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Grounding Question

Practical Motorsport Wiring - Club Level

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So, I'm watching the video on grounds. You mention grounding to engine block and chassis are the two grounding methods. I have a FuelTech ECU and it has some that say MUST go to battery without spicing. They said it is called clean grounding, Then they have some called dirty grounding. This could be a silly question as what way is correct.

Best practice is to always follow the manufacturers recommendation. However, I think you can get a good ground from other places, but I would test that by looking at the ground signal with an oscilloscope to verify it was a "clean' signal even if attached to the chassis or engine block.

As David said.

What the potential problem is is variations in the ground/earth potential that will affect the voltage the ECU registers across the whole circuit.

Every wire that has a current flowing along it will have a voltage drop, the higher the current and/or lower the gauge the greater the drop. This is fine when it's a solid length with no other earth points being attached to the wire, but when other devices are grounded on the same wire there will be changes in the voltage gradient in the wire, so ground voltage may be 0V at the far (battery) end, at the first device it may actually be +0.2V (all relative to the battery -VE terminal), if there are different grounds along then instead of a consistent drop, it 1/4 of the way along it may be +0.18 instead of the expected +0.15, 1/2 way it may be +0.13V instead of +0.10V9, 3/4's it may be +0.10V instead of +0.05V, and these examples of values may, in turn, change as different grounded devices turn on and off, or have varying current passing through them.

As most sensors are sensitive to voltage, or rather the ECU is reading the voltages/currents is, these variations will be sending differing values to the ECU - this is the exact reason why common/STAR grounds are important for most electronics' circuits, where milli-volts (thousandth), and even micro-volts (millionth), will be the units used.

Some circuits it doesn't matter, such as lights, fans, etc, if there are slight fluctiuations.

So, if in any doubt, follow the directives of the ECU manufacturer - it can avoid chasing down really tricky transients.

I've wired a FuelTech FT550 on multiple occasions using the HPA method, it works excellent. I've never used the method in the FT documentation because it's wrong.

It's funny because Holley demands the same and it has me scratching my head too.

Many of the ecu manufacturers installation guides have a blurb about good grounding and star point etc, where as they just say "must be to battery" and nothing else. Haltech have a good visual guide I've referenced many times.

I have in general grounded the ecu to the block or head. I especially feel this is important with 3 pin ignition coils that don't have a dedicated trigger return, for the risk of a ground offset between the ecu and the ignition coils causing a false fire. Id rather the engine not run at all without a block ground then false fire coils.

I don't know if direct to the battery is wrong, but its just not that simple. The entire system has to be designed around the battery negative being the star vs the block or chassis etc. I assume for these companies that are using cheaper components (cough holley terminator, FT is also building to a pretty reasonable cost and they had to save money somewhere) its easier to enforce the battery negative as the only way because it probably makes for less strange and hard to diagnose issues their tech line would struggle to support.

I always like to compare to what the OEM's are doing, but they build to different goals. Only OEM certified techs are intended to work on their vehicles, their wiring harnesses can be much more complicated, their ecu's much more expensive and 0 need for end user adjustments. Their calibrations also need to be dead on all the time and their ecu's capable of basically diagnosing themselves. Far cry from what the aftermarket is dealing with lol.

I think this is an extremely worthy discussion as good grounding is so integral to everything working and yet its confusing. Like how do we feel regarding using the chassis as a conductor?

I blame stereo and alarm system 'installers' from the 80s and 90s for both modern day good and bad practices :P The bad being what people saw and adopted, the good being what people have done to try and educate/combat what people started doing.

The negative battery terminal isn't what I'd suggest, but I suspect Fueltech have made a smart move and saved their customer service team a lot of work with their suggestion. Grounding to the negative battery terminal will work in almost any scenario if done reasonably securely, while grounding to the engine or chassis can go terribly wrong if you don't follow guidelines the HPA courses lay out. For example, if you bolt your ground to a powder coated intake manifold, or a composite chassis component, you're not going to get the desired result. For a clean install though, I like the HPA methods.

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