Crossfire forum

 

I dont know if this is all that correct...

For example it says that the engine holds 6.1qts of oil... ? (with filter).

Correct me if im wrong but I thought that the engine held 8 to 8.5 qts... ?

Oh, and by the way, do non supercharged xf's have map sensors? (it says on this manual but I havent been able to locate it in the engine... ?)

 

That doesn't make sense. How could a forced induction motor use a MAP sensor. Kinda pointless like having vacuum assisted power brakes.

 

I believe in the earlier manuals it was a misprint in the 2005 owners manual is says 8.5 qts.

 

Yeah, I have AllData at work, and for my 04 it says 6 or 6.5. and it deffenitly took more. And Forced induction cars have MAP sensors, why not?

 

It is not pointless it is what everyone that has extremely modified forced induction cars ultimately want, less restriction and better air fuel management... Such as a AEM EMS system you get a map sensor and an air temperature sensor and you have the best air/fuel system there is and all with no intake restriction.

 

Without getting to technical, MAP stands for "manifold absolute pressure". These sensors compare vacuum reading inside the intake manifold to the outside atmospheric pressure, 14.7 psi at sea level. Many manufactures call them by other names but MOST cars have them and if you ever remove them or disconnect the vacuum source not only will you set a code and a check engine light your "performance" and idle will suffer. If you have a turbo or supercharger they typically are used to sense "boost" pressure, but some OEM's use two, one for vacuum and one for boost pressure, again, sometimes they use different names.

Greg

 

I think in another thread it seemed the Crossfire has both MAP and MAF Manifold Air Flow, strange if it's true.

MAP can be just as important on a NA engine as forced induction one, I suppose you could think of it as a measure of how much air the engine is trying to suck in - and so an indication of how much fuel is needed.

Actually I don't think it is essential to use either a MAP or MAF some systems seem to use just a wideband sensor, throttle position and rpm - they are not exactly tuned for economy or emmisions and usally run very "lumpy" cams that MAP sensors struggle with.

 

Crossfire forum

 

MAF stands for MAss Air Flow, and it's usually located on the plenum or ductwork before the air filter housing. It isn't used for sensing manifold pressure / vacuum, it senses the amount of air flowing into the air filter assembly.

 

Opps sorry, typed manifold cause I was also writing about MAP sensors in the post. Not much in the name Air Flow is the important bit.

Checked the service manual and the Crossfire does have both MAP and MAF sensors, wonder why they went for both.

 

errrr... what happened to the link?

 

Depending on valve overlap, engine vacuum is generated. The MAP sensor would be placed below the throttle plate and it compares the amount of vacuum to sea level pressure or whatever pressure you at from altitude if used with a BARO sensor. This comparison is in the fuel mapping within the ECM. Use of MAP sensors are known as a "Speed Density" system and aren't as efficient as a MAF or Mass Air Flow sensor the "counts" the incoming air and measures in grams/cm3. There are different types of MAFs like a Vane Air Flow and the hotwire that uses current to heat a resistor in the intake air charge and that charge cools the resistor. The current is then altered to keep that resistor at a specific temp. When I made the comment about the MAPs being useless in a forced induction environment, I stand by that for the simple fact that with a supercharger there isn't a vacuum. There is always pressure greater than one atmosphere within the intake plenum. In a NA environment, vacuum is greatest @ idle (normally 17-22 inHg) and then as the throttle plate opens (stepping on the accelerator) atmospheric pressure is let in equalizing the pressure above and below the throttle plate which is how that specific sensor "measures" air. It really doesn't measure air but extrapolates or makes a guess.

 

Vacuum will be present in the manifold of a supercharged car for considerable proportions of the engines operation, this is because the throttle restricts air admision. The difference comes when a NA engine is at wide open throttle, at that point the MAP gauge will read close to atmospheric, the charged engine will read boost from the MAP gauge. That reading will be used for fueling, ignition timing and diagnostics.

I think you underestimate the value of a vacuum (or more precisely differential in pressure) in metering fuel, a well set up carb isn't doing any "guessing".

Anyone know if the SRT uses a bypass in the manifold to reduce pumping losses at part throttle? (when there is a vacuum reading in the manifold).