91 ls400 hard to start after sitting overnight?

Ive tried replacing the fuel pressure regulator and that did no difference. The car runs and starts perfectly all day but when it sits
over night and I get into it in the morning it will crank and crank for 10 seconds before it starts. Is there a check valve in the fuel pump that can be leaking fuel back as well??
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:) wrote:

A leaky injector is more likely.
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St. John
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Did you check fuel pressure with a fuel pressure gauge as I recommended or did you just replace the fuel pressure regulator? If you checked fuel pressure, what was the pressure after sitting overnight?
Bad fuel pumps tend to be all or nothing, that is, they work or do not work, unless the tank has been run dry a few times, in which case they can get worn. I've never seen the inside of the fuel pump, but I don't think it has a check valve.
A fuel pressure gauge installed in the fuel line ahead of the fuel pressure regulator and after the fuel pump will indicate whether the fuel pump itself is bleeding pressure back down, but I doubt if it is the fuel pump.
The car may have a cold start injector which supplies extra fuel when cranking. If it or the cold start injector circuit (timer, wiring, coolant temperature gauge, etc.) were bad, it would be hard starting any time the car is cold-soaked, say after 4 hours.
Check for leaks in the intake between the air filter and throttle body, check manifold vacuum, especially in the hoses leading to the fuel pressure regulator.
I always recommend checking stuff before replacing parts - fixing a car will be a lot cheaper that way!
--

Ray O
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On Mon, 19 Feb 2007 11:52:51 -0600, Ray O wrote:

Hey Ray,
I think you're right on! I'd like to add that carbon buildup can cause similar symptoms (older vehicles).
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