So where does the fuel pressure go?

[FastWoman]

All I can contribute here is that fuel pressure retention is not a problem on my car, as I have a primer switch I hit to bring fuel pressure up to spec before ever turning the key. My system is pretty tight anyway, and it holds pressure. It's mostly a quirky habit of mine to prime before starting, so I suppose that's why I still do it. (That's what I need to do to start our boat.) The car starts fine even after several days without hitting the primer switch. Anyway, cold starts are no problem. Warm starts (after sitting 20-30 min) are rough.

Zed, I think your theory about sticking parts could be meritorious; however, the little needle is metal, and the body is plastic. The plastic should expand more than the metal when hot, so tolerances should get sloppier. Besides that, I've never had problems with my injectors in a hot engine. The problem is only with a warm restart -- and not right away, but only after sitting 20-30 min -- and not after sitting for a couple of hours or even several days.

The best theory I've heard, that many people insist is impossible, is that fuel is vaporizing inside the hot injector, so that fuel vapor, rather than liquid fuel, is being injected. less fuel can be injected as a vapor than as a liquid (under the same pressure), hence the lean running. As a student of physics and physical chemistry at one time, I can assure everyone that given a high enough temperature, gasoline WILL vaporize at [pick your pressure] psi. The only question is what temperature and what pressure, and that depends on the gasoline formulation, which varies seasonally.

Edited January 12, 2012 by FastWoman

[Zed Head]

I like the "vaporizing inside the injector" theory also. I'm just throwing out other possibilities. I've not seen the inside of an injector or studied any diagrams closely so don't know if anything could bind when hot or not. I was thinking more of the metal piston inside the electrical windings though, the solenoid, not the fuel valve components. It has more mass and might explain why it takes so long for the problem to go away once it occurs. Who knows, maybe there's an area of the electrical contacts that can open under expansion.

I have a bunch of old injectors, I'm surprised I haven't cut one or two open yet.