I guess I'll have to try bogging mine next time I go for a tow and see what happens to the pyrometer. Kind of hard to bog with an auto except around 45-50mph in OD.

 

Doesn't work that way on a CR unless you drastically modfy the fueling curves.

Fueling is determined by APPS position AND boost AND rpms. If you cannot get an rpm rise you will NOT get a large fuel rise. You can mash the throttle all the way to the floor if you want and it will only fuel what the max table entry is for the parameters. Fueling is reduce by a percentage when rpms drop under about 2200 rpms, they drop a larger percentage under 1800 rpms, then drop even a larger percentage under 1600 rpms. You will always burn less fuel at 1600 as opposed to 1800 as opposed to 2500 no matter what APPS position is. Stock tunes seldom will push EGT's, thats the way they were designed. You can drive foot on the floor at 2000 rpms and never push the EGT's into a danger zone as long as boost can be maintained for the amount of fuel being delivered.

EGT's drop after shifting due to boost going higher not neccessarily due to less fuel. Works the same way with an auto as it does with a manual. If it can't maintain speed within a percentage of APPS movement the auto downshifts for better effect. With a manual the operator makes that determination generally when speed falls below acceptable levels. If you don't downshift a manual it just doesn't go.

 

I cannot really say one way or the other regarding how it 'technically' shoud work, my comment is strictly based on what I have seen in my gauges and driving, purely observational.

I also realize that since I do not have the privledge of access to the programming that is in firmware, I cannot analyze what is taking place when. All I know is that by downshifting to a lower ratio that is more capable of holding my speed, I get a lower EGT at a lesser pedal.

I have seen some fairly high EGT's before I have downshifted, maybe the pedal/computer is not allowing the fuel feed I am applying, but then, black smoke or black haze happens also, that IS a sign of unburned fuel or over fueling as far as I have read and been told.

I do know that boost DOES play a role, I just have not paid much attention to the boost at the time, so I did not give a reference about boost for that reason.

CD

 

See if you can add more air to it. If you can get some air to it it will help it out. I cut my air box and put a 3in pipe down behind the frunt bumper droped 200 on temp on the Egt.

 

I was really perplexed by the claims on this thread of low rpms = high egts. So on the way home Friday night I drove just fast enough to get it to drop into OD (~45mph on the straight and level) let off a little to let the RPMs settle in around 1200, slowly rolled on the fuel to get it to "bog" (sort of), and checked the pyrometer (about 850°), boost at near zero psi. Then I hit the OD lock-out, rpms jumped to roughly 1900, boost up to about 5-7 psi and..... (drumroll please) pyrometer dropped to 825°. Tried it several times with the same result. I guess it makes sense since boost (air) would cool the egts.

I guess I'm a believer now- but to the original point of the thread: This is only matters when towing heavy, and really only applies to manuals as far as I can tell (as it's hard to bog an auto, even when towing heavy). Obviously boost is what lowers EGTs, so just grab a lower gear, seems like a better solution than re-gearing the diffs. These trucks can run all day at 2900 rpm.

 

I put 4.56's in a truck and regretted it. granted it was a 6 banger dakota when i was in high school but it would have problems turning 33's so i went with 4.56 gears from 3.92's. it was expensive and killed my mileage (doubt it would kill your mileage) but in my honest opinion, I would drive on your 37's until they wear out and buy some 34-35 inch tires and upgrade your downpipe and intake to bring the egt's down.

 

Thanks for the report SOhappy. I know it's hard to bog an auto but it can be done. I would imagine some of the dearching stuff people talk about with autos is kind of in that bog or no bog stuff as far as the tranny is concerned. Easy to bog a standard when the only brain that downshifts is your own.


CD

 

Drop a gear get your RPMs up and your EGTs will drop and be considerably easier to manage. A regear would definitely help your issues with 6in lift and 37s, however you need to weigh your options.. How often do you tow vs unloaded driving... Mileage will suffer unloaded with a 4.56 gear set

Lugging the engine = trying to accelerate in too high a gear = High EGTs

Only sure way to lower the EGTs is back out of the fuel or drop a gear... simple

 

Yes your wastegate is kicking in and attempting to limit you boost. 24/25 sounds about right...

Your experience with dropping a gear and lowering your EGTs is the norm. The lower boost #s with higher RPM is also normal. Boost is a function of the load on your motor. In the lower gear your motor is not having to work as hard to pull the load so it produces less boost

 

I thought the wastegates on the HOs were set at 32 psi, and the SOs around 22 psi. My SO was about 22 psi until I did the boost elbow (), now I'm at 32 psi . That extra boost is a real kick-in-the-pants.