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One of the best electrical tests and mostoverlooked is called the voltage drop test. When a resistance check is called for, typically the factory troublecode charts will instruct you to check a ground for proper resistance, or check a wire for continuity. An ohmmeter is not always the best way tocheck for resistance. An ohmmeter isonly able to pass a couple of micro amps thru the circuit. This is not enough to truly gauge the trueresistance of a circuit or connection or component. The 996 models are now over 10 years old andwiring problems or ground problems are very possible to occur.
Let’s remember that unwanted resistancewill cause many electrical and engine performance issues.
The 996 and 997 are extremely wellengineered vehicles but are not immune to electrical issues that can be tracedback to resistance issues. An example ofhow resistance can affect a circuit’s current flow is as follows; if aconductor has 100 strands of wire and half of them are broken, the wire willnot be able to handle the current flow; the wire will heat up and become aload. This load will drop the availablevoltage and current. The end effect willbe a system or component that will not function properly or will not functionat all.
The engine management's sensors areextremely suseptible to high resistance problems. The end effect will usually be erroneoussensor signal outputs. If you have a badsensor ground, the sensor signal voltage will actually rise and cause inputsignals to become false and the Dme will output a wrong command.
A voltage drop test can also let us know ifwe have a connection issue, a bad connection will also cause a loss ofvoltage/current. With this test we canbegin to isolate what can be the cause of your electrical or engine performanceproblem. To perform a volt drop test wewould place a voltmeter across the suspected area in question, whether it is acomponent, connection, ground eyelet, or a section of wire. We must always check a circuit while it isoperational, basically on. The test isdone by measuring the difference in voltage between two points in the circuit.
The lower the voltage reading, the lowerthe resistance and the higher the voltage means that you have a definite high resistanceissue at hand.
If we recall ohms law that 1volt will push1 amp thru 1 ohm of resistance, you will see that if you raise the resistance,you will not be able to have the 1 volt and 1 amp flow thru the higherresistance. The voltage will be lostbecause the resistance becomes a light bulb basically. This relationship betweenvoltage, resistance and current flow shows that even the smallest amount ofextra resistance can and will have significant affect on the circuit.
Voltage drop Test: Ground side circuit
This test will check the ground circuit forhigh resistance, or an open circuit. Thetest is performed by measuring the difference in voltage between a point in thecircuit and ground. The circuit must bepowered. If the ground is bad, thecomponent will not function properly because a component or circuit requires agood ground to complete the circuit. Thereading will be a higher than normal voltage that is left over since thecomponent was not able to drop it all due to it not functioning properly.
Small current connections..........................0.0V
Large current connections e.g. fuel pump, headlights etc..........................0.1V
Ground connections....................................0.1V
High current cables, starter harness............0.3V
Switch or relay contacts..............................0.3V
Always test and don't guess.
Sebastian Vizcarra
http://meistertech.blogspot.com/
Let’s remember that unwanted resistancewill cause many electrical and engine performance issues.
The 996 and 997 are extremely wellengineered vehicles but are not immune to electrical issues that can be tracedback to resistance issues. An example ofhow resistance can affect a circuit’s current flow is as follows; if aconductor has 100 strands of wire and half of them are broken, the wire willnot be able to handle the current flow; the wire will heat up and become aload. This load will drop the availablevoltage and current. The end effect willbe a system or component that will not function properly or will not functionat all.
The engine management's sensors areextremely suseptible to high resistance problems. The end effect will usually be erroneoussensor signal outputs. If you have a badsensor ground, the sensor signal voltage will actually rise and cause inputsignals to become false and the Dme will output a wrong command.
A voltage drop test can also let us know ifwe have a connection issue, a bad connection will also cause a loss ofvoltage/current. With this test we canbegin to isolate what can be the cause of your electrical or engine performanceproblem. To perform a volt drop test wewould place a voltmeter across the suspected area in question, whether it is acomponent, connection, ground eyelet, or a section of wire. We must always check a circuit while it isoperational, basically on. The test isdone by measuring the difference in voltage between two points in the circuit.
The lower the voltage reading, the lowerthe resistance and the higher the voltage means that you have a definite high resistanceissue at hand.
If we recall ohms law that 1volt will push1 amp thru 1 ohm of resistance, you will see that if you raise the resistance,you will not be able to have the 1 volt and 1 amp flow thru the higherresistance. The voltage will be lostbecause the resistance becomes a light bulb basically. This relationship betweenvoltage, resistance and current flow shows that even the smallest amount ofextra resistance can and will have significant affect on the circuit.
Voltage drop Test: Ground side circuit
This test will check the ground circuit forhigh resistance, or an open circuit. Thetest is performed by measuring the difference in voltage between a point in thecircuit and ground. The circuit must bepowered. If the ground is bad, thecomponent will not function properly because a component or circuit requires agood ground to complete the circuit. Thereading will be a higher than normal voltage that is left over since thecomponent was not able to drop it all due to it not functioning properly.
Small current connections..........................0.0V
Large current connections e.g. fuel pump, headlights etc..........................0.1V
Ground connections....................................0.1V
High current cables, starter harness............0.3V
Switch or relay contacts..............................0.3V
Always test and don't guess.
Sebastian Vizcarra
http://meistertech.blogspot.com/
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c337cc
March 22, 2010 - 04:13 PM
Good point Sebastian. How have you been? I read that foolishness on the Rennlist Tony sent me. You can lead a horse to H2O but you can't make them drink. Howard
vizcarra44
March 24, 2010 - 04:49 PMc337cc, on March 22, 2010 - 05:13 PM, said:
Good point Sebastian. How have you been? I read that foolishness on the Rennlist Tony sent me. You can lead a horse to H2O but you can't make them drink. Howard
Hi Howard,
Long time,
I hope all is well in the good ol'south,
Regards
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