2.7T misfire diagnosis
#11
09-11-2009, 11:14 PM
Is this engine a 2.7t? or ??? (I assume 2.7t for now….)
I am probably getting “too basic” but will help to understand my thought process….
When t/s misfires keep in mind that each cylinder is an “engine” all by itself. It requires air, fuel and spark.
Air:
All the other cylinders are getting air. I can not think of anything that could stop you from getting air in only one cylinder without some other major problem.
Fuel:
#5 is in the middle of the left bank on a v6 engine. The fuel rail passes over it and #4 and #6 are getting fuel… so that only leaves the injector and the electrical signal to the injector. Could be -- but not really likely…
Spark:
Each cylinder has its own spark plug, spark plug “wire”, coil, “Ignition control module” channel and output from the ECU. (And wires between these items.) You say you have swapped coil packs and spark plugs. (I assume with “known good” items… you have 5 of each in your car!)
The only other “easy” item is the Ignition control module. (AKA igniter, final power module ect.) On my A6 2.7t these are located on top of the air cleaner. (They are attached to a heat sink that is cooled by the intake air.) Each module “controls” one bank of three cylinders. On my car, it is possible to swap the wiring without moving the modules themselves. Be sure to swap both connectors… they are color coded and the module should have the same color on both ends. If you remove the module, be sure to use some heat sink compound when reinstalling it. (Easy to find at computer shops as it is used on CPU’s.)
If you do this and the misfire moves to #2, you have found your problem. If it stays with #5, get out your wiring diagram and meter the next step is checking the wires. (Then fuel injector and finally the ECU.)
I am probably getting “too basic” but will help to understand my thought process….
When t/s misfires keep in mind that each cylinder is an “engine” all by itself. It requires air, fuel and spark.
Air:
All the other cylinders are getting air. I can not think of anything that could stop you from getting air in only one cylinder without some other major problem.
Fuel:
#5 is in the middle of the left bank on a v6 engine. The fuel rail passes over it and #4 and #6 are getting fuel… so that only leaves the injector and the electrical signal to the injector. Could be -- but not really likely…
Spark:
Each cylinder has its own spark plug, spark plug “wire”, coil, “Ignition control module” channel and output from the ECU. (And wires between these items.) You say you have swapped coil packs and spark plugs. (I assume with “known good” items… you have 5 of each in your car!)
The only other “easy” item is the Ignition control module. (AKA igniter, final power module ect.) On my A6 2.7t these are located on top of the air cleaner. (They are attached to a heat sink that is cooled by the intake air.) Each module “controls” one bank of three cylinders. On my car, it is possible to swap the wiring without moving the modules themselves. Be sure to swap both connectors… they are color coded and the module should have the same color on both ends. If you remove the module, be sure to use some heat sink compound when reinstalling it. (Easy to find at computer shops as it is used on CPU’s.)
If you do this and the misfire moves to #2, you have found your problem. If it stays with #5, get out your wiring diagram and meter the next step is checking the wires. (Then fuel injector and finally the ECU.)
#12
09-13-2009, 02:09 PM
4,5,6 all at the same time.
Check you harness. Disconnect terminals from the coils and run your hand back. It may have burned through on the manifold or have been pinched in a previous repair.
Measure your voltage at the coil and check your power at the ECM. There are several terminals in the ECM box that could have loosened or corroded, so pull them and check each one. I pinch the terminals by inserting a tiny screw driver so they are tight and apply dielectric grease when I reinstall them.
It sounds to me like a wiring issue. Keep in mind that continued use with low voltage to the coil packs might end up causing them to fail too.
Check you harness. Disconnect terminals from the coils and run your hand back. It may have burned through on the manifold or have been pinched in a previous repair.
Measure your voltage at the coil and check your power at the ECM. There are several terminals in the ECM box that could have loosened or corroded, so pull them and check each one. I pinch the terminals by inserting a tiny screw driver so they are tight and apply dielectric grease when I reinstall them.
It sounds to me like a wiring issue. Keep in mind that continued use with low voltage to the coil packs might end up causing them to fail too.
#13
09-14-2009, 05:57 AM
This is why you should not highjack threads
pain777,
Here is an example of why it is not a good idea to tack your problem onto a old thread. Jackmup has just given great advice for the original problem (Misfire on the whole bank) that may or may not help you with your problem. It is normally a good idea to start a new thread for a new problem to lower the confusion level.
For a SINGLE CYLINDER MISFIRE, the harness IS a possibility. But there are other more likely possibilities that should be worried about first.
My vote is on the Igniter.
Here is an example of why it is not a good idea to tack your problem onto a old thread. Jackmup has just given great advice for the original problem (Misfire on the whole bank) that may or may not help you with your problem. It is normally a good idea to start a new thread for a new problem to lower the confusion level.
For a SINGLE CYLINDER MISFIRE, the harness IS a possibility. But there are other more likely possibilities that should be worried about first.
My vote is on the Igniter.
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