Engine/Transmission (1998.5 - 2002) High EGT Black Smoke and Running Warmer than Normal

[jeepit]

FWIW my buddy just replaced the lower boot under the oil filter area. His metal connections on the AC hose rubbed a small hole thru the boot causing increased smoke.

 

[Houser]

You can test your intake system for leaks by Shooting air into the compressor housing through the waste gate actuator elbow. Clamp some plastic over the compressor inlet to hold back the pressure. use one of the clamps from the intake elbow to clamp on the layers of plastic. preset your air regulator to 20 psi so you dont blow things apart.
I use a regular air gun and a peace of 1/4" hose then bend the hose to seal in the pressure while I look and listen for leaks. Just did mine. took about 15 mins.

Mike
Palmer, Ak.

 

[AH64ID]

Ever adjust your valves? You'll see the overlap.



I think you'll find some level of overlap on any piston-driven engine. Using the inertia of the exiting relatively higher-mass exhaust gas to help pull in a fresh air charge is more efficient than stopping the flow and restarting it. Even in a boosted engine, the exiting exhaust gas creates a relatively lower pressure inside the cylinder to help pull in the air charge and purge the spent gasses (or creates less of a restiction for them to enter anyway).



As far as the no soot thing, you are correct: in normal exhaust brake deceleration soot would be minimal or nonexistant. But as the engine nears idle and the fueling starts to ramp up again, or if idling with the EB on, there will be soot.



Your IAT increase after the cam install is a pretty cool observation. The aftermarket cams I looked into did increase overlap, and that is probably what you're seeing. I've also read about less boost and a less effective exhaust brake after a cam install, but that was from a company that didn't make cams, so take that for what it's worth. I didn't notice any change in either. What did you use to read the IAT?

I have an email into the company who ground my cam.



I still don't see overlap working on a motor where exhaust pressure is almost always higher than boot pressure, even if its just 1% higher.



My exhaust brake does show less backpressure now than before, but it feels the same or stronger. My theory on why the pressure is lower is that with exhaust valve open longer more exhaust stays in the cylinder, and thus less in the manifold and lower pressure. . but with more in the cylinder there is more air to compress and makes the braking stronger... Just a theory, as I really don't see how more exhaust duration can allow for a weaker exhaust braking scenario as they run off of exhaust flow.

 

[KBrennan]

FWIW my buddy just replaced the lower boot under the oil filter area. His metal connections on the AC hose rubbed a small hole thru the boot causing increased smoke.

I have not been able to pressure test it yet but my boots are very soft and gummy on the outsied. To be safe I ordered a new set form Stylin Motors. They are tested to 110 PSI so I think my 20-30 psi wont even tickle them. Even with over night shipping the entire set with SS clamps was only $238. Dodge wanted $174 just for one boot no clamps. You know these dealers could make thier companies more profitable if they didn't drive away customers by price gouging.

 

[PC12Driver]

I still don't see overlap working on a motor where exhaust pressure is almost always higher than boot pressure, even if its just 1% higher.

That doesn't jive. Any normally asperated piston engine has more pressure in the exhaust than intake, always. They all use some level of overlap to promote scavenging, and they're always woking against the pressure gradient.



You're focusing your microscope on pressure. Zoom out a bit and factor in mass (exhaust is heavier than intake air) and inertia. And how the exhaust valves are smaller than the intakes to increase velocity and the scavenging effect as the piston hits TDC and both sides are open.



Picture driving a boat up river. Pick up some speed and shut off the engine. Inertia will carry the boat upriver for a little while before it slows and eventually starts flowing back with the current. While inertia carries it upstream for that little while it still creates turbulence behind it, which is essentially water filling back into the void that the boat just left (an area of low pressure). The river current represents the positive pressure in the exhaust, the boat is the exhaust pulse, the engine is the piston pushing the exhaust out of the engine, and the turbulence is the low pressure caused by the vacating exhaust. Overlap takes advantage of that last little bit of inertia before the positve pressure in the exhaust (river current) wins and reverses the exhaust flow (boat).



When you think of the actual internal pressures going on in the cylinder and at the valves when the engine is running (several hundred psi), 10-20 psi difference between the exhaust manifold and intake manifold is really insignificant. Like I said above, pop the valve cover and take a look. It's pretty obvious that it exists in our engines.



And to actually contribute something to the OP's thread (sorry about the hijack), I agree with the others about looking for a boost leak. You could have a leak small enough that the turbo could still compensate. Peak boost would remain the same, but drive pressure (exhaust backpressure) will be higher. Black smoke and high egts would result. Since you're replacing the boots, now would be a real easy time to make a couple of caps and pressure test the intercooler.

 

[AH64ID]

Good points... I am waiting to hear back from the guy who ground my cam for confirmation.

 

[cerberusiam]

You're focusing your microscope on pressure. Zoom out a bit and factor in mass (exhaust is heavier than intake air) and inertia. And how the exhaust valves are smaller than the intakes to increase velocity and the scavenging effect as the piston hits TDC and both sides are open.

Sorry, you have that backwards intake charge is always heavier and denser than exhaust charge. If it wasn't the engine could not breathe correctly and would never run. The reason the exhaust valves are smaller is the same volume at lower density can flow thru a smaller area. .



A stock turbo on a 2nd gen doesn't create enough drive pressure to overcome the boost charge. Even a stock 3rd gen with much higher DP doesn't do that.



The cam profile on a 24V has little to no overlap and that occurs at the end of the exhaust stroke when the bulk of the exhaust is gone. The overlap just promotes better scavening so the intake air forces more exhaust out. Exhaust gasses never back up into the intake on an design. Pull the cam specs and see where the overlap is in relationship to crank position and its apparent.



Gas engines NEVER mix intake charge with exhaust charge. When that happens you get massive explosions in in the intake with things flying around. :-laf Only a hard parts failure will allow exhaust back into the intake on a turbo charge diesel.



Dirty sensors in the intake are almost always from using oiled filters and turbos leaking into the intake. An EB just makes it worse on a worn turbo by pushing pressure past the turbine and thru the bushings into the compressor. DP is high and there is no boost pressure to balance it.



If the IAT and MAP get fouled they don't read correctly and the engine over fuels. Simple as that. If your running an oiled filter get rid of it, otherwise your turbo is probably worn. Running 20-30 lbs on an HX35 is a good indication a boost leak is not at the root of the problem.

 

[KBrennan]

Well I put the new boots on and all the insides were as clean as a whistle. However there was some cracking on the inlet boot to the intercooler. it was also as soft as Charmin TP. Possible air leak there under pressure. getting the new boots on was an SOB. They did not squish like the old stock ones. New injectors are going on in the morning.

 

[KBrennan]

Ok here we go. This is what I observed after installing the 275RVs and new Inter coler inlet and outlet boots. Black smoke is only when I get on it. Let me know if this sounds good or should I be looking for more issues.



Load: 12,000 lb Fifthe Wheel

Amb. Air Temp 98

Altitude 6000 to 7000 feet

Relitive Humidity 25% avg



On Level to slight incline road w/AC on:

Boost 10-15

EGT 950-1150

Engine Temp normal



Up hill 3% to 5% grade w/AC on or off, 5th or 4th gear

Boost 20-28

EGT 1100-1250

Engine Temp High but still in the normal range

Revovery to to flat running temps was fairly quick. Maybe 45 to 90 secs. Maybe a bit faster



Down hill

Boost 2

EGT 250-400



Now I did notice that at the higher boost levels with lots of throttle there was a sound like russing fluid through a pipe comming from the drivers side that I have not heard before. Would this be the higher fuel flow for the new injectors? It goes away the second I come off the throttle.

 

[cerberusiam]

The numbers don't sound bad for conditions and altitude. With the extra fuel smoke is to be expected and as long as you it isn't smoking at normal cruise it should be good.



Doubtful you will hear anything in the fuel system that would create the noise you are talking about. Fuel delivery is measured in cc's and that would be hard to hear.



Could just be more air now that you have fixed the soft boots and added fuel. You might simply be getting to the point where the turbo is maxed and the WG is opening.

 

[PC12Driver]

Sorry, you have that backwards intake charge is always heavier and denser than exhaust charge. If it wasn't the engine could not breathe correctly and would never run. The reason the exhaust valves are smaller is the same volume at lower density can flow thru a smaller area...

No need to apologise. You're confusing mass and density. Not the same thing.

Remove fuel from the equation. The mass of the air going into the engine is equal to the mass of the air going out of the engine. The number of molecules doesn't change (mass), just how tightly they're packed.

Now add fuel back into the equation. On the intake side you have air only. The exhaust side has that same mass of air plus the fuel that was added, therefore the exhaust has more mass.

stock turbo on a 2nd gen doesn't create enough drive pressure to overcome the boost charge. Even a stock 3rd gen with much higher DP doesn't do that.

An HX-35/12 runs over 40psi of drive pressure to get 30 psi of boost, and the engine runs fine at those numbers. Obviously there's more going on than pressure differentials.

The cam profile on a 24V has little to no overlap and that occurs at the end of the exhaust stroke when the bulk of the exhaust is gone. The overlap just promotes better scavening so the intake air forces more exhaust out. Exhaust gasses never back up into the intake on an design. Pull the cam specs and see where the overlap is in relationship to crank position and its apparent.

"Little" and "no" are not the same. The 24v engines do have some. And yes, it does occur at the end of the exhaust stroke because the inertia of the exhaust leaving the cylinder is what helps pull in the fresh air charge. It doesn't "promote" scavenging, the whole reason it exists is to enable scavenging. You're thinking along the lines of a supercharged engine that is always running more psi in the intake than the exhaust. We're happy with 1:1 in our engines, but realistically we can get as high as 1. 5:1 (exhasut:intake) and still have a good running engine. The intake charge won't do much pushing by itself if the exhaust pressure is 50% higher.

Cam specs? Sure, I've looked at them when I was buying my cam. Notice that the higher-rpm cams for our engines have more overlap? Gotta keep the inertia of the gasses up for the high-rpm velocities.

AGas engines NEVER mix intake charge with exhaust charge. When that happens you get massive explosions in in the intake with things flying around. :-laf Only a hard parts failure will allow exhaust back into the intake on a turbo charge diesel.

Obviously a gas engine won't idle very well with 30psi of back pressure either. And diesels don't have fuel in their intake manifold. Let's keep this apples to apples.

Dirty sensors in the intake are almost always from using oiled filters and turbos leaking into the intake. An EB just makes it worse on a worn turbo by pushing pressure past the turbine and thru the bushings into the compressor. DP is high and there is no boost pressure to balance it. .

My intake boots are all nice and dry, as is my intake horn. My sensors will get soot covered. They were sooty after 20k miles with my exhaust brake on my new truck (not a worn turbo), and then stayed relatively clean for 80k miles with the exhaust brake off and my larger turbo on. The idea of getting dirty sensors from idling with an exhaust brake on is not new, or uncommon. Do a search.

If the IAT and MAP get fouled they don't read correctly and the engine over fuels. Simple as that. If your running an oiled filter get rid of it, otherwise your turbo is probably worn. Running 20-30 lbs on an HX35 is a good indication a boost leak is not at the root of the problem.

Not quite. A fouled MAP sensor typically sticks on the low side, preventing fueling since it "sees" low boost. A fouled IAT sensor will mess with the timing a little, since it is now insulated a bit with soot. Maybe you'll get a few degrees of egt swing, but nothing like the OP was experiencing. And our engines can run an HX35 to 40+ psi if the wastegate is tied down, so loosing 10-20 psi and still seeing 20-30 on the guage is very possible. 40-50psi of drive pressure and only 20-30psi getting to the engine? Yeah, that'll smoke and get a bit hot.

 

[cerberusiam]

You're confusing mass and density. Not the same thing.

Remove fuel from the equation. The mass of the air going into the engine is equal to the mass of the air going out of the engine. The number of molecules doesn't change (mass), just how tightly they're packed.

Now add fuel back into the equation. On the intake side you have air only. The exhaust side has that same mass of air plus the fuel that was added, therefore the exhaust has more mass.

Not confusing anything, just understand it better than you. The whole basis of your assumption is wrong and negates everything all the way to the end.



You cannot talk about mass unless you are also talking about flow thru the engine. Mass changes as does the flow characteristics. Since an air mass is defined by pressures and temp it is definitely different at each end. Yes, density also changes when the molecules are packed tighter. The tighter the molecules are packed the higher the density goes and the more the air masses. Thats basic physics.



A higher density mass will always overcome a lower density mass, again basic physics. The amount of fuel added doesn't even come close to the differences between and incoming charge at 100 degrees and the exhaust charge at 1000 degrees. Given the intake valves are quite a bit larger than the exhaust ones and they are backed by a higher density mass weighing more under the same or more pressures, there is no back feeding exhaust into the intake under normal circumstances.



Combustion actually removes molecules by changing their state so mass does change.



The overlap is not even close enough in size and timing to promote any exhaust in the intake. Otherwise all engines would suffer from this and thats just not true. You will find that a lot of EB setups don't have these issues. If what you are saying could be true, then every EB would cause the same results and every engine without would have the same issues. It just doesn't happen irregardless of a few opinions that thats the only thing possible.



At one time popular opinion was the world was flat. Guess that wasn't exactly true either.

 

[PC12Driver]

Not confusing anything, just understand it better than you. The whole basis of your assumption is wrong and negates everything all the way to the end.



You cannot talk about mass unless you are also talking about flow thru the engine. Mass changes as does the flow characteristics. Since an air mass is defined by pressures and temp it is definitely different at each end. Yes, density also changes when the molecules are packed tighter. The tighter the molecules are packed the higher the density goes and the more the air masses. Thats basic physics.

Tell ya what. I'll give you a couple links to read.

Mass

and

Air Density

Specifically the parts where mass has nothing to do with temperature or pressure, or that air density is defined by pressure and temperature.

Then get back to me about how you understand things better than I do.

 

[PC12Driver]

Now I did notice that at the higher boost levels with lots of throttle there was a sound like russing fluid through a pipe comming from the drivers side that I have not heard before. Would this be the higher fuel flow for the new injectors? It goes away the second I come off the throttle.

Some folks have described a boost leak as a sound of rushing water. I'd go back and double check all your clamps between the compressor and the intake horn. Also, take a peek at the intake horn gaskets (bottom and top of the heater grid) and any of the bolts on top of the intake manifold cover (the piece that the grid sits on). Those bolts run into the intake manifold, and if any are missing or loose, could be a source of a boost leak.



Your numbers don't sound too far off. Maybe a touch warm. But the rushing water sound, especially if it's new after messing with your boots, is certainly worth looking into.

 

[cerberusiam]

Tell ya what. I'll give you a couple links to read.

Mass

and

Air Density

Specifically the parts where mass has nothing to do with temperature or pressure, or that air density is defined by pressure and temperature.

Then get back to me about how you understand things better than I do.

You might want to post links that don't blow your theories out of the water. Continuing to assert 1000 degree air has more density than 100 degree air at roughly the same pressure is not doing your case any good.



Keep your misconceptions if thats what gets you thru the day.





Derail over. :-laf

 

[PC12Driver]

You might want to post links that don't blow your theories out of the water. Continuing to assert 1000 degree air has more density than 100 degree air at roughly the same pressure is not doing your case any good.



Keep your misconceptions if thats what gets you thru the day.





Derail over. :-laf

So to recap our physics lesson for the day:



1) I stated that the mass of the exhaust output is greater than the intake air charge.



2) You said I was wrong, because the intake air is more dense.



3) I corrected you, pointing out that mass and density are two different things.



4) You offer a counter explanation, again confusing mass and density.



5) I offer links to definitions and formulas showing no correlation between mass and density whatsoever.



6) You post again that I am wrong, and state that I am "continuing to assert 1000 degree air has more density than 100 degree air at roughly the same pressure. " Go back and read my posts. I never said anything remotely resembling that statement. I'm only supporting my original statement that mass and density are not the same thing.



Seriously, don't pretend to know more about air density than I do. My job is all about air density.



Tell you what, if you still believe that temperature and pressure effect mass, show me a formula that says so. Physics is pretty well defined, so there should be one if you're right. I'll give you a cookie if you do.



Or if you now understand the difference between mass and density, how they're not even a little bit related at the basic physics level, and that you obviously misunderstood the point I was trying to make because of your misuse of the terms "mass" and "density," then all is forgiven.



Oh, and :-laf

 

[Vaughn MacKenzie]

FWIW, soot in the intake area (under the intake plate) isn't unusual at all on trucks with exhaust brakes. . . the two trucks I've seen with EBs we've taken the intake plate off of were rather sooty in there, but the soot didn't travel beyond that point (the air horn was clean). Most certainly it blows back out the intake valves. Have read about many others experiencing this on this board over the last 10 years.

 

[KBrennan]

Ok here we go. This is what I observed after installing the 275RVs and new Inter coler inlet and outlet boots. Black smoke is only when I get on it. Let me know if this sounds good or should I be looking for more issues.



Load: 12,000 lb Fifthe Wheel

Amb. Air Temp 98

Altitude 6000 to 7000 feet

Relitive Humidity 25% avg



On Level to slight incline road w/AC on:

Boost 10-15

EGT 950-1150

Engine Temp normal



Up hill 3% to 5% grade w/AC on or off, 5th or 4th gear

Boost 20-28

EGT 1100-1250

Engine Temp High but still in the normal range

Revovery to to flat running temps was fairly quick. Maybe 45 to 90 secs. Maybe a bit faster



Down hill

Boost 2

EGT 250-400



Now I did notice that at the higher boost levels with lots of throttle there was a sound like russing fluid through a pipe comming from the drivers side that I have not heard before. Would this be the higher fuel flow for the new injectors? It goes away the second I come off the throttle.

The return trip had the same numbers. Now a strange thing. after Idroped the trailer and went for a run into town I noticed that when I hard excelerated and the boost went over 20# the rushing sound was not noticed. So I am thinking that rules out an air leak. if I can find a way to get the EGTs to drop about 200 degrees I will be very happy with the new injectors and the power output.

 

[cerberusiam]

if I can find a way to get the EGTs to drop about 200 degrees I will be very happy with the new injectors and the power output.

Upgrade the turbo compressor is about the easiest way. Actually, the numbers are not that bad. You should be able to run with those all day with no problems. Works on my 12V.

 

[PC12Driver]

The return trip had the same numbers. Now a strange thing. after Idroped the trailer and went for a run into town I noticed that when I hard excelerated and the boost went over 20# the rushing sound was not noticed. So I am thinking that rules out an air leak. if I can find a way to get the EGTs to drop about 200 degrees I will be very happy with the new injectors and the power output.

Don't sweat those numbers. You're pretty close to where my stock HO was. And if the factory is okay with those level of temps, then you're doing just fine. You're gonna run hot when you're pushing that much air with the 5ver. Remember, you can hold 1250 all day long (assuming your injectors are nice and balanced, and your pyro is accurate).



A larger compressor is not the answer in this case. It'll only help egts at high RPMs, and hurt anything else below. You'll find yourself downshifting earlier and more frequently in the hills. When towing, your "level ground" boost will be lower, and the egts will be higher. In the hills, you might see lower temps after the downshift. I've currently returned to the stock turbo after trying several combinations for this very reason. Towing performance and egt control is much improved. I'll see around 950* on flat ground with the 11k 5ver in tow (stock turbo, 275s, untapped Comp), so you're right in line with my temps.



What are you using for boost fooling?

I see you have a leveling kit. What size tires are you running?

What gear ratio do you have?