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Old 06-20-2011, 03:39 PM   #1
brkro86
 
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Default 04 mustang intermittent starting problem

Hi,

Once in a while, after the car has been warmed up, I'll go into a store and when I come back out and try to start it will crank for about 5 seconds before it does anything. The cranking sounds normal, not slow or anything at all. Once it catches, it will idle around 100-300 rpm for 3-5 seconds as if it's going to die, unless I give it some gas. My car only has 30k miles on it so what the hell?... :/

Fyi, my dad's 2011 GT does the same exact thing. So, Idk if it has anything to do with old parts, maybe its just something that is inherent with some fords?

Any ideas? Does anybody else have the same problem? Thank you!
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Old 06-20-2011, 05:55 PM   #2
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might be a tps issue there very well known for that
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Old 06-21-2011, 12:25 AM   #3
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Hmm. Ok. would that throw a code? I haven't had any cel's yet, but then again its very intermittent as of now. I will keep it in mind though, thank you!
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Old 06-21-2011, 08:49 AM   #4
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It is a common issue, heat soak vapourises the fuel in the fuel rails and the start-up AFR goes lean.

There is a function in the tune named Cranking A/F Ratio that can maps ECT against AFR while starting the engine--this can be tweaked to make it less of a problem...

Here are the settings I run:

Click the image to open in full size.

You can see that I enrichened the mix at 200°+ ECTs...
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Old 06-21-2011, 09:35 AM   #5
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do you have a fuel pressure gauge? if so the pressure may just be bleeding down. The long crack is the time it takes for the gas to get from the pump the the injectors.
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Old 06-22-2011, 10:05 AM   #6
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Originally Posted by PROMETHEUS PRIME View Post
do you have a fuel pressure gauge? if so the pressure may just be bleeding down. The long crack is the time it takes for the gas to get from the pump the the injectors.
Nope, my car doesn't have that gauge. Wouldn't it crank for a long time on cold starts too then b/c the pressure isn't built? It only does it on warm starts (and it only happens once in a while as I mentioned), also I always wait a couple of seconds with the ignition on before starting for the fuel to build up a lil bit.
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Old 06-22-2011, 11:14 AM   #7
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Quote:
Originally Posted by brkro86 View Post
Nope, my car doesn't have that gauge. Wouldn't it crank for a long time on cold starts too then b/c the pressure isn't built? It only does it on warm starts (and it only happens once in a while as I mentioned), also I always wait a couple of seconds with the ignition on before starting for the fuel to build up a lil bit.
Yeah if it was leaking down you would have a long crank also in the morning. If you have a manual fuel pressure gauge you can see the fuel pressure when this occurs. Thats how I usually diagnose it to see if it's a fuel problem. It could be the pump going bad, or the relay getting hot. 8 times out od 10 it's the pump. Also check to make sure the theft light is not flashing fast when this occurs.
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Old 06-22-2011, 12:37 PM   #8
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Quote:
Originally Posted by brkro86 View Post
Nope, my car doesn't have that gauge. Wouldn't it crank for a long time on cold starts too then b/c the pressure isn't built? It only does it on warm starts (and it only happens once in a while as I mentioned), also I always wait a couple of seconds with the ignition on before starting for the fuel to build up a lil bit.
It happens because engine heat "soaks" the fuel in the rails to a point that when the injector opens (for the very short time it opens while cranking) the fuel boils at the sudden pressure drop--the mix goes lean and the car doesn't like to start.

Telling the tune to make the cranking mix richer by lengthening the injector pulse. It is still partially vapourised fuel passing through the injector, but there is more of it.

My '03 did this quite a bit here in Florida before I altered the cranking AFR function. There was a narrow window of time during which it did not like to start, 4 to 7 minutes. If you started it again almost immediately, or 10 minutes later, there was no problem; but inside that window...
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Old 06-22-2011, 02:40 PM   #9
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Thanks cliffyk, that makes perfect sense. And sorry that I didn't respond to your first post, I actually didn't notice it until now.. I need to start going through the thread each time lol.

Also thanks prometheus for your help too. If this issue does get worse (past the limits that cliffyk mentioned) then I will suspect a fuel issue.
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Old 06-22-2011, 03:36 PM   #10
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If it's a pump issue as well it will be a suuuppper long crank. As in it may take a minute or two to start. Not cranking it for 2 mintes straight though lol. So try cliffyk's fix first.
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Old 06-22-2011, 03:36 PM
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