Surging help needed!
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Senior User
Joined: Sep 2009
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Surging help needed!
I am working on a buddy's 1989 Ford 4.9 EFI and it has been surging at idle. It will idle just fine for about 30 seconds and then start surging and eventually stall. Replaced map sensor on firewall. Has a new IAC. Hooked the computer up and am getting code 42 after doing the running test. I'm at a loss. New plugs,wires,rotor, rotor cap, fuel pumps, tanks,lines, throttle body has been cleaned,TPS is working. Sprayed carb cleaner everywhere and have not found a vacuum leak anywhere on the engine.
Thanks in advance guys
Thanks in advance guys
Logistics Pro
Joined: Dec 2003
Posts: 3,774
Likes: 860
From: Foothills of NC
I've lived with this for going on 27 years. If you find a fix, let me know.
Mine will idle good cold for a minute or so, then start surging until it dies. After the engine reaches a certain temp, the surging will quit.
I've thought about putting a small resistor in the ECM temp sender wire to make the ECM think the truck is a few degrees colder than it is to see if that helps. I've checked the reisitance values of my sender through out the cold to warm heat range, and it is right on.
Mine will idle good cold for a minute or so, then start surging until it dies. After the engine reaches a certain temp, the surging will quit.
I've thought about putting a small resistor in the ECM temp sender wire to make the ECM think the truck is a few degrees colder than it is to see if that helps. I've checked the reisitance values of my sender through out the cold to warm heat range, and it is right on.
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Senior User
Joined: Sep 2009
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FIXED!!!!
I have found the cause of the surging problem. The fuel pressure regulator must have a hole in the diaphragm and is pushing fuel through the vacuum line into the intake throwing the computer wack. Pull vacuum line of regulator start truck and fuel will drizzle out of the line if yours is bad. Replacing regulator tomorrow.
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