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Wierd weak spark on a V6

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Hello everyone. I have some wierd issue here with a standalone managment.

I got a 6g72 with weak spark. But the weak spark is intermittent. It also seems some coils fire but the timimg light doesnt pick it up. (The light works on other cars).

The coils work but they dont work well enough.

The ECU controls a relay that supplies 12V to the coils. The ECU then internally grounds the pin at 4.0ms dwell time to fire.

I have tested:



Coils (new)

Relay (new)

Ground loops

Plugs (new)

Plug leads (new)

Coil dwell time (3.5 to 4 m.s)

The issue is definately with the coils.

If i unplug the coil while the car is running suddenly its fine. When i connect it to tue spark plug suddenly it drops again.

If i take all this off and put it on another car everying runs perfect. Just on this car something is off. All injectors spray properly and arent cloged all cylinders have proper compression.

Just stumped on this. Everything works but it doesnt.

Is there anything else i can look into?

My plan next is to reduce the 12V in from the bat+ to the coils and manually control it.

Then i can use an ignition module like the factory spec PTU and make use if tye positive drivers on the ECU to see if that makes a difference.

Any input would be appreciated. Thanks in advance.

Here is a vid of the issue. The "dead coil in the video doea actually fire but for some reason it doesnt fire strong enough. Engine heads block and gearbox are all grounded properly to bat negative..

Have a look at the vid below

Attached Files

Sounds like you need an oscilloscope with a current clamp.

Did you check the Engine/Trans ground strap?

Yes my initial idea was ground issue. So i added a new strap for block heads trans to the star point. Didnt make difference.

When we placed the ECU on a simulator tester it is fireing all coil drivers as they should.

Coils get power directly from bat + through a relay that is controlled by ECU to the coil then coil is ground by ECU. There are no other links inbetween.

So i was like okay cool dead plug. Replaced plugs. No diff. Been through 5 sets of plugs.

Yet when i bench test the spark plugs. I earth one sparg plug to the engine and look at the spark. They all give me proper blue spark.

Next idea was drop a Volt meter on each coil and see whats up.

When i put the osciolsope on its jumps around like the line on a Richter scale during an earthquake. But i think its because my scope scale is 10ms it cant go lower. My dwell time is 4.0ms at this point

Resolved. The 6g72 coilpack has a short 5cm or so wire harness from the engine harness connects to the connector then to each of the 3 coils.

Not sure if it was the wires or their gauge but when i replaces those the spark issue went away. Even though they tested as functional they were not functional. I had continuity and the resistance was within spec so it wasnt a break in the wires.

Either way its working now. Dno why but it is.