Does the ORM not work so well in hot weather? Bad EGR?

Bill.Barg · **Posted:** Wed Sep 12, 2007 12:14 am

Has anyone noticed that the ORM effect (better mileage) seems to not work as well at ambient temperatures above 90 F? Is this a sign of a bad EGR valve, perhaps?

I have been using the SGII to track inlet air temperature while using the ORM and without ORM. I note the EVIC ambient temperature and the engine water temperture as well.

With the ORM, the inlet temp does not change much from idle to cruise to WOT. The early data shows that the difference in ambient air temp and inlet temp (DeltaT) is not constant, however (it should be, I believe). On hot days above 90, the delta T is 50 F. On cooler days it is 30 F. I am suspecting that the unpluging of the MAF might not disable the EGR valve throttling all together ??? Maybe, once high exhaust temps are measured, it opens the EGR anyway, for instance. Or maybe my EGR is sticky and/or malfunctioning.

Without ORM the DeltaT is 72F with max value of 95F. The extra heat is from the exhaust gas recirculated into the intake, of course. I have noticed the Inlet air temperture vary quite a bit (cruising, WOT, idle). I have also noticed, during extended idle (5+ min), the inlet temp drop, in a matter of seconds, by 30 deg. I assume this is the EGR closing, but why? At least I know that the egr valve is actuating some amount.

One last comment on the ORM.... on my engine, the best I get in town is 20.5 mpg with the ORM and 18.5 without (EVIC readings). When the ORM is first done, and the EVIC reset, it seems like the mileage has gone way up (25mpg) and there is noticable increase in "driveability". After a time (100 miles), both effects seem to wear off. Strangely, when I put the MAF back on, it seems to improve driveability.

On a 300 mile roadtrip at 70 mph, with ORM, the mileage from ODO/gallons pumped mathced the EVIC at 22 mpg

In summary, I am really surprised with folks quoting 30+ mpg. I am trying to find out what is going on with my CRD, knowing that the dealership wont be much help. Something is fishy with my EGR valve, I believe, since the ORM does not work the miracle for me.

Any wisdom from you, CRD sages?

Threeweight · **Joined:** Mon May 14, 2007 5:57 pm **Posts:** 679

I've noticed that on long road trips I tend to get better mileage in the first hour than I do in subsequent hours (according to the EVIC). I chalked this up to the lack of a fuel cooler and warming temps of the diesel in my tank, but maybe it is EGR related.

W/ the ORM, my vehicle averages 28-30 on long highway trips (on a recent 120 mile trip, I was averaging 30-32 for the first hour, then 29-30 for the 2nd, all fairly flat interstate). This is while maintaining 64-65 mph (my CRD's economy drops dramatically as speed increases beyond 65).

My city driving is almost all stop and go, and I'm averaging around 20-21 there.

With a full load of camping/fishing gear, plus a Thule cargo box on the roof, I averaged 24-25 on a 600+ mile road trip last week.

All of this is w/ the ORM and 235/75/16 AT tires.

Bill.Barg · **Posted:** Wed Sep 12, 2007 1:11 am

Thanks for the info 3wgt.

Ya, the drop in mileage after the first hour is interesting. It is like the ECM makes a bad calculation based on temperature measurements.

You dont have a lift, right?

Maybe my 2" lift drops the mileage by 2mpg. My roof cage might be like your Thule box droping the MPG by 4 at 65 mph.

Bill

Threeweight · **Joined:** Mon May 14, 2007 5:57 pm **Posts:** 679

No lift (my 235/75's rub a bit at full lock). I was shocked at how big of a hit my relatively aerodynamic roof box had on my MPG.

Other factor I should have mentioned---all of this is with a brand new NAPA Gold air filter (replaced two weeks ago). I am convinced the intake system on these CRD's is way too restrictive. I doubt it made much of a difference, but the high highway mileage also came right after an oil change (6k miles on 0w40 Mobil 1 to a fresh sump of Rotella 5w40).

It would be interesting to compare an oil sample from your rig to that of another CRD, and see how much soot is being left in your oil.

nescosmo · **Joined:** Sat Jul 14, 2007 11:17 pm **Posts:** 202

Has any body tried to bypass the air cooler from the cac hoses, maybe the restriction will be gone by doing this.

That will be something very interesting to do.....

Does the ORM not work so well in hot weather? Bad EGR?

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