Ignition Coil

neoslowmo, Mar 19, 1:59am
I know one of mine is playing up on the open road and under load.
It's not bad but I know it's there.

But when taking it to the Mechanics - them putting it on the computer and running tests - comes back as everything's fine.

Suggestions I could say to them so they can find the fault and believe me?
trade4us2, Mar 19, 2:10am
I had the same problem. The auto electrician had not plugged a lead properly into one coil, and broken the Bakelite cover over the coils.
Later I discovered that the body computer was turning off every few minutes because of bad earth connections. I don't know which computer writes the codes away, but no error codes have ever been found.
skin1235, Mar 19, 2:10am
could be it is fine too, and your dizzy has a few thou too much tolerance in the bushes, causes misfire at high revs

the high load scenario is more likely to be plugs, you need to pressure test them,I bet you'll find one of them is missing at high pressure
macman26, Mar 19, 2:11am
So what is the symptoms? What sort of vehicle, make model? Loosing power on the open road?.
Could also be a fuel supply problem, vacuum leak ,timing issue, wrong fuel just for starters.
intrade, Mar 19, 2:17am
find a professional mechanic not some swaptron morons who can only read out codes and think that is how you fix cars.
missing can bei either spark or fuel.
With diagnostic equipment you look what the fueltrims are to make a destition what needs further investigating
intrade, Mar 19, 2:19am
good accurate post.
neoslowmo, Mar 19, 2:22am
2006 Commodore SV6
symptoms, I will use this:

Decelerating as coming up behind someone, we hit a over taking lane so I go to speed up.
I'll get a hesitation
there will be a thump
a miss

then she will take off as usual - I say it is my ignition coil as it's happened before couple years ago and had it replaced and it was running fine.
Looking over the Holden Forums people on there say the same thing for the symptoms.

I just find it a little strange the computer isn't picking up the misfire when it's there.
neoslowmo, Mar 19, 2:23am
I use Holden - since they should know Holden vehicles
intrade, Mar 19, 2:28am
dont jump to conclusions a 2006 GM is extreme complex in mimiking sysmptoms i guerantee you you can not guess things and one needs to look at fueltrims. you can do that even your self with a 15us$ obd2 connector fueltrim is global obd2
there is long therm and short therm fueltrim both of these should be at zero bouncing up and down if all is ok then you can rule a lot out as cause
neoslowmo, Mar 19, 2:33am
Seems to be the same for me - not throwing up any error codes
neoslowmo, Mar 19, 2:37am
So would they be able to see if the air/fuel mix is out testing my vehicle?
intrade, Mar 19, 2:41am
error codes only get stored if the problem exists constant. it will be in the freeze frame if anything ever got stored. only 1 condition gets stored in the freeze frame even if there where 5 problems the first one use the freeze frame uses up that.
The problems get logged when the engine computer mesures operations outside its controlled programed window.
if it comes back inside this window for enough times the code gets dumped but the freezframe keeps that 1 who ever made it first in to there untill it is erased.
fueltrim window is only maxed out at 25% correction below this no code will be triggered. but you can have serious problems with fueling and no codes.
Codes are not what to read out to fix a car.
codes are mearly symptoms to tell you what direction of testing you should go, and not parts that need to be replaced
intrade, Mar 19, 2:43am
yes if they have a clue at all there is loads of main dealers with no clue what so ever even in switzerland. its mind bogling thinking how these morons are going to fix cars.
If they dont know what fueltrim is forget it they have no clue

http://www.easterncatalytic.com/wp-content/uploads/2012/10/Fuel-trim-graphic-EC_Fuel_Trim_Diag.jpg
motorboy2011, Mar 19, 2:47am
Infrared laser temperature prob aimed at each exhaust port one at a time, missing one will be a little colder
bigfatmat1, Mar 19, 2:59am
they could use a scope a coil that is faulty will feed voltage back into the primary this can often be seen at idle no load. Fuel pressure and a amp clamp on scope on the fuel pump powersupply
gsimpson, Mar 19, 3:30am
Try putting a tank of 98 in it if you usually use 91.
neoslowmo, Mar 19, 5:15am
Thanks for the suggestions I will be getting them tested.
poppy62, Mar 19, 3:08pm
I reckon its a crook spark plug. Had a similar problem.
_frodo_, Mar 19, 3:14pm
I had a bad shudder under acceleration in my 2005 vz sv6. It had done 123000kms and was one original spark plugs. Changed them out and problem was fixed.
intrade, Mar 20, 3:11pm
i found a crook sparkplug with my pico scope on a 1977 stingray v8
brand new plugs. i got 4 channels so can scope 1 bank at the time then bingo follow my bnc wire to the plug that is not showing a nice burn , more easy when you can connect to ignition leads. as coil on plugs are harder to detect a problem like this with secoundary pickup pedal probbe is all you could use.
GM are suposed to use the pico scope as oem test equipment , but if they are morons with no clue then they wont even know that a pico-scope is mandetory now to test for fault finding.
intrade, Mar 20, 3:16pm
http://sandyblogs.com/techlink/?p=2879
there is car specific software they get even a swaptron moron with fancy workshop could hook it up to a component for testing with the instructions and flowchartes written in to the software.
i got no oem instructions i have to know what i am doing all i do get is the instruction how you should hook it up but its not always going to work like that on every car. but hey i am not a swaptron following flowcharts.
skin1235, Apr 21, 10:08am
when were the plugs installed, and have they been pressure tested yet

start with the basics
the issue is typical of a plug breaking down under load