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http://s4.zetaboards.com/lexusaltezzaclub/topic/1148393/1/#new



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High Resistance Between Engine & Chassis
Topic Started: Jul 31 2009, 04:15 PM (913 Views)
Leiden
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NZ, Whangarei
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I was bored and went around the engine bay with a multimeter and discovered there's an 11ohm resistance between the block and the negative battery post while idling. With the Engine Off its 0.05ohms, with just the key on the ON position its about 6ohms.

That seems awfully high...

I measured between the Earth Terminal Block in the ECU Box and the Negative battery terminal and it was 0.05ohms resistance. Most components pull their earth from there but I've seen a few grounding points around the motor where components pull their earth from the block.

Could it be possible that one of the grounding points from chassis to engine has failed, or somewhere in the loom a ground wire has failed.
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xnickx
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Many post regarding this:
http://z4.invisionfree.com/lexusaltezzaclu...?showtopic=7487

http://z4.invisionfree.com/lexusaltezzaclu...?showtopic=1885

http://z4.invisionfree.com/lexusaltezzaclu...p?showtopic=602

http://z4.invisionfree.com/lexusaltezzaclu...?showtopic=1743

http://z4.invisionfree.com/lexusaltezzaclu...?showtopic=3659

+ many more!
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Leiden
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NZ, Whangarei
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None of those posts said anything about the High Resistance between the Engine Block and the Chassis, it was more of a 'anyone else experienced this' type thread.

11ohms would cause severe voltage drop considering the ignition coils grab their earth feed from the head, the ECU also grabs a reference earth from the terminal near the knock sensor.
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Soiled Altezza
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11 ohms isn't really that high.

In saying that I did put a grounding kit in a long time ago.
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Leiden
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Shouldn't the resistance stay a constant 0.05ohms anywhere since the entire earth system in a vehicle comes back to a single point?

Wouldn't higher resistance indicate that the earthing system isn't capable of carrying the required load adequately?

Also the amount of resistance varies by current draw, so with the motor off there is no resistance because no components are drawing any current. With the key in the ON position a few components are drawing current, but with the motor running the current draw is at its highest so increasing resistance would indicate an inadequate earthing system wouldn't it?
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cpufix
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Paraparaumu, Wellington
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Certainly sounds like a faulty earth connection 11 ohms is not good.

Is this only when the motor is running.

Not sure if Altezzas have it, but earlier cars had a starter resistance which gets shorted (zero ohms) when the motor has started ie after starter cranking - anyone else know ???

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Leiden
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With no key in the ignition I get 0.05ohms,

With key in ON position but engine off I get 6ohms,

With key in ON position and engine running I get 11ohms.

As far as I know all the earths are tightly connected. There's the main one which runs to the startor mounting bracket, the one from the firewall to the rear of engine, and the one which runs from the passenger fender to the auxiliary mounting bracket/head.

Strange thing is the Alternator should become the main earth when the engine is running not the battery but that still means there's a problem between the engine & chassis being earthed properly.

It would be intesting to see others results, easy as popping the bonnet and poking around with a multimeter on resistance setting. Those with and without earthing kits.
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xnickx
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Leiden,Jul 31 2009
05:26 PM
None of those posts said anything about the High Resistance between the Engine Block and the Chassis, it was more of a 'anyone else experienced this' type thread.

I posted that before the thread title was edited from something regarding an earthing kit?

So my reply was directed at what has been posted about earthing kits and reviews
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Leiden
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I wasn't starting anything just saying the thread was more related to the high resistance rather than the earth kits, saw the title suggested otherwise and changed it :)
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caveman
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Tauranga, NZ
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will have a look at mine later today in same manner as above

we have an earthing kit so will disconnect and do the tests.

will post both kit on and off results :)
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Leiden
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Sweet, will be good to know :)
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greeneyes
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Hmm... I get zeros, off or on or running, although it depends if I have it on steel or alloy a bit.

That's from the battery -ve to the exhaust manifold cover or head or odd bolts. Sometimes the alloy head gave a resistance.

Using an oldish analogue meter I use for checking electric motors etc at work, the cheapest thing you can buy, not a fancy electronic digital that is prone to random currents...
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Leiden
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I've got a FLUKE Multimeter and another cheapo Digital Multimeter they both give the same results,

I've drawn out a simplified version of the entire earthing system for the ECU so I'm going to go poking around until I find something thats not right.

Did the alloy head give any resistance as high as mine?

Will also go around measuring voltage drop
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caveman
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Tauranga, NZ
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righto been there and done that 3SGE 5AT

disconnnected the earthing kit
disconnected stereo power wire (capacitor in line)

and picked various points back to the battery earth, ncluding the Vin plate, head, shock towers, intake and exhaust and intake manifold.

key off all 0 ohms
key ACC 0 ohms
Running 0 ohms

earth kit connected same results.

stereo power connected same results.

can only guess you must have a fulty wire somewhere ?, possibly broken frayed cores. may be enough to give you a 0 (ish) resistance engine not running then loaded with the motor running = FAIL

Having a little trouble explaining what i mean but try swapping out the earth strap engine to body, and maybe the body to battery. and look for the possible problem.

no ground loop with the stereo when the engine is running ?
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cpufix
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Paraparaumu, Wellington
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Hi Leiden

Disconnect each earth lead one at a time and then test from batt -ive to the end of the disconnected lead.

Only way you're going to find the faulty one.


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Leiden
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From what I can tell the battery -ve goes directly to the startor bracket rather than the chassis, unless its grounded under the battery to the chassis before heading to the startor?

I did a little test by running a independent wire from the engine to the chassis and the resistance dropped from about 26ohms down to 23ohms,

I measured the resistance of all the wires running from the engine to the ecu (main ecu earth) and the ecu to sensors with the engine off and they were all less than 0.05ohms, but with the key in the ON position the resistance along the main earth wires increased to about 6ohms.

Also just to note, did you use a digital or analog multimeter?
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caveman
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ahh forgot about that. new battery / calibration analogue
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Leiden
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So there's a problem with using digital meters because of noise in the lines or something?

Grr a time when an old school analogue would come in handy :(
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greeneyes
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Well, they're very sensitive and can respond to stray currents and feedback, whereas the analogues are pretty basic and need a good shove to make them work.
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Lharris
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generally we don't worry about checking the resistance between the engine and battery.

if your going to do this though, you'd disconnect the neg terminal of the battery and check between the lead and engine.



most accurate way to check if everything is happy, is to check the voltage drop.

for example:

meter set to Volts, red lead on battery pos terminal, black on the neg terminal = 12.9v


meter set to Volts, red lead on battery pos terminal, black on the engine = 12.85v

you'd be looking out for a voltage drop great then .3v ish before you need to worry.
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nz_climber
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As said above, depending on the meter you won't get a accurate reading of resistance with power applied and current flowing.

So best to set your meter to mV and measure the voltage drop between engine and earth terminal etc
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Robo
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Informative, but we do realise this thread was from over a year ago right?
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ke_70
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still good to know though
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