You should Know this
Power balance verification is one of many useful tests in a diagnostic technician’s arsenal. This one, in particular, can help narrow down the root cause of those troublesome P0300 multiple cylinder misfires. The basis of this test is to disable the contribution of the cylinder by cutting off fuel or spark temporarily and measuring the drop in engine speed (RPM). Generally speaking, cutting off spark by deactivating a coil on a plug is not recommended for long periods of time. Removing spark is risky on vehicles with a catalytic converter system due to a heated mixture of air and fuel being sent to an even more intensely hot component (catalyst substrate). Where it can and most likely will create self-ignition events. That can damage the catalyst system and lead to more drivability problems.
This is why fuel deactivation is recommended on the ice (internal combustion engines) of today. If it’s necessary to perform this test by disconnecting the coil on plug because you do not have a scan tool that can do it for you. It is important to make sure to only do it for short periods. The cylinder that has an issue will have the least RPM drop compared to a healthy cylinder. Which will create a very noticeable RPM drop.
Practical Application
It has been a while since I personally had to incorporate this tactic into my diagnostic process. Recently, I ran across a 2010 Ford Edge that had its timing chains replaced by a shop for a flashing check engine light concern on acceleration. Needless to say, after arriving at the shop and gathering information on why timing chains were installed on this vehicle.
I chose to ignore any data they gathered in order to start with a clean diagnostic approach.
A visual inspection of the ignition system revealed no damage or unplugged components/connectors. An initial scan actually provided no DTCs at all, to my surprise. While at idle, the vehicle ran very smoothly, not a peep coming from it indicating an issue was present.
Due to this one characteristic, I now know what direction to head in my diagnostic approach. Installing my amp clamp and checking battery voltage on this vehicle’s generator output with all loads, such as headlights, A/C HVAC fan, and radio on, gave me no insight into the current state of charging/power supply systems as being at fault. In fact, the generator is definitely healthy and capable of doing its job.
So I quickly switched my diagnostic approach slightly to further pursue a misfire under load concern. 25 minutes into my drive, the vehicle began to buck back and forth, stumble, and even stall.
Drivability Issue
Finally, customer concern is present, especially upon acceleration. These symptoms become noticeable: lacking power, unable to accelerate, and nearly stalling multiple times. I continue to run my dynamic power balance test as the SES light is flashing with a misfire on cylinder 1, according to the scan tool. While the dynamic power balance test actually tells a different story. Looking at the graphical representation of cylinder performance, an issue with cylinder 5 is also present. ECM data during this drive accumulated a total of 1,197 misfire events already.
I grab my graphing meter to check the voltage and amperage of cylinder 1 coil at idle with no misfire present and at 1,500 to 2,000 RPM with a misfire present, to confirm cylinder 1 coil does have issues. I swap coil 1 to cylinder 2, and I run another dynamic power balance test. The misfire moves to the front bank on cylinder 2 while a misfire is still present on cylinder 5. So once I return back to the shop and pulled the coil on the plug from cylinder 5, I immediately notice the boot was a lot shorter than the others or any automotive coil-on-plug boot I have ever seen.
Out of sheer curiosity, using my borescope to look into cylinder 5 reveals a broken off boot in the cylinder.
Along with taking a closer look at cylinder 1 coil that was now on cylinder 2 I find inside of the other a faulty coil’s boot is damage internally also.
These two coils were arcing off into the cylinder head instead of passing the high amperage current into the spark plugs, creating the multiple cylinder misfire.
Concluding Thoughts
During this entire process, I had my graphing meter logging every piece of measurement obtained. Due to in graphing mode, the memory depth is very small. The logged data definitely provided some interesting insights into what was occurring during my diagnostic process. This information was another clue that led to revealing the root cause of this vehicle’s drivability issues.
I recommend for the shop to replace all coils and plugs due to their age and torn boots, causing incorrect arcing. During its verification drive, all previous concerns were no longer present.
Tools Used (receive 25% off with discount code “Legacy” at Curien Shop)
N2 Neuron https://www.curienllc.com/shop
https://www.amazon.com/Curien-N2-Neuron
Curien Amp Clamp https://www.curienllc.com/product-page/low-current-amp-clamp
Phil’s Short Electrical Piercing Probe (5-7/8″) https://www.aeswave.com/Phil-s-Short-Electrical-Piercing-Probe-5-7-8-p9904.html
Autel MaxiSys 909