Question on speed-density airflow calculation
16 October 2003, 09:56 PM
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Ok first off this isn't Impreza related, but as most of the techies on here seem to have a good grasp of speed-density ECUs (i.e. no MAF) I thought this would be a good place to ask.
I have a 1994 Audi 2.0 bought for doing my daily commute, which has a bosch motronic speed-density fuel injection system. Recently it's started suffering a major power loss intermittently, the engine won't die (idles perfectly) but has so little power it won't go over 30MPH in any gear and won't rev over 2500 RPM with the foot to the floor and the car in neutral. This can suddenly occur then after some random time it goes back to normal and drives perfectly again.
Connecting to the diagnostic computer threw up a few faults, some of which were probably due to me disconnecting a few sensors trying to pinpoint the problem. The one which caught my eye was the throttle position sensor, I'm guessing that if this has an intermittent fault it may cause the ECU to have serious trouble working out the amount of airflow into the engine thus it won't supply the required fuel.
I have very little knowledge of speed-density systems so would like to know if the above symptoms are likely to be caused by a faulty TPS. I guess this sensor has a much more important function than it would with a MAF-based system. Would the car still run with the sensor disconnected (obviously with reduced power/drivability)? Is it wise to try cleaning it?
Thanks for any help
I have a 1994 Audi 2.0 bought for doing my daily commute, which has a bosch motronic speed-density fuel injection system. Recently it's started suffering a major power loss intermittently, the engine won't die (idles perfectly) but has so little power it won't go over 30MPH in any gear and won't rev over 2500 RPM with the foot to the floor and the car in neutral. This can suddenly occur then after some random time it goes back to normal and drives perfectly again.
Connecting to the diagnostic computer threw up a few faults, some of which were probably due to me disconnecting a few sensors trying to pinpoint the problem. The one which caught my eye was the throttle position sensor, I'm guessing that if this has an intermittent fault it may cause the ECU to have serious trouble working out the amount of airflow into the engine thus it won't supply the required fuel.
I have very little knowledge of speed-density systems so would like to know if the above symptoms are likely to be caused by a faulty TPS. I guess this sensor has a much more important function than it would with a MAF-based system. Would the car still run with the sensor disconnected (obviously with reduced power/drivability)? Is it wise to try cleaning it?
Thanks for any help
18 October 2003, 12:32 AM
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I know very little about speed-density airflow calculation...
I presume the ECU hasn't developed a case of Dyscalculia?
If not, then it's most likely a sensor of some description.
A TPS can be made easily as a potentiometer with a "wiper" on a resistive track. You could probably test it quite nicely with a miltimeter - set the throttle to various positions and measure the resistance.
My favourite idea is that there is something adrift with the MAP sensor. It could be a leaky pipe, or the sensor itself...
You'll probably find something useful here: I just googled for "speed-density airflow calculation"
http://www.sts.sae.org/membersonly/techinfo/articles/article5.htm
I presume the ECU hasn't developed a case of Dyscalculia?
If not, then it's most likely a sensor of some description.
A TPS can be made easily as a potentiometer with a "wiper" on a resistive track. You could probably test it quite nicely with a miltimeter - set the throttle to various positions and measure the resistance.
My favourite idea is that there is something adrift with the MAP sensor. It could be a leaky pipe, or the sensor itself...
You'll probably find something useful here: I just googled for "speed-density airflow calculation"
http://www.sts.sae.org/membersonly/techinfo/articles/article5.htm
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