Inaccurate Boost Number Issues?

[badbajawa]

Okay, I'm having a bit of a strange issue that is kind of hard to describe finally got it all in one good video for reference.

Remember that the truck is compounded, so turbo issues are not necessarily felt the same.

I'm having an issue where the boost reading in the mm3 will be substantially wrong but still has boost.

I finally put mechanical boost and exhaust pressure gauges in it to see what was happening.

You can see that when the boost is reading incorrectly, it seems as though the VGT may be trying to close to build growth, but when the boost is reading correctly, the vdt is open, and exhaust pressure drops significantly.

I put a new map sensor in it a couple of days ago, and I put a city diesel turbo actuator on the factory turbo yesterday.

The issue has been around for a while seems as though it potentially is getting worse, but it might just be that I can now see the exhaust pressure doubling.

This may be a Ray question,n but I figure I will ask to see if anybody else has dealt with it before I bug him.

VIDEO LINK: https://youtube.com/shorts/YWUnsJsJVKk?feature=share

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[IGOTACUMMINS]

Let's ask @DRD?

Thank you,
igotacummins

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[DRD]

I cannot explain why the MM3 is slow to read boost.

The boost read by the tuner is a feed from the MAP sensor.

The boost read by the manual gauge is the most accurate, assuming the boost is read at the intake horn or intake side of the cylinder head.

If this is the case, I would take what the manual gauge is showing, which is truly happening.

The VGT has to close up when the first roll in the throttle to help start building boost, and then it must open up to allow the engine to breathe on the top end so that much is normal.

I would love to know what boost reads via a scan tool or the vehicle information display (if equipped) to see how that compares to what the MM3 shows.

Do make sure any MAP sensor used is a stock replacement sensor.

10-bar MAP sensors typically don't work out well when used.

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[badbajawa]

I did use a stock-level sensor.

My only concern is that the boost reading on MM3 seems to be tied directly to the exhaust pressure spiking.

That video was constant throttle on a slight grade towing.

If I tow and climb a steep grade and it does it, I have seen it almost immediately jump to the 90 PSI back pressure range.

I usually get out of it as I'm not sure what's safe there.

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[badbajawa]

Also, the boost on the MM3 reads the same as what's on the dash.

Most of the time, it's accurate in the 5 psi range to the mechanical gauge. When the mechanical gauge reads about 15, the MM3 and dash will say 22ish, and by the time the mechanical gauge reads 30, they will be back in sync.

(All this is during normal running; if it's doing the low boost, then disregard)

I have a scan tool I can try and see if it stays matching.

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[badbajawa]

Well, now this is strange.

This morning I cannot get the exhaust brake to engage at idle to warm the truck up.

I turned on the whistle tune, and it started doing its thing. Then the exhaust brake kicked on and tried to choke itself out at about 90 psi.

This morning I set up a different dash on the mm3 monitoring turbo speed VGT desired and VGT actual to see if there were anything strange that would stand out.

About 2 seconds into my morning steep grade Ii did its boost dance, everything but the mechanical red 9 to 10 psi.

If I gave it more throttle, the boost went down on the digitals VGT went immediately from 33% to 72%, both on desired and actual.

A couple of questions do I need the factory exhaust pressure sensor?

Do either of the sensors immediately leaving the air filter to have the ability to affect boost reading?



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[DRD]

No, you don't have the exhaust back pressure sensor on a 2014 model.

You do need the exhaust back pressure circuit wiring to remain so that it does not short out if the sensor is removed.

A shorting exhaust backpressure circuit or even a faulty exhaust backpressure circuit can cause the VGT to do crazy things.

No sensors behind the air filter have anything with reading actual boost pressure.

Only the MAP sensor does that.

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[badbajawa]

I have an OEM map sensor overnighted to me the other day.

I bought the only one in my area, knowing it may not last as something to try.

Symptoms did not seem to change, but I'll try that; otherwise, I'm growing concerned about a wiring issue with the map sensor potentially.

It doesn't feel tuning related at all.

The truck is seemingly trying to correct the false data it's receiving.

Does anybody with input on how to test the wiring to the map sensor out there?

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[AK Bob]

I have an OEM map sensor overnighted to me the other day.

I bought the only one in my area, knowing it may not last as something to try.

Symptoms did not seem to change, but I'll try that; otherwise, I'm growing concerned about a wiring issue with the map sensor potentially.

It doesn't feel tuning related at all.

The truck is seemingly trying to correct the false data it's receiving.

Does anybody with input on how to test the wiring to the map sensor out there?

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Attached is the OEM troubleshooting information for the MAP sensor on your 2014.

I hope this helps; odd that you do not see any trouble codes.

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[badbajawa]

Attached is the OEM troubleshooting information for the MAP sensor on your 2014.

I hope this helps; odd that you do not see any trouble codes.

Thanks, I'll give it a read.

The only thing I can come up with is the second turbo is forcing it to cooperate even though the truck doesn't seem excited about it.

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