[FIXED] 06 f250 6.0 diesel low power possible 5v ref problem

Ok so I'm working on a 2006 f250 superduty with the 6.0 diesel and 140k on the odometer this truck has low power and boost fluctuates on hard accel wot boost goes from 25 to 15 and back and forth aprox 4 seconds a cylcle and you can hear the turbo noise following the same cycle. power balance doesn't show any cylinders low and relative compression sounds perfect. Checked for high pressure oil leak and didn't find any . I test drove and logged the data on my scan tool to review all sensor inputs while the boost is fluctuating and my boost sensor map sensor and exhaust pressure sensor all agreed boost was fluctuating and maf peaks over 4.5 volts and the hpop keeps up with the desired pressure with no problems and I could not max the pressure regulator running it hard so that all looked good . But then while I was looking through the log I noticed vref only showed 3.5 volts the while time yet several sensors had gone above 4v...? How is this possible ? I haven't gotten a chance to hook the scope up or check the voltage on the 5v line I will get back to that this evening and let you know what I find . In the mean time anyone have any ideas?

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hi yes that is weird scanner danner has some excellent vids on the five volt reference the 3.5 on just a part of the circuit is weird I would start unplugging sensors to try and narrow down which one is pulling it down there is something pulling your reference line down and it is affecting your maf signal to the pcm I imagine this is a cause of turbo burps

Hey chief I do plan to disconnect 5v sensor when I get back to it but all the 1s I monitored the voltage all went over 4 volts which means that there has to be over 4v available to them.... I'm going to have a look at a diagram and see how many 5v ref lines there are on this 1 and which 1 of them is monitored I know the maf made it to 4.5 which is right on spec . I kind of suspicion egr causing turbo cycling

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Well looking at the diagram I show 2 5v ref lines and both have 5v on them so I don't know where the ecm is reading 3.5v from I also disconnected all the sensors and none made a difference to the vref. I think I'm going to pull and clean turbo and do an egr delete . I noticed some injectors sticking when it was cold,maybe it's going to be time to put injectors in this truck..

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Hey Ben, you're thinking of a binding VGT actuator ring? Let me know what you find. I've seen these cause low boost, but usually not in a cycling way as you witnessed. Do you recall what the VGT% PID does at WOT?

Sure sounds like that VREF PID is BS! :lol: Have you tried the injector buzz test? Maybe run it with the engine cold and hot, see if you can catch one that sounds significantly different.

Hey Tyler yes I did buzz test cold and hot and all were even. I did snapon turbo test and that was all good and responded to the actuator as expected I'm putting together a leak test kit to pressurized this turbo piping I don't see the intercooler seal pushed out but who knows maybe there's a crack i can't see . On a wot road test it had low power above 2500 rpm and boost gauge swings back and forth 10 psi bit engine power doesn't change which really has me wondering if the boost problem is a reaction to something else I would think power would fluctuate like crazy with a 10psi change in boost at the intake . Also the cylinder power balance shows a couple cylinders bouncimg between 0 and -2 at idle and about the same at wot

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Ben wrote: Hey Tyler yes I did buzz test cold and hot and all were even. I did snapon turbo test and that was all good and responded to the actuator as expected

Ah crap, good idea! I forgot all about the turbo functional test. :blush:

I'm putting together a leak test kit to pressurized this turbo piping I don't see the intercooler seal pushed out but who knows maybe there's a crack i can't see .

Let me know what you end up putting together? I don't have a good solution for pressure testing intercoolers besides the regular smoke machine, other than buying one of those pressure test sets.

On a wot road test it had low power above 2500 rpm and boost gauge swings back and forth 10 psi bit engine power doesn't change which really has me wondering if the boost problem is a reaction to something else I would think power would fluctuate like crazy with a 10psi change in boost at the intake . Also the cylinder power balance shows a couple cylinders bouncimg between 0 and -2 at idle and about the same at wot

Interesting... What's the EBP and VGT% doing during the surge? I know the EBP is one of the inputs for turbo function, so I'm wondering if there's a plugged pressure tube and/or skewed sensor.

Hey Tyler I ran to local hardware and picked up a 4 inch boot and plumbing cap I'll drill a hole in it and attach a air fitting and pressurized to 25psi
The map ebp and vgt are all mirrors of each other as vgt goes up so does the exhaust and manifold pressures when but starts cycling down so does both pressures

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5he whole no difference in power lewd me to believe it's not flowing the boost so I disconnected the exhaust before the cat and ran it with no difference

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Ok so I checked the turbo piping for leaks and all I found was a very small amount of bubbles in the turbo to hot pipe connector and a slight amount of air from oil cap (blow by rings I assume) I'll send you a few snap on data recordings later see if you spot anything I missed.

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Dang, I was hoping the EBP was gonna be a slam dunk. :lol: But it sounds like you've been over it already!

I'd be happy to look at the data when you get a chance. I've got my Power Stroke training manual around, too, might see if it has any ideas.

I'm fairly certain the motor isn't capable of flowing enough air as the boost goes from 10 to 20 psi power output doesn't change, it has major turbo lag . I'm really starting to think whoever done the head gaskets maybe didn't adjust the valves properly I may pull valve covers and take a look I also suspicion a hpo leak at dummy plugs as I see the injection pressure regulator gets up to 75%

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Hey Tyler I sent you the data logs there's 1 from each data stream at 0 to wot then there's another set at idle and another I believe there's a set with koeo to show map and exhaust intake pressure

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Well I got some time today to pull the turbo and split it and I found the unison ring is worn wear the actuator lever controls it allowing it to wobble back and forth probably causing the boost fluctuation so I'm going to order a unison ring and see if that cures it all or if there is something else going on

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I got your data, sir, I'll have a look at it later tonight.

Was this head gasket service recent? I don't have much experience adjusting these valves, unfortunately. The last 6.7L Cummins I did had valve last specs that were WIDE open. Probably coulda eyeballed it and still hit spec. :lol:

I don't know when the heads were done I just see that it has the arp stud kit in it , see what you think of the logs I'll let you know in a couple days how I make out with the unison ring

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Here's what I put together for a pressure tester this 1 is 4 inch and closes down to 3.5 , I also got 1 to do 3 inch

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I like your thinking here, sir. I'm all about repurposing plumbing fittings for automotive applications .

I got your email, too. You must be like me - save EVERYTHING and sort it out later. :lol: Going over it right now.

Ok new unison ring fixed turbo fluctuation or at least cut it way down. It feels like a slight misfire at wot/ high rpm I have to look at yet but all in all runs much better

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Chalk that up as just because it passes snapons boost test doesn't mean it's good like in the case of the worn ring it let the vanes move back and forth causing the actuator to over compensate

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