back to square one
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Elder User
Joined: Mar 2004
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From: mohave valley, arizona
back to square one
well i have replaced about every sensor you can think of on mt 90 4.9 and still it doesnt want to start when cold and also surges under 50 mph. i even replaced the intake manifold and throttle body gasket along with all new orings for the fuel injectors, good fuel pressure, checked all hoses for vacuum leaks but nothing. funny after i put it all back together it started right up and high idle high and was perfect. but after driving it i could feel the surge again and after sitting 6 hours it started but stumbled. i even checked back pressure of the exhaust. guess the only things left are the distributor and pcm to replace but i have a feeling ill still have the same problem. im thinking its something its something minor but i have run out of things to look for short of cutting into all the wiring harness and see if i can find something.
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Joined: Aug 2009
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From: Delta,UT
I would imagine you already checked these things but you didnt mention them... Did you check simple things like the plugs and ignition wires? Did you pull the codes? check pcv valve? Pulling any stored codes might tell you what you need to know.
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Elder User
Joined: Mar 2004
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From: mohave valley, arizona
the IAC is new. as for codes i get a 22 which says map. i bought a new map but it ,ade no difference. strange thing is once i put it all back together, it had sat for 24 hours, i reached in the cab and it started right up first time and idled perfect, better than its done in years.
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Elder User
Joined: Mar 2004
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From: mohave valley, arizona
no i only disconnected the battery for about 10 minutes. well this morning it started stumbling again. one time when it was doing this i disconnected the fuel pressure regulator and it smoothed out. yet i checked the fuel pressure and the regulator and they tested good. i know the pressure goes up when the regulator is disconnected, and it does, about 7-8 psi, but why then would that cause it to run better.
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OK... there are a few things that could cause a stumble on an otherwise good motor. Crossfire between plug wires is one, seperate them as much as possible and try to avoid running any parallel and in close proximity. Next take it for a decent run on the highway and then stop and pull the plugs. What color are they.. tan brown or more white? If they are all white then you have a lean burn problem, look for a malfunctioning or leaking air injection tubing. If only 1 plug is white then you have a bad/dirty injector on that cylinder.
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From: Renton, WA
no i only disconnected the battery for about 10 minutes. well this morning it started stumbling again. one time when it was doing this i disconnected the fuel pressure regulator and it smoothed out. yet i checked the fuel pressure and the regulator and they tested good. i know the pressure goes up when the regulator is disconnected, and it does, about 7-8 psi, but why then would that cause it to run better.
Can you repeat this, when it's stumbling will pulling the vacuum line off the reg smooth it out every time?
Can you constantly moniter the fuel pressure?
Senior User
Joined: Jul 2009
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You have a code 22, MAP Sensor out of range? Have you checked the Vacuum to the MAP Sensor? How about the MAP Sensor Circuit (MAP to ECM)...I had a customers vehicle in and it had a similar symptoms,except for the MAP sensor code..The Fuel tank was rusty and coming apart and clogging the Fuel strainer..But if i was you i would explore the Code 22 more..Good Luck