Under boost at idle? Really? - Ford Powerstroke Diesel Forum
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Old 10-16-2012, 10:42 AM
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Under boost at idle? Really?

Ok I'm ready to break out the hammer. I have a 2004 F350 with 24,000 miles. It is consistantly throwing a "turbo underboost " code when backing out of the garage or pulling out when the engine is cold. Turbo had new unison ring 3000 miles ago. i cant find any leaks at the intercooler boots. If i let the truck warm up for about3 or 4 min its ok.It has goten to be pretty regular. what would cause this. Its at idle when there isnt any boost before the RPMs come up. Is there a sensor that could be going bad?
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Old 10-16-2012, 12:15 PM
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Do you have an egr? How does it run? Does it smoke? Do you have a monitor?

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Old 10-16-2012, 01:20 PM
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It seems to run fine. It does'nt run rough and the Turbo spools up fine when the RPMs come up. It does still have the EGR. The delete is sitting on the bench waiting for me to find time to put it on. I have an EDGE evolition that i use for monitoring. It tells me as soon as it throws the code. Usually when backing out of the garage at idle but has also done it when pulling out after the engine has sat and cooled for a while. The thing I don't understand is at idle or verry Low RPM the Turbo is'nt making any boost so why is it reading under boost? I am new to diesels and not sure where to look next. the evolution does'nt tell me much . Thank you for any help you have to offer.
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Old 10-16-2012, 01:29 PM
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Make sure the rubber hose and sensor that connect to the right side of the intake is not clogged. I think that is the maf sensor. Maybe your egr is also slightly stuck open too.

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Old 10-16-2012, 02:10 PM
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Thank you. I did clean the EGR not too long ago also. I will check both of those
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Old 10-16-2012, 06:45 PM
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Wow 2004 with 24000 miles, was this truck only driven to church on Sunday

^^^^MAP could very well be a issue, it regulates the egr by measuring the boost from the turbo, now being the truck has so few miles the turbo may be a bit stiff and not doing what pcm wants it to do.

Will the edge tell you turbo desired position? It kinda sounds like the turbo is not closing at low rpms, what boost #s do you see wot after engine is at operating temps?

Last edited by mhatlen; 10-16-2012 at 06:58 PM.
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Old 10-17-2012, 04:19 AM
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What about the ebp sensor? Wouldn't it throw a code like that if it was plugged or failing?

Last edited by Merc82; 10-17-2012 at 04:20 AM. Reason: spelling
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Old 10-17-2012, 04:56 AM
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I believe the ebp sensor is ignored with newer strategies in the early MY.

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Old 10-17-2012, 08:24 AM
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Doesn't hurt to ask! That's how ya learn, learn something new every day!
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Old 10-17-2012, 10:25 AM
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Wow. Thanks for all the input. The EBP sensor is clear and so is the tube. Going to check the MAP and EGR now that it is cold. Not real sure where the MAP is though. Mhatlen - No the Edge does not tell me Turbo position. It does read 25-26 at WOT though and seems to sopool up pretty well. When It first starts up cold the exhaust sound changes after it idles for a few minutes and it sounde like the turbo spinning. Is that what you meand by "stiff" ? Also this is a 2004.5 model if that helps., Built in June 04. Thanks again for all of the help.

Last edited by motorman173; 10-17-2012 at 01:28 PM.
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