Hard Hot-Starts

[CalLook67]

A couple of times over the last week or so, always when the engine's up to temp, has been sitting for more than 30 minutes but less than 90 minutes, and the ambient temperature is over 90 degrees farenheit, my 9-5 has had major trouble starting. It cranks over, and will try to fire, but will cough and sputter and won't get up to idle speed, then will die. If it's doing this, it doesn't matter if I leave the key on for a few seconds to try and let the fuel pump build pressure, it just won't start without some throttle modulation.

It's very similar to how my aircooled VW Bug used to hot-start before I put phenolic spacers between the carburetors and manifolds, when the fuel was just boiling out of the float bowls while the car was sitting after being run on a hot day. On a carbureted old car with a mechanical fuel pump, this sort of behavior is understandable, but it's pretty concerning out of a modern car with a turbo and fuel injection. Once it starts properly, it runs fine and hasn't shown any check engine lights, so I don't think it's anything major enough to attract the OBD-II's attention.

My best guesses so far are either a weak fuel pump, or vapor lock, but I want to hear some more thoughts on it. The fuel gauge has also been acting strange, whenever I fill the tank to completely full, it reads completely empty for at least half an hour of driving-time before coming back online, which is why I think the issue may be related to the fuel system.

[GeoffR]

Try the crankshaft position sensor.

[CalLook67]

Try as in check to see if it's going out, or try as in throw a new one in?

[GeoffR]

Try as in check to see if it's going out, or try as in throw a new one in?

Given that the effort required is the same either way I would replace it.

[CalLook67]

So it happened again this weekend, I had stopped at a shop for about 30 minutes after an hour of highway driving in heavy traffic. I was able to get it started with only a few stabs to the throttle before it settled into its normal idle, but after about 30 seconds of driving it finally threw a check-engine light. Conveniently I was headed to another auto parts store that would let me use their scanner to check it. I was actually pretty surprised to only see one code, a P1181 code for a sustained lean condition. I cleared the code with their scan tool, and in the day and a half since, have driven in hotter weather, lots of stop and go, and done errands like I was doing prior to the CEL code, and it hasn't come back.

I still haven't installed the new CPS I bought a few weeks ago due to having no time/energy, but since the code was related more to fueling, I'm sort of back to leaning towards something in the fuel system. Any thoughts?

[Digger]

Next time it acts up like this, unplug the MAS and turn the key, if it starts easy and runs smooth give your mas airflow sensor a super good cleaning and if it keeps happening replace it with a new one.

[CalLook67]

Since the CEL came back on while running errands last night, even though it started normally, I'll keep that in mind! Thanks for the tip!

[Methuselah]

I agree with Geoffr about the CPS, the other possibility is relatively low fuel in the tank. I used to have this issue in Australian summers with similar temperatures when I had a Volvo. If the tank was low on fuel - as in less than 1/4 full, the heat in the engine compartment was sufficient to heat up the remaining fuel and if you stopped, the car would not start until it cooled down. If you are having this issue with relatively low fuel, try filling the tank and see if it resolves - basically a very cheap fix if it works for you.
Good luck