• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

Surging Idle after 3g Install

  • Thread starter Thread starter 66stangbluework
  • Start date Start date Oct 9, 2006
6

66stangbluework

New Member
May 5, 2005
113
0
0
Oct 9, 2006
#1
  • Oct 9, 2006
  • #1
Just installed my 3g Alternator and the idle surges, I have not yet installed the 4g ground could this be the problem. Very dissapointed. I have no voltmeter.
 

Snikt89GT

New Member
Sep 6, 2006
264
1
0
Deland, Florida
Oct 9, 2006
#2
  • Oct 9, 2006
  • #2
66stangbluework said:
Just installed my 3g Alternator and the idle surges, I have not yet installed the 4g ground could this be the problem. Very dissapointed. I have no voltmeter.
Click to expand...

I didn't upgrade the ground and i'm not having a problem.
 
6

66stangbluework

New Member
May 5, 2005
113
0
0
Oct 9, 2006
#3
  • Oct 9, 2006
  • #3
now the black/red wire is supposted to be hooked up to the post on the back of the alternator right? along with a 4g wire going from the post to the positive post on the starter solinoid?
 

Snikt89GT

New Member
Sep 6, 2006
264
1
0
Deland, Florida
Oct 9, 2006
#4
  • Oct 9, 2006
  • #4
66stangbluework said:
now the black/red wire is supposted to be hooked up to the post on the back of the alternator right? along with a 4g wire going from the post to the positive post on the starter solinoid?
Click to expand...


That's how I did it (and how most instructions read), but some people on here will tell you that's wrong and just to put the 4G wire on and not the stock ~10G wires.

You really need a voltmeter to check if it's running properly at idle
 
6

66stangbluework

New Member
May 5, 2005
113
0
0
Oct 9, 2006
#5
  • Oct 9, 2006
  • #5
im so worried I fried something *bangs head into wall repeatedly* If I have a new 4gauge wire running from the post on the 3g to the post on the solinoid do i still need the black/red wires
 
6

66stangbluework

New Member
May 5, 2005
113
0
0
Oct 9, 2006
#6
  • Oct 9, 2006
  • #6
also if the serpentine belt was too tight would it do this?
 

Snikt89GT

New Member
Sep 6, 2006
264
1
0
Deland, Florida
Oct 9, 2006
#7
  • Oct 9, 2006
  • #7
66stangbluework said:
also if the serpentine belt was too tight would it do this?
Click to expand...

I highly doubt it, why do you think it's too tight?
 

jrichker

StangNet's favorite TOOL
In Remembrance. Thank you for your contributions
Mar 10, 2000
27,512
2,813
234
Dublin GA
Oct 9, 2006
#8
  • Oct 9, 2006
  • #8
66stangbluework said:
im so worried I fried something *bangs head into wall repeatedly* If I have a new 4gauge wire running from the post on the 3g to the post on the solinoid do i still need the black/red wires
Click to expand...
The black/orange wires should be left connected at the starter solenoid but not connected to the 3G alternator. That prevents any overload or fire problems when you use a properly fused 4 gauge power feed from the alternator to starter solenoid.

The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects. The best
place for the block ground is where the battery ground for the
starter bolts down.
The 3G has a 130 amp capacity, so you
wire the power side with 4 gauge wire. It stands to reason that the
ground side handles just a much current, so it needs to be 4
gauge too.

The chassis ground and battery pigtail ground go to the bolt being
pointed at in the following photo.

Picture courtesy timewarped1972

Once you have fixed your ground problem, see "Help me create the Surging Idle Checklist" at http://forums.stangnet.com/showthread.php?t=534062
for help with your idle problems. The first post contains all the updates to the fixes. I continue to update it as more people post fixes or ask questions.
 

Attachments

  • ground.webp
    29.6 KB · Views: 142
6

66stangbluework

New Member
May 5, 2005
113
0
0
Oct 9, 2006
#9
  • Oct 9, 2006
  • #9
Thanks All. The system was just not used to a good amperage I guess. Everything worked out after it ran for a bit. I thought the belt was too tight because the pully off of the 3g was a little bigger. I was just bieng paranoid. Thanks for the help :SNSign: :SNSign:
 
6

66stangbluework

New Member
May 5, 2005
113
0
0
Oct 9, 2006
#10
  • Oct 9, 2006
  • #10
Thanks All. The system was just not used to a good amperage I guess. Everything worked out after it ran for a bit. I thought the belt was too tight because the pully off of the 3g was a little bigger. I was just bieng paranoid. Thanks for the help :SNSign: :SNSign:
 

HISSIN50

"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
31,179
34
129
Oct 9, 2006
#11
  • Oct 9, 2006
  • #11
Glad you got it. If you had the battery disconnected during the install, it indeed could have been relearning where it needs to be. I've seen a few 5.0's idle-hunt, idle low when cold, etc for a few drives after the KAM is cleared.

Review JR's post to make sure it's all copacetic and that you have the additional power ground pathway and you should be good.

Enjoy!
 
You must log in or register to reply here.

Similar threads

8
Foxbody high rpms and surging rpms
  • 86foxseth
  • Jun 9, 2026
  • Fox 5.0 Mustang Tech
Replies
4
Views
217
Fox 5.0 Mustang Tech Jun 13, 2026
Noobz347
3
Electrical Starter solenoid green wire?
  • 387lx
  • Jun 1, 2026
  • Fox 5.0 Mustang Tech
Replies
3
Views
161
Fox 5.0 Mustang Tech Jun 2, 2026
AeroCoupe
C
Engine Idle cuts out
  • claypoolxx
  • Mar 7, 2026
  • Fox 5.0 Mustang Tech
  • 2
Replies
25
Views
797
Fox 5.0 Mustang Tech Jul 24, 2026
alutwon
G
Idle surging after warm up
  • GALLY3309
  • Jun 10, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
1
Views
136
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Jun 10, 2026
Noobz347
Engine Surging idle on start-up
  • keel
  • Aug 11, 2025
  • Fox 5.0 Mustang Tech
Replies
16
Views
945
Fox 5.0 Mustang Tech Oct 31, 2025
keel
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?