Engine grounding, crankcase position sensitivity?

[rjcthree]

While I believe I may be suffering from battery weakness (not holding a charge, not a lot of depth to the charge, causing cranking voltages to fall into the 9V range If it doesn’t fire on the first or second blade) I’ve had two indications of possible grounding issues in the past two flights over two consecutive days. First is my CPI2 doesn’t want to shut down cleanly after its countdown, during yesterday’s and today’s flight. The second is jumpy oil temperature indications, which was new today. Oil temp goes from normal 180F to 120F, jumping back and forth for a few seconds, or it may hang on 120F for a couple minutes, but jumps back to 180F ( 180F previously determined plausible with a separate TC). It seems like all the other threads talk about oil temp going high with grounding issues, though...

There’s a bunch of thread history on Dynon sensor ground, not so much yet on the CPI2, and I started this whole thing with a grounding question. Frustrating. Yeah! I get to pull the cowling again!

[TS Flightlines]

It did serve the purpose---to get another hose made.
Tom

[n82rb]

I agree 100% with carl on this one, what is the biggest current device on the airplane? the starter, as carl stated all the current that goes through the starter needs to go back to ground. so since it is the biggest draw, why route it through bolts,castings,gaskets,ect to get to the back of the case to to go to the ground wire. just put the ground to the starter and eliminate a lot of possible resistance points.

bob burns
rv-4 n82rb

[JonJay]

Originally Posted by n82rb

I agree 100% with carl on this one, what is the biggest current device on the airplane? the starter, as carl stated all the current that goes through the starter needs to go back to ground. so since it is the biggest draw, why route it through bolts,castings,gaskets,ect to get to the back of the case to to go to the ground wire. just put the ground to the starter and eliminate a lot of possible resistance points.

bob burns
rv-4 n82rb

Per plans has worked for thousands of RV?s. All of the airplanes I have owned, certified or otherwise, use case grounds. Must work.
I personally don?t want another wire in my already tight harness going forward nor the added bit of weight even though it?s probably less than a pound.
Like always, build it like you want, but I have never been hurt following the plans. It really isn?t that difficult to install a case ground properly.
I see a lot of posts about starter issues. They all start with the ?must be a bad ground? but most end up being a bad battery or one of the solenoids.

[lr172]

Originally Posted by JonJay

Per plans has worked for thousands of RV’s. All of the airplanes I have owned, certified or otherwise, use case grounds. Must work.
I personally don’t want another wire in my already tight harness going forward nor the added bit of weight even though it’s probably less than a pound.
Like always, build it like you want, but I have never been hurt following the plans. It really isn’t that difficult to install a case ground properly.
I see a lot of posts about starter issues. They all start with the “must be a bad ground” but most end up being a bad battery or one of the solenoids.

+1

This approach is well proven. 100's of millions of cars have been produced without a dedicated ground at the starter. Battery ground goes to engine block. If the approach were flawed, I think it would be obvious by now. Nothing wrong with doing it; But I fail to see the need. The fact that a case ground needs ongoing maintenance, does not necessarily mean it is a bad idea.

Larry

[rjcthree]

The difference with us and two decades of automotive/heavy truck is almost all of the return paths tend to be back to the ECU for sensors (and most powered equipment). Where we get into trouble is case grounding of a sensor signal. Automotive started doing away with that in the 80?s, mostly. It essentially became required with OBDII (mid 90?s) not so much in writing, but in expectations of self-diagnosing faults, and further reliance on digital tools to rapidly diagnose issues in a warranty environment with the simultaneous gap of technician skill availability growing larger each year. It?s only gotten more important from there with respect to safety systems. Refer to ISO26262 in case you care....

You will still find more than one fat drivetrain to chassis ground on most ground vehicles.

[lr172]

Originally Posted by rjcthree

The difference with us and two decades of automotive/heavy truck is almost all of the return paths tend to be back to the ECU for sensors (and most powered equipment). Where we get into trouble is case grounding of a sensor signal. Automotive started doing away with that in the 80’s, mostly. It essentially became required with OBDII (mid 90’s) not so much in writing, but in expectations of self-diagnosing faults, and further reliance on digital tools to rapidly diagnose issues in a warranty environment with the simultaneous gap of technician skill availability growing larger each year. It’s only gotten more important from there with respect to safety systems. Refer to ISO26262 in case you care....

You will still find more than one fat drivetrain to chassis ground on most ground vehicles.

I have seen all of that. My 10 has 100% dedicated sensor grounds; The block ground really only services the starter and alt, though it helps to tie the engine ground to airframe ground to deal with the nasty spikes floating around the block from the ignition (EI wasted spark) . I still don't see auto's using a dedicated ground to the starter, though I have seen them add small gauge grounds for the solenoid (likely for the reasons you mention). They reliably use the large gauge chassis to block grounds for the motor and it seems to work quite well.

If I were to run a dedicated ground, it would be to the alternator, as the safety of flight factor is much higher for me (elec dependent engine) than the starter.

I feel that a dedicated ground to the starter is just as likely to need maintenance as a std grounding strap between the airframe and the block. Corrossion between the starter and block is mostly a non-issue as both are aluminum, at least with contemporary starters.

Larry

[Carl Froehlich]

Originally Posted by lr172

I have seen all of that. My 10 has 100% dedicated sensor grounds; The block ground really only services the starter and alt, though it helps to tie the engine ground to airframe ground to deal with the nasty spikes floating around the block from the ignition (EI wasted spark) . I still don't see auto's using a dedicated ground to the starter, though I have seen them add small gauge grounds for the solenoid (likely for the reasons you mention). They reliably use the large gauge chassis to block grounds for the motor and it seems to work quite well. SNIP

Larry

One note of caution, if you have more than one firewall ground wire to the engine (or anything attached to the engine) it needs to be as big as the ground wire for the starter.

Consider a single ground wire for the engine - and that it fails. The starter would not work and you would go find the problem. Now consider the same scenario where you have engine sensors or such with separate grounds. These separate grounds will now try to carry the starter current - and will fail. If lucky you will not take out the panel but that has happened as well.

If your sensors are truly not grounded to the engine then this is not an issue. This would be the case for standard, modern EMS systems with three wire sensors (e.g. +5vdc reference, signal, ground).

For pMags it is important to ground the pMag to the engine case, not the firewall. This is for the above reason as well as you want the pMag to still work if you loose the firewall ground. The pMag internal generator wants engine ground for the plugs to work, just like a standard magneto.

On the wasted spark, the spark still happens just like it does for the power stroke. No need to do anything about it other than normal practice for spark plug leads.

Carl

[rjcthree]

Larry, what oil temp sensor do you use on your -10? Thanks