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Digital Dash Problem - This one's unique!

Mr Dark

Well-known member
Joined
Feb 26, 2002
Messages
103
Location
Sauk Rapids, MN, USA
Corvette
1985 White Coupe
This post is long, so bear with me. I have a 1985 Corvette which I've had for about a year. Ever since I've owned it, I've noticed that whenever the climate control is moved from "off" to any other position, the oil pressure drops drastically, the water temperature rises drastically, and the gas gauge loses about 1/4 tank. When the lever is moved back to "off", all returns to normal. Last Saturday, I turned on the air and turned the fan on high. The fan didn't come on, but the dash died. I carefully checked the fuses and there is no problem with any of them. I don't know what's wrong, but it's got to be a problem between the climate control and the dash. I've got no heater/air conditioning fan and no dash. I'm at my wits end trying to figure this out. Has anybody out there experienced or even heard of a problem like this? I really don't know what else to do besides head for the dealer and remortgage the house to pay for it! Unless somebody out there can save the day. I appreciate any advice you can give.
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Ok a few questions first

1) was the car an outside car most of it's life?

2) How electrically/ electronically inclined are you?

3) How rusted are the frame rails... specfically the ones nearest the firewall?

4) Do you have a clean garage that you can tear the car apart?

5) Do you own a test light,voltmeter & soldering iron?

6)Has there been engine/tranny work done recently?

7) do the turn signals & High beam indicator still work?


Answer these questions FIRST....

Then we may proceed

My HUNCH at this point..it's a system ground...but WHERE.. that's the trick?

Vig!
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Ground points on a C-4

This is an old post of mine showing the ground points.....

You are interested in the following
G-201**
G-125
G-109
G-101**
G-114
G-115
G-104**

They are not all broken... but I'll bet one or more are coroded.

** means High probability



Gettin grounded C-4 1988

FRAME GROUND POINTS


G-401
Pass side door behind seat, behind plastic trim
About where the top of door line is.. ON THE BODY
10 mm bolt into frame metal, single wire.
This goes to the splice for grounding the entire ASS end of the car.

G-320
Left side of cargo compartment about where 401 lives on opposite side. ABS ground (total system)
& left side hatch strut for rear window defogger.

G-201
Is the ground for the entire cabin area. Behind instrument panel, left hand side, near steering column.

G-125
Pass side by toe kick panel,Dash grounds etc.

G-109
The Frame ground point for the AC Blower motor sensors & relays, spark ESC module, Washer pump.
On the frame rail, pass side, below the hi pressure
A/C cutout switches.


G-104 MAS IMPORTANTE'******************
The big gorilla from the Neg side of the battery
to the drivers side of the engine block with the ground braid & other Grounds!!!!
ECM,Fuel pump relay, Mass sensor & relays, tranny position Etc.

And

G-101
The little wire off the neg side of the
battery to frame rail & to Ground braid.This is the the ground strap.. the braided chunk of wire connects FRAME to ENGINE!!!!

G-115
Drivers side, foward frame rail, By horn.
Ground for headlight, horn, evap cansiter, turn & marker lights.

G-116
Mirror of G-115

G-117
Ground for Fan(s) & fan relays
By fan on frame rail twds pass side
on the cross member between the left & right frame rail on top.

This should be very similar for all c-4's but it's out of the 88 book.

Mike
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Annnnnnnnd

Under the dash is the AMBIENT TEMP OVERRIDE SWITCH.


The location of this little beast, where your left foot would normally rest... follow your TOE up under the dash ( about 2 more inches ) and you will find a little can.... which has a LIGHT BLUE and a BLACK with white tracer....

This CAN is attached to the top right of the bulkhead connector going through the firewall for the wiring harness.

Jump these two pins together...

I do not thing that's the problem however.


You have verified you have power to all the circuts....by doing what exactly....

Vig!
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
I'll give you the next steps when you answer.

If you do not have the proper stuff at this point..you can do more harm that good.


Vig!
 
Joined
Aug 30, 2002
Messages
1,533
Location
Colorado Springs, CO USA
Corvette
84 Z51 auto R.I.P. 89 black roadster SOLD
Agreed!

Definately sounds like a flaky ground somewhere.

If it helps I have schematics (with ground locations) for '84...I don't know how similar '84 and '85 are electrically.
 
D

Dan85

Guest
I had the same type problem on my 85. I traced the ground wires , and found they connected to one of the bellhousing bolts on the top lefthand (drivers) side. It was kind of hard to get to, but cleaned and tightened connection and problem solved. I hope this helps.
 
Joined
May 29, 2002
Messages
8,655
Location
Missoura Ozarks
Corvette
2012 💯 4LT GS Roadster
Dan85 said:
I had the same type problem on my 85. I traced the ground wires , and found they connected to one of the bellhousing bolts on the top righthand side. It was kind of hard to get to, but cleaned and tightened connection and problem solved. I hope this helps.

:upthumbs Welcome to :CAC
 

Mr Dark

Well-known member
Joined
Feb 26, 2002
Messages
103
Location
Sauk Rapids, MN, USA
Corvette
1985 White Coupe
OK a few questions first

1. I'm guessing the car spent most of its life inside, but I'm not entirely sure - I've only had it a year.

2. I replaced the battery in the car - does that count? I really haven't done much in the way of electronics repair. I just want to be sure I don't do more damage than good.

3. I'll check that out this morning.

4. Yes, I have a garage.

5. No, I don't own those things, but I would be willing to purchase them. What do you recommend?

6. No, there has been no recent engine or tranny work. The only thing done recently was an oil change.

7. Yep, they work just fine. They're the only things that work.

I replaced almost evey fuse in the fuse panel. I went out and bought an assortment of fuses and just started replacing.

Thanks to everyone who has responded so far! To geekinavette - my understanding is that the 84 and 85 are identical, so I think the schematics would be applicable to my car. Is it something you could email? Dan - where would I find the bellhousing bolts you speak of? I'll check them out. Again, many thanks to everyone for the information! I'll be back on-line a little later.
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
G-104 MAS IMPORTANTE'******************
The big gorilla from the Neg side of the battery
to the drivers side of the engine block with the ground braid & other Grounds!!!!
ECM,Fuel pump relay, Mass sensor & relays, tranny position Etc.

( Location... drivers side near oil filter... Jack the car up and follow the battery negative cable to the block... there will be a junction of about 6 wires there.. some coming from the actual engine harness. On an 88 it's on the side of the block)

And

G-101
The little wire off the neg side of the
battery to frame rail & to Ground braid.This is the the ground strap.. the braided chunk of wire connects FRAME to ENGINE!!!!

Location...drivers side of frame rail on the S shaped bend of the frame rail about middle.

Look down@ frame rail by edge of battery(positive side) you should see it.


Vig!
 

Mr Dark

Well-known member
Joined
Feb 26, 2002
Messages
103
Location
Sauk Rapids, MN, USA
Corvette
1985 White Coupe
So I should just look to see that they're properly connected and not corroded? I'll do it. I'll only be able to be on here off and on since I have to finish work and prepare for a weekend trip, but as I have the opportunity, I'll post what I've found. Again, thanks for your advice!
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
So the first tool

Go to Sears and buy a GOOD 12volt automotive test light.

Replacing fuses is ok buy you have NO IDEA whether or not power is going there.


Do the driver's information panel light's light
( check engine.. BRAKE etc)

Do the night instrument lights work ( back illumination for all the switches in the DIC panel)?

Important note here

The ground for the dash lights( the illumination source for the LCD's) and the ground for the Turn & High beam are the same EXTERNAL WIRE ( D1 ) on side of Dash cluster.

The first test will be.....

Check with test light ( both sides of the fuse) power to the following crkts.

LCD fuse

CLSTR fuse

TAIL fuse

and

INST fuse

Note...G-201 is the common ground point for A/C & cluster.


Vig!
 

Mr Dark

Well-known member
Joined
Feb 26, 2002
Messages
103
Location
Sauk Rapids, MN, USA
Corvette
1985 White Coupe
I'll stop at Sears and look for a light. I haven't had much luck so far. I can't jack the car up far enough to get underneath it and nobody in town sells ramps big enough for my tires. I dropped the front panel (under the steering wheel) and looked behind the dash as well as I could, but I didn't see any ground wire. To top it off, I've now discovered that neither my odometer or windshield wipers work anymore either. :(
 
Joined
Aug 30, 2002
Messages
1,533
Location
Colorado Springs, CO USA
Corvette
84 Z51 auto R.I.P. 89 black roadster SOLD
Ok I have some diagrams here that I think will help (IF '84 and '85 are similar enough). These are straight out of the '84 Corvette GM Shop Manual.

First, here are the main battery frame ground (G113, batt to frame) and engine ground (G100, frame to engine) locations. START WITH THESE! (right Vig?):

http://home.adelphia.net/~bhitchcock/images/batt_cables.jpg



Next, there are two grounds from the instrument cluster, G101 and G110:

http://home.adelphia.net/~bhitchcock/images/instrument cluster inputs_outputs.jpg

G101 is the illumination ground, G110 is the signal ground, but also serves as the AC blower and WS wiper ground...A-HAH!

Here is the location for G101, inside the driver's side door hinge panel (the other ground wire there, G106, is for the radio):

http://home.adelphia.net/~bhitchcock/images/speaker_IP ground.jpg




And here's the location for G110 (the most likely culprit I think), driver's side tranny bell housing bolt (THAT'S gonna be fun to get to!):

http://home.adelphia.net/~bhitchcock/images/inst ground_G110.jpg



Now if you're going to dig into the tranny bell housing ground wire (G110), also check out the two ground wires on the back of the driver's side cylinder head, just because you're already back there:

http://home.adelphia.net/~bhitchcock/images/G161_G129 ground location.jpg

One of those is the ESC/O2 sensor ground, the other is an ECM ground.



Good luck, hope this helps!

Bill
 
Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
Mr. Dark, if you have a WalMart or Pep Boys or Parts America locally, they sell Rhino Ramps - these are easily wide and strong enough. If your front dam scrapes, put a 1x4 or 2x4 piece of lumber in front of the ramp to raise you up a bit. That's what I do now and it works fine.
[RICHR]
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Re Grounds

When possible... remove the grounds clean the connection point and re assemble.... if NOTHING else re crank em down.

So that the plan......
Let us know your findings... so we may further assist!

Do you have the FACTORY stereo in there, or an aftermarket?

Vig!
 

Mr Dark

Well-known member
Joined
Feb 26, 2002
Messages
103
Location
Sauk Rapids, MN, USA
Corvette
1985 White Coupe
geekinavette - Thanks for the diagrams - they are going to be very helpful!

rrubel - I'll try Wal-Mart. Thanks for the heads up!

vigman - The stereo is aftermarket. I had it installed in April. The dash was doing funky stuff before the stereo, though, so I don't think that's it.

Again, thanks to everyone for their input! I will keep you informed. Unfortunately, it won't be until next week. We're heading up to Duluth, Minnesota tomorrow to see the last B29 that's able to fly and to meet Paul Tibbets, pilot of the Enola Gay. It's living history and I just can't pass it up, so I won't be back for a few days. Hope you all enjoy your long weekend!!!
 
Joined
Oct 30, 2001
Messages
2,273
Location
Glen Burnie, MD, USA
Corvette
1986 Bright Red Coupe
Wild! I think you can be forgiven for not working on the Vette this weekend... :) I didn't realize anyone from the Enola Gay was still alive.
[RICHR]
 

Mr Dark

Well-known member
Joined
Feb 26, 2002
Messages
103
Location
Sauk Rapids, MN, USA
Corvette
1985 White Coupe
Car Repaired

I wimped out and took the car in for repair. It's now fixed and driveable (and my wallet has a huge hole - 6 hours of shop time). According to them, it was the G140 ground that was bad, and bad in two places. They first looked at the ground connection and found it to be bad. After correcting that, the problem still didn't go away, so they traced the wire through the wiring harness and found that it had been compromised from rubbing up against something. So they replaced a section of it. According to the invoice, they needed to remove the distributer (or parts of it), shield, wiper motor, etc. If they're telling the truth (I've never dealt with them before - they're the local GM dealer), I would not have had the technical skills to make these repairs. So what do you guys think? Is there such a ground that could have caused this problem? Again, I thank you all for all of your input. I really have learned a lot! :) :) :)

On a non-related note, I did meet and get the autograph of Paul Tibbets. He was the pilot of the Enola Gay that dropped the first atomic bomb on Hiroshima. The Enola Gay wasn't at the show, but "Fifi", another B-29, was. Although some might not agree with what we did back in 1945, I was truly honored to meet Mr. Tibbets and get his autograph. There were also some thankful WWII vets telling Mr. Tibbets about how they had finished fighting in Europe and that they were scheduled to be shipped off to the Pacific until he helped end the war. It really was a memorable experience.
 

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