Spark Coils, trying to pass info along
#1
03-29-2014, 10:21 AM
Spark Coils, trying to pass info along
Hello all, I have a 95 X300 purchased 2007 with 57k miles. This one went another 60k with minimal problems. At that point the coil pack problems started. I am an EE and avionics aircraft tech with excellent electronic shop available. My usual was to send the cat to the local Euro shop and not deal with it myself. After many events of stalling, transmission light on (replaced TCM) and terrible mileage I purchased a OBDII USB converter and started analyzing codes. To make a long story short, bad coils do not necessarily make a code show up. After spending better than 2k on parts and repair over the last 3 years I would like to pass along what has been found.
The X300 coil system has several issues related to the high voltage circuit (secondary coil). First item is that when installing a coil one must must make sure that there is a little springiness about .050 to .100 before screwing down the coil to the cover. If there is not any springiness then the tip of the coil pin is not touching the tip of the spark plug thus making a second gap for the spark to jump over. NGK seem to be OK but from experience Champions are a bit shorter. To use Champions it is necessary to make a small spacer to fit under the spring inside of the coil boot. Thickness of spacer is .31 and dia is .375 This extra secondary voltage needs to be supplied by the coil which will destroy the coil Note that there are may be burn throughs on the rubber coil boot for these. Also a note to replace rubber O rings on the cover to preven oil pooling around the spark plug. (I know everybody already knew this)
Another item, it appears that new and used coils showing open (greater than 1 megaohm) secondaries (measure from spark coil tip to one of the two primary pins) do work for a while. Apparently open secondary coils can spark over for many miles and still operate. When the spark over problem continues to excessive misfire, ie MILight comes on when serious misfire occurs then the secondary spark over is bad enough to need replacing the coil. Yes, the secondary spark current is reflected back to the computer because of this design. NOTE because of this circuit, secondary spark overs that cause low engine stoppage (ie up to 1500 rpm) are in fact causing an engine processor reset. This condition is the cause of many driving secondary issues. Quitting while idling is very annoying and without any codes never seems to get solved. Some misfires are so bad as to trick the TCM so another $wild $goose $chase to search for these.
The OEM coils seem to have as many secondary problems as the cheap aftermarket units. Last road trip $500 repair installed a Beck Arnley replacement. A check of the secondary coil resistance shows a few thousand ohms, looks like somebody at BA is paying attention to the design of the secondary coil. Price for these on ebay was noted at about $80.
Conclusion, the coil problems are costing all of us a lot of time and money. The codes do not correctly show failed coils until they are essentially dead. Complications of transmission computer, oxygen sensors, and other items such as catalytic converters, brake problems because we need to keep the engine revved, are involved potentially thousands to repair. Moral of the story, if in doubt buy a few new coils and start swapping or buy a whole new set if $$ is available.
Best;
Greg
The X300 coil system has several issues related to the high voltage circuit (secondary coil). First item is that when installing a coil one must must make sure that there is a little springiness about .050 to .100 before screwing down the coil to the cover. If there is not any springiness then the tip of the coil pin is not touching the tip of the spark plug thus making a second gap for the spark to jump over. NGK seem to be OK but from experience Champions are a bit shorter. To use Champions it is necessary to make a small spacer to fit under the spring inside of the coil boot. Thickness of spacer is .31 and dia is .375 This extra secondary voltage needs to be supplied by the coil which will destroy the coil Note that there are may be burn throughs on the rubber coil boot for these. Also a note to replace rubber O rings on the cover to preven oil pooling around the spark plug. (I know everybody already knew this)
Another item, it appears that new and used coils showing open (greater than 1 megaohm) secondaries (measure from spark coil tip to one of the two primary pins) do work for a while. Apparently open secondary coils can spark over for many miles and still operate. When the spark over problem continues to excessive misfire, ie MILight comes on when serious misfire occurs then the secondary spark over is bad enough to need replacing the coil. Yes, the secondary spark current is reflected back to the computer because of this design. NOTE because of this circuit, secondary spark overs that cause low engine stoppage (ie up to 1500 rpm) are in fact causing an engine processor reset. This condition is the cause of many driving secondary issues. Quitting while idling is very annoying and without any codes never seems to get solved. Some misfires are so bad as to trick the TCM so another $wild $goose $chase to search for these.
The OEM coils seem to have as many secondary problems as the cheap aftermarket units. Last road trip $500 repair installed a Beck Arnley replacement. A check of the secondary coil resistance shows a few thousand ohms, looks like somebody at BA is paying attention to the design of the secondary coil. Price for these on ebay was noted at about $80.
Conclusion, the coil problems are costing all of us a lot of time and money. The codes do not correctly show failed coils until they are essentially dead. Complications of transmission computer, oxygen sensors, and other items such as catalytic converters, brake problems because we need to keep the engine revved, are involved potentially thousands to repair. Moral of the story, if in doubt buy a few new coils and start swapping or buy a whole new set if $$ is available.
Best;
Greg
The following 3 users liked this post by semiflex:
#2
03-29-2014, 07:12 PM
Back around 15 years ago (when I worked at the local Jag dealer) my buddy (shop foreman) finally figured out why the engine stalled and ECM was 'resetting' after a misfire 'stumble' on a customer X300.
The ECM would lose communication with WDS when one of the coils 'arced'. The datalogger screen would indicate that the ECM was shut down and communication needed to be re-established.
He told me to come over and watch when it happened and sure enough the ECM lost communication when the engine misfired from a faulty coil.
We figured the voltage surge backfed to the control module so we replaced the faulty coil and the engine stopped the stalling problem. I think he replaced all the coils but I don't remember.
Glad you found the the problem on your car.
bob gauff
The ECM would lose communication with WDS when one of the coils 'arced'. The datalogger screen would indicate that the ECM was shut down and communication needed to be re-established.
He told me to come over and watch when it happened and sure enough the ECM lost communication when the engine misfired from a faulty coil.
We figured the voltage surge backfed to the control module so we replaced the faulty coil and the engine stopped the stalling problem. I think he replaced all the coils but I don't remember.
Glad you found the the problem on your car.
bob gauff
The following 2 users liked this post by motorcarman:
BigBossRadio (04-03-2014),
First Jag XJR (04-04-2014)
#3
03-30-2014, 01:45 PM
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