Rough start troubleshoot - '78 280Z

[Alda]

Hi Everyone,

 

I read many posts in the archives and lots of Google searches but I would love your advice on my specific case.

I have a '78 unrestored 280Z that used to run like a charm and I'm not getting rough startup and probably heat problems?

 

I am pretty noobish with mechanic (learning from 0) so bare with me.

 

Symptoms:

A vast majority of the time, the car will 'cough' a lot at startup and runs rough for about 5 to 10 seconds. I'm usually flooring it for a split second during ignition to avoid stalling and then gently rev til the engine runs smoother.

I feel like the problem occurs more when the outside temperature is very hot (I live in SoCal), however my car is garaged and the problem also occurs in the morning.

The car seems to run better warm and if I stop it after driving it for a couple mile and restart it in the next 10 minutes it will fire right away (like even faster than modern cars, I just push the starter and boom! When that happens I feel almost suspicious of how fast it starts).

Finally, I had a problem 2 times. The car stalled after a few miles (usually hot day and driving a bit sporty). It stalls and doesn't turn back on. I had to push it to the side of the road and let it sit for 10-20 minutes before it'd start again.

 

I changed sparks, fuel filter, ignition coil.

 

Any advices appreciated. Stuff that I could check myself would be even better (keep in mind I'm a noob)

 

Thanks a lot,

M.

 

[NewZed]

Sounds like a weak fuel pump.  A fuel pressure measurement would tell.  Leave the gauge attached and look at it when the problem happens.

[Alda]

The fuel pump is a good lead and I will check it.

However I did a few test in the past few days and the problem seems to be happening more after the car has been sitting in the sun / exposed to heat.

The fact that it died on me 2 times out of the blue and didn't want to start for a little while sounds like it would be something else than the fuel pump (?)

 

 

I initially though of heat soak problem but the fact that it usually starts perfect when the engine is hot seems to go against that theory.

 

[seattlejester]

Hmm, I would be more likely to believe vapor lock if it was a carb'd car, but with fuel injection and the higher return rate back to the tank that doesn't seem as likely. 

 

You can test the fuel pump theory by carrying around a can of starting fluid. Next time it dies, take off the filter open the AFM and spray some starting fluid in it and see if she fires right up. If so, then definitely a fuel starvation problem. Rust in the fuel line or gummed up lines would be the culprit.

 

The fact it dies out of the blue means you ran out of something. Either voltage for powering the fuel pump, fuel pressure, voltage for energizing the coil, or voltage for the ecu. Just have to figure out which one of those is more likely. Get a gauge on the fuel line and I bet when it dies the fuel pressure reads 0. If it doesn't then you have to move onto the electronic bits. 

 

You said you replaced the spark, how about the rotor and cap? What condition were the spark plugs in? If you were consistently running out of fuel it would be on the whiter side.