502Mag MPI re-starting issue
05-26-2020 | 12:57 PM
#1
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From: Omaha, NE
502Mag MPI re-starting issue
One of my 1997 502's is giving me some warm re-start issues. Engine cranks and fires right up cold. To restart warm, if fires and dies. I Have to advance throttle a bit for it to start and then its fine and idles when I return the throttle back. I have replaced the IAC and it still does it. This is not my occasional Vapor Lock condition, but something else. TPS maybe? Any hints or diagnosis would be appreciated.
05-26-2020 | 03:03 PM
#2
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Joined: Nov 2009
Posts: 4,198
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From: KY
Could be a few things, MAP, IAT or injectors. Injectors may be leaking and need to be cleaned and flow tested. If they haven't ever been done it would be a good thing to do
Check fuel pressure, if its to high this could be causing it to be to rich 37 psi
Check fuel pressure, if its to high this could be causing it to be to rich 37 psi
05-27-2020 | 12:07 PM
#3
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For the suspect motor, there should be yellow tygon hose from the top of the VST to the intake manifold. See if there is any fluid and or residue of fluid in the line. If so you likely have fuel percolating out of the VST into the manifold, effectively flooding the engine. There is a diaphragm inside the VST that deteriorates with age and fuel from the VST will seep through and escape via that yellow tube.
The fact that adding throttle helps start the motor during this warm condition does two things. First it increases air flow via opened throttle blades helping to clear extra fuel, and second, advancing the throttle will force the MEFI controller into a 'flood clear mode" by shutting off the injectors. Depending on the MEFI that is usually between 25-75% TPS.
I've had this condition happen on my motor always thinking it was vapor lock, when in fact it was not vapor lock but this ruptured diaphragm causing the situation you just described.
The fact that adding throttle helps start the motor during this warm condition does two things. First it increases air flow via opened throttle blades helping to clear extra fuel, and second, advancing the throttle will force the MEFI controller into a 'flood clear mode" by shutting off the injectors. Depending on the MEFI that is usually between 25-75% TPS.
I've had this condition happen on my motor always thinking it was vapor lock, when in fact it was not vapor lock but this ruptured diaphragm causing the situation you just described.
05-27-2020 | 02:07 PM
#4
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Registered
Joined: Feb 2012
Posts: 266
Likes: 16
From: Omaha, NE
For the suspect motor, there should be yellow tygon hose from the top of the VST to the intake manifold. See if there is any fluid and or residue of fluid in the line. If so you likely have fuel percolating out of the VST into the manifold, effectively flooding the engine. There is a diaphragm inside the VST that deteriorates with age and fuel from the VST will seep through and escape via that yellow tube.
The fact that adding throttle helps start the motor during this warm condition does two things. First it increases air flow via opened throttle blades helping to clear extra fuel, and second, advancing the throttle will force the MEFI controller into a 'flood clear mode" by shutting off the injectors. Depending on the MEFI that is usually between 25-75% TPS.
I've had this condition happen on my motor always thinking it was vapor lock, when in fact it was not vapor lock but this ruptured diaphragm causing the situation you just described.
The fact that adding throttle helps start the motor during this warm condition does two things. First it increases air flow via opened throttle blades helping to clear extra fuel, and second, advancing the throttle will force the MEFI controller into a 'flood clear mode" by shutting off the injectors. Depending on the MEFI that is usually between 25-75% TPS.
I've had this condition happen on my motor always thinking it was vapor lock, when in fact it was not vapor lock but this ruptured diaphragm causing the situation you just described.
