MAP sensors and such

[ChrisCNC]

Okay, I must be really tired...
what kinda freak thinks about MAP sensors all day?

Some comments made by Cody got me thinking about the MAP sensor on my truck, 2003, 7.3L Ford Diesel.

Since these sensors are only accurate to about 23 psi, what happens when someone upgrades the turbo? Pretty much any turbo upgrade will get you over the 23 psi point (why else upgrade?), won't the 38R's that are so popular now putting out 30 psi pretty easily? Does this mean that unless the MAP sensor is upgraded somehow, that the engine is actually running lean? Are there other programming points of interest that are available that will get you there instead of relying on MAP sensor readings?

And if one did upgrade the MAP sensor, you could no longer return to your stock tune, correct? This may not be an issue unless you're running something like the Gryphon/Edge unit where you're supposed to return to stock before you download anything. Doing so with an upgraded MAP sensor would effectively disable the engine.

Are the older trucks, like mine (2003), using a MAP sensor that is a dual cylinder pressure transducer? or are they running the newer MEMs Style Pressure Sensors?

I read somewhere that the PCM used to take a MAP reading before the engine was started to get an "atmospheric" base reading to compare post start MAP readings against. If this were true, wouldn't it be useful to stop the vehicle part way up a good climb so the MAP sensor could readjust itself for altitude? That be a good one, "...really officer, I had to pull over so my MAP sensor could recalculate for the current barometric pressure...":notallthere:
I guess it work as well as any other excuse.

I know, I know...get a life... :matt-roloff:

[dietoremain]

First of all you cant really make a diesel run 'lean' not in the way of a gas motor where it causes detonation and damage, etc.... and yeah I dont understand myself how bill tunes for over 23 psi or so(im sure he can chime in), but i do know that he removes the overboost code so you can get higher boost on the motor without the PCM gettin in the way... :P

[cleatus12r]

The PCM with factory tuning only cares about the first 12.76 PSI anyway. That's why it doesn't care if you're at 18 PSI, 24 PSI, or 8000 PSI. It will fuel the same after 13 PSI. The only reason the truck does not fuel more than what you're already getting above 13 PSI is that the stock injectors are giving all the fuel they can.

One more thing, why does everything that's not stock have to be an "upgrade"? It's only an upgrade if it works better than stock and FEW things work better than stock. "Upgraded" compressor wheels that are actually a "downgrade" in most instances and "upgraded" intakes that DO NOT give your engine more than an stock intake and usually feed your engine WARMER air are more like "downgrades". Seriously.

[ChrisCNC]

That's the type of information I'm after Cody, thank you! I'm very interested in this stuff and know very little about it all.

I'm starting these threads with little knowledge (obviously) so I appreciate it when you, Bill or others that really know how things work provide an answer. I'm interested in this and know little, I'd like to learn more. I know you guys are busy and don't have time to be a tutor (nor would you want to, probably I'm sure I'm probably 1 of about a bazzillin people wanting to glean information from you) So I REALLY appreciate any time taken to help me better understand what's going on. I'm reading other forums and articles as I have time, but it's not a very effecient method of learning since I have to weed through other self-prescribed experts that are really full of 'stuff' other than knowledge.

My premise (until your last post) was that:

- Given that engines run on fuel and air, there must be an optimal fuel/air ratio range. I assume that diesels have a broader range than gas but that if there is too much air and not enough fuel then the engine is running too lean and too rich if it is vice-versa.

- The MAP Sensor measures absolute mainifold pressure so it would be a likely place for a programmer to get their information to maintain the ratio with varying burdens on the engine. If a programmer wanted to attempt to stay in the ratio range through extended accels, extended towing or other engine loads then they would want a sensor (or sensors) that would provide them with the information they need throughout a targeted RPM range.

-If a provided sensor is unable to do this then I would think that it could be improved or "upgraded".

However, the stock injectors are typically maxed out at 13 psi, that would help explain why accurate higher boost numbers aren't all that critical and that the fueling strategy becomes pretty trivial at boosts exceeding this number. I'm sure you're still in a pretty optimal fuel ratio range well beyond that number too which really would take care of probably 90% of all typical driving. Is there a boost number that comes to mind that is beginning to be too much air and not enough fuel?

What psi's are bigger injectors good for (just rough estimates) like stage I, stage II injectors? I know that in gas engines, that rich/lean fuel mixes will act to lower/raise EGT's. Is the same true for diesel engines? i.e. when the engine is running under-fueled that the egt's go up? I've ridden in small planes where the pilots have individual control of the fuel mix to each individual engine cylinder and have a pyrometer on every exhaust port and while in steady flight will adjust the ratios to each cylinder until they have EGTs the same on all exhaust ports. Of course this is more critical because of altitude.

At what point in your opinion would it make sense to replace a stock turbo (other than because it was needing replaced because it was damaged)? Seems to me that the stock turbo would cover the needs of a lightly modified truck pretty well.

Thank you again,

[cleatus12r]

My premise (until your last post) was that:

- Given that engines run on fuel and air, there must be an optimal fuel/air ratio range. I assume that diesels have a broader range than gas but that if there is too much air and not enough fuel then the engine is running too lean and too rich if it is vice-versa. A diesel engine technically doesn't run lean as the power and speed of the engine are completely controlled by the amount of fuel injected. That's it. Idle A/F ratio can be anywhere between 65-80:1 and maximum power is usually between 16-18:1. Anything more than that is just smoke and heat. Too lean to fire will result in white smoke.

- The MAP Sensor measures absolute mainifold pressure so it would be a likely place for a programmer to get their information to maintain the ratio with varying burdens on the engine. If a programmer wanted to attempt to stay in the ratio range through extended accels, extended towing or other engine loads then they would want a sensor (or sensors) that would provide them with the information they need throughout a targeted RPM range. The PCM doesn't care about rich or lean. It doesn't know what the air/fuel ratio is, nor does it care. Basically, if the desired engine speed is 2000 RPM, there will be enough fuel injected to maintain that RPM based on load. That's it.

-If a provided sensor is unable to do this then I would think that it could be improved or "upgraded". No need as explained above.

However, the stock injectors are typically maxed out at 13 psi, that would help explain why accurate higher boost numbers aren't all that critical and that the fueling strategy becomes pretty trivial at boosts exceeding this number. I'm sure you're still in a pretty optimal fuel ratio range well beyond that number too which really would take care of probably 90% of all typical driving. Is there a boost number that comes to mind that is beginning to be too much air and not enough fuel? I wouldn't say that the stock injectors are "maxed out" at 13 PSI, but any pressure reading above 13 PSI will not cause the PCM to command any more fuel based on boost.

What psi's are bigger injectors good for (just rough estimates) like stage I, stage II injectors? It depends on the truck. Every truck will react differently to different injectors. At the point of installing different injectors, tuning will be critical to getting the most from the engine.I know that in gas engines, that rich/lean fuel mixes will act to lower/raise EGT's. Is the same true for diesel engines? Why do the exhaust gas temperatures go up when making more power in a diesel? i.e. when the engine is running under-fueled that the egt's go up? Don't apply gas-engine logic to a diesel. Lean mixtures in a gasoline vehicle are volatile and hot (up until the cylinder starts misfiring due to being too lean). Rich mixtures in a gasoline engine usually run cooler at the expense of being terribly inefficient. Diesels on the other hand are completely opposite.I've ridden in small planes where the pilots have individual control of the fuel mix to each individual engine cylinder and have a pyrometer on every exhaust port and while in steady flight will adjust the ratios to each cylinder until they have EGTs the same on all exhaust ports. Of course this is more critical because of altitude.

At what point in your opinion would it make sense to replace a stock turbo (other than because it was needing replaced because it was damaged)? Seems to me that the stock turbo would cover the needs of a lightly modified truck pretty well. I can't make the call on what point the stocker should be replaced. It's a judgment call on the driver. I plan on running my stock turbocharger until it blows and right now it's supporting 400 HP just fine. I'll be running hybrids on it one of these days. I like the stock turbo right now, but it does cause a good bit of restriction on the top end. I have run aftermarket turbochargers and components, but nothing more than drop-in replacements. I can say with absolute certainty that since my tastes are way different than everyone else, that sometimes "upgraded" turbochargers become HUGE "downgrades".





Don't think too hard about this. It's FUEL over TIME. More fuel equals more heat and more push on the top of the piston. Nothing more.

[ChrisCNC]

Thank you Cody! I really appreciate it.

Think I'll start investigating the fuel delivery side of things (I can just hear your excitement :yikes2:). I'd like to understand this side of it better. Sounds like a programmer would really need some accurate inputs from this side of things to do much good.

Thank you again, have a great week!