for spark at each cylinder. I'm assuming that checking it while engine is running would be indicative of the spark condition? I believe I saw this Christmas light test in FSM, but as I recall it I would need to disconnect the electrical plug and connect it to the light. As I mentioned earlier, when I disconnected one of the injectors, i broke the connector in the process, so if I'm to do it on all of them, I may as well prepare for few hours of wiring work and installing new injector connectors...

I have replaced the distributor cap and rotor as well as ignition coil. Beyond that I did not touch ignition system.  I will try to read up some more in FSM and see what other tests I can do without taking distributor apart and possibly messing up the timing (so I was told...)

Edited August 10, 2015 by Marios280Z