Hooked up battery backwards... misfire issue

[STL WRX]

Ok here's what happened. Alternator went out, alternator replaced and father hooked up battery backwards and heard a "POP" on the passenger side of the engine bay. Now when you start the car it will idle up like normal but once the rev's come down to around 700rpm the car starts missing. When driving the car it misfires horribly and is undrivable. When you remove the alternator signal connector (green) on the alternator or the 10amp "meter" fuse the car runs great and doesn't misfire though runs on battery power and the voltage drops greatly. Has anyone else had this happen? What did you replace?

So far items replaced after the battery was hooked up backwards:

New 80amp main fuse
New alternator
New gauge cluster
All fuses and replays check out to be fine
New battery
Ive chased wires for shorts and found nothing.
Replaced all 4 coilpacks and sparkplugs

I have had alot of help from Cougar4 here on nasioc and this thread was his suggestion to see if anyone has done this and if they had the same misfire issue after hooking up the battery backwards.

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[hybrid gti 2]

ouch

Did you check the battery cables? Specially the negative from the battery to the engine.

Need to tell more about what happens when. As misfires are hard to diagnosis.

[axelthrasher]

Try some additional grounding wires. It sorta sounds to me like it might be some ****ty grounds. Just run some additional grounds to a few things and it may help. (Check out Paranoid Fabrications ground wire kits, I run one and couldn't be happier for the price and all. Plus Shane is really helpful.)

[vision.dynamix]

How did he hook up the battery backwards? The cabels barely reach as is, nevermind to the other side of the battery.

[rick-l]

Link to Original Thread

[Cougar4]

I woke up early this morning and while laying in bed awake this problem poped into my head and I did some more thinking on this. It appears you don't want to try out my idea of using a filter capacitor to see if that will eliminate the noise problem so I guess you should try something else. We have brought this up earlier and I think you need to look at the grounding system and check for bad grounds that may have been damaged when the battery was connected in reverse. Check for trouble particularly around the battery area but also check the engine and chassis ground leads. This is what Rick-l has been saying also. I know from past experience others have had this same kind of trouble and by cleaning the ground connections the problem cleared.

You may also be able to find the trouble area by making a ground jumper lead. Tie one end to the negative battery post and then touch the other end to suspected bad ground points while the engine is running to see if the missing clears.

[STL WRX]

I have tried grounding the neg battery side to many points on the engine but it still misses. Subaru tech called me today and says SOA says its the ground side of the ecm is blown... could this be?

I have tomorrow off and wed and thur off next week to try and diagnose if I dont end up trading it. LOL

I am not giving up just yet.

[hybrid gti 2]

I was going to say that might be possible but was unsure as there are to many misfire possibilities.

[rick-l]

Originally Posted by STL WRX

. Subaru tech called me today and says SOA says its the ground side of the ecm is blown... could this be?

I hate to just throw parts at something but you might not have a choice. Could be that SOA has some previous experience with this.

Do they have a spare they could try without you having to buy a new ECU with no guarantee of success?

[STL WRX]

Originally Posted by rick-l

I hate to just throw parts at something but you might not have a choice. Could be that SOA has some previous experience with this.

Do they have a spare they could try without you having to buy a new ECU with no guarantee of success?

No they dont... I dont wanna buy a computer and it not work, though I am sure I would get my money back but its the fact rent and bills are more important right now.

[Cougar4]

Originally Posted by STL WRX

I have tried grounding the neg battery side to many points on the engine but it still misses. Subaru tech called me today and says SOA says its the ground side of the ecm is blown... could this be?

That advice could very well could be true but I have one exception to it. That is the alternator. Why does disabling it clear the trouble?

There could be some filtering inside the ECU that is there to filter the power input and alternator noise and I would not be a bit surprised if some filter caps got damaged on the positive side of the power input or, some ground leads in the ECU were damaged. This was mentioned in earlier posts. You could remove the ECU and and open it up to check things out inside it and this is pretty easy to do. I have repaired them in the past for different problems. Check for obvious signs of damage like burned capacitors or wires.

If it does come down to getting another ECU you could try to find a used on or rebuilt one. It would be a lot less expensive than a new factory unit, by at least half I would guess.

[STL WRX]

Originally Posted by Cougar4

That advice could very well could be true but I have one exception to it. That is the alternator. Why does disabling it clear the trouble?

There could be some filtering inside the ECU that is there to filter the power input and alternator noise and I would not be a bit surprised if some filter caps got damaged on the positive side of the power input or, some ground leads in the ECU were damaged. This was mentioned in earlier posts. You could remove the ECU and and open it up to check things out inside it and this is pretty easy to do. I have repaired them in the past for different problems. Check for obvious signs of damage like burned capacitors or wires.

If it does come down to getting another ECU you could try to find a used on or rebuilt one. It would be a lot less expensive than a new factory unit, by at least half I would guess.

Hahahaha the tech that worked on my car had the top off the ecu when he was fumbling around with the multimeter chasing wires. He said the electronics in the car was fine but then again at the end of the day he said I had water in my gas.

Cougar, is there anyway to check the grounds on the ecu?

[STL WRX]

Pinouts for the ecu.... I may pull individual wires out (grounds) and see if the missing stops to pinpoint the problem if its in the ecu or wiring.


ENGINE (DIAGNOSTICS)(H4DOTC) > Engine Control Module (ECM) I/O Signal

ELECTRICAL SPECIFICATION



Content
Connector No.
Terminal No.
Signal (V)
Note

Ignition SW ON

(Engine OFF)
Engine ON (Idling)

Crankshaft position sensor
Signal (+)
B135
2
0
***8722;7 — +7
Sensor output waveform

Signal (***8722;)
B135
11
0
0
—

Shield
B135
21
0
0
—

Camshaft position sensor
Signal (+)
B135
1
0
***8722;7 — +7
Sensor output waveform

Signal (***8722;)
B135
10
0
0
—

Shield
B135
21
0
0
—

Throttle position sensor
Signal
B135
7
Fully closed: 0.2 — 1.0

Fully opened: 4.2 — 4.7
—

Power supply
B135
9
5
5
—

GND (sensor)
B135
19
0
0
—

Rear oxygen sensor
Signal
B135
17
0
0 — 0.9
—

Shield
B135
26
0
0
—

GND (sensor)
B135
19
0
0
—

Front oxygen (A/F) sensor heater
Signal 1
B84
5
0 — 1.0
—
Waveform

Signal 2
B84
4
0 — 1.0
—
Waveform

Rear oxygen sensor heater signal
B137
13
0 — 1.0
—
Waveform

Engine coolant temperature sensor
Signal
B135
18
1.0 — 1.4
1.0 — 1.4
After warm-up the engine.

GND (sensor)
B135
19
0
0
After warm-up the engine.

Vehicle speed signal
B134
1
0 or 5
0 or 5
“5” and “0” are repeatedly displayed when vehicle is driven.

Mass air flow sensor
Signal
B136
13
—
0.3 — 4.5
—

Shield
B136
8
0
0
—

GND
B136
7
0
0
—

Intake air temperature sensor signal
B135
27
0.3 — 4.6
0.3 — 4.6
—

Exhaust temperature sensor
Signal
B135
16
—
2.7 — 2.8 (750°C)
—

GND

(sensor)
B135
19
0
0
—

Tumble generator valve position sensor RH
Signal
B135
23
Fully closed: 3.8 — 4.9

Fully opened: 0.2 — 0.9
—

Power supply
B135
9
5
5
—

GND

(sensor)
B135
19
0
0
—

Tumble generator valve position sensor LH
Signal
B135
13
Fully closed: 3.8 — 4.9

Fully opened: 0.2 — 0.9
—

Power supply
B135
9
5
5
—

GND

(sensor)
B135
19
0
0
—

Tumble generator valve RH (open)
B136
4
0 or 10 — 13
0 or 13 — 14
Waveform

Tumble generator valve RH (close)
B136
5
0 or 10 — 13
0 or 13 — 14
Waveform

Tumble generator valve LH (open)
B136
10
0 or 10 — 13
0 or 13 — 14
Waveform

Tumble generator valve LH (close)
B136
11
0 or 10 — 13
0 or 13 — 14
Waveform

Wastegate control solenoid valve
B84
24
0 or 10 — 13
0 or 13 — 14
Waveform

Starter switch
B134
16
0
0
Cranking: 8 — 14

A/C switch
B134
2
ON: 10 — 13

OFF: 0
ON: 13 — 14

OFF: 0
—

Ignition switch
B134
5
10 — 13
13 — 14
—

Neutral position switch (MT model)
B134
8
ON: 10 — 13

OFF: 0
ON: 13 — 14

OFF: 0
—

Neutral position switch (AT model)
B134
8
ON: 0

OFF: 10 — 13
ON: 0

OFF: 13 — 14
—

Test mode connector
B134
14
5
5
When connected: 0

Knock sensor
Signal
B135
4
2.8
2.8
—

Shield
B135
22
0
0
—

Back-up power supply
B84
10
10 — 13
13 — 14
Ignition switch “OFF”: 10 — 13

Control unit power supply
B84
2
10 — 13
13 — 14
—

B84
3
10 — 13
13 — 14
—

Sensor power supply
B135
9
5
5
—

Ignition control
#1
B137
24
0
13 — 14
Waveform

#2
B137
23
0
13 — 14
Waveform

#3
B137
22
0
13 — 14
Waveform

#4
B137
21
0
13 — 14
Waveform

Fuel injector
#1
B84
1
10 — 13
1 — 14
Waveform

#2
B137
6
10 — 13
1 — 14
Waveform

#3
B137
5
10 — 13
1 — 14
Waveform

#4
B137
4
10 — 13
1 — 14
Waveform

Idle air control solenoid valve
Signal
B137
10
0 or 13 — 14
0 or 13 — 14
Waveform

Fuel pump control unit
Signal 1
B134
13
0 or 5
0 or 5
—

Signal 2
B137
15
10 — 13
10 — 13
—

A/C relay control
B84
27
ON: 0.5 or less

OFF: 10 — 13
ON: 0.5 or less

OFF: 13 — 14
—

Radiator fan relay 1 control
B84
17
ON: 0.5 or less

OFF: 10 — 13
ON: 0.5 or less

OFF: 13 — 14
—

Radiator fan relay 2 control
B84
28
ON: 0.5 or less

OFF: 10 — 13
ON: 0.5 or less

OFF: 13 — 14
Model with A/C only

Malfunction indicator light
B84
15
—
—
Light “ON”: 1 or less

Light “OFF”: 10 — 14

Engine speed output
B137
9
—
0 — 13, or more
Waveform

Purge control solenoid valve
B84
16
ON: 1 or less

OFF: 10 — 13
ON: 1 or less

OFF: 13 — 14
Waveform

Manifold absolute pressure sensor
Signal
B135
8
1.7 — 2.4
1.1 — 1.6
—

Power supply
B135
9
5
5

GND (sensor)
B135
19
0
0

Fuel tank pressure sensor
Signal
B135
15
2.3 — 2.7
2.3 — 2.7
The valve operates when fuel filler cap is removed and reinstalled.

GND (sensor)
B135
19
0
0
—

Pressure control solenoid valve
B84
22
ON: 1 or less

OFF: 10 — 13
ON: 1 or less

OFF: 13 — 14
—

Drain valve
B84
11
ON: 1 or less

OFF: 10 — 13
ON: 1 or less

OFF: 13 — 14
—

Fuel tank sensor control valve
B84
23
ON: 1 or less

OFF: 10 — 13
ON: 1 or less

OFF: 13 — 14
—

Fuel level sensor
B135
25
0.12 — 4.75
0.12 — 4.75
—

Fuel temperature sensor signal
B135
6
2.5 — 3.8
2.5 — 3.8
Ambient temperature:

25°C (75°F)

Blow-by leak diagnosis signal
B137
2
0
0
When disconnection (malfunction) = 5

Small light switch
B134
17
ON: 0

OFF: 10 — 13
ON: 0

OFF: 13 — 14
—

Blower fan switch
B134
9
ON: 0

OFF: 10 — 13
ON: 0

OFF: 13 — 14
—

Rear defogger switch
B134
3
ON: 0

OFF: 10 — 13
ON: 0

OFF: 13 — 14
—

Power steering oil pressure switch
B135
24
10 — 13
ON: 0

OFF: 13 — 14
—

Front oxygen (A/F) sensor signal (+)
B84
29
2.8 — 3.2
2.8 — 3.2
—

Front oxygen (A/F) sensor signal (***8722;)
B84
19
2.4 — 2.7
2.4 — 2.7
—

Front oxygen (A/F) sensor shield
B84
18
0
0
—

SSM/GST communication line
B134
21
Less than 1 ***8592;***8594; More than 4
Less than 1 ***8592;***8594; More than 4
—

Torque control 1 signal
B134
19
More than 4
More than 4
—

Torque control 2 signal
B134
18
More than 4
More than 4
—

Torque control cut signal
B137
14
8
8
—

AT diagnosis input signal
B135
20
Less than 1 ***8592;***8594; More than 4
Less than 1 ***8592;***8594; More than 4
Waveform

AT load signal
B135
28
4.3 — 4.4
0.9 — 1.4
—

GND (sensors)
B135
19
0
0
—

GND (injectors)
B137
8
0
0
—

GND (ignition system)
B137
18
0
0
—

GND (power supply)
B137
17
0
0
—

B134
22
0
0
—

GND (control systems)
B134
7
0
0
—

B134
15
0
0
—

GND (front oxygen (A/F) sensor heater 1)
B84
9
0
0
—

GND (front oxygen (A/F) sensor heater 2)
B84
8
0
0
—

[Cougar4]

You can check the ground connections using an ohmmeter. You should able to find a common ground point like the ECU chassis to tie one probe of the meter to and then check each of the ground pins with the other probe. You may also want to back probe the connector pins going to ground to make sure they are ok.

One possible problem with this testing could be is if there is a bad filter cap on the power input to the ECU your ohmmeter will not see that and you will be wasting your time. If you would follow my advice about installing the filter caps as I stated in post #27 of the original thread we may be able to save a lot needless time and testing.

[STL WRX]

I went to radioshack and got the caps you said to get and as soon as I hooked the leads up they arched and popped. I think I may have messed up but as of this moment I am taking it to the dealership and dropping it off. I am going to call Fred my service manager and just tell them to find the problem and call me before they order anything.

Appreciate all the help.

[Cougar4]

A small amount of arc should have taken place hooking up the 10 uf cap. That is just a normal charging up action going on of the capacitor. It is also polarity sensitive so if it wasn't connected correctly it will pop.

The smaller capacitor should not have sparked and that is the one I was really interested in seeing what happened. If you want to try it still you don't have to worry about polarity. Just don't let the positive connections short to ground.

You're welcome for the help and if you just don't want to fool with this problem anymore I understand. I suspect that a replacement ECU will fix this trouble.

[STL WRX]

Well I took it and dropped it off at the dealership and left the keys and a note with a salesman. They will see it in the morning and I bet the tech that worked on it will crap his pants... either that or quit.

HAHAHAHA LOL!

I hope to have her back soon and this time running!

[Cougar4]

I would guess they will first try a different ECU since Subaru said it was most likely bad.

[Skoloseven]

Wow. Following this thread.

[STL WRX]

So I go up the dealer and ask the tech if he had found the problem and he says this "The STI gauge cluster is whats causing your car to misfire since its not made for your car and that's what the problem is" So I get pissed off and tell him that's not the issue (since hundred of guys with WRX's have STI clusters and their cars run just fine) and also the car misfires even with the old WRX cluster in and this issue happend after the battery was hooked up backwards way before the STI cluster was even thought of and ordered. Then he changes his whole story saying he thinks it may be the computer. I then ask him why he said it was the cluster and he kept avoiding my question. So tomorrow when I call up there for and update if he hasn't' found the issue I am going to speak with the service manager and ask for a more competent mechanic to work on my car, not someone that avoids my questions and had worked on my car since 8am to 4pm and not found any real issues.

He couldn't even tell me why the car runs when you unplug the meter fuse and then misfires when you plug it back in.

Stay tuned.

[ronzogonzo]

possibly a fried coil pack? that is an electrical item. im just guessing but, i really dont think you fried your ecu. thats why you have fuses

[06WRBScoob]

What kind of voltage do you have when the car is running? It is possible that you fried your voltage regulator, possible undervoltage causing missfire. When you dissconect the wires is takes the alternator out of the loop. I would check your battery & all big power connections.

[STL WRX]

Tried new coilpacks and sparkplugs.... didnt fix it.

there is a new alternator on it so the regulator is fine.

Voltage is 14.5 when the car is running.

[Cougar4]

Originally Posted by STL WRX

So I go up the dealer and ask the tech if he had found the problem and he says this "The STI gauge cluster is whats causing your car to misfire since its not made for your car and that's what the problem is" So I get pissed off and tell him that's not the issue (since hundred of guys with WRX's have STI clusters and their cars run just fine) and also the car misfires even with the old WRX cluster in and this issue happend after the battery was hooked up backwards way before the STI cluster was even thought of and ordered. Then he changes his whole story saying he thinks it may be the computer. I then ask him why he said it was the cluster and he kept avoiding my question. So tomorrow when I call up there for and update if he hasn't' found the issue I am going to speak with the service manager and ask for a more competent mechanic to work on my car, not someone that avoids my questions and had worked on my car since 8am to 4pm and not found any real issues.

He couldn't even tell me why the car runs when you unplug the meter fuse and then misfires when you plug it back in.

Stay tuned.

Sorry to hear that. This is the very thing I was afraid would happen and tried to warn you about earlier if you did this. A big bill would be run up in trying to find the trouble.

This problem is not typical and truely requires the skills of an expert electrical technician that understands electrical noise. I really think though you have already eliminated most if not all the possible sources of this trouble except the ECU. Since SOA has already stated that they believe the trouble is inside it I am surprised the service shop has not tried replacing it first off.

You might try shopping around the salvage yards in your area to see if you can locate a used ECU. It would save you a lot of money over a new one.

[STL WRX]

Originally Posted by Cougar4

Sorry to hear that. This is the very thing I was afraid would happen and tried to warn you about earlier if you did this. A big bill would be run up in trying to find the trouble.

This problem is not typical and truely requires the skills of an expert electrical technician that understands electrical noise. I really think though you have already eliminated most if not all the possible sources of this trouble except the ECU. Since SOA has already stated that they believe the trouble is inside it I am surprised the service shop has not tried replacing it first off.

You might try shopping around the salvage yards in your area to see if you can locate a used ECU. It would save you a lot of money over a new one.

They only charged us an hour labor for all day work... we know the service manager LOL!

We are waiting for subaru to send a test ecm to see if thats the issue.