What am I missing - MPG

thermorex · **Posted:** Fri Dec 05, 2014 9:59 am

ArmyChief wrote:

thermorex wrote:

This is what he posted a while ago, for sea level:

17.5g/s is close to the factory 18.2g/s flow number and most likely the rocker arms are still in good shape.
Flow rates below 15 g/s most likely exhibit some degree of rocker wear. Below 13g/s and all the rockers are wasted.

Thanks sir, I'm assuming that's with EGR Closed, as EGR would lower those numbers.

That's a good question, since egr may kick in when engine is at operating temperature on a stock tune... I'd assume it's with his tune. Also, not sure if it measures flow, in which case it shouldn't matter...

ArmyChief · **Posted:** Fri Dec 05, 2014 10:22 am

thermorex wrote:

ArmyChief wrote:

thermorex wrote:

This is what he posted a while ago, for sea level:

17.5g/s is close to the factory 18.2g/s flow number and most likely the rocker arms are still in good shape.
Flow rates below 15 g/s most likely exhibit some degree of rocker wear. Below 13g/s and all the rockers are wasted.

Thanks sir, I'm assuming that's with EGR Closed, as EGR would lower those numbers.

That's a good question, since egr may kick in when engine is at operating temperature on a stock tune... I'd assume it's with his tune. Also, not sure if it measures flow, in which case it shouldn't matter...

MAF by definition is the sensor that reports ALL air entering the engine.

gmctd · **Posted:** Fri Dec 05, 2014 10:59 am

Test is performed at idle - EGR is never used at idle or any unloaded rpm above idle - 'nuther words, revving the engine gets no EGR

thermorex · **Posted:** Fri Dec 05, 2014 11:23 am

Cool, I thought egr is used when idle and light throttle and not when throttle heavier. Good to know.

Chief, what I didn't know is if by air, it's clean air or air with whatever it contains, including egr, (which from gmctd I get is not happening) I think it's last but I wasn't sure.

76Bronco · **Joined:** Thu Nov 06, 2014 9:57 am **Posts:** 18

Im curious how some guys claim 30-32 mpg. I know I wouldnt get that with a lift and larger tires than stock.

gmctd · **Posted:** Fri Dec 05, 2014 3:36 pm

thermorex wrote:

Cool, I thought egr is used when idle and light throttle and not when throttle heavier. Good to know.
EGR is used only when ECM senses conditons that produce oxides of noxious, based on throttle position, Rail Pressure, BOOST, rpm, gear range, time interval, coolant temps:
- high-power hi BOOST conditions, as in towing up grades
- heavy acceleration, as when towing
- rapid acceleration, as in full-throttle acceleration (yeah, you get it when showing-off, eh)
- deceleration at hiway speeds
- deceleration from hiway speeds, as in exiting down off-ramp to service-road speeds - towed loading increases application in these events due to extended deceleration intervals
- several other conditions involving variations of all\any of the above
- but not at idle - cannot even imagine a condition which would require exhaust dilution at idle
Besides, the MAF sensor is in the air filter box B4 the compressor inlet, which could not possibly sense normal EGR input
Chief, what I didn't know is if by air, it's clean air or air with whatever it contains, including egr, (which from gmctd I get is not happening) I think it's last but I wasn't sure.

thermorex · **Posted:** Fri Dec 05, 2014 4:39 pm

gmctd wrote:

thermorex wrote:

Cool, I thought egr is used when idle and light throttle and not when throttle heavier. Good to know.
EGR is used only when ECM senses conditons that produce oxides of noxious, based on throttle position, Rail Pressure, BOOST, rpm, gear range, time interval, coolant temps:
- high-power hi BOOST conditions, as in towing up grades
- heavy acceleration, as when towing
- rapid acceleration, as in full-throttle acceleration (yeah, you get it when showing-off, eh)
- deceleration at hiway speeds
- deceleration from hiway speeds, as in exiting down off-ramp to service-road speeds - towed loading increases application in these events due to extended deceleration intervals
- several other conditions involving variations of all\any of the above
- but not at idle - cannot even imagine a condition which would require exhaust dilution at idle
Besides, the MAF sensor is in the air filter box B4 the compressor inlet, which could not possibly sense normal EGR input
Chief, what I didn't know is if by air, it's clean air or air with whatever it contains, including egr, (which from gmctd I get is not happening) I think it's last but I wasn't sure.

Good info, thanks a lot!

thermorex · **Posted:** Fri Dec 05, 2014 4:46 pm

76Bronco wrote:

Im curious how some guys claim 30-32 mpg. I know I wouldnt get that with a lift and larger tires than stock.

There is a fellow Crd-er (crdjoe?), he said he got 40+ by folding the side mirrors and going a bit under 60 in 5th, even the trucks would pass him. Not sure what tires and pressure he had. Personally, screw the mileage, I prefer to drive my way. But getting 30+ is not uncommon, provided you go a long way with 70-ish, highway, very light acceleration and can keep a constant speed. Be sure you really know the odo errors, take a long trip and use gps for measuring the distance when you calculate the mileage.

Forgot to add, I have bfgoodrich ta ko 245x70x16, the max size that fits with stock suspension, and also have a bush guard and Mopar lights on the jeep, which doesn't help in aerodynamics, and still got a bit over 30. But I can only get that on long trips, regular highway commuting (work, mall, grocery store, etc) gets me about 23-25, summer, depending on traffic.

senatorjohn · **Posted:** Fri Dec 05, 2014 6:45 pm

The other sensor on the air box is there to measure air filter restriction.
If there is a large pressure drop across the air filter, this sensor reading is compared with the barometric pressure sensor in the ECM, and a fault code is set as far as I can work out, section 9 page 759 in the KJ service manual.

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

gmctd wrote:

thermorex wrote:

Cool, I thought egr is used when idle and light throttle and not when throttle heavier. Good to know.
EGR is used only when ECM senses conditons that produce oxides of noxious, based on throttle position, Rail Pressure, BOOST, rpm, gear range, time interval, coolant temps:
- high-power hi BOOST conditions, as in towing up grades
- heavy acceleration, as when towing
- rapid acceleration, as in full-throttle acceleration (yeah, you get it when showing-off, eh)
- deceleration at hiway speeds
- deceleration from hiway speeds, as in exiting down off-ramp to service-road speeds - towed loading increases application in these events due to extended deceleration intervals
- several other conditions involving variations of all\any of the above
- but not at idle - cannot even imagine a condition which would require exhaust dilution at idle
Besides, the MAF sensor is in the air filter box B4 the compressor inlet, which could not possibly sense normal EGR input
Chief, what I didn't know is if by air, it's clean air or air with whatever it contains, including egr, (which from gmctd I get is not happening) I think it's last but I wasn't sure.

It might be because you have a tune that you do not see much egr usage anywhere. A stock CRD will have EGR open at idle for 60 seconds, then it shuts off. This assumes a warm engine, below 20C coolant the EGR is off. At full load the EGR shuts off on the KJ or it would have trouble making boost and would smoke something fierce. EGR is used to varying degrees from idle to about 75% load and rpm 760-3500. The full load power curve is off the emission cycle and not regulated, thus calibrated to make plenty of NOx, while trying to minimize smoke.

gmctd · **Posted:** Fri Dec 05, 2014 8:29 pm

Seems like good input, and GDE should definitely know, but seems very odd that DCJ could get EPA certification by generating NOX, the very emission that EGR is designed to prevent in all passenger vehicles, incl 1500-series vehicles, and since 2002 in commercial vehicles rated 2500 and up - did they convince EPA that no-one would be accelerating quickly at full BOOST?

FYI, folks and gentle readers: NOX is generated at high combustion temperatures - EGR serves to reduce combtemps below NOX-producing levels

What's the object of EGR idle - quick cylinder\piston warm-up to improve cold compression temperatures? Seems like ECM would need to cut idle fuel to reduce black smoke during EGR injection, making for poor idle quality

GreenDieselEngineering · **Joined:** Sun Jun 07, 2009 5:10 pm **Posts:** 1111

The emission mapping is based on FTP75, SC03 and US06 test cycles. None of these operate the engine at full load. For BIN10 (what KJ CRD was certified to), when outside the test cycles the manufacturer can calibrate the engine as they see fit. In those regions it is tuned for power and low smoke.

The FTP75 has many idle portions on the test and with no egr at idle the engine still makes quite a bit of nox. NOx formation is mainly driven by the flame front speed as this controls peak firing temps. You can see 2200k even at idle in local regions in the combustion chamber. The best ways of slowing the flame front speed is reducing oxygen, retarded timing, and multiple pilot injections. Increased mixing in the chamber will also play a role (swirl rates, bowl shape, injector nozzle design), but this stuff is done early in the design phase.

gmctd · **Posted:** Fri Dec 05, 2014 10:26 pm

Ok, interesting stuff and I'm learning - gotta cook supper so I'll be back - but, first......

Folks and gentle readers, the Diesel engine pumps a full load of oxygen\nitrogen mix (atmosphere) into the cylinder on each intake stroke - compress that mix, inject a little fuel, burn a little oxygen, and we got idle - with a whole lot of oxygen remaining in the mix
(inject more fuel and we got power - inject a whole lotta fuel and we got a whole lotta power, but that's for later)

Because we injected a full shot of idle fuel (BPI), the flame front expands quickly (explodes), quickly raising combustion temps - hi temperature converts some of the remaining oxygen\nitrogen mix to nitrous oxide NOx, and we gots pollution - and that terrible rattle Diesel engines were so infamous for.....Before Pilot Injection and controlled burn with no explosive power

Now, here I understood Pilot Injection would control NOx at lower rpm, with small pilot injections to get the flame started, increasing fuel as flame progressed to max burn, then more small pilot injections to taper the burn off, ending combustion - EGR not necessary

naturist · **Posted:** Mon Dec 08, 2014 11:04 pm

PALiftedKK wrote:

seems like you are getting good mileage compared to every one else on this forum. I get around 12 city and 15 highway and off-road, and that's driving like a snail.

the only thing I could think of would be to reset the ecu. not sure if you have an electronic radiator fan but if not install one and that would take of a load on the engine.

clean off the MAF sensor.

you own a jeep, not a Prius!

Say what?

The only times I've EVER gotten 12-15 mpg was when I was towing a full size travel trailer, 5K lbs and 8 feet x 8 ft front wall. I get around 25 overall, and have gotten as high as 34.75 mpg when the wind was right. Those mileages are calculated by hand, btw, I don't even have the EVIC.

That said, with winter diesel, those figures will drop 10%.

What's more, I don't drive like a snail. On the open highways around here, 60-65 is all the faster the law allows.

user113 · **Posted:** Mon Aug 10, 2015 9:03 pm

thermorex wrote:

Since you have an arb bumper, would you mind answering a question? How much do you think the arb bumper will affect the front suspension ground clearance, more precisely, hat would be the difference between stock, plastic bumper and arb bumper in suspension "sagging", is it going to drop more than 1/2 inch?

Sorry, I didn't see this earlier. I have a Jeepin-by-Al Adjust-a-strut lift, too. I have not adjusted the struts after putting on the bumper. I did not measure the ground clearance, but the difference at the wheel arches is an inch and a half.

What am I missing - MPG

Who is online