Super Contributor

Re: CAT G3520C DET issues

The signal generated by the detonation sensor is basically an AC sinewave, usually on a DC carrier signal to allow hte ECM to determine if the accelerometer is present.


False detonation can be ther result of a number of things, such as mechanical noise from valve events and gear train noise.

Electrical problems can also contribute, I have seen AC battery chargers, bad grounds, bad starting batteries and engine wiring harness problems all contribute.


So first check I'd make from here is to take a good quality DMM and do a power survey of your engine. Start at the batteries and measure in DC Volts from DC+ to DC-, DC+ to GND and DC- to GND. Make sure you find a GOOD ground reference point, I usually clean off a spot on the engine block with a wire wheel or abrasive pad. After you take and record the readings in DC volts, change the meter to read AC Volts and make the same measurements again. If any of the AC voltage readings are greater than 150 mV, set the meter to read AC frequency and measure the frequency and record. Repeat this measurement procedure at the starters, power distribution box and at the power input to the ECM.  Take a complete set of readings with the engine off, and repeat the readings with the engine running on load. Compare results.


What you are looking for is basically two things,  that when measuring DC volts, the readings between DC+ and DC- Should be the same as the readings between DC+ and GND, and that there should be 0 volts between DC- and GND. When measuring in AC volts, if any measurement is above 150 mV, then use the frequency reading to help determine the source. Such as multiples of 60 typically mean you have ripple from the AC power source in North America (multiples of 50 Hz in other parts of the world). If the AC voltage is present above 150mV and the frequency is erratic, that is noise and figuring it out is harder.


Most noise issues are the result of poor grounding and bonding practises, and can also result in deteriorated wiring in on engine harness's. Noise can also be generated by ignition system components like coils and spark plugs.


If at this point there is no apparent culprit, than more complex troubleshooting will be required. I end up using an oscillioscope in a lot of cases to determine the root cause of many of these type problems. Carefully looking at the engine operating parameters can also be usefull. If you lean out the engine, in cases of true detonation the detonation levels should reduce, however if they actually go up, then the ignition system is a good candidate as a source of the problem. Compare ignition energy readings as you make changes to see if you can find indications of what may actually be going on.


Your original post is pretty lean on details,like how many hours on the engine, how many hours since last major service, did problem start after some work or adjustments being done?  What type of fuel, what ambient conditions, where in the world are you?


More details will usually get yo better answers, and many times, in reviewing those details in preparing a post, the solution or root cause may present itself.


Hope that helps, MikeL.

New member

Re: CAT G3520C DET issues

so as of now and numerous more tests ive concluded that it is not true detonation something somewhere is making the ecm think theres detonation in other words an electrical problem or interference so now the question is what can cause an engine to think its detonating even after changing the det sensor harness and the ecm`s

New member

Re: CAT G3520C DET issues

anyone have any ideas on what might be causing this


New member

CAT G3520C DET issues

one of my gensets is detonating on all even cylinders the other side of the engine works fine and this just started happening out of the blue ive replaced wiring harnesses the computers checked and set the valves and timing with no avail and the genset was recently overhauled and ran great for a few months please help