do our trucks have an oxygen sensor in the exhaust system somewhere? if so, where is it?

i know that most (if not all) modern fuel injected gasoline engines have oxygen sensors in the exhaust system to optimize the air fuel mixture in the cylinders, and also to optimize performance of the cataylsts (dual stage in most cars since the 90s (?)).

since our engines are fuel injected, i'd assume there's an exhaust oxygen sensor somewhere, but haven't seen one or heard one mentioned in this forum - or in my reading of the shop manual, for that matter.

then as a follow-on question (since there are definitely a bunch of experienced and smart guys out there in this forum), if there is no exhaust oxygen sensor, how exactly does our engine optimize performance/effeciency. i've read a thread or two referencing the PCM fueling strategy, but that was a while ago and, of course, i can't find those threads now.

just curious really, if anyone has the time to answer...

 

No 02 sensor.

The psd is fuel buy PCM, engine oil temp, and MAP sensor

 

That's not a dumb question at all. No, our diesels don't have an oxygen sensor and they don't need one. Let me explain. In a gas engine, the air to fuel ratio is critical to proper combustion. The O2 sensor in the exhaust reads the amount of oxygen in the exhaust and send a signal back to the engine computer that it uses to decide how much fuel to inject to keep the engine running at the optimal A/F ratio (the MAF sensor also plays into this calculation). In a diesel, the engine is designed to run lean all the time. If you looked at the intake setup of a naturally aspirated diesel, you would notice that there is literally NOTHING in between the filter and the intake valves. There is no throttle body, no carb butterfly, nothing. This is because the diesel engine will suck as much air as it can every time the piston goes through its intake stroke. The only variable in the combustion equation is the fuel. In essence, you mash the skinny pedal and your engine just adjusts fueling and nothing else. If the truck runs rich, it smokes, if it runs lean, nothing bad happens. That is one (very big) reason why the diesel design is so much more efficient. There is no restriction in the intake track whatsoever. That's also another reason why diesel engines are such great candidates for turbo charging. The more fuel and air you can shove in there, the more power you will make, and the proportions of the fuel to air aren't nearly as critical. Your oxygen sensor is the rear view mirror. If it is pouring black smoke, yup, it's running rich!

 

thanks for the explanation. makes perfect sense. though, i still contend that it was a dumb question - especially considering the fact that i'm a mechanical engineer and actually took a class in college called 'mobile power plants' - a fancy name for a class on internal combustion engines. however, that was many years ago by now and if i recall correctly - which i probably don't - the main focus was on stirling, otto cycles and the like and not too much on engine design itself. plus the prof wasn't the best. yeah, that's it - i'll blame it on him.

aaaaanyhow - anyone care to expound on what the MAP is and how it factors into the PCM's equations? i've read it referenced quite a bit lately, but don't actually know what it stands for. since its connected to the vacuum pump and the output side of the turbo compressor, i just assumed it was a differetial measurement on air pressure going into the cylinders, but that was just my assumption.

your explanation does make it make alot more sense to my as to how its possible to add so much power to these engines above stock. just pour in more fuel until you're running too rich, then get a bigger turbo to stuff more air in there. then rinse and repeat until you blow the heads off the block!

 

Hahaha, well that's about right, actually.

As far as the MAP sensor goes it is only connected to the intake plenum and just reads boost pressure and feeds back that information to the PCM so it can adjust fueling as the boost pressures change. It just helps the PCM fuel more efficiently at varying boost levels so it doens't just dump 75% of the capacity of the fueling system at 75% of the throttle pedal. It allows the fueling to be varied based upon the amount of air being forced into the cylinder.

For more on "mobile power plants" and some new (and some old) technology in that area, check out this series I worked on this past summer. Check out the series called "The internal combustion revolution" especially. That blog was a little hobby of mine when I had time to "tinker" with it.
Energy | tinkererstoolchest

 

MAP is Manifold Absolute Pressure. The PCM uses MAP as part of the calculation to know how much air is in the cylinder so that it can inject the proper amount of fuel.

 

again, thanks for the info, guys.

knowing about the MAP sensor function really makes me want to get my new turbo on there, as my current one has 2 bent fins (presumably from swallowing grit from the old stock airbox that used to be on there). with the fins bent backwards from their proper orientation, they're actually pushing air out of the intake, so getting a properly-functioning turbo on there should raise the MAP reading at a given RPM, telling the engine to pump more fuel. good to know.

nate - i skimmed your site there. very cool info. i'll have to follow the links on the site soon. that opposing piston design is particularly interesting. i was just visiting a military vehicle builder for work who uses detroit diesels almost exclusively. one of the engineers there turned me on to the 2-stroke detroit diesels - i forget the name now. no intake and no compression stroke - just a big old supercharger to cram air into the cylinder after the exhaust valve closes. and he was right, those engines really do scream when you step on the accelerator - twice the combustion events at a given RPM. cool stuff.

 

Here is some good reading ...

Ask a Mechanic - A deep look at the 7.3L Power Stroke

 

Thanks for the kind words, it was a whim that I entertained for a while. I have to be in the creative mood to write for it though, and lately I just haven't had the time or desire to do much writing.

Yeah the two stroke Detroit diesels are pretty impressive! There are a couple guys that run those in pulling rigs in the OSTPA tractor pulling circuit and they do sound pretty cool going down the track! From what I near the OPOC engines are one of the more promising up-and-coming engine designs right now and Navistar has actually gotten involved in the R&D, so the design must be gaining some traction.

I take it you have another turbo to put on or are you planning on rebuilding yours?

 

I do have another turbo - its used, though. its in good condition, but i'll rebuild it ahead of time and swap it on while i'm doing my tranny swap. figured i'll be doing a 3" downpipe and probably attend to the up-pipes then as well, so might as well get as much done as i can with the tranny out.

as for those 2-stroke diesels - i have no clue if its possible, but if/when my powerstroke engine bites the dusk, i'd love to get a hold of one of those 2-strokers to put in there. from what i hear - and it makes sense - emissions are very tough to tackle on those 2-stroke engines, so they're more or less limited to military and off road applications these days. ...or, as i see it, swap-ins for older diesel trucks not subject to newer emissions standards.

keep those write-ups going - you have a new reader... regarding your generator work - do you have any experience with the generator heads and the electronics? i have a F250 gas engine truck that won't be street legal come July, and i've been toying with the idea of turning it into a generator on wheels by hooking up to the PTO on the zf5 trans. i'm sure i'll never do it, but i'm also sure its possible to make it work with enough time (and probably lots of money)

 

Thanks, man. I do appreciate it.

If you have a turbo that you can rebuild ahead of time and just swap on, then it should be a pretty simple thing to do.

I do have some experience with generators and their electronics. I was an electrician by trade for 11 years, and while the generators weren't a part of what I did on a daily basis, I am familiar enough with the technologies and fundamentals that I am "good and dangerous" in that regard. I think it should be pretty easy to do what you're talking about, but you're going to need to have a gearbox in the equation somewhere. The majority of generator heads are designed to run at around 3600 RPM (60 hertz is 60 cycles -- or RPM a second). 60 cycles or RPM a second times 60 seconds is 3600 RPM (minute). So to pull that off, you have to either spin the output shaft of the PTO at 3600 RPM, which I don't think is possible with the PSD since its redline is lower than that, or you have to gear up that output to make it 3600 RPM. On a diesel genset, you either run the engine at 3600 RPM OR you gear up that engine speed to make it 3600 RPM. The easiest way of doing that is with the use of belts and sheaves. The nice thing about that approach is that you could gear the setup to work when you're running the engine at 1200 RPM. The 7.3 has more than enough torque to run a good sized generator head at that speed and it is still pretty efficient. I think I want to say that Navistar rates the engine to use something around 2/3 of a gallon of fuel an hour at that speed, which isn't bad for a big genset. Of course that depends on the load, etc, etc. The downfall of that kind of setup is that you're going to be looking at running multiple belts to handle the power you're going to be using. How many belts you need will depend on the size generator, but you can figure that out easy enough when the time comes. It sounds like a pretty cool project! If you ever do end up doing it, you will have to be sure to take lots of pictures and do a write-up on the process.

 

yes, if i ever do it, i will definitely document it.

from where i sit today, it seems like it would be a pretty simple set-up, though i say that in regard to alot of projects i've yet to start :-) then in reality, it takes me forever and costs alot more than i had hoped.

step one is the generator head - i'm not sure where to get a hold of a decent-sized 240V generator head. as always, i'd like a good, used one, but not knowing how to properly evaluate one, i'd probably have to buy new. the truck i'd be using for the base is actually a F250 5.8L gasser, so turning 3600 rpm all day shouldnt be a problem. that said, i looked briefly at PTO units for the zf5, and while they're pricey, there are some gearing options available. a belt (or more likely a chain) or a transmission of some sort would be required to mount the generator head up above the frame of the truck, though - assuming i can't sqeeze it in behind the trans next to the drive shaft. then, a presettable auxiliary idle controller would be used to keep the motor turning at 3600 (or whatever the geat setup dictates) under different load conditions.

if i got the setup working OK with the gas engine, i'd then be looking to swap the motor and trans for a diesel setup - because, as you point out - heating oil is just red dyed pre-ULSD diesel fuel and i'm sitting on a 1000 gallon oil storage capacity. even an IDI would be OK for this application, i'd think. ...or maybe a 2-stroke detriot diesel!

man, i wish i had time for all this fun stuff.

 

I guess something else that could work and may address several of those concerns at once would be to use a divorced transfer case behind the PTO. That would serve to do a couple things. One is that it would allow you to use a drive shaft to relocate the generator head to wherever you had room for it, the other thing it would let you do is that if you turned the transfer case around backwards (swapping the input and output shafts) you would be able to use it to gear UP the output shaft. Fuel efficiency being what it is, you would then be able to use the generator at a lower engine RPM. Using a divorced transfer case (a NP205 is a great choice) would allow you to do all of this pretty easily. I agree that an AIC would be the way to go to control the engine speed. On a diesel you could also get a custom chip that would have, in essence, a high idle setting at the speed you needed too.

For a generator head, I would decide what size you need and then watch Craigs List and stuff like that. Another good source for stuff like that (if you don't mind travelling to get it or paying to have it shipped) is GovDeals.com. They deal in government surplus items and they can have some great deals on things like this from time to time.

The possibilities are only limited by your imagination and budgets, . All it takes is time and money, right!?