Question about 6.7L Boost, EGT, and Rail Pressure

[Rogan]

I just stuck gauges in my 07.5 DRW.   I noticed on flattish ground at 70mph, 6th gear (G56) I'm at 2150-2200 (3.73) RPM, 900-1100*F, and about 16-18k RP.   Boost is zero..

In my old '96, it'd carry about 6-8psi, and about 750-900F EGTs..

 

Is this normal for a 6.7?   No boost, and EGTs that high?  It's all stock.

 

Thanks.

[AH64ID]

The boost and EGT's seem fairly normal, but the RP seems high. 

 

What kind of load?

[Rogan]

5 minutes ago, AH64ID said:

The boost and EGT's seem fairly normal, but the RP seems high. 

 

What kind of load?

This is just cruising @70mph fairly flat interstate.

[AH64ID]

I'll pull out my computer later this week and peek at the stock tables for comparison. 

[Rogan]

Hey, John..

So..  UPDATE..  My OEM intake tube was all cracked and full of holes in the rubber pieces, so I bought a "cold air intake w/filter" for an interim fix. 

I threw my GoPro under the hood for S&Gs and pointed it to the air filter..   Low and behold, the filter was sucking closed rapidly..  So I ran down and grabbed a 4" inlet K&N (again, this is a temp solution, as I'm trying to source an oem intake pipe so I can reinstall the stock airbox) and swapped the filter..  the truck seemed a tad more responsive, throttle-wise.   Took it back out onto the same stretch of road I was on when I went to pick up the new filter...   

Mind you, on the way back from getting the new filter, with the old one still in place..  60mph, 0psi boost, 1100F, 15k rail..

 

After the filter swap, same section, 60mph, 6th gear as before..   0psi boost, 700F EGT, ~12k rail pressure.  

 

 

[AH64ID]

Those numbers are more inline. The load must have run up with the restriction. 
 

I’ll still peek at the OEM tables when I get a minute. 

[Rogan]

much appreciated, sir.

[AH64ID]

Looks normal for about 25% load, which seems inline for a DRW at 70 mph. 

[Rogan]

cool cool.  thanks for checking!

 

Question:  with that high of rail pressure and EGTs, would that contribute to less MPG?

I was getting 15-16 on a highway trip 200mi, at 70 on cruise.

 

[Rogan]

Week later, still good..  70mph, 750-775F, 13ishK rail pressure, zero boost.   14.5mpg..  UGH.

 

[Dieselfuture]

Maybe some drag  bigger tires, brakes sticking

[Rogan]

265-70-17.  rolls free.

 

[Dieselfuture]

Dirty air filter  

Seems you should get 18s or better. Something isn't right, wore out injectors?

[Rogan]

21SEP, as stated a few posts back, I replaced the air filter.   Injectors are new Bosch with < 2000 mi on em.  Matter of fact, the entire engine is < 2000 mi.

I was surprised, too, with the fuel economy (or lack of) that low.   I miss the days of my '96 12V 5spd getting 27mpg @ 68mph  lol

[Dieselfuture]

On 9/20/2021 at 7:32 PM, Rogan said:

Boost is zero.

Did you check for boost leaks

[Rogan]

I'll take a look, but I doubt there are any.  On that note, I've only ever seen a max of about 21psi, but I'm not sure what the 6spd max boost is, anyway.

 

[Dieselfuture]

Maybe wastegate is sticking open 

[Rogan]

It's a VNT....

[AH64ID]

After driving 1000 miles in mine last week the boost seems a little low, but only a couple psi at cruise. I cruise quite a bit lower on the rpm band thou. 3.42’s and an AS69RC with taller tires.
 

I think you should be peaking higher, but I don’t know for sure. My 18 is 385/930 and peaks around 28. 
 

New motor will take 10-15K miles to break in and get better mileage. What all was replaced?