Team3S: 3000GT & Stealth   Thursday, January 1 2004   Volume 02 : Number 334
 
 
 
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Date: Wed, 31 Dec 2003 00:32:56 -0000
 
From: "Jeff Lucius" <jlucius@stealth316.com>
 
Subject: Re: Team3S: Car won't start
 
 
 
Well I didn't disconnect my battery's positive cable (don't want to re-set the radio presets). But with the (+) cable off the battery and the VOM meter probes touching the battery (+) terminal (not removed I hope  ) and any ground on the car, the path you are measuring is the from battery (+) terminal through the battery, out the battery (-) terminal, down the battery ground cable, along the chassis ground, to some grounded part of the engine (in this case the plenum). The resistance will be less than 0.1 ohm if the battery and the ground straps/cable are in good shape.
 
 
 
Now I did recently check the resistance between various engine parts and the chassis on my Stealth. In all cases (plenum to heads, heads to each other, head to block, all the above to chassis) the reading on my DMM was 0.0 (in reality it will be some small number less than 0.1 ohm). That's good. There should be very little resistance between all these big chunks of metal if they are grounded correctly (ground straps and cables and grounding contacts in good shape and of sufficient size).
 
 
 
Going from the battery (-) terminal to any point on the engine or chassis (without paint, etc) should yield similar results. My battery is in the rear compartment so I did not do these measurements.
 
 
 
Between the battery (+) terminal and (-) terminal (no cables attached) you should see something less than 0.01 ohms - if your meter is capable of measuring that low, most handheld meters are not and you will see 0.0 ohm. That is good also. The internal resistance of the battery should be between 0.001 and 0.01 ohms so that current can flow freely. This is why it is a very bad idea to short the batt (+) and (-) terminals.
 
 
 
So the resistance along the complete path from batt (+), when the (+) cable is not on the terminal, to any ground location should be a *very low number*. I would say 4 ohms is *very high*. But that could be attributed to contact resistance between the probe and object or between a ground cable/strap, or to a battery that is wearing out (deposits on the plates, low electrolyte level). If it was me, I would check resistance across the ground straps/cable for the engine and also suspect a bad battery, assuming you really had made good contact with the meter probes.
 
 
 
With both battery cables connected, I just measured the resistance on my Mitsu pickup truck between the batt (-) terminal and engine and got 0 ohms (the DMM only goes down to ~0.1 ohm so the actual value is less than that). Again, that is good. I also measured resistance between the batt (+) terminal and engine and again got "0 ohms". But be sure the DMM (+) probe is on the engine and the DMM (-) probe is on the batt (+) terminal. Otherwise you will see an open (0L on a DMM). Why? Because to measure resistance, the digital multimeter (DMM) supplies a small voltage, ~300 mV for my meter and this range. This small voltage cannot overcome the much larger voltage supplied by the battery with the DMM (+) on the batt (+) terminal (in fact the meter reads ~12.55 volts when measuring between batt (+) and engine, as it should with both batt cables attached). The voltage supplied by the DMM must go "with the flow" rather than "against it". And when we measure this way "with the flow",!
 
  the path is from engine to chassis to batt (-) through the batt to batt (+) - just as described above.
 
 
 
Someone mentioned "And yes, that value should be far greater then 4 ohms. 4 ohms would draw 3 amps from the battery (if I remember ohm's law correctly)"
 
 
 
Ohm's Law only applies to a complete circuit, which does not exist in this case. There is no draw (current flow) on the battery with the (+) cable off the terminal. And with the (+) cable on the terminal there still is no draw (no current flow) along the path described in Dan's test *unless* a device of some sort is operational (engine, clock, whatever). And in that case, the current flow (which could be measured by disconnecting the batt (-) cable and placing the ammeter or DMM between the free cable and the batt (-) terminal) would be determined by the voltage and resistance of the device and its associated complete circuit.
 
 
 
Again, the 4 ohms Dan measured is bad not because it is too low, but because it is too high.
 
 
 
Jeff Lucius, <http://www.stealth316.com/>
 
 
 
- ----- Original Message -----
 
From: "Dan Labonte" <danlabonte@cox.net <mailto:danlabonte@cox.net>>
 
To: <team3s@team3s.com <mailto:team3s@team3s.com>>
 
Sent: Tuesday, December 30, 2003 9:14 AM
 
Subject: Team3S: Car won't start
 
 
 
So that I am not chasing a ghost, can someone measure the resistance from the positive battery terminal (with terminal removed of course) to their intake plenum?
 
I am thinking it should be around 22K ohms, mine is only 4 ohms.
 
 
 
Thanks
 
 
 
Dan
 
 
 
 
 
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Date: Wed, 31 Dec 2003 01:17:52 +0000
 
From: mjannusch@comcast.net
 
Subject: Re: Team3S: Car won't start
 
 
 
> So the resistance along the complete path from batt (+),
 
> when the (+) cable is not on the terminal, to any ground
 
> location should be a *very low number*. I would say 4 ohms
 
> is *very high*.
 
 
 
No, that is not correct.  Your testing methodology is flawed by testing resistance on a circuit already containing voltage.  Why should the path from the battery to ground be a near-short?  I'd say 4 ohms is very low for what should be a near-open circuit.  You cannot obtain meaningful resistance measurements from testing a circuit where a portion already contains a charge.
 
 
 
Someone needs to disconnect their positive connection at the battery, and measure ohms from the positive cable to the negative cable.  If nobody else wants to, I'll do it tomorrow after work (have to take the cover off the car to get at it).
 
 
 
> And in that case, the current flow (which could be
 
> measured by disconnecting the batt (-) cable and placing
 
> the ammeter or DMM between the free cable and the batt
 
> (-) terminal) would be determined by the voltage and
 
> resistance of the device and its associated complete circuit.
 
 
 
No, you need to disconnect the positive terminal at the battery to take voltage off the circuit in order to measure resistance.
 
 
 
> Again, the 4 ohms Dan measured is bad not because it
 
> is too low, but because it is too high.
 
 
 
I'm going to have to respectfully disagree with you on this one.
 
 
 
- -Matt
 
'95 3000GT Spyder VR4
 
 
 
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Date: Wed, 31 Dec 2003 01:24:52 +0000
 
From: mjannusch@comcast.net
 
Subject: Re: Team3S: Car won't start
 
 
 
> So the resistance along the complete path from batt (+),
 
> when the (+) cable is not on the terminal, to any ground
 
> location should be a *very low number*. I would say 4 ohms
 
> is *very high*.
 
 
 
Actually, I reread this and see where the difference is.  You aren't measuring the same circuit that Dan measured.  What you are measuring should be very low resistance, but what he is measuring should be significant resistance.
 
 
 
- -Matt
 
'95 3000GT Spyder VR4
 
 
 
***  Info:  http://www.Team3S.com/Rules.htm  ***
 
 
 
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Date: Tue, 30 Dec 2003 20:34:41 -0500
 
From: "Dan Labonte" <danlabonte@cox.net>
 
Subject: Re: Team3S: Car won't start
 
 
 
Jeff,
 
 
 
I was following your fuel pressure sender instructions from your web site
 
when I came upon this issue.  Just to be more clear the battery is out of
 
the car and I jumpered it up to check for and leaks in fuel line when the
 
starting problem occured.  I am thinking that the resistance should be more
 
like XX K Ohms from battery + to any ground.  On my wifes minivan (were I
 
swiped a second battery from) I measured 22k Ohms as a comparison.  I follow
 
your discussion on low resistance accross the grounds, but I am thinking it
 
should be higher across the terminals.  The 55K I measured on VR-4 from the
 
starter battery cable connection to GND.  I am measureing with plus
 
terminanl off the battery so I think that is the differance between out
 
measurements.
 
 
 
The 4Ohms is from the second battery cable that goes into the engine bay
 
fues box.  (Speaking of which anybody have a spare IOD connector jumper?
 
Mine seems to be missing).  So that 4ohms has to be a summation of wire
 
resistances that make the short to ground.  55k would lead to a current draw
 
of around 200micro amps with the car just sitting there, 4ohms would drain
 
the battery in about 5 minutes with the car just sitting there.
 
 
 
The short is then from the 40Amp BATT fuse white/black stripe wire.  I
 
traced that wire to the driver side fuse box (connector C-68) which supplise
 
power to a number of multi-purpose fuses.  (I am getting warmer nower) so it
 
is one of the connector harness to this box, the box it self, or one of the
 
devices.
 
 
 
Thanks
 
 
 
Dan
 
 
 
 
 
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Date: Tue, 30 Dec 2003 20:38:33 -0500
 
From: "Dan Labonte" <danlabonte@cox.net>
 
Subject: Re: Team3S: Car won't start
 
 
 
> Someone needs to disconnect their positive connection at the battery, and
 
measure ohms from the positive cable to the negative cable.  If nobody else
 
wants to, I'll do it tomorrow after work (have to take the cover off the car
 
to get at it).
 
>
 
Thanks Matt but no need to go to the trouble.  I am convinced I have a sort
 
and I am determined to find it this evening.  I have to many mods in my
 
garage waiting to be installed for this to hold me up any longer
 
 
 
Dan
 
 
 
 
 
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Date: Wed, 31 Dec 2003 15:01:23 -0000
 
From: "Jeff Lucius" <jlucius@stealth316.com>
 
Subject: Re: Team3S: Car won't start
 
 
 
Dan,
 
 
 
Doh! I thought when you said "positive battery terminal" you meant the terminal on the battery. Now I see you mean the terminal on the end of the battery *cable* (should have been obvious I guess  ). Ignore my comments, which still happen to be correct except that as Matt pointed out a DMM needs to measure resistance on a "circuit" without a potential difference across it. The extra potential messes up the DMM internal calculations.
 
 
 
Yep, taking the long way around should be open except for the circuits running through the alarm, ECU, and radio (and whatever else may be active with the ignition off).
 
 
 
Jeff Lucius, http://www.stealth316.com/
 
 
 
- ----- Original Message -----
 
From: "Dan Labonte" <danlabonte@cox.net>
 
To: <team3s@team3s.com>
 
Sent: Tuesday, December 30, 2003 6:34 PM
 
Subject: Re: Team3S: Car won't start
 
 
 
***  Info:  http://www.Team3S.com/Rules.htm  ***
 
 
 
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Date: Wed, 31 Dec 2003 22:09:19 -0000
 
From: "Jeff Lucius" <jlucius@stealth316.com>
 
Subject: Team3S: Current draw with ignition off
 
 
 
Motivated by Dan's thread "Car won't Start", I performed the measurements Dan requested.
 
 
 
On my '92 Stealth TT, I disconnected the battery positive cable and measured the current draw between the disconnected cable and the battery positive terminal with a DMM. Current started at about 360 mA and then reduced to a stable and repeatable 14.5 mA. I am guessing the higher mA reading reflects some action of the ETACS. That measurement is with all doors and the hood closed (my battery is in the rear compartment).
 
 
 
I then went in the engine bay and measured between my distribution block and the ground on the firewall and then the plenum. In both cases resistance was a repeatable 929 ohms.
 
 
 
These numbers are fairly consistent with each other but not exactly. Battery voltage at the time was about 12.2 volts.
 
 
 
V = IR or R = V/I or I = V/R
 
 
 
12.2 v / 929 ohm = 0.0131 A or 13.1 mA
 
12.2 v / 0.0145 A = 841 ohm
 
 
 
Wondering if 14.5 mA is a reasonable current draw, I checked my 1987 Mitsu pickup, which has not a single computer built into it. Having only a dash clock to draw current, I measured 7.3 mA. about half what the Stealth draws. The Stealth has ETACS, a radio, the ECU, and a multitude of other devices that have a wire that goes directly to the battery.
 
 
 
So it seems that 14.5 mA draw is reasonable. Does anyone else here have current draw measurements to compare to?
 
 
 
Thanks,
 
 
 
Jeff Lucius, http://www.stealth316.com/
 
 
 
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Date: Wed, 31 Dec 2003 15:32:21 -0800
 
From: "Andy" <awoll1@pacbell.net>
 
Subject: Re: Team3S: Current draw with ignition off
 
 
 
Jeff:  14.5 milliamps is extremely low.  It speaks well of Mitsu's design.
 
My BMW's (all 4 of them) all pull about 100 to 200 ma with everything off.
 
Their batteries go dead if left for 2 or 3 weeks.  My Stealth will set for a
 
month and start up every time.
 
 
 
Andy
 
 
 
 
 
 
 
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Date: Thu, 1 Jan 2004 13:00:05 -0500
 
From: "Dan Labonte" <danlabonte@cox.net>
 
Subject: Re: Team3S: Current draw with ignition off
 
 
 
Well I got the VR-4 started.  I did not measure current draw but here are
 
some resistance values for Jeff's notebook.
 
Resistance across battery terminals: 28K Ohms
 
Resistance across battery terminals (With a door open) 4-15 ohms.
 
So looks like I was chasing a short in the open door (doh.)  Well at least I
 
have all the wiring diagrams commited to memory now.
 
 
 
Dan
 
 
 
 
 
 
 
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End of Team3S: 3000GT & Stealth V2 #334
 
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