Electrical ecm draw

wifoxbody · Sep 15, 2021

Hi I have a battery draw 10.64 I tracked it down to the ECM if I unplug it the draw goes away . Disconnected just about everything alt. wiper every connector i can find pulled All the fuses / relays .could the ecm be bad ? it runs great but the battery go dead.

manicmechanic007 · Sep 16, 2021

10.64 what? Car is a what?
The ECM has KAM that takes juice to work properly (Keep Alive Memory)
Your radio and your air bag module also take voltage to function
Your GEM module and the ABS as well
Above and below 200 miliamp total draw used to be the cut
If You are above a 200 miliamp draw I would worry

manicmechanic007 · Sep 16, 2021

If you do not drive the car enough
And the battery goes dead
You will be buying a battery every 9 months or so
A battery is only good for about 5 or 6 complete drains
The battery will be no good
It will not hold a charge
Drive the car or buy a battery tender is all you can do
Perform a negative draw test and report back the ma reading
You all should learn to perform the above test with a DVOM

wifoxbody · Sep 16, 2021

manicmechanic007 said:
10.64 what? Car is a what?
The ECM has KAM that takes juice to work properly (Keep Alive Memory)
Your radio and your air bag module also take voltage to function
Your GEM module and the ABS as well
Above and below 200 miliamp total draw used to be the cut
If You are above a 200 miliamp draw I would worry

wifoxbody · Sep 16, 2021

1989 mustang 5.0 it has a a draw of 10.64 volts .

Hoytster · Sep 16, 2021

wifoxbody said:
1989 mustang 5.0 it has a a draw of 10.64 volts .

Draw is measured in amperage, not volts. Can you explain how you are measuring the draw of the ECU? It sounds like you are just measuring the battery voltage itself.

Hoytster · Sep 16, 2021

Here is a write up on how to properly measure parasitic draw in an auto electrical system as reference.

Testing for Parasitic Draw with a Multimeter | Test Meter Pro

As long as you have a multimeter and a bit of savvy, you don’t need to be a professional to check for parasitic draw. See this basic step by step process...

testmeterpro.com

manicmechanic007 · Sep 16, 2021

Yes look up negative draw test
You are reading the dead battery voltage the 10.64v
Disconnect the negative battery terminal
Place the negative meter lead on the battery post
Positive lead on the negative battery cable you removed
Switch the scale to 10A setting
The current the car is using runs thru the meter
On the 10A scale 200ma is a real small number
I have 3 DVOM's I use
Use an autoranging meter for this test if you can

manicmechanic007 · Sep 16, 2021

Usually start that test with just a test light
Put a test light between the post and cable
You should see a very dim glow (that's the 180ma that a properly functioning car draws)
Open a door or the glovebox and the test light gets full bright
If you have a meter attached at that point
The meter will read 1 to 4 amps and your battery will be dead within hours
Good luck

wifoxbody · Sep 16, 2021

Hoytster said:
Draw is measured in amperage, not volts. Can you explain how you are measuring the draw of the ECU? It sounds like you are just measuring the battery voltage itself.

I have the deg. cable off and going between neg. battery post with a multimeter to neg. battery cable and getting
10.60 volts the 0 when disconnect the ecm

wifoxbody · Sep 16, 2021

manicmechanic007 said:
Yes look up negative draw test
You are reading the dead battery voltage the 10.64v
Disconnect the negative battery terminal
Place the negative meter lead on the battery post
Positive lead on the negative battery cable you removed
Switch the scale to 10A setting
The current the car is using runs thru the meter
On the 10A scale 200ma is a real small number
I have 3 DVOM's I use
Use an autoranging meter for this test if you can

i have the multimeter between neg. cable and neg. post and getting 147ma at 20m on multimeter 0 when ecm disconnected I also put a 12 volt test light between neg. cable a nd neg. post and it is very bright no light when disconnected the ecm

manicmechanic007 · Sep 17, 2021

wifoxbody,
147ma looks good (within spec)
When you say very bright light
Do you mean it is just as bright as if you just went post to post on the battery?
If that is the case the processor may very well have a shorted driver or something wrong with it
Book would ask us "is it warm to the touch" (the processor) "does it pass the smell test" Does the processor smell burnt?
Most common battery issue I used to find that was alternator field staying lit (on) all night
Check it by disconnecting the alternator
See if a screwdriver sticks to the alternator with the key on
You may just need a new battery if it will not hold a charge
Meaning it will not let you start the car after say a ten day wait

manicmechanic007 · Sep 17, 2021

Replaced quite a few processors over the years
Only two actually needed it
The rest got replaced on a whim under warranty
Ford hated that
Used to send bulletins saying that the processors they were getting back were found to be functioning properly
Meaning Ford would deny the claim and then the dealer would back flag the technician
Quickly learned to let the smoke out of them before sending them back

manicmechanic007 · Sep 17, 2021

That 89 you have is quite forgiving as far as running the wrong ecm
Pick up one or two from the junkyard even if it is from a truck the car should run
Get one from the same year and the same number of cylinders
Light will be on and may run poorly (clutch vs auto et al)
That way you can test it by letting it sit a few days and retesting the battery
Once you get it figured out you will have a spare processor that will run the car for test purposes
All of you should have a spare processor if you plan on keeping your car forever
A good factory rebuilt ecm is a hard thing to find when you actually need one and they are not going to get any cheaper

manicmechanic007 · Sep 17, 2021

If you brought that car into my shop
First thing I would be checking is if it has an aftermarket radio and where did they hook the illumination wire
Second the glove box light and the dome light circuit
Followed by brake light and horn circuits, horn relay
Then power locks windows accessories like fog lights and the foglamp and headlamp switch connectors
Looks like you have done all that
Then finally the weird stuff processor alternator
147ma should not give you a bright light
I am giving your processor a pass from here
Get another test processor anyway

wifoxbody · Sep 17, 2021

manicmechanic007 said:
If you brought that car into my shop
First thing I would be checking is if it has an aftermarket radio and where did they hook the illumination wire
Second the glove box light and the dome light circuit
Followed by brake light and horn circuits, horn relay
Then power locks windows accessories like fog lights and the foglamp and headlamp switch connectors
Looks like you have done all that
Then finally the weird stuff processor alternator
147ma should not give you a bright light
I am giving your processor a pass from here
Get another test processor anyway

thanks for the help I dont know what I am going to do maybe drive every day and disconnect battery when not in use like the last owner.

90sickfox · Sep 19, 2021

Auto and manual computers are different and you could burn a circuit in the ecu if swapped. The o2 sensor circuit is wired different.

147ma is a small amount of draw. That shouldn't kill the battery over night. There are a bunch of circuits that run through the computer that could be causing a draw.

Have you checked the condition of the electrical part of the ignition switch ?

Remove the computer and open the case. Check for gunk around the bottom of the capacitors and for burned traces on the board. Also, like above, smell it to see if it smells like burned plastic. Check for melted stuff on the board. If it's causing the draw something shorted out and will be melted, burned, cracked, or throwing up on the board.

If the battery reads above 14v running at 1500rpm and goes to 10.**v when cut off for a few minutes the battery is probably bad. When was it last replaced ? I've seen 3 month old " new " parts store batteries go bad.

manicmechanic007 · Sep 20, 2021

I have ran the wrong processor on many trucks and cars for test purposes
The only thing you are going to possibly burn is the processor
That is what he is testing anyway
The only light I used to get was for clutch interlock on the automatics
Shift solenoid codes on the manuals
No smoke
note;
I gave his processor a pass because it had less than a 200ma draw
He could plug another in and test the draw on it just for his sanity

Electrical ecm draw

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Testing for Parasitic Draw with a Multimeter | Test Meter Pro

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Electrical ecm draw

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