2G Coil on Plug issue

[jed344]

I am a little stumped right now. I have built a few coil on plug set ups with 300m coils over the years and use one i built right now on my car.

Other then resistance is there a way to test 300m coils for being bad?

A friend of mine we decided to swap to coil on plug as even with his ARC-2 box we had hit a wall with spark blow out. He got a used set up and we found was wired wrong for his car so it was rewired and still acted as if it had bad coils. I tested resistance and it showed to be to high. He then got another used Spark Tech COP that was wired right to start and did the same thing. I tested resistances on each coil and at the triangle plug and confirmed it matched my resistance and wired correctly. We grabbed another Spark Tech COP from a running car wired the same and same resistance and his car fired right up.

Something is clearly wrong with this coil on plug but can the coils be bad and still test good on resistance?

 

[jdxnc]

From my experience with customer cars, the 300m coils are just crap and cause more issues than they're worth. If you're going to do a COP setup use the OEM Denso Prius coils, much better quality, I haven't actually seen one fail personally yet.

 

[TerminalTalon]

Visual test. Check the coil itself and the wiring. Do you know which cylinder or is it in general misfiring?

 

[1990TSIAWDTALON]

I run stock coils on 10:1 motors at 40lbs of boost on stock coils to 9k. Plugs (6's) are gapped real tight, at .018", for reference.
I do run an ArcII Box on both cars setup that way.

 

[jed344]

I have used the 300m for coil's for a long time and I know there are better options now days yes. This COP matched the resistance of my coil's and cut to same length.

Today I pulled mine off my car that is also wired the same and dead nuts the same resistance and his car ran perfect. This leads to a issue with his coil on plug but I have no clue as the resistance is same, wired the same, ect. This car I built the engine, ported the head, and tune. For reference of why I felt we hit limit of stock coil even with ARC-2 I will explain.

We have before gone quite far on stock ignition with ARC-2 and around this point we always hit the wall. This car at 31psi and only 11 degrees of timing trapped 139mph at the shootout. The car run's 8's for plugs and at the time on stock coils was gapped down to .016. This was at 38-40 psi and me adding a degree or two up top on timing. Logging well over 80lb/min. I know other's have done more but we have never been able to go farther then this and with the old school 300m we have.

The plan is to swap the car to a Haltech and change coils. This was more about my confusion how his coil on plug could test the same as 2 others yet his acts up and the others work fine. We also on all the cars this one included have extra block grounds, head grounds, and car does not drop under 13.8v at wide open. The car will pull clean at say 40psi and 11 degrees but plugs show it wants more. When I add some timing it will blow out spark, the car though wakes up like a animal. I have not with this specific car ran it on the dyno to find MBT but based off plugs and data it looks like what I expect around 13-15 degrees for MBT.

 

[luv2rallye]

Another test you can do is observe the spark length and intensity with the old screwdriver trick. Remove all COPs and spark plugs. On test COP reconnect harness but don't connect to spark plug. Instead place a long screwdriver all the way in the end that was on the spark plug. Keep screwdriver shank (or an attached wire to it) 1/8" from ground metal so a spark can jump across to ground (simulates spark plug gap). Make sure you have heavy insulated gloves on and stand on at least 2 dry rubber mats. Have someone crank the engine and watch the spark. You should see a strong blue spark. Experiment with how far away from the metal you can move the shank and still get a strong spark. Repeat on other COPs.

 

[jed344]

Another test you can do is observe the spark length and intensity with the old screwdriver trick. Remove all COPs and spark plugs. On test COP reconnect harness but don't connect to spark plug. Instead place a long screwdriver all the way in the end that was on the spark plug. Keep screwdriver shank (or an attached wire to it) 1/8" from ground metal so a spark can jump across to ground (simulates spark plug gap). Make sure you have heavy insulated gloves on and stand on at least 2 dry rubber mats. Have someone crank the engine and watch the spark. You should see a strong blue spark. Experiment with how far away from the metal you can move the shank and still get a strong spark. Repeat on other COPs.

I plan to mess with this more soon here as now the car is put away for the winter. We still are very confused. The car ran some on my coil on plug and acted as expected. His coil on plug on my own car acted up. So even though his is wired the same and same resistance there is a issue. I am suspecting it has to do with the coil spring in the boot not making good pressure or contact on the plug and coil. We have made sure all is the same length wise but it almost has to be. I may try my springs and boots too as that would also confirm this theory.