Does pilot injection affect fuel economy?

[hobigusn]

I was just reading up on the differences between the 04 and the 04. 5. Does the pilot injection of the injectors or the extra HP of the HO CTD affect fuel economy? What has everyone been seeing?

 

[p-Bar]

I think the pilot injection you refer to makes the engine quieter. The 04. 5 up use 3 injection events the last is to keep the cat hot for emissions. Yes the mileage went down on these trucks . The best in my opinion is the 04 HO. Hope this helps others will chime in if I am wrong

 

[rscurtis]

The pilot injection may actually help FE. It's the post injection on the "600" and later engines that saps FE and helps to give that black oil that so many complain about.

 

[hobigusn]

I think the pilot injection you refer to makes the engine quieter. The 04. 5 up use 3 injection events the last is to keep the cat hot for emissions. Yes the mileage went down on these trucks . The best in my opinion is the 04 HO. Hope this helps others will chime in if I am wrong

I would agree, an 04 HO is best but im active duty in California. It's 04. 5 HO or i get stuck with the 04 235 hp. I'm going back to Michigan in a year so i could get a 04 HO but it would have rust on it and the Cali trucks look brand new. What to do?

 

[scootergmc]

I would agree, an 04 HO is best but im active duty in California. It's 04. 5 HO or i get stuck with the 04 235 hp.

That would be true if you're buying new six to seven years ago. Used '03-04 305/555 are out here, just check the engine stickers.

 

[GCroyle]

Go for the good looking rust free truck.



Salt belt vehicles can look good and be ugly in a just a few years. Former Buckeye native, lost several cars due to salt damage.



Do we see you as USN? it's buried in your signature, safe travels Sailor, thanks.

 

[rbattelle]

In my opinion, pilot injection probably has negligible effect on fuel economy - assuming the engine is designed to operate at a given bulk FAR (ratio of total fuel mass to air mass).

If we compare two identical engines operating at the same FAR during the combustion cycle, then I think the presence or absence of pilot injection is irrelevant to fuel economy.

If, on the other hand, we compare two identical engines operating at the same FAR, but introduce a late post-combustion fuel event into one of the engines, the net fuel economy of that engine will necessarily be lower (on an absolute basis) than the one without the extra post-combustion fuel injection, even if the post-combustion event occurs during the expansion stroke. It's harder to say what the fuel economy might be on a power-specific basis (power specific fuel consumption), since it would depend heavily on the timing of that third injection.

An interesting question, then, is if we compare two identical engines, one with 3 injection events (pre, main, and post), and one with only 2 (pre and main), operating at the same power output, which has better fuel economy?

This question is hard to answer definitively, since we don't really know the relative ratios of each of the 3 injection events on the one engine. Neither do we know where on the expansion stroke the third event occurs. Nevertheless, it seems "intuitive" that whatever the ratio and timing, that third slug of fuel would reduce fuel economy.

Ryan

 

[p-Bar]

In my opinion, pilot injection probably has negligible effect on fuel economy - assuming the engine is designed to operate at a given bulk FAR (ratio of total fuel mass to air mass).



If we compare two identical engines operating at the same FAR during the combustion cycle, then I think the presence or absence of pilot injection is irrelevant to fuel economy.



If, on the other hand, we compare two identical engines operating at the same FAR, but introduce a late post-combustion fuel event into one of the engines, the net fuel economy of that engine will necessarily be lower (on an absolute basis) than the one without the extra post-combustion fuel injection, even if the post-combustion event occurs during the expansion stroke. It's harder to say what the fuel economy might be on a power-specific basis (power specific fuel consumption), since it would depend heavily on the timing of that third injection.



An interesting question, then, is if we compare two identical engines, one with 3 injection events (pre, main, and post), and one with only 2 (pre and main), operating at the same power output, which has better fuel economy?



This question is hard to answer definitively, since we don't really know the relative ratios of each of the 3 injection events on the one engine. Neither do we know where on the expansion stroke the third event occurs. Nevertheless, it seems "intuitive" that whatever the ratio and timing, that third slug of fuel would reduce fuel economy.



Ryan

That's what I really meant to say. Thanks Ryan I always enjoy reading you "injections" on these threads

 

[jjdiesel]

That's what I really meant to say. Thanks Ryan I always enjoy reading you "injections" on these threads

I feel the same way about Sheldon's... uhhh, I mean Ryan's comments! Good job!

 

[hobigusn]

Go for the good looking rust free truck.



Salt belt vehicles can look good and be ugly in a just a few years. Former Buckeye native, lost several cars due to salt damage.



Do we see you as USN? it's buried in your signature, safe travels Sailor, thanks.

That's correct. Engineman (Diesel mechanic) second class active duty Navy stationed in San Diego. Still working on the signature, haven't found my CTD yet. Still looking and asking lots of questions on TDR.

 

[rbattelle]

That's what I really meant to say.

Things like this thread are interesting to think about, because there's always the quick, intuitive answer, but then if you think a little deeper it often opens up other questions.



Ryan

 

[cerberusiam]

The pilot injection may actually help FE. It's the post injection on the "600" and later engines that saps FE and helps to give that black oil that so many complain about.

Yes and no, and, not really.



Pilot injection is used on all the CR engines for emissions and NVH purposes, it doesn't have a large effect on economy.



The post injection event does impact mpg if you drive such that it is activated frequently, otherwise it does not play into economy or black oil.



There are other factors on the 600 that contribute far more than the 3rd event to the problems, chiefly injection timing and cam profile. The late injection timing pushes way more soot into the EGR effect and saps the available power. Both will slightly lower efficiency over the pre-04. 5 engines simply by what they are intended to do, lower emissions. The side effect is there is more soot dumped to the oil.



The CAT only needs 800 degrees or so to perform its function, its not tied to the 3rd event in any way. The 3rd event is triggered by load and rpm to counteract the emissions jump under those conditions. Its entirely possible to keep the CAT hot enough to do its job and still not get into activating the post event.



Trying to compare the 03-04 and 04. 5+ is problematic because the cam profile is different as is the electronic control. When you redo the mechanical differences and reset the injection timing the mileage is so close its hard to tell the difference. The post event really doesn't play a part then as long as you drive around it.

 

[hobigusn]

Yes and no, and, not really.



Pilot injection is used on all the CR engines for emissions and NVH purposes, it doesn't have a large effect on economy.



The post injection event does impact mpg if you drive such that it is activated frequently, otherwise it does not play into economy or black oil.



There are other factors on the 600 that contribute far more than the 3rd event to the problems, chiefly injection timing and cam profile. The late injection timing pushes way more soot into the EGR effect and saps the available power. Both will slightly lower efficiency over the pre-04. 5 engines simply by what they are intended to do, lower emissions. The side effect is there is more soot dumped to the oil.



The CAT only needs 800 degrees or so to perform its function, its not tied to the 3rd event in any way. The 3rd event is triggered by load and rpm to counteract the emissions jump under those conditions. Its entirely possible to keep the CAT hot enough to do its job and still not get into activating the post event.



Trying to compare the 03-04 and 04. 5+ is problematic because the cam profile is different as is the electronic control. When you redo the mechanical differences and reset the injection timing the mileage is so close its hard to tell the difference. The post event really doesn't play a part then as long as you drive around it.

I only have 2 choices in Cali for 04- 05 CTD. The 235 HP 04 or the 325 04. 5- 05 HO CTD. I find it much easier to buy in state then to try to buy a truck out of state. I was trying to see how badly the post injection affect milage and if it would be worth going out of state with all the hassle. So my thinking was that a 235 hp engine will have to work harder then a 325 hp engine to move the same truck. Work harder means useing more fuel. So which engine would get the worst mileage? Or am i just over thinking this?

 

[cerberusiam]

I only have 2 choices in Cali for 04- 05 CTD. The 235 HP 04 or the 325 04. 5- 05 HO CTD. I find it much easier to buy in state then to try to buy a truck out of state. I was trying to see how badly the post injection affect milage and if it would be worth going out of state with all the hassle. So my thinking was that a 235 hp engine will have to work harder then a 325 hp engine to move the same truck. Work harder means useing more fuel. So which engine would get the worst mileage? Or am i just over thinking this?

IIRC, if the vehicle has over 8000 miles all the Cali CARB stuff doesn't apply anymore. It should be the same as an in-state truck, pass the emissions test.



Trying to compare which one is the best is tough becuase it will vary with use. In certian circumstances the lower HP truck will work harder and get worse mileage. In other situations it will be better.



The 600 engins are easier to get more power out of and they have the better pieces to stand the EGT's. The 235 engines will be an SO with not all the valve and vlave seat updates and none of the better piston cooling of the HO's. Overall, they will get better mileage.



An 04. 5-05 is a good solid vehicle with very few problems. The plastic tank on the early 05's is the biggest gotcha but its just parts. The electronics on the 06+ are a bigger problem and can be annoyingly expensive. Your not gonna loose either way you go so make the best deal for what you want and like.

 

[HOBrian]

I feel the same way about Sheldon's... uhhh, I mean Ryan's comments! Good job!

That's funny right there!!!



You wouldn't think that came out of a 30 something year old!!



Always a joy to read your posts Ryan!!!!!