7.3 trouble starting - Ford Powerstroke Diesel Forum
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post #1 of 4 Old 10-06-2010, 06:08 PM Thread Starter
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7.3 trouble starting

long story short had problems starting a while ago. ended up doing a complete motor build. new coated pistons, rods, head job ect. no expense was spared in this build. the problem is it still wont start very well. did a couple of tests tonight and found compression to be at 300psi on a cold engine. did a leak down test with removing the rocker arms and pressurizing glow plug hole and found it wont keep any pressure in the cylinder for more than 10 seconds once air is shut off. you can hear the air excaping rapidly and can feel it coming out the breather hole on driver side. does not feel like it is coming out the intake or exhaust. so basically we are thinking it is the rings because everything is coming out the bottom. what do you guys think? we have tons and tons of hours and not to mention $$ invested into this engine for it to not start again.
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post #2 of 4 Old 10-06-2010, 06:16 PM
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What breather on the driver side? Intake tube?

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post #3 of 4 Old 10-06-2010, 07:33 PM Thread Starter
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breather on the driver side that used to go into the intake.
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post #4 of 4 Old 10-07-2010, 03:25 AM
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Driver side breather would the the CCV. (crank case vent) Yes, you're absolutely right. The air pressure is escaping by the piston rings, into the crank case, and out the CCV. (might also be escaping out the oil dipstick tube as well)

Here's my question, and it might seem like a kind of silly question. But did you stager the piston ring gaps? They need to be staggered by about 120* off from one another. If they're in line with each other, then you'll lose your pressure.

Which cylinder's did you do the leak down test on? All 8? Are all of the tested cylincer's leaking the air pressure to the crank case?

If all the tested cylinders are losing air, and all the pistons were assembled by the same person/ people, I'd be willing to be it's just that the piston ring gaps aren't staggered. (but, that is of course my opinion, but it's also the "first" thing that comes to mind, especially since the motor was just completely rebuilt)

Hope that helps.


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