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  My 90 needs some help

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Author Topic:   My 90 needs some help
motorhead102482
Journeyman

Posts: 5
From: Bellevue, NE 68123
Registered: Jun 2005

posted 06-05-2005 01:34 PM     Click Here to See the Profile for motorhead102482   Click Here to Email motorhead102482     Edit/Delete Message   Reply w/Quote
First off, i'm decently skilled when it comes to automobiles, but i'm just having some problems. My 90 mustang has a charging problem. It runs like the alternator isn't working. The battery drains as i drive it and i get no charge indication on my voltmeter. The alternator is new, and i have had it checked and the auto parts store says it's good. I checked the wiring to and from and all around according to the wiring diagrams and it checked fine as far as continuity goes. When i run the car i checked the voltages coming off the windings of the alternator and i'm only getting like 11.8 v. Also, my 90 has a lot of vibration when revving up to 3000 rpms or so. Would it be more likely that it is my flywheel or my driveshaft, or could it be my ujoints on my driveshaft. Any help or advice would be appreciated.

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motorhead102482
Journeyman

Posts: 5
From: Bellevue, NE 68123
Registered: Jun 2005

posted 06-05-2005 02:00 PM     Click Here to See the Profile for motorhead102482   Click Here to Email motorhead102482     Edit/Delete Message   Reply w/Quote
also, i would like to know if there are any common places that oil likes to leak. I have some oil leaking from the back of the engine and i'm not sure if it's the valve covers or the head gaskets, would i see a lot more problems if oil was leaking from the heads other than just leaking oil. I"m not overheating and dont have coolant in the oil.

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ddenton749
unregistered
posted 06-06-2005 08:46 AM           Edit/Delete Message   Reply w/Quote
Q1: The voltage at the large wire on the back of your alternator should be between 13-15 volts when the car is running (over 1000 rpm's). You should also see that same voltage at the positive battery terminal. I would start by checking for bad connections at all of the connections from the battery terminals to the solenoid to the alternator.

Q2: Is this a 5.0? Common places for oil leaks are valve cover gaskets, rear main seal, and the PVC valve gromment at the back of the engine behind the intake plenum. Under the PCV valve there is a mesh screen that clogs.

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club
"Tank, I need an exit."
"I may not have gone where I intended to go, but I think I have ended up where I needed to be."
AIM, YM: topdnmustang

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motorhead102482
Journeyman

Posts: 5
From: Bellevue, NE 68123
Registered: Jun 2005

posted 06-06-2005 06:41 PM     Click Here to See the Profile for motorhead102482   Click Here to Email motorhead102482     Edit/Delete Message   Reply w/Quote
There is no large wire on the back of the alternator. This has an internal voltage regulator. There are two plugs each with 3 wires on them. There is less voltage on the battery and solenoid when the car is running than when it is off. I probed the wires with a DVM and they have the same voltage as the battery when running. All the conncections check good when i continuity checked them with an ohmmeter.

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ddenton749
unregistered
posted 06-07-2005 08:06 AM           Edit/Delete Message   Reply w/Quote
How old is your battery? What is the battery voltage with the car off? It should be 12 volts. An internal short in the battery will do strange things.

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club
"Tank, I need an exit."
"I may not have gone where I intended to go, but I think I have ended up where I needed to be."
AIM, YM: topdnmustang

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ddenton749
unregistered
posted 06-07-2005 08:10 AM           Edit/Delete Message   Reply w/Quote
Q3: "Also, my 90 has a lot of vibration when revving up to 3000 rpms or so. Would it be more likely that it is my flywheel or my driveshaft, or could it be my ujoints on my driveshaft."

Is it a vibration or a misfire?

If the vibration occurs with the cart in neutral, I would start by looking at the balancer or flywheel/clutch/torque converter.

If the vibration only occurs while driving, start looking at u-joints, etc.

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club
"Tank, I need an exit."
"I may not have gone where I intended to go, but I think I have ended up where I needed to be."
AIM, YM: topdnmustang

IP: Logged

ddenton749
unregistered
posted 06-07-2005 09:31 AM           Edit/Delete Message   Reply w/Quote
back to Q1: There are two plugs on your alternator. The upper one is the voltage regulator. The lower one has two large wires and one small one. The bigger wire (blk/org) supplies the charging current to your battery by way of the connection at the starter relay. The other big wire supplies power to the alternator stator windings. The voltage regulator switches the current to the stator windings to control alternator output.

There should be 13.5 to 14.5 volts at the blk/org wire when the car is running. (Back probe the plug) Remember, these alternators on the Fox's aren't the best. You will need to check the alternator output with the engine over 1,000 rpm's.

Check all of your connections at the starter relay. Take them apart and clean them. Also there is a fusible link in the wire that goes back to the alternator (stator). Check all of your fuses under the dash and if you have a dash light, make sure it is working. (It should light when you turn the key on.) I'm pretty sure it won't charge unless the light bulb is working. Maybe someone will check me on that.

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club
"Tank, I need an exit."
"I may not have gone where I intended to go, but I think I have ended up where I needed to be."
AIM, YM: topdnmustang

IP: Logged

motorhead102482
Journeyman

Posts: 5
From: Bellevue, NE 68123
Registered: Jun 2005

posted 06-07-2005 05:33 PM     Click Here to See the Profile for motorhead102482   Click Here to Email motorhead102482     Edit/Delete Message   Reply w/Quote
The vibration occurs all the time. The engine sounds pretty smooth and has lots of power. It's a lot harder when driving though. Would a misfire in these cars cause a lot of vibration, and if so what would be the most likely causes.

The light on the dash, where is it located, and how does it work. If the bulb is burned does it not pass current from the alternator? I have an aftermarket voltage gauge, but my stock one still works also. Both are reading low. So i'm not sure if i have a light since i have a gauge? I don't have a fuse block breakdown either, but i tried checking the fuses and couldn't find any that were bad. Can u tell me which one specifically is for the charging circuit. Also, the alternator and battery are less than 4 months old. I also tried cleaning the terminals on the solenoid to make sure there was no corrosion causing my problems. The battery with the car off is about 12.25 V.

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ddenton749
unregistered
posted 06-08-2005 09:33 AM           Edit/Delete Message   Reply w/Quote
Q3: The vibration is a tough one to diagnose from here. How about some basic info. We know it's a 90. What engine, trans, mods, body style, etc is it? Does the vibration occur when you rev it in neutral? Tell us more.

Q1: There's a light shaped like a battery in the center of the dash just above the steering column cover. It should light when you turn the key to "on". You should also see the other lights like CEL, etc. I'm reasonably sure that this light has to work in order for the alternator to charge. The regulator needs some current flowing through this circuit with the resistance of the bulb in order to work. Now, hopefully somebody will confirm this because it's a PITA to change the bulb.

12.25 volts is good for the battery when the engine isn't running.

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club
"Tank, I need an exit."
"I may not have gone where I intended to go, but I think I have ended up where I needed to be."
AIM, YM: topdnmustang

IP: Logged

ddenton749
unregistered
posted 06-08-2005 10:12 AM           Edit/Delete Message   Reply w/Quote
Form a post on Corral.net:

"Sounds to me like your alternator is not getting a "turn-on" signal. Not that this is your problem, but I had the exact same non-charging issue when I replaced my gauge cluster, and left out a little resistor used by the "charging" idiot light. The alternator was never getting a signal that it needed to start putting out current. Can't tell you how to fix it, but I would bet your problem is with the wiring going to the alt. Only other thing might be a bad regulator in the alt (which can be checked by any auto parts store)."

Check for the battery light in the dash. If it's not working, replace the bulb. (And all of the others while you have the dash apart.)

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club
"Tank, I need an exit."
"I may not have gone where I intended to go, but I think I have ended up where I needed to be."
AIM, YM: topdnmustang

IP: Logged

motorhead102482
Journeyman

Posts: 5
From: Bellevue, NE 68123
Registered: Jun 2005

posted 06-09-2005 05:23 PM     Click Here to See the Profile for motorhead102482   Click Here to Email motorhead102482     Edit/Delete Message   Reply w/Quote
yes, i think you are right about the no turn on signal to the alternator. I have no engine lights on the dash at all. I'm wondering if something shorted out somewhere. I'll look into it. I have a 5.0 engine, a tremec 5 speed. A 2 door hatchback body type. Yes, the vibration seems to be even when it is neutral.

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ddenton749
unregistered
posted 06-09-2005 08:11 PM           Edit/Delete Message   Reply w/Quote
You should have the battery light, Check Engine Light (CEL), Air Bag light (If you have one), etc. I had to take my dash apart because the CEL was burnt out. That may be all that's wrong with yours. Take the dash apart and change all of the bulbs. I think there are 16 or 18 of them.

If the gauge lights and turn signal lights work then the printed circuit is probably ok.

As for the vibration, the first thing I would suspect is the clutch. You may have lost one of the springs in the clutch disk or the pressure plate.

------------------
'73 Convertible, 351C 2V
'91 LX Convertible 5.0
Member: Valley Forge Mustang Club
"Tank, I need an exit."
"I may not have gone where I intended to go, but I think I have ended up where I needed to be."
AIM, YM: topdnmustang

IP: Logged

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