Misfire on all cylinders
06-23-2007 | 11:19 PM
#31
Burning Brakes
Joined: Feb 2006
Posts: 1,128
Likes: 0
From: Chicago area, IL USA
Paul - think of the regime that the engine is running in when you're at the track. If you're aggressive, you're in the upper 1/3 of the rev band, spending most of your time at or near WOT.
Heck yes, you're going to use a lot of fuel. We can do the math if anyone wants to... but we can only do a theoretical calculation, bc we don't know everything that the DME knows in real-time. Tight air/fuel ratio control is critical to ensure proper catalyst operations, but depending on engine temp and load, the "proper" number can vary a lot - from 10:1 to 18:1. We can't solve this multivariate equation easily (but the computer can!) - so the theoretical math will be for a single state and not representative of the real car on a real track (especially with me driving :-).
And - in terms of the onboard computer's calculations - why would they be incorrect? The DME is firing the injectors as required to maintain proper engine parameters per its fuel mapping and real-time sensor inputs.
I'll go out on a short branch and say that the MPG calculation input data probably comes from the DME. Since the DME knows _exactly_ how much fuel is being used - why would it lie to the display?
Sounds like Conspiracy Theory to me. Doesn't make sense in such a tightly controlled environment. The car gets acceptable - no, actually - really great gas mileage under light use and on the open road at legal speeds. My PCM display trip summary synchs within a fraction of a gallon with the pump when I fill up. And yeah, I know that most US gas pumps are corrected to 60 degrees F - so I could be getting "shorted" a bit when I fill up in the summer heat.
If I drive like I'm on fire, I get single digits. Also, I think that you'll find that instantaneous mileage numbers when accelerating through 160 mph are also in the single digits...
But I get 27 on the freeway at 70 in 6th. :-)
Heck yes, you're going to use a lot of fuel. We can do the math if anyone wants to... but we can only do a theoretical calculation, bc we don't know everything that the DME knows in real-time. Tight air/fuel ratio control is critical to ensure proper catalyst operations, but depending on engine temp and load, the "proper" number can vary a lot - from 10:1 to 18:1. We can't solve this multivariate equation easily (but the computer can!) - so the theoretical math will be for a single state and not representative of the real car on a real track (especially with me driving :-).
And - in terms of the onboard computer's calculations - why would they be incorrect? The DME is firing the injectors as required to maintain proper engine parameters per its fuel mapping and real-time sensor inputs.
I'll go out on a short branch and say that the MPG calculation input data probably comes from the DME. Since the DME knows _exactly_ how much fuel is being used - why would it lie to the display?
Sounds like Conspiracy Theory to me. Doesn't make sense in such a tightly controlled environment. The car gets acceptable - no, actually - really great gas mileage under light use and on the open road at legal speeds. My PCM display trip summary synchs within a fraction of a gallon with the pump when I fill up. And yeah, I know that most US gas pumps are corrected to 60 degrees F - so I could be getting "shorted" a bit when I fill up in the summer heat.
If I drive like I'm on fire, I get single digits. Also, I think that you'll find that instantaneous mileage numbers when accelerating through 160 mph are also in the single digits...
But I get 27 on the freeway at 70 in 6th. :-)
06-25-2007 | 01:55 PM
#32
Rennlist Member
Joined: Aug 2006
Posts: 9,050
Likes: 1,781
From: Chicago, IL
When you're cruising on the highway getting 20+mpg, you're using maybe 60 horsepower. When you're at the track, you're using 300+ horsepower. Five times more fuel consumption. Do the math.
Last edited by Mike Murphy; 06-25-2007 at 04:09 PM. Reason: misspelling
06-25-2007 | 02:18 PM
#33
Instructor
Joined: Nov 2006
Posts: 105
Likes: 0
From: rhode island, usa
just had a check engine light on my 97 tt not long after I topped off with Mobil after using sunoco 93. Turned out to be a bad or fouled #1 plug which triggered the fault code I don't know if there's a difference in these fuels. Anyone know?
Pete
Pete
