Engine hesitates at startup. Anyone seen this before?

[Kiritsugu]

So shortly after we got our '04 Boxster S, we noticed that sometimes, when we try to start it up, it hesitates for about 2-3 seconds before finally starting the engine. Sometimes it took multiple ignition cycles to get it to start up. It wasn't nearly consistent at the time, so we couldn't do more than sit back and see what happened. Now, it's starting to become more frequent and I was wondering if any of you had seen this problem before. We had our battery checked, and it seems to be running fine. Thanks for any help you can offer!

[Ghostrider 310]

If it's cranking well it's not the battery, in general you need to look for spark or fuel delivery problems. How old are the plugs, when was the fuel filter last changed, check the gas cap for vapor lock but I doubt it's that. Getting the codes read would be a great place to begin.

[Kiritsugu]

Originally Posted by Ghostrider 310

If it's cranking well it's not the battery, in general you need to look for spark or fuel delivery problems. How old are the plugs, when was the fuel filter last changed, check the gas cap for vapor lock but I doubt it's that. Getting the codes read would be a great place to begin.

Actually, we had a check engine light for a vapor leak close to when we got it. Could you elaborate on the Gas cap issue? And we thought, after talking to someone with a similar issue, that it might be a bad chassis ground as well...

[Ghostrider 310]

Someone else will explain it far better than I but in general it's a heat induced, if the cap isn't venting it can build up and stop fuel delivery. What you are describing sounds more like a vacuum leak.

[shadrach74]

Originally Posted by Kiritsugu

Actually, we had a check engine light for a vapor leak close to when we got it. Could you elaborate on the Gas cap issue? And we thought, after talking to someone with a similar issue, that it might be a bad chassis ground as well...

Whoa... You need to be specific symptoms. Now that you mention chassis ground it seems as though you're suggesting it's a cranking issue. Does the car crank normally but the engine hesitates to light off smoothly or is it cranking inconsistently?

[shadrach74]

Originally Posted by Ghostrider 310

Someone else will explain it far better than I but in general it's a heat induced, if the cap isn't venting it can build up and stop fuel delivery. What you are describing sounds more like a vacuum leak.

You're confused about a number of different fuel related issues.

Vapor lock has to do with heat, atmospheric pressure and the vapor pressure of the fuel being used (it's just one of the reasons why some airplane engines cannot run auto gas) Vapor lock occurs when liquid fuel vaporizes with in the fuel system and the fuel pump cavitates due to any number of factors like heat, low pressure from a partial inlet blockage, or a "soft" pump that creates a pressure slack in the system by not maintaining constant pressure...or some combination issues causing the fuel system pressure to fal below the fuel's vapor pressure.

All the gas cap vent does is equalize the internal tank pressure to ambient.

[Kiritsugu]

Originally Posted by shadrach74

Whoa... You need to be specific symptoms. Now that you mention chassis ground it seems as though you're suggesting it's a cranking issue. Does the car crank normally but the engine hesitates to light off smoothly or is it cranking inconsistently?

The crank is fine. When it does decide to respond, the engine comes to life without a problem.

Now we think it might be the ignition switch. I understand what a shot in the dark this is, and honestly I'm only posting here because at least I'll seem like an idiot on the internet rather in person when a mechanic can't reproduce our problem. We've gone through a whole list of possible problems, but can't track it down to anything. I'll keep looking into it, but, thanks!