C5 A6 4.2 misfire in one cylinder.....
#1
10-09-2009, 11:43 PM
C5 A6 4.2 misfire in one cylinder.....
Here is the problem
2000 A6 4.2 ART engine code has been misfiring in cylinder 7. I have swaped coils, spark plugs and replaced the fuel injector. Nothing. Still misfiring in that cylinder. When driving on the highway, the car has a very noticable shake when the engine is under load until you left off the gas and then its smooth. Then when you start increasing the engine load, the shake increases. I am at a loss as to what it could be.
Any suggestions?
2000 A6 4.2 ART engine code has been misfiring in cylinder 7. I have swaped coils, spark plugs and replaced the fuel injector. Nothing. Still misfiring in that cylinder. When driving on the highway, the car has a very noticable shake when the engine is under load until you left off the gas and then its smooth. Then when you start increasing the engine load, the shake increases. I am at a loss as to what it could be.
Any suggestions?
#2
10-10-2009, 06:58 AM
Inspect your wiring just to be certain it's not crushed or burnt. Clean and tighten the Coil and injector terminals (scrape them a little with a nail file and use a small screw driver or pick to tighten up the female connectors then apply dielectric grease to them. Insure they are getting a very tight connection. I have cured a few misfires this way.
If it is not electrical or injector. Eliminate them by doing a noid test. For the coil I use a LED with a built in resistor $1.00 from radio shack. I stuff it in the harness between the ground and the trigger wires and watch it to see if it misfires. You can do the same with the injector. This will only tell you that it is actuating. Confirming that the wiring is OK.
Use a vacuum pump and determine if anything is leaking into the cylinder.Try stuffing a hose into the bottom of the cylinder after it has sat for a while, and suck anything that may be in there out. Does it smoke on start-up or any other time? Are you missing oil or coolant?
Inspect coolant for carbon and oil for water/white film.
Perform A Compression and leak down test. Do all the cylinders an bank 2 and compare them.
Follow the misfires via vag-com. When does it record misfires? How many and how often?
Pull the valve cover and inspect the Cam lobes. compare 7 to a known good cylinder and inspect the lifter buckets
After that you need to check the Valves, hydraulic lifters...meaning you will need to pull the head. It is possible you have a bad seat, bad guide, burnt, sticking or bent valve.
Lets hope it just a loose connection. You may not be able to detect it on idle. It's probably misfiring all the time.
If it is not electrical or injector. Eliminate them by doing a noid test. For the coil I use a LED with a built in resistor $1.00 from radio shack. I stuff it in the harness between the ground and the trigger wires and watch it to see if it misfires. You can do the same with the injector. This will only tell you that it is actuating. Confirming that the wiring is OK.
Use a vacuum pump and determine if anything is leaking into the cylinder.Try stuffing a hose into the bottom of the cylinder after it has sat for a while, and suck anything that may be in there out. Does it smoke on start-up or any other time? Are you missing oil or coolant?
Inspect coolant for carbon and oil for water/white film.
Perform A Compression and leak down test. Do all the cylinders an bank 2 and compare them.
Follow the misfires via vag-com. When does it record misfires? How many and how often?
Pull the valve cover and inspect the Cam lobes. compare 7 to a known good cylinder and inspect the lifter buckets
After that you need to check the Valves, hydraulic lifters...meaning you will need to pull the head. It is possible you have a bad seat, bad guide, burnt, sticking or bent valve.
Lets hope it just a loose connection. You may not be able to detect it on idle. It's probably misfiring all the time.
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