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Discussion Starter #1
Ok, so the wifes 2000 4.6 wouldn't start this morning, I went out and took a look at it and behaved as if it were out of gas or the ignition was dead. After LOTS of pumping the accelerator there was NO fuel smell as one would expect if it were getting fuel but not starting.

After checking all the vacuum lines and electrical connections it still wouldn't start or even give a hint of having fire\fuel. On a whim, I pulled the EGR? vent on the front of the driver side valve cover(I think that's the right part) and covered it with my thumb and had her turn it over.

The car started right up as if it were happy as always..I removed my finger, plugged it back into the valve cover and it kept running fine. On restart several times since then today it has started right up and acted normal...

This made no sense to me and I don't want her to wind up stranded on the side of the road with something that needs a repair.

Has anyone had a similar experience or know what may have caused this? I've spent an hour or so reading the forums and have seen mentions of replacing the EGR and IAC but I wanted to get some opinions before I jump right into replacing parts as I have no way to know which it is since it's running fine now.

Many thanks in advance for any suggestions or thoughts.

Beamin1
 

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Discussion Starter #4
The line running from the driver's side valve cover is the make up air for the PCV system. I have doubts that disconnecting this breather line is the true solution to the problem.

Here's a crank with no start check list. Pay special attention to the part about confirming operation of the fuel pump and PATS.

http://www.allfordmustangs.com/forums/4-6l-tech/336452-1997-mustang-wont-ignite.html#2984838
Like I said, it made no sense to me, my purpose for pulling it was to check for vacuum while the starter turned the motor, it's a simple eliminator for a broken\jumped timing belt. I was quite surprised when it actually started on the first bump with my thumb on it, after trying for a few mins at least while checking connections etc.

As posted, I didn't leave it disconnected, it started right up when I plugged the line itself with my thumb, I plugged it right back in while the car was still running, starts and runs fine since - just trying to figure out how this would have any effect at all.

Will go through the list in the morning when there's light - thanks for the helpful link!
 

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IF plugging the PCV make up line makes a difference in starting THEN there must be a vacuum leak in the PCV system.

Likely what's happening is the un-metered air is making the MAF read low.

Bottom line is that even a tiny vacuum leak will cause problems.
 

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Discussion Starter #6
Ok, first night below freezing again and it's happened again, this time no luck getting it to start - I went through the no start checklist last week and didn't have anything fail, car has been running fine since last time it did this so it's made it more difficult to diagnose till now.

My question is this; does the fact that this is only happening when it drops below freezing overnight narrow down the troubleshooting at all?
 

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On the crank with no start check list there are several test with questions about the results. With zero feedback don't have much to go on.

If asking for my best guess, bad fuel pump. However, to know for certain would require the fuel pressure to be cross checked with an external pressure gauge.

Another possible "trick" is to hit the center of the gas tank with a rubber hammer when it won't start. If it then starts right up, the diagnosis is confirmed.

Good luck.
 
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