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Old 07-22-2009, 08:36 AM   #1
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never start the first try when engine is cold

it always takes 2 or 3 try to start the jeep when the engine is cold

when it's hot, it start right up. what would cause that?
new engine, new spark plug, plug wire distributor cap...

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Old 07-22-2009, 10:16 AM   #2
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Have you checked the voltage at the pump in the gas tank? It maybe turning on but not giving the needed pressure to kick it over. But when you try 2 and 3 times then it finally goes it runs because you use less pressure then the first start.

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Old 07-22-2009, 10:43 AM   #3
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The usual cause of a slow start after it's been sitting a while like overnight, but starts up if it has been running recently, is a leaky anti-drainback valve inside the fuel pressure regulator. The fuel rail next to the fuel injector is supposed to remain pressurized with fuel to give you a fast start but if that anti-drainback valve leaks, the fuel rails's fuel will drain down and back into the gas tank.

The next morning you go to start your TJ, first check the fuel rail for fuel pressure before attempting to start it. On the fuel rail is a black plastic cap you unscrew that covers a Schraeder valve (like a tire stem valve) for connecting a fuel pressure valve to. But what you can do is just unscrew the cap and after placing a rag underneath, push on the pin underneath. If no fuel squirts out or if just a dab dribbles out, your problem is likely anti-drainback valve letting the fuel drain out and back down into the gas tank.

The anti-drainback valve which is inside the fuel pressure regulator sits atop the fuel pump so you have to drop the gas tank to get to it.
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Old 07-22-2009, 11:11 AM   #4
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ok, thanks, i'll check this
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Old 07-22-2009, 12:22 PM   #5
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A simple "fix" for this is this (I have this problem in my Grand Cherokee so I know this works) when you first get in and turn the key just turn it until all the dash lights light up (don't crank it over) and slightly press on the gas pedal for not even a full second and let off immediately. This "refills' the line and she starts first crank.

When the engine is hot it means you have driven it recently enough that it hasn't drained back, hence the immediate starting.

I know, it's not a FIX, but it beats double and triple cranking, and if you cannot perform the real fix (or can't afford it) this is a safe way to over-ride the problem.
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Old 07-22-2009, 12:30 PM   #6
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cool, i'll try this when i get off work..
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Old 07-22-2009, 12:33 PM   #7
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That only works if the anti-drainback valve is only kinda-sorta leaking. If it is leaking enough to allow all of the fuel rail's fuel to drain completely down into the tank, or it has sat long enough for a kinda-sorta leaking valve to allow the fuel lines to completely empty, it takes a lot more time than that for the fuel pump to get the fuel all the way back up to the fuel rail than just the few seconds until the dash lights light up. When the fuel lines are empty, it takes quite a bit of pump time to get the fuel all the way back up to the fuel rail.
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Old 07-22-2009, 12:37 PM   #8
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Thanks Jerry, good to know. I think mine must be in the "kinda-sorta" category.

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Old 07-22-2009, 05:24 PM   #9
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Sorry to kinda hijack, but could this problem also cause missing on a cold engine? Mine does the same thing where it wont start the first or second time after sitting but it also misses when you blip the throttle before the engine has been running for 5-10 minutes. Thanks.
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Old 07-22-2009, 05:32 PM   #10
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It not likely the fuel pump is causing the missing. You can verify that the fuel pump is putting out the pressure it needs to with a fuel pressure gauge that screws onto the fuel rail's Schraeder valve. Normal fuel pressure should be pretty darned close to 49 psi.
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Old 07-22-2009, 06:12 PM   #11
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ok, I know that the anti drainback is leaking really badly. as soon as you shut the engine off you can watch the pressure guage drop very quickly from running pressure to zero. would this bad of a leak make a difference? I'll do the test again because I dont remember what the pressure is when the engine is running. Thanks

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