Help Needed - Long Post

[89_Nach]

I posted this in the Fox specific forum, but no luck there so I decided to put it in here.

A few days ago, I got on the car pretty good. I was doing a 2nd gear dry burnout to be more specific. Shortly after that, I began smelling something like a burning odor. I had had a leaf get caught in my headers a while back and was thinking that it might just be that again. Well, several members of my club and I drove up to Tanglewood for the Festival Of Lights. We waited in line like 2 hours to get in and I smelled the odor periodocly. We get half way through the park and pull over at a restroom/concesion place. I go to start my car back and nothing happened. It tried to turn over and everything, but just wouldn't spin over. Acted exactly like a dead battery.

Well, I get security to come out with a jumper box and jumped me off. Car ran fine after that, but I noticed on the way home that I was running like 10 volts max.

This has happened to me before. About a year ago, I sarted smelling a burning odor and had problems starting the car. I replaced the alt (90A) and the batery, just to come to find out that the negative battery cable was shorting out. Well, I looked at the cable this time. The main cable is fine, but that smaller gauge cable that ties into the neg cable apears to be shorting out. I haven't tracked it back to the place of origin yet, but I believe it is in there with the coil and starter relay somewhere.

Anyways, do any of you have any idea why I would be shorting this out? And why did it do it when I was romping on it pretty good? I am normally able to figure out almost any car issue, but this one has me stumped. ???

OK, I have posted this at a couple different places. here are some of the responses I have received:
1-Coil problem
2-starter bolt (??)
3-weak or cracked engine mount
4-ECM groud wire
5-alternator wiring

The guy who posted up the #4 response also posted this quote from the ProFlow website:
"Check the computer ground wire on the negative battery. Disconnect the negative terminal from the battery and find the small black wire and measure the resistance. The value should be 0.2 ohms or less. If this measurement is above 0.2 ohms, then add an additional 10-gauge wire to the negative battery terminal to the frame connector. Run self-test again. When you relocate the battery to the trunk, most people chop the wire from the negative terminal to the frame, and ground the battery using a short cable to the frame rail in the trunk. This will cause the vehicle to run lean and very erratic due to poor grounding of the electrical system and ECM ground. Using a welding cable, connect the battery negative terminal to the engine in the same place it was connected before the move. Use a second 10- gauge wire from the battery negative terminal to the frame connector (near the washer bottle for 88-94 models. On newer models follow the old wire from the negative terminal to the frame.) It must be restored."

What do you all think!!?? I really don't want to have this happen again. It's pissin' me off!!!!

 

[jrichker]

The small black wire coming off the negative batery cable is the battery to chassis ground. Normal current throught this wire is about 30-65 amps. More that and you get smoke. Either there is a device such as a stereo pulling excessive current or the starter or alternator has lost its ground.

Here's my standard tech note on grounds...

Grounds are important to any electrical system, and especially to computers.

1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.

2.) 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 alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery.

4.) All the sensors have a common separate ground. This includes the TPS, ACT, EGE, BAP, & VSS

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or head bolt.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally.

See http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103#volt for help troubleshooting voltage drops across grounds

 

[89_Nach]

Great info jrichker.
Tell me what you think about this:
I have two smaller gauge wires coming off the negative cable. One of them is connected to something, which I believe is the computer ground. The other is connected to nothing at all. Do you think if I connected that extra wire to a ground that it would cure my problems?
Anything that you can think of that I can do to actually FIX this problem, please let me know.
Again, I appreciate all of the good information.

 

[89_Nach]

ttt
Go to get this fixed

 

[jrichker]

Great info jrichker.
Tell me what you think about this:
I have two smaller gauge wires coming off the negative cable. One of them is connected to something, which I believe is the computer ground. The other is connected to nothing at all. Do you think if I connected that extra wire to a ground that it would cure my problems?
Anything that you can think of that I can do to actually FIX this problem, please let me know.
Again, I appreciate all of the good information.

Yes, do connect the extra black wire to ground. It is the battery to chassis ground. It won't fix any short circuits or excessive current draws, but it will provide a needed ground path. Very important little piece of wire...

 

[89_Nach]

Sounds good. I plan on re-routing my 12v supply spplices for my nitrous and gauges at the same time I hook that extra cable to a ground. I really hope that will take care of my problems.
So, just to be 100% sure, all three wires coming out of the negative battery post should be connected to a ground? The main cable to the block, one of the smaller gauge wires to the computer, and the other smaller gauge wire to a chassis ground. Correct?

 

[jrichker]

Sounds good. I plan on re-routing my 12v supply spplices for my nitrous and gauges at the same time I hook that extra cable to a ground. I really hope that will take care of my problems.
So, just to be 100% sure, all three wires coming out of the negative battery post should be connected to a ground? The main cable to the block, one of the smaller gauge wires to the computer, and the other smaller gauge wire to a chassis ground. Correct?

You are correct.

 

[4dStang]

Where is the smell coming from, inside the car or under the hood?

I just replaced an ignition switch last night that was giving me intermittent problems.

It sounds like you have trouble shooted all the starter and ground wires. Thats what I did to no avail.

Foxes had a recall on the ign switch. Poor connections in the switch can cause the car to not start one time and start another. My car acted just like yours and would start fine, I would drive and shut it off. I would get back in and no start. Jumping it would get it going again. So, I replaced the alt, starter, power and ground wires over a month and came to find it was all a 15 dollar part. Mine did not burn though, maybe because it is an SN-95. But I have replaced fox body ign switches too, they can have a tendancy to short out due to corrosion, that's what the recall was for.

 

[89_Nach]

Good info.
The smell is actually the smaller gauge wire coming off the battery (the computer ground) burning through it's insullation. That's why I think if I attached that second small gauge wire to a chassis ground it should take a lot of resistance off of the other wire.

 

[HISSIN50]

im sorry to sorta jack the thread, but since we have Joe on this topic....

i also have 3 wires on the neg terminal on my 88 GT vert (the big hog cable, a smaller [~10 gauge] wire and a smaller yet [~14 gauge] wire.

the smallest one (like a 14 gauge wire or so) is not attached to anything - sounds like it should be. the intermediate sized wire (~10 gauge or so) is attached to the inner fender, to the rear of the battery. so where should this smallest wire go? it sounds like it is the dedicated computer ground. would the car run w/o it? tips on finding the other end of the wire so i can reconnnect it (its run path, color, etc)? i checked Tom's diagrams (and likely missed it).

many thanks in advance if one has time to answer.

 

[89_Nach]

I'd like to know this too, because I believe mine is hooked up exactly as you are saying.

I took the car out last night. Cranked just fine. Volts were fine. No odor at all. Then, I got on it pretty good for a small stretch of road and, what do ya know, I can smell the burning odor! So it is primariy happening when strain is being put on the engine. I am going insane just thinking about fixing this damn thing!

 

[jrichker]

im sorry to sorta jack the thread, but since we have Joe on this topic....

i also have 3 wires on the neg terminal on my 88 GT vert (the big hog cable, a smaller [~10 gauge] wire and a smaller yet [~14 gauge] wire.

the smallest one (like a 14 gauge wire or so) is not attached to anything - sounds like it should be. the intermediate sized wire (~10 gauge or so) is attached to the inner fender, to the rear of the battery. so where should this smallest wire go? it sounds like it is the dedicated computer ground. would the car run w/o it? tips on finding the other end of the wire so i can reconnnect it (its run path, color, etc)? i checked Tom's diagrams (and likely missed it).

many thanks in advance if one has time to answer.

The computer ground has a cylinderical shaped quick connect about 1" diameter & 2" long: the wire size is 12-14 gauge. I haven't seen an aftermarket ground cable with the quick connect on it.

I cut the quick connect off the computer side of the wiring and used a crimp on ring terminal when I replaced my ground cable. I bolted the computer ground to the same spot on the chassis as the battery to chassis ground. The ground wire comes from the bundle of wires under the starter solenoid, so it would be easy to loose in the confusion.

 

[89_Nach]

jrichker - Where do you recommend grounding that other pigtail that is not currently connected to anything? Do you think this will permanently fix my problem?

Are you saying that you grounded the computer to the same place as the other pigtail (battery to chassis) ground? Like asked above, where the heck is the battery to chassis ground suppossed to be located?

I am hoping to get this resolved this afternoon so I can get the bottle filled up and have some fun during the holiday weekend.

 

[jrichker]

jrichker - Where do you recommend grounding that other pigtail that is not currently connected to anything? Do you think this will permanently fix my problem?

Are you saying that you grounded the computer to the same place as the other pigtail (battery to chassis) ground? Like asked above, where the heck is the battery to chassis ground suppossed to be located?

I am hoping to get this resolved this afternoon so I can get the bottle filled up and have some fun during the holiday weekend.

Aside from the big wire that bolts to the block, all the other ground wires should connect to a common ground near the battery. Just clean off a spot nice and shiny and bolt them all down together.

I was editing my last post which now has more of the info you are looking for. Sorry, but I think that if you read it now that I have finished making it easier to understand, you'll find more help.

.

 

[89_Nach]

Thanks!
There is actually something grounded to the top of the radiator support right beside the battery. That should work right? There is also a ground in the similar location but on the other side of the rad support by the passenger fender. That is where I have my nitrous components grounded.

I cut the quick connect off the computer side of the wiring and used a crimp on ring terminal when I replaced my ground cable. I bolted the computer ground to the same spot on the chassis as the battery to chassis ground.

Does this mean that the computer wire does not go to the battery? It just goes straight from that mess of wires near the coil stright to a ground, then the battery to chassis ground is located in the same spot? It think this is what you are saying. Sorry for all the questions. But when it comes to wiring, it is always better to be safe than sorry.

 

[HISSIN50]

The computer ground has a cylinderical shaped quick connect about 1" diameter & 2" long: the wire size is 12-14 gauge. I haven't seen an aftermarket ground cable with the quick connect on it.

I cut the quick connect off the computer side of the wiring and used a crimp on ring terminal when I replaced my ground cable. I bolted the computer ground to the same spot on the chassis as the battery to chassis ground. The ground wire comes from the bundle of wires under the starter solenoid, so it would be easy to loose in the confusion.

Joe, thanks so much.

IIRC, the previous owner had the dealer replace the cables and i do have that little connector a few inches off the neg terminal (it looks like a blue butt connector, but now that you mention it, it could be a bullet-type connector). i will tear through my rats nest of wires off the solenoid (feeds for relays and such. arrgh. LOL) and see if i can find that wire. i'll either route it back to the battery (oem look) or simply use the same ground as the other smaller wire off the neg terminal (chassis ground). many many thanks, Joe!

 

[89_Nach]

Well, I think I git it fixed!
I took the additional pigtail to a ground on the rad support. I also tracked the other wire back to it's origin. It is grounded behind the battery with another wire, which I assume is the computer ground. Anyways, I took it out for some blasts today and had absolutely no problems.
While I was at it, I checked my TPS. It was set at 1.08!!!!! I took it down to .95 and the difference in throtte response and overall performance is incredible!
Thanks jrichker and too anyone else who provided assistance.

 

[HISSIN50]

89 Nach, congrats!

ok im back. 89 Nach (or Joe - though i hate to bother him again):
on the chassis ground, do you remember if the chassis ground has another wire terminating at that ground with it (the bolt next to the battery)? i have the chassis ground (from neg battery terminal) and another black wire (maybe 12 gauge) that is on the same ring terminal at the chassis ground. the 12 gauge wire has a glass fuse lookin connector about 3 inches from the ground bolt. im trying to figure out if someone did a professional job of grounding the puter ground (doing a nice terminal with the neg terminal to chassis ground) or if my puter ground might still be loose somewhere. i cant find it in the rats nest.

TIA for any thoughts of advice.

 

[jrichker]

89 Nach, congrats!

ok im back. 89 Nach (or Joe - though i hate to bother him again):
on the chassis ground, do you remember if the chassis ground has another wire terminating at that ground with it (the bolt next to the battery)? i have the chassis ground (from neg battery terminal) and another black wire (maybe 12 gauge) that is on the same ring terminal at the chassis ground. the 12 gauge wire has a glass fuse lookin connector about 3 inches from the ground bolt. im trying to figure out if someone did a professional job of grounding the puter ground (doing a nice terminal with the neg terminal to chassis ground) or if my puter ground might still be loose somewhere. i cant find it in the rats nest.

TIA for any thoughts of advice.

The fuse looking thing is the computer ground quick connect I was trying to describe. The ground pigtal could have a ring termnial and the computer ground quick connect on the same wire. It would make sense to do it that way, since it would be cheaper to manufacture.

 

[HISSIN50]

The fuse looking thing is the computer ground quick connect I was trying to describe. The ground pigtal could have a ring termnial and the computer ground quick connect on the same wire. It would make sense to do it that way, since it would be cheaper to manufacture.

thanks so much Joe. i had a feeling, but was not sure at all (i have not seen the original configuration to know what to look for). so it sounds like the puter has its ground (since there are two OEM grounds on the chassis ground bolt, including the one with the glass-fuse holder connector).

again, many thanks.
Happy New Year!