Unexpained MPG drop

[p-Bar]

And that should be pretty well regulated.

 

[petersonj]

One point of clarification for pete - barometers aren't calibrated for elevation,

Actually, I said,

barometers are usually calibrated to compensate for elevation at a specific location

Before my original response you wrote,

I'm only curious because I found the PID for ambient pressure at the ECM, read it out, and it was at 29.20 inHg today but the barometer was at 30.34 inHg.

I do not know where you live in Nebraska, but the lowest elevation in Nebraska is just under 1,000 feet above sea level. So, assuming that your source of the 30.34" hg barometer reading came from a typical source (example, the nightly news) and your elevation is at least 1,000 feet above sea level, then the PID reading of 29.20" hg for ambient pressure at the ECM would probably be correct.

Replaced the sensor - same pressure reported engine off or engine on Still about 1" Hg low.

Again, I think the reading is correct. If your 30.34" hg source is the reported station pressure (absolute pressure) from a nearby airport, then I can see your concerns, otherwise I think everything is normal.

- John

 

[TSimonson]

I got the baro from the METAR at Epply Airfield, that's why I was concerned. That should be the altimeter setting to get you at the correct elevation above sea level when you're on the ground (like the truck always is ). Obviously the ECM doesn't care about elevation, only absolute pressure to adjust fuel schedule.

Voltage to the harness checks good. 5.01V (found the range is 4.75 - 5.25V from Cummins). Time to look at the ECM end.

 

[PawsWet]

QNH from a METAR does not report absolute pressure. It is station pressure corrected to sea level. Said another way, it’s close to what an absolute pressure measurement would read if you were to dig a hole to the depth of mean sea level at the airport and measure pressure at the bottom.

KOMA (Eppley Airfield) is 985 feet above mean sea level. That’s close enough to 1” or 1000ft for diesel work. I don’t believe this pressure measurement is your issue.

 

[mfurrh55]

I got the baro from the METAR at Epply Airfield, that's why I was concerned. That should be the altimeter setting to get you at the correct elevation above sea level when you're on the ground (like the truck always is ). Obviously the ECM doesn't care about elevation, only absolute pressure to adjust fuel schedule.

Voltage to the harness checks good. 5.01V (found the range is 4.75 - 5.25V from Cummins). Time to look at the ECM end.

Did you find out what problem was? Just left tdr hanging!

 

[TSimonson]

So sorry - Haven't forgotten about TDR, but I have no progress to report. Lot's to do at "real" work and maintain the orchard on the side. I'm still working this, just not as actively. The one guy I'd been referred to is retired and moved out of state, so still looking for someone in the local area that may be able to help diagnose. Barring that, I might break down and get a Smarty S-06 and see where that leads. No other local options to flash a stock ECM back to stock. No one here can even talk to the 3rd gens. I will figure this bad boy out!

 

[TSimonson]

TDR Friends,
So after two job changes, a move, getting both kids out of the house happy, healthy and gainfully employed, I've finally had some time to look at this a little more. Here's the quick recap so no one has to read 6+ years of posts:
- 10/2014, 113k miles. Noticed a significant drop in MPG during last leg of the trip moving from NV back to NE - 17.3 to 14.7. Thought it was a bad tank of fuel. Low MPG persisted. Pre 10/2104, average MPG 16.0 (including lots of car hauling). Post 10/2014 (60k miles), average MPG 13.7 (hauled two cars a total of 50 miles).
- Immediately checked all the usual driveline suspects, no issues. Subsequently replaced one wheel bearing and a bunch of failing driveline u joints during routine maintenance checks.
- 3/2015, 119k miles. Replaced 48RE (reman) based on excessive noise. Took 3 days to flush the cooler, but it all ended up good. Filter has been clear since then. No change to MPG
- 8/2016, 131k miles. Replaced CP3 and injectors (reman) after finding a bunch of metal shavings in the return catch pan during a pressure test. Pulled the tank to clean and replaced feed tubes. No change to MPG.
Anecdotally, I think the EGTs are high (900s), even on freeway onramps empty. But I have no pre-2014 data to support.

So that's the summary until two weeks ago when the local diesel place got their chassis dyno back up and running. Brought the truck in for three runs, just for giggles. Two at 10% load and one freewheeling. I don't see any smoking gun, but I don't have any pre-2014 data to compare it to - usually the point of running a chassis dyno. But I'm kind of out of straws to grasp so I figured I'd give it a shot and see if anyone has another stock HO 600 to compare it to.

I think I'm a little short on torque between 1800 and 2000 RPM, but maybe what I was seeing online was an engine dyno, not torque at the wheels. So I'm also trying to filter through a few data logging runs I've made with my ancient Edge Insight CS. Just trying to figure out what's relevant among RPM, rail pressure, calculated torque, calculated HP, engine load, accelerator position, and boost.

If anyone has any suggestions, I'm all ears. If nothing else, I'm happy to post a stock chassis dyno curve for a 3rd Gen. Maybe it will make someone else feel better

 

[AH64ID]

Any idea what the correction factor and smoothing settings were on that dyno run? Thats much more than stock power to the wheels should be, so I’m guessing a skewed correction factor.

Got the uncorrected dyno? Should be around 285/520 to the rear wheels.

 

[TSimonson]

I should have included that last night - CF is 1.05. Don't have smoothing or the uncorrected dyno, and the shop didn't keep the data, only the screen shot. I was a little "disappointed". Totally agree the dyno shows way more than stock power to the wheels. The shop assumed I had a tuner, so they didn't question any of the results. I had a bunch of questions since I don't have a tuner. But without the actual data, I got no answers

 

[cerberusiam]

What gear was the run made in? Did you lock the TC and hold it locked? You will short on power low unless hold the brakes and spool the turbo before starting the run, have t make at least 12 psi to get full fueling at any rpm. Not sure what those load percentages were, definitely not engine or there was a massive correction factor.

 

[Tuesdak]

BTW, when I pulled the PRV there was significant "mung" on the inside of the valve (pic also attached). #ad

Looks like left over metal, but I haven't checked it - waiting for the fuel to evaporate in the 40 degree garage.

When this PRV dried up what did you find exactly? Any warranty on the work, CP3, or injectors remaining? This looks like it might be expensive. Debris left over in the rail and then injector hangs open from it is an engine meltdown nightmare. Maybe it wasn't anything, but, if it was I would pull injectors to be tested, compression test, leakdown test the engine while you are there just to be sure, and consider if the flushed items need to be replaced as flushing didn't cut it.

I would verify the lift pump is producing the required pressure say in case debris is clogging it's screen (if equipped). They can die many ways including low voltage to em. It wasn't clear if it was replaced with the CP3 or not.

Did you eliminate all exhaust leaks? The manifolds on these engines warp and leak. I went through two including warping the high end AFE Stainless Steel before I got a 2 piece manifold. Check the intake for leaks including debris punching a hole in the intercooler. I believe a smoke machine can be used for both. (I was looking for an unusual noise when I found the soot outlined leak toward the cab on #6.)

 

[TSimonson]

So as far as the dyno runs, I wasn't there when they ran them, but was told they were in 1st gear, WOT, TC locked. "10% load" is resistance on the rollers - last run at 0% was free wheeling. Just to be clear, I knew there was a low chance I was going to find a "smoking gun" from the dyno. I've always thought a chassis dyno was good for comparing changes based on mods / tunes, not absolutes. In other words, 'this tune added 7.5% max HP'. Since I can't go back in time and get a dyno run on my 2014 truck from the same shop, I can't show a change in performance. But like I said, I'm grasping at straws at this point. And when I got these graphs back, I was more interested in the torque curve. I was expecting something more like what OZY posted last year where torque peaks around 2k RPM then stays pretty flat until around 2800 RPM then dies.

I was more interested that my torque peaks around 2800 RPM. I thought that was odd, since no one ever drives there. Of course HP is going to climb since it's a function of torque and RPM, but I was always told torque was flat from "1600 to 2800". As you guys called out, there are a lot of variables, but I looked at that chart and thought TC might be a suspect. But if the consensus is the curves are "normal", even if the absolute values are wrong, so be it. I no delusions that I'm making 608.5 lb ft of torque at the wheels. I'm way more concerned I'm making 37% more torque at 2700 RPM than I am at 2000 RPM. That seems off to me.

So on a related note, like I said above, I've made more than a few data logging runs. Any suggestions on what might be relevant? I've been tracking RPM, rail pressure, calculated torque, calculated HP, engine load, accelerator position, and boost. Comparing a few pairs, I haven't found anything interesting yet.

 

[TSimonson]

Tuesdak - Sorry I hit post before answering your questions. So that "mung" turned out to be plastic. So yes, went back and had the whole fuel system looked at while I was there in the shop. Cleaned injectors by hand, new feed tubes, pulled the CP3, pressure and return lines, tank, no issues since. They're pretty good folks. No issues since then.

Lift pump was replaced under the recall in '09, but not with the CP3. Pulled it with the tank, no mung. Still 20k rail pressure.

I've seen the punctured intercooler you describe on a 2nd gen, but no leak on this truck. I did have a small leak at the turbo, but no leaks at the manifold. If seen that soot outline you describe though - dead giveaway.

 

[Timd32]

Looks like you are right on track middle of the pack.

https://www.fuelly.com/car/dodge/ram_2500

Sounds like you have a really nice truck and it's well cared for.

Good luck on the quest for MPG. If you happen to figure this out looking forward to how you figure it out.

 

[TSimonson]

Yep, after 7 years on and off chasing MPG lost overnight my wife and kids think I'm nuts. Maybe, but I'm stubborn too.

 

[Darkbloodmon]

Something like this would eat away at me too, explanations help me sleep but unresolved intermittent issues drive me insane.

I haven't read through the whole thread (yet), but are you on stock programing?

 

[TSimonson]

Yessir, stock tune. No tune ever applied.

 

[Tuesdak]

I wonder if you are using the A/C more now than you did in the past? I would get 21 MPG with the A/C off and 16 MPG with it on with my MT 2003 2WD. The engine fan locked up can suck fuel down quick.

 

[Darkbloodmon]

Just read through, not a bad read compared to my NV5600 saga....

I'm of the ECM camp. Has your ECM ever been flashed to the latest updated version with DRBIII?

I know its not an apples to apples comparison but I was chasing down a hanging idle on my 03 6MT, and a no input engine acceleration at idle. This prompted me at that time to do injectors (BBI). I had no change what so ever after new injector installation. So I ordered a new FCA from Genos, install it. Still no change at all.

At the time all this was occurring, I was flying blind without gauges, and I didn't have a full exhaust system. The exhaust had rusted out dropping a 4-5ft section of pipe off the end of my muffler while I was driving home from work one day. To the point, I didn't have a tail pipe to observe smoke color or haze and she was loud.

I cave, and take it to the local FCA stealership and ask for a re-flash on my ECM after telling them that the injectors are new as well as the FCA. It took them a few attempts to connect their DRBIII to my truck but they did finally and explained to me that "my ECM was so far out of date with software that it had not recognized a change in the FCA or injectors when they were replaced" I took this with a block of salt. But sure enough I didn't have a hanging idle, or engine acceleration at idle without input following the reflash to the latest updates.

I'd try looking for a specialist with the hardware and software or getting the DRBIII yourself if possible and flashing the latest updates before custom tuning. HP Tuners has some pretty good PIDS and data logging variables. I've seen some examples of it being used to trouble shoot by Optimal Welding, He supports EFI live as well.

 

[TSimonson]

So first, I want to thank everyone again for ALL the input. It's one big reason I love it here.

Tuesdak - So I've wondered that same thing, and gone weeks without using A/C to see if that made a difference. Zero difference.

Darkblood - I've been thinking along those lines for about the last 5 years. I also caved. Since I wanted to avoid the dealer, I brought it right to Cummins outside of Omaha. Made an appointment, gave them the VIN, then got there and they said they wouldn't even look at it - they didn't have a computer that would talk to it. That was 2016. So I brought it to a dealership. After wrestling with it for 2 1/2 hours, they came back and said their computer couldn't flash it. All their computer could get out of the ECM was the VIN. Apparently they had recently gone through an "upgrade" with all the other dealerships in the area and couldn't talk to the 3rd gens. Needless to say, it only reinforced my opinion of dealerships. I've been beating the bushes for a no kidding stock reflash since then, but no luck so far. I'll move that back up on the list - I appreciate the kindred spirit!