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Rough idle/stalling after slight overheat

zerodevil

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Joined
March 24, 2008
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City, State
Anchorage, AK
Year, Model & Trim Level
2008 White Limited V8
long story short, after my engine(4.6L V8) had a slight overheat (no coolant over-flow at all, just a warning light), it developed a slightly rough idle. i wouldnt mind except when its warming up in the morning it tends to stall out. the engine runs smooth as silk when under load and has pleanty of power, so i doubt i warped a head or anything. its got a new iac, new egr, new fuel filter, new spark plugs, and new ignition coils. the only things i can think could still be wrong are bad o2 sensors, or bad cylinderhead temp sensor, or maybe even a PCV valve. anyone else have any ideas? no codes of corse either.
 


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matt0248

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July 12, 2010
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City, State
Chicago
Year, Model & Trim Level
02 XLT V8
Does it only do it cold? After it warms up it runs and idles fine? If so you may have a slight intake gasket leak. Or even a slightly cracked manifold. I am not certain but, is there a possible failure point where the intake could crack internally and leak coolant into the intake. This could explain the rough running and stalling cold. Another thought, is the fuel pressure regulator ok? meaning its not leaking fuel into the vacuum hose.
 




zerodevil

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City, State
Anchorage, AK
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2008 White Limited V8
no the roughness is still there, but it is bad enough to stall the engine untill it has been run and is at opperating temp. I havnt checked intake manifold gaskets or the manifold yet, i guess ill do that after i replace these sensors. I have no idea on how to check the regulator.
 








matt0248

Active Member
Joined
July 12, 2010
Messages
761
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City, State
Chicago
Year, Model & Trim Level
02 XLT V8
no the roughness is still there, but it is bad enough to stall the engine untill it has been run and is at opperating temp. I havnt checked intake manifold gaskets or the manifold yet, i guess ill do that after i replace these sensors. I have no idea on how to check the regulator.

ITs pretty simple to check the Fuel Pressure Regulator. Its located passenger fuel rail to the front of the rail. It has a vacuum line going to it. Remove the vacuum line to see if there is any raw fuel in it. With the line off you can cycle the key on and off to prime the fuel system and recheck. Plug the vacuum hose with a golf tee and start and run the truck, recheck for any signs of leaking. The last trick I have is to (with the truck off) Cut a very thin strip of paper, small enough to go into the vacuum port in the regulator. Stick the strip into the vacuum port and wait 10 minutes. Remove it and see if it appears damp and smells like fuel.
 




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