High EGT's/High Boost/Vibration (OverFueling?)

[brickerd]

Hello everyone, this is my first post on here so if I screw something up, sorry. Anyway, I've got what I tihnk is a problem and may be for others with the vibration issue, but I hope someone can confirm or lead me in the right direction.



What I have noticed is that when I start the truck cold in the morning and travel for about 15-20min at highway speed the EGT's and Boost will slowly start to climb. The EGT's seem to be running around ~600 @ 70mph on flat highway normally; when this situation happens it will go up to ~900 and the boost will go from ~5psi to ~18psi. I've also tried to reset the overhead console to see what fuel consumption/MPG are and it goes from ~19 down to ~10 MPG, which seems like an overfueling condition to me. While this is happening the truck gets a vibration like it's out of time and at times it gets really bad. This also seems to get worse with a load on the truck. Then after about 10 minutes you start to drive out of this problem and things go back to normal. Strange huh?



I had the truck at the dealer yesterday to do the CO2 recall, check on the flashing "check engine" light recall, and this problem. All that they found was a code related to the "check engine" light flashing (like many people have) and reset it. They then called they Cummins support line and they said the the code in the ECM is stating that there is a low voltage on the pin that controls the Exhaust Brake; so they started to blame that since I have a PacBrake installed. I then informed them that the brake isn't using the ECM and is completely manual; so now they don't know.



Needless to say, I just drove the truck on the highway for the first time and I still have the problem, so does anyone have any ideas as to what my problem could be? Are these EGT/Boost numbers consistant with what others have? Could other people have this same sitation that is causing the vibration many people are seeing?





Thanks, Don



P. S. Sorry for the long post, just wanted to get all details down for everyone.

 

[Prairie Dog]

Welcome Don, The flashing check engine light does not normally cause a code to be stored, so if you have one there's some kind of real problem. I've never heard of anyone else having a problem like that, I hope they take care of you and make it rite.

Good luck,



Scotty

 

[brickerd]

Thanks for the info. What do you think about the EGT's? Do you know what is normal for running empty on flat land?

 

[Vaughn MacKenzie]

Your problem definitely sounds like the exhaust brake is engaging while you're driving. I would contact Pac-Brake and tell them about the symptoms you are having. Continuing to drive it with this issue probably isn't too good for your engine.



An EGT of 600 and boost around 5psi is normal for cruising. 18psi and 900 is what you'd expect towing a heavy load.



Vaughn

 

[brickerd]

Not trying to be agumentative, just trying to understand your logic. Why do you say "Your problem definitely sounds like the exhaust brake is engaging while you're driving. " The brake is either on or off (if spring is working properly) and you can really hear it when it's on. I even turned the brake on to verify this yesterday that when the brake is on the boost drops to 0 (I would assume it's because there is no airflow hence no turbo spin and no boost), alhtough the EGT's do jump right up to 1,000. Are you thinking that maybe the spring isn't functioning and it's allowing the brake to close partially? I think I mentioned it in my original post, but if not, my PacBrake is completely manual and not hooked into the computer at all, so I have to hit the switch to engage it.

 

[mbaston]

did you purposefuly not hook the pac brake to the ecm? It is my understanding that the new PacBrake is designed to work with the ecm.

 

[Mathew Clausen]

With the boost going up that high - there has to be extra load being applied somewhere. My A/C makes a slight vibration at certain speeds and you can notice a change in boost if you watch carefully - but I would think the belt would fry off before causing the engine to pull 18psi boost. I would expect as you found with the pac on - no boost - but maybe if it is partly on that would just put extra load and still allow increase boost to compensate. Can you mechanically block it somehow to verify (wire or a spacer or something)? Whatever is going on is taking some serious power!



Mathew

 

[brickerd]

I understand what your thinking. I'm thinking that it's getting to much fuel. More fuel, hotter temps. Hotter temps, faster air flow. Fast air flow, faster the turbo spins, and so on. Does that hold true and/or make sense to anyone? I did think about tieing the exhaust brake open just to make sure that wasn't it. I'm going to go out after work today and put on a tie-strap and test that. The only thing that makes me think is that if it was coming closed partially why wouldn't it do it all the time? I couldn't come up with an answer which is why I think it's electrical/computer related, or a sensor giving bad info to the computer.

 

[Mathew Clausen]

Keep in mind - with a diesel - the throttle IS the amount of fuel. You can't really "overfuel" (well - you can but that results in smoke). At a given speed - boost is a pretty good indicator of power output (at least relative output). You are correct in that boost will increase with more fuel, and you are correct that you are requiring more fuel than normal to run that speed. But - something has to be putting additional load on the engine to cause that. Brake drag? Seems like it would be really smoking. Fan coming on (you would hear that I think)? What else is there that would take big power?

 

[brickerd]

OK, time to ask a dunb question. What do you mean that the throttle is the fuel? Isn't the fueling still controlled by a computer vs. old cars where a throttle cable went directly to a carb? Isn't the computer saying that there should be x amount of fuel for a given throttle position with y amount of load? Granted that y may be increasing, which is what I think you are saying, but couldn't the thing (scientific term) that tells the computer that y is increasing be bad? I would assume that there are many sensors that tell the computer what y is, so couldn't any of them be bad?

 

[rbattelle]

The throttle position sensor tells the computer how much fuel (volume) to dump into the engine. I don't think it's a function of RPM. As load increases, RPM will decrease; no change in throttle position means the engine is now running rich, which will increase boost and EGT accordingly. Normally, the operator will recognize the engine is beginning to lose ground and increase throttle a bit to compensate and regain the lost RPM. I believe this is why many of us have noticed that as RPM increase, you have to continue to increase your throttle or the engine "peters out" at a specific RPM/load/throttle position. I've never seen a diesel fuel map, so I'm no expert on the control system... this is just the way I've come to understand it.



I agree with the previous posts that something (we don't know what) is loading your engine down. Have you noticed you need to apply more throttle (to maintain speed) as the boost and EGT climb? The extra throttle required could be very slight.



I'm interested in the results of tying off the exhaust brake... this problem is very fascinating. Please do let us know what happens in detail...

 

[brickerd]

Yes, I do have to increase the throttle to hold the same speed. I do think it is load dependant since the faster I go the worse it gets and if I have a load on it's worse.



I understand what your saying about load and I think tieing the brake closed will be a good test; but if the brake was opening at all wouldn't you think the boot would go down some instead of up? I basing this on the fact that if you turn the brake on normally, the boost will drop to ~0 right away and the EGT's go up right away; where as in this case they both start to go up. I don't know, just thinking out loud.



I will post when I find out more and/or as this issue goes along.

 

[MCummings]

Here's the deal.



1PSI Boost = roughly 11HP (on 2nd Gens)



5PSI boost would mean your truck is making about 55HP. That is a good number for flat land cruising.

(Turbo, and exhaust housings get this number all out of whack)



A sudden jump to 18PSI would equal 198HP (or depending where your boost sensor is, this could be all the way up to rated power)



You can't get 18 PSI without a good sized load, hill, or a fair amount off acceleration.



Are you sure that after 15-20 minutes of driving you aren't trying to hunt down and kill a PowerStroke on a hill?? That would explain the high boost and EGT.





JUST HAD AN IDEA



If your truck is an Auto, you could have the little valve swelling causing your auto to overheat and bindup (anti-drain back valve?), this would explain the vibration, high boost, and high EGT. It's taking alot of power to turn a sick auto.

If you don't have an auto, then,, nevermind



BTW: You can't go from 5 PSI to 18 PSI and not have either an increase in load (Hill/headwind), or increase acceleration.



Hope this helps.



EDIT: Just noticed you have a 6-speed... Maybe it's the gears binding up? Is there any extra noise when the truck needs alot of power to keep goin' ?

 

[rbattelle]

A partial restriction in your exhaust piping (such as that caused by a partially-closed exhaust brake) will increase boost initially, then decrease it to zero as the exhaust path closes to zero (or near zero). That's because the flow rate across the turbine drops so low that it can no longer rotate, and boost ceases. But, if you meerely restrict the exhaust a bit, load on the engine increases and RPM decreases, so you have a richer condition at the turbine. This causes an increase in turbine speed, and hence an increase in boost pressure. Then you notice that you're starting to slow down, so you give it some more throttle to compensate. That further increases boost and EGT until eventually everything equalizes at the new load. Later, something is happening to reduce the load and you notice a corresponding decrease in boost and EGT.

 

[Mathew Clausen]

With a gas engine - you control power by "throttling" the carb or fuel injection - i. e. open or close the butterflys which controls amount of AIR entering the engine. Then the computer (in modern cars) or carburator controls the amount of fuel to get the correct air/fuel ratio. On gas engines the air/fuel ratio target is constant (14:1 I believe). So if the sensors are messed up - you could have rich or lean condition that would make it run bad get poor mileage.



On a diesel - there is no "throttling" of the air. The intake is always wide open. The air/fuel ratio is not constant. Power output is determined by the amount of FUEL. At idle the ratio is very "lean". There is an upper limit of the air/fuel ratio - based on smoke and/or EGT's. A turbo just helps get more air in so that you can put more fuel without too much smoke or egt. On electronic diesels - the computer is looking at many things and controlling amount of fuel and timing (and pilot injections as well). But the end result is still that the power is controlled by the amount of fuel and the boost is relative to the power output (at a given speed).



Back to your situation - I could see a bad injector or timing or a plugged air filter causing higher EGT's (slightly) - but that would come with lower boost. To have higher boost along with that - I think something must be sucking power away somewhere.



Mathew

 

[brickerd]

Thanks for the Air/Fuel explaination, that helps clear up a few things in my head. I was trying to compare it to much to a gas engine.



As far as gears binding up, I don't hear anything different then I do normally.



As far as eating PS's, well not normally. I have a 1hr+ commute to work and I just put her on 70, and then kick back and listen to the XM radio. At least that's what I try to do. Lately I've been watching every gauge like my live depended on it to try and figure this thing out.



I understand the comment about the E-Brake closing partially, and it makes sense, but that part that still doesn't make sense is that it happen at roughtly the same time into the trip every time; although I've still going to tie it shut and see if I still have the problem. As much as I hate to think that there is something wrong with the PacBrake, I really want this to be fixed.



Thinking of another thing that I thought was normal, but maybe not from the replies. If I start out in 2nd (which I normally do while empty) and take it to 2200 and shift, then do the same for 2nd, I'm in the upper teens as far as boost. Now this is normal acceleration, not pushing it, but not babying it either. Of course it drops right back down as soon as I shift. Actually the EGT's do about the same thing, which I would consider normal since they both dorp real quick. Is this not normal? Should the EGT's not go up that high unless I'm loaded/pulling?

 

[rbattelle]

Before you head for work tomorrow, try to tie off the brake so there's no way it can close at all... that way we can at least eliminate it from the list of possibles.

 

[brickerd]

That's exactly what I want to do, although it won't be until Monday that I get to actually verify if it did anything or not since I'm not traveling to work tomorrow. I looked at the brake today and think I can tie it off to something to keep it closed. The other thing that I looked at if this is the problem, is being able to add the capability to also force it open with air, as compared to now when it just relies on spring pressure to open it up. I'm thinking that when I installed it I couldn't move it easly by hand where now I can, but I'm not 100% sure how it was originally.



I'll keep everyone posted as to the process, etc. of this problem. The dealer is also going to talk with their diesel tech tomorrow and give me a call to see if they can come up with anything.



I missed a question earlier, sorry. Yes, the PacBrake is compatible with the ECM, just like the Mopar Brake is. I had the brake originally wired through the ECM and didn't like the extended delay, etc. so I removed that and made it 100% manual, which seems to work out really good (at least for me). The only thing that I don't like is I have to wait for it to build up pressure. I want to add a storage tank so that I have instant braking. I also want to add some "real" air-horns at that time. Basically a summer project since I hate working in the driveway when it's cold out.

 

[brickerd]

FYI,



I tied the Pac-Brake closed over last weekend and have driven the truck twice since and I still have the problem. So I guess the good news to folks with the Pac-Brakes, is that it doesn't seem it caused the problem, which is good in my book also.



I've been working with the dealer on this issue and went to them on Monday evening so that they could equip my Truck with a "Co-Pilot" to record the situation so that they could see everything that was going on. This is something different for me. I had heard of these boxes before but had never seen one, let alone thought one would work on our TD's. Anyway after about 45min, they determined that they didn't have the right cable for the 03 TD and that they had to order one; so I get to go back next week and try to get it installed again. I'm just hoping that it will show something, I really don't want to continue with problem in case it's hurting the engine, etc. If they don't/can't fix it soon I may look at the lemon-law aspect. I've never dealt with anything with the lemon-law, can someone give me some advise on what I should do if I pursue that avenue?

 

[Marco]

It's the timing.

brickerd,

The problem you describe in your first MSG can be nothing else than the timing.



Sounds like the timing slips to retarded in some way at some point.



Lower timing ( less ° ) will raise the boost and EGT. Obviously even if the boost is higher you won't get more hp because the combustion takes place too late. Thus the need to increase the throttle to keep up the speed... .



You surely have a problem with a sensor ( Crank/Cam) or more likely with the ECM itself.



Marco