Team3S: 3000GT & Stealth Thursday, January 1
2004 Volume 02 : Number 334
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Date: Wed, 31 Dec 2003 00:32:56 -0000
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.
- ----- Original Message -----
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
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
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
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Date: Tue, 30 Dec 2003 20:34:41 -0500
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
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
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).
- ----- Original Message -----
Sent: Tuesday, December 30, 2003 6:34 PM
Subject: Re: Team3S: Car won't start
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Date: Wed, 31 Dec 2003 22:09:19 -0000
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,
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Date: Wed, 31 Dec 2003 15:32:21 -0800
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
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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