ok, this has been a recent ongoing problem. On my 85, I've had alot of work done to it, engine performance yadayadayada, just recently the rpm light started coming/going--I figured there was a loose wire coming off the dist. I don't think that is the problem, so I ignored it, then the fuel rate option quit working and last of all, now the miles/hour don't work along with the actual odometer no longer rolling over. And I'm sure everyone in here would first of all agree that the digi cluster is taking a dump. Well thats what I thought, so I found a guy who repairs these clusters, http://www.advancedelectronics.org I found him on ebay, for $160 he would fix your cluster. I sent it to him, he checked it prior to fixing it and ran it about 12 hours before sending it back to me--supposedly he claims it is as new again. But when I hooked it up today--same problems....So I'm out like $200 for absolutely nothing. He claims the processor circuit had a crack in it and he replaced it. How would anybody else explain this, or where to troubleshoot 1 problem to see if it clears up on the speedo? the speedo just reads "0" constantly on those options that are out. Here is a FYI, the ecm WAS replaced by the same shop that did the engine/tranny, is it possible that the ecm controls these options...This can't be coicidence all these happen all of a sudden. I hate wiring in cars!!

 

Borrow a friends cluster and try it. Did you check the connector that plugs into the display its self? See if there are any wires "loose" or something. If you aren't getting a steady power source to it they can get really geeky as well.

 

I think you need to start checking your grounds!!!!!

 

thats possible Rick, but what where do I look to check the digicluster gx ?

 

The cluster uses signals from the distributor to display rpm. You need to determine if there are pulses on the white (on my 87) wire, terminal C2 of the distributor when the engine is running. The best way to do this is to use an oscilloscope. If there are, then the cluster is suspect. Miles, mpg, and speed require pulses from the transmission and again, you need to determine if pulses are being generated when you are underway, or when the rear wheels are turning. These pulses are on the yellow and purple (on my 87) wires to the cluster. These wires are on contacts K and C of connector C237 (on my 87). If you have pulses, then the cluster is suspect. It is a lot of work, but if you can find someone with an 85 and try your cluster in his dash, you can determine if your cluster is ok.

 

OK, this all sounds to familiar!!!, what I'd like you to do is this....take off the coil cap on the distributor...check to see if MAYBE, one of the wires isn't pinched and arcing...this causes the same symptoms you have described...don't ask me how I know NAH, I need to confess....forgive me father!
when I put my new coil in...I did that, and Gordon, bless his heart, wanted me to send in my digi dash.
Make sure you have the two wires..white to tach, and pink, or red to Bat.

 

I just hope the gx would be my major problem to check. Where would the gx be located for the digi cluster?

 

the guy that did my digi cluster just told me the gx is located on driverside back of engine block--is that an easy place to look ? Its too dark out riht now to look

 

bump....my last question

 

There are a bundle of grounds there. Side of block, just below head and about an inch from bellhousing.

 

There's also one on the drivers door pillar, you have to pull some of the carpeting back to see it.Front pillar.The ground Agent86 refers to is kinda hard to see, but look in front of the battery on the frame rail and you'll see a braided metal cable bolted to the frame-make sure it's clean and follow it up to where Agent86 said.That's where you'll find the bundle of ground wires.

 

The ground for my cluster is on a left side bellhousing bolt. This is not your problem though. If it was, nothing would light up but the turn signals.

As mentioned, the vss and tach wire go directly to the cluster, those aren't computer issues.

Maybe your speedo signal is no longer there. Did they attempt to correct the speedo with a new plastic gear, or do any work around this wiring? It can't calculate mpg, speed, or odometer without that input. The factory rpm (upshift light?) you mentioned could be controlled off speed and gear switches too. GM likes doing things backwards like that.

 

I had alot of the samethings.
I docUmented everything on a thread under under form general information. I thought I would post the causes of my problems and the fix. Maybe it will be of help to someone.
After I traced as many grounds that I could find (Found 12 in all) and unbolted and rebolted anything electrical that I could. I noticed while i had the battery out that the fuse box cover next to the battery looked a bit like it might have been sticking up just a hair. Upon inspection I found that the 2 60 amp fuses were loose as well as the ecm fuse. I pushed them in a little better then 1/4 inch. Fired the car up and had the same problem so I went a bit farther trying to remove the red cover asI could see a hot spot on the terminal. The red cap would not come off due to the red lid having been so hot it welded itself to the fuse box. After an hour of playing with it I was able to work it off. The Lug was rusted and burnt. (Plastic had melted on the lug from the lid)
I took some sandpaper and cleaned the lug and the 2 metal transfer contacts that charge the fuse box. I put it all back together and my oil pressure reads 40 to 60lbs where it was reading 20 to 30. Battery gauge shows a steady 14 volts it was showing 10. the A/C switches are all now working as well as the stereo lights and windows. And No more back firing and no more all dummy lights coming on.

I have drove the car for 45 minutes and so far so good before I could not even get out of the drive way.

Now the question is why this happened would you pull these fuses to change the opti-spark? I have never pulled these fuses only the inside fuses. Why did the lug and box get so hot? Could this be from the fuses not making full contact and sparking?

I wanted to thank everyone that has offered their help.

 

Not sure how this information is going to help me ?? I have an "85" model, and I checked the fuses--this is most likely a grounding issue and I took my car to a trusty mechanic I know--hopefully he will have it wrapped up by tomorrow afternoon. Driving to his shop today I pulled over and filled up my tank and out of nowhere my mileage/odometer/fuel rate worked!! but my tach is still at 0 along with the coolant level reading 299 degrees.--its gotta be a gx problem..

 

You should purchase the electrical manual for your car. IF you could find the common ground to the cluster, you could simply run a jumper from the cluster to a known ground.

 

If it's not a ground problem(which I suspect it is) then, it maybe a bad connection-or corroded connection in the bulkhead connection. Killebrew-who is the guru, when it comes to our C4s and especially digi dash display problems, says most of our problems lay in that connection, BTW, there's also an ambient switch fix to help a ground problem. It could also be a connection problem with the digital dash..which alot of us have had to deal with.

 

Check my post on the ground location. It should be reachable from under the car.

 

Not hardly, sorry CC, but you can't reach it from under. It's on the top of the engine behind the drivers side head...a mother to get at.

 

Well, I figure if you can get to the bolt to remove an auto tranny, you should be able to get access to this ground. Then again, I was in there when the trans was out of the car. Of the 6 bellhousing bolts going clockwise around from the oil filter. This ground strap is on bolt #2.


It's G140, this grounds the instrument panel sending unit signals, the window squirter, and wiper motors.

Do your wipers and squirter work?

 

problem was found and fixed----WEIRD, coolant wire was burned on a header or somewhere behind the block throwing hot temp signals. Tach filter was bad, and the biggest problem was the cluster wire plug wires needed to be adjusted in the wire harness....The guy that fixed it said it works flawless now, course now that I have a rebuilt cluster too--who knows!!!