High EGT's, no smoke, full fueling, and vanes working - WFT?

[nskyline34]

How can a (basically) stock truck have 1300* EGT's while cruising at 60 mph on flat ground with a small trailer and not be blowing any smoke? Sorry for the long read, but it's got me stumped.

My 2006 LBZ 280k miles (285/65-18's, 5" exhaust, EGR blocked, and running a hypertech on level 3) has some odd sh*t going on. Going down the road to work (cruising about 65 on the freeway) it will get about 17mph avg. I think it should be higher, but I'm going to blame it on winter fuel and running oversized tires.

When I pull my enclosed 18' trailer with a couple dirt bikes in it things get a little interesting - mileage goes out the window. The trailer weighs about 6k - nothing remotely crazy.

In the past cruising at 60-65, down a nice flat open stretch of highway and I'll get about 10-11 mpg. If the horsepower gods are smiling on me maybe 12 mpg with this trailer. (This was going to be my last trip before I dug into the issue because this is NOT normal) I would expect fuel mileage to be around 13-14mpg. But the truck feels like it's pulling a damn house. I've got a 3500 LLY 12k lb excavator and dump trailer that all in all weighs about 28k lbs going down the road and it pulls that just as well as the 2500 pulls the enclosed trailer!? (I mean across flat ground - obviously a hill is a whole different ball game with that much weight). Driving around town from light to light, the truck seems totally fine. Starts great, idles smooth, etc. Its when you get into the upper gears that things go south.

This weekend things got a lot worse though...

Leaving the track I stopped to grab fuel before heading home - about a 250 mile trip, most of it is flat, there is one hill that's about a 6% grade for 4 miles and then 1 mountain pass towards the end. Basically driving through the plains and rolling hills (maybe a slight breeze for a head wind ~5 mph?) I was seeing about 1200-1300* EGT's?!?! AT 60 mph?! Truck doesnt blow any smoke or even the slightest haze. FRP was at 23k-24k psi and cubic fuel rate was in the 90-100mm^3 range. So it was fueling almost as hard as it could. Just to maintain 60-65mph I was running at about 50-55% throttle input (all measurements are from an Edge CTS monitor). Boost was only running about 5-9 psi during this time. I feel like the truck should've been making more boost and using less fuel. I manually dropped it down to 5th gear to get a little more rpm (1900-2k in 5th) to help drop the EGT's and this brought them down to about 1100-1200* - most everything else remained unchanged.

I went through an entire tank of fuel in about 105 miles!!! There was a pretty decent hill in the middle of the trip - but nothing crazy. For reference in my old 2003 Cummins I made the same trip with the same trailer and still had a 300 mile range left. I know its a little apples to oranges - but I'm just saying that the fuel consumption was ridiculously high.

Mid way home I put the stock tune in it - and it didnt change a thing. EGT's were maybe a little lower, and mileage a little worse but nothing too much.

I can hear the turbo vanes change at idle and then on decel I can feel the exhaust brake working and I can watch the vanes change on the screen too.

Checked trailer brakes and bearings before this last trip over the weekend and everything was perfect (trailer is about 2 years old so it should be fine).

Fresh fuel filter on it right before I left. Merging on the freeway after one of my fuel stops I did see it hit about 20-22psi boost, so I dont think it's a boost leak. Plus if it was a big boost leak it would be rolling a little coal or at least a haze - but it runs as clean as a Prius.

One thing I did find odd was that the fuel temps got really high - upto 156* (didnt hit the 160* limp mode mark though I backed way out after I saw 155 and it ticked upto 156 before dropping). Injector balance rates and fuel rates at idle are all fine (highest is 1.5 and lowest is 2.1 at idle in neutral, and in gear they get even closer to zero).

So why in the world would the truck be fueling so hard, and making so little boost - but not blowing any smoke? I have a couple different hypothesis about what it could be, but I dont want people to start thinking down the same road I am, I want people to do their own reasoning and see if there are any other ideas? So what in gods name do you guys think it is? and what I should check?

Only codes are P0401 and then 2 glow plugs. The 0401 has been on since I did the EGR block off about 25k miles ago so it's not that.

 

[2004LB7]

Sounds like a plugged cat or something else in the exhaust but you say it has a 5" exhaust, so???

What was it averaging timing wise during that trip on the highway?

 

[nskyline34]

Sounds like a plugged cat or something else in the exhaust but you say it has a 5" exhaust, so???

What was it averaging timing wise during that trip on the highway?

It seriously felt like it was trying to tow a house. Like all the brakes were being applied. (Yup I did check brakes and nothings hanging up)

Yea 5" straight out the back.

Dang it - the one thing I didnt check was timing. What are you (and should I be) expecting?

I'm not crazy right? Like 1200-1300* is really abnormal for towing down the flat highway like that right?

I'm wondering if the some of the vanes in the turbo are gone and the unison ring is only controlling some of them. Basically enough to make the sensor think its working and enough to change the pitch of the exhaust, but not enough to get it to spool under load like this?

 

[Dozerboy]

Maybe you got some bad fuel or injector issues. The truck feels and gauges are fine unloaded even when you drive it hard?


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[nskyline34]

I was wondering the same thing - thinking it was some kind of fueling issue. Rail pressure will hold steady under WOT from about 10mph to 100mph+, and Injector balance rates are all well within spec.

To make things more interesting I towed a buddies 24' enclosed trailer (same height and width as mine, just another 6' longer). Once I merged on the freeway I reset my avg mpg on the DIC and then when I got off the freeway at his exit the DIC said 14.4 mpg. Once I got home I hooked up to my trailer, merged on the freeway and reset the DIC in the same place. I ended up turning around half way because it never got over 10mpg and knowing that it was a gradual climb over the next several miles to the exit, there was only one way the mpg was going to go - and it wasnt up.

People will say the DIC doesnt know what its doing, but the truck felt like it was working MUCH harder towing my 18' vs the 24'. EGT's were about 300* higher and the cubic fuel rate was about 40% higher too - so something was causing it to work MUCH harder.

So to me this narrowed things down to being the trailer. The trailer is about 2 years old now and has less than 3k miles on it - not even enough miles to see a wear pattern in the tires yet. Never curbed a wheel, hit anything, towed anything too heavy etc. I measured the alignment on it and everything is pretty dang close to spot on. The only two variances I found was that the rear axle has about 1/8" of toe in and measuring from center to center on the axles the driver side is 33-1/8" and the driver side is about 33-1/4". Measuring from the hitch to the out front of each tire on the front axle is even as well. Technically this isnt 'perfect' - but when I change the alignment on my car for the street vs the track it has never made mileage drop by anything notifiable - let alone 50%. So I'm not sure that the alignment of the trailer is the problem?

If its not the alignment on the trailer then the only other thing it could really be is that there's a brake dragging or something? When I pulled the brakes apart there wasnt any abnormal amount of wear or anything like that and they all spun nicely too? (bearings felt fine as well but regreased them for kicks while I was there anyways).

I made a joke to my GF that this is God's way of saying I need to buy a new trailer - unfortunately, she didnt think it was nearly as funny as I did... lol

Any ideas? I'm pretty much at a loss at this point?

 

[nskyline34]

Also I did tear apart the truck to be sure - trying to leave no stone unturned. I found out the unison ring was pretty stuck. I tried to move it by hand but it wouldnt budge. I had to pry it off with a screwdriver. It was stuck about half way or maybe a little less than half way (like the vanes were a little on the closed side of half way).

The scary part about this is that the VPS on my CTS2 was reading and sweeping from 0-100%. So does this mean that the CTS2 is reading the desired vane position and not the actual position?

I dont think this is my issue because if the vanes were stuck, hauling the heavier/larger trailer shouldve had even worse mileage.

Does anyone know how this could happen? Or could the vane solenoid be capable of pushing/pulling extremely hard? I mean I pulled out the sensor and the solenoid, had a buddy hold the turbo and I grabbed the unison ring and tried to spin it and I moved him instead of having the ring rotate even a fraction of a degree...

I really wish I could say to hell with it all and go get an L5P and an aluminum GN trailer... :roflmao:

 

[2004LB7]

I was wondering the same thing - thinking it was some kind of fueling issue. Rail pressure will hold steady under WOT from about 10mph to 100mph+, and Injector balance rates are all well within spec.

To make things more interesting I towed a buddies 24' enclosed trailer (same height and width as mine, just another 6' longer). Once I merged on the freeway I reset my avg mpg on the DIC and then when I got off the freeway at his exit the DIC said 14.4 mpg. Once I got home I hooked up to my trailer, merged on the freeway and reset the DIC in the same place. I ended up turning around half way because it never got over 10mpg and knowing that it was a gradual climb over the next several miles to the exit, there was only one way the mpg was going to go - and it wasnt up.

People will say the DIC doesnt know what its doing, but the truck felt like it was working MUCH harder towing my 18' vs the 24'. EGT's were about 300* higher and the cubic fuel rate was about 40% higher too - so something was causing it to work MUCH harder.

So to me this narrowed things down to being the trailer. The trailer is about 2 years old now and has less than 3k miles on it - not even enough miles to see a wear pattern in the tires yet. Never curbed a wheel, hit anything, towed anything too heavy etc. I measured the alignment on it and everything is pretty dang close to spot on. The only two variances I found was that the rear axle has about 1/8" of toe in and measuring from center to center on the axles the driver side is 33-1/8" and the driver side is about 33-1/4". Measuring from the hitch to the out front of each tire on the front axle is even as well. Technically this isnt 'perfect' - but when I change the alignment on my car for the street vs the track it has never made mileage drop by anything notifiable - let alone 50%. So I'm not sure that the alignment of the trailer is the problem?

If its not the alignment on the trailer then the only other thing it could really be is that there's a brake dragging or something? When I pulled the brakes apart there wasnt any abnormal amount of wear or anything like that and they all spun nicely too? (bearings felt fine as well but regreased them for kicks while I was there anyways).

I made a joke to my GF that this is God's way of saying I need to buy a new trailer - unfortunately, she didnt think it was nearly as funny as I did... lol

Any ideas? I'm pretty much at a loss at this point?

When you jack the trailer tires off the ground do they spin freely? Also you could try and measure the temperature of the drums with an IR temperature gun and see if any of them are dragging after a short run

 

[kiwilml]

Another thing, is the front of ya'lls trailers the same shape? Like flat nose vs v nose or something?

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[nskyline34]

When you jack the trailer tires off the ground do they spin freely? Also you could try and measure the temperature of the drums with an IR temperature gun and see if any of them are dragging after a short run

Great idea and I did measure. Avg was about 65* all around and the biggest variation between the highest and lowest was about 10* IIRC.

Jacked the trailer up and spun each wheel - the brakes are really loose so you dont even hear them drag. You can give each tire a one-handed half-assed spin and it will spin for easily 4-5 revolutions.

Another thing, is the front of ya'lls trailers the same shape? Like flat nose vs v nose or something?

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From an aero perspective my 18' is more aerodynamic as it has an 18" V-nose (so barely anything). My buddies 24' is nice and flat.

I got really nerdy with it last night and measured everything again with the alignment and I got that on the driver side the front wheel has about 1/16" toe in and the rear wheel has about 3/16-1/4" toe in. I was hoping for somehting more like, 1-1/16 of an inch so it would be absolutely glaringly obvious, but no luck. At about 1/8" this equates to approximately 0.4-0.5* of toe...

Since my truck is torn apart, I'm going to steal my GF's Cummins and do a baseline test run to get mileage, then I'm going to pull both front wheels off the trailer, strap the axle up and do a test drive, and then do the same with the rear tires off of the trailer. I'm hoping that one of these tests will yield something interesting.

I noticed yesterday that the outside of the tread on all 4 tires have some odd wear patters - almost like cupping or feathering (?). I was originally thinking this could be related to something with the alignment, but I was also thinking since its a tandem axle, when you turn, one of the tires will drag sideways more than another so I figured that would cause the wear. I was thinking maybe its due to under inflation, but I've never ran them more than 10psi off of max rated pressure, and the wear is only on the outside - not the inside too like it would be if it was low pressure.

Any other ideas?

 

[KyleC4]

Well I’m going to throw something out of left field here. If trailer mechanically appears ok, what about trailer wiring? Could something possibly be back feeding the circuits causing your truck to drive poorly......? That’s all I can think that would be different between yours and buddies trailer if everything mechanically on trailer is good.

 

[nskyline34]

Just did a drive down the usual section of freeway with my GF's Cummins - SOB got 15.3 mpg and it felt totally fine?! Then when I actually tried to get good MPG and set the cruise at 58-59mph vs 62mph, the damn thing got over 17 mpg... EGT's always stayed cool (approx 700-800) and the truck didnt feel like it was pulling a house (which mine usually does when I tow that trailer)

Now I'm wondering if KyleC4 is correct about the trailer wiring, or if it is indeed my truck. I'm not sure how I could go from getting 14.4 mpg with one trailer, grab lunch, hook up to another trailer and get less than 10. Is it possible that the vanes were working ok for the 24' trailer and then not working for hauling mine? Like they got hung up? I know its hard to speculate, but now I'm really anxious to get the thing back together and test it all out...

To Kyle's point, I'm going to go through the wiring on the trailer and check it out. Actually screw that - I'm just going to do a test drive without the damn thing plugged in and see how it goes. Then there's no power going to anything to possibly back feed or something. lol That will have to wait though until after this weekend though because I need to finish the turbo cleaning and porting and reinstall it...

This is definitely driving me insane...

 

[TheBac]

Try one thing at a time, otherwise you'll keep chasing your tail and you will end up in a tight-fitting white coat with wrap-around sleeves.

Duramax's are very sensitive concerning mileage and rpm, not mph. Under 2000 rpm makes a big difference.

 

[Bonestock]

We’re you cruising in 6th gear under load? If so drop to 5th and see what happens.

 

[NC-smokinlmm]

Bad thermocouple. Try another one and see if EGTS change.

 

[gmac32]

Make sure your MAF is reading correctly. That plays a big role