Base timing

[Nazgul]

Hello To All....

I have read this fine forum with great interest for a while now in anticipation of me having a Corvette of my own. Well....my older brother in Cincinatti OH has had a black 85 coupe sitting in his garage since about 1990 and informed me if I flew out to get it going....I would be driving home in it....so....it cost 196.00 for a round trip ticket.....just in case I couldnt get it going.....I have it home with me now....He lost interest in it because the clear coat came off the front hood....Chevrolet would not paint it for him so he parked it....only about 49,000 miles....unfortunately the transmission quit about a week after it got here....I have had the transmission replaced with one called The Black Maxx and it seems to be better than the origional. Which brings me to the first question I would like to address.....my mechanic said to change the transmission he had to remove the distributor to drop the back end of the engine.....The car seems to not be running as it did before...timing wise...not shifting....I wanted to verify the base timing and have found out about disconnecting the EST? wire to the computer....when I look on the sticker under the hood it says set to 6 degrees....and then after that it has (DR).
What does the DR mean.....I have the factory service manual....a haynes,chilton.Charles Probst,and motorbooks chevy fuel injection book and see no mention of that at all......secondly....I also have an autoxray scanner and was wondering where the information displayed comes from?...the ECM? or the prom....which is some sort of shift chip he installed long back? May I thank anyone and everyone in advance for any help they can now....or ever will supply and I look forward to the day I may myself help someone out....Your all a bunch of lucky buggers to have these cars......and thanks to my brother I am amoungst you now.........Geoff

 

[vetteboy86]

First of all welcome to the best corvette forum out there. I have loved this site from the moment I became a member. To your questions: I have always known the timing to be 6 degrees advavced. I do not really know what DR means at the moment. I have my timing set at about 10 degrees advanced. I am not sure where the info for the scanner comes from. The PROM is programable read only memory, so i dont know how different conditons and codes would be stored there. I am guessin that it comes from the ECM, however I could be totally wrong. Either way someone will be along soon to continue what I have said or correct me on either account.


Good Luck

Craig

 

[406shark]

I'm no expert on computer controlled cars to say the least, but my guess would be that the DR possibly means "in Drive."

I'm sure someone here will be able to tell you for sure.

Good luck, and I wish I could say my '77 only cost me $196.00 plus a tranny.

Jeff

 

[Mart]

The guys are correct about the 6* base timing. But I run mine about 8-10.

Not sure about the DR, I sure would not want to do the timing in drive, you set the min idle in drive.

Mart

 

[vetteboy86]

I think the timing sticker should say something like 6 degrees at 600 RPM's. The only way I would see if you needed the car in drive to time it is to lower your idle to check the timing. I guess that would be the idiot way to do it though. Are you getting any backfire of the engine. This would possibly relate to an incorrect timing setting.

Keep us posted.

Craig

 

[Nazgul]

the car has never backfired.......however....idle wanders a bit more than before...my spark knock count on the scanner is up to about 120....once I get to whatever speed I want to tavel at engine seems to run fairly smooth....stumbles a bit at accelleration but recovers and smooths out again at new speed....and I think it heats up a bit faster at idle than it did before...I have a 180 degree t stat and it cruises at just about 180 +/- 5 drgrees or so....just climbs faster at stop lights it seems....no coolant leaks or low fluid..and I checked the sticker again and it says (DR) right after the 6 degree on the sticker. My scanner also shows I am always calling for A\C....park neutral always flip flopping....IAT only reads either 123....or 203 with an occasional flash to a normal temperature...goes between open and closed loop however never gets any o2 cross counts.....I am not that familiar with all this scanner stuff but these seem like glitches to me.....that was the basis for my ecm question.....does my prom id number identify in any way by manufacturer or exact type of programming on it? anyway....thanks for all the input so far....maybe I should track down the grounds for all the computer stuff....car had sat like almost forever....just seems like this happened right after tranny swap.....Have a great day all.......Geoff

 

[Edmond]

that was the basis for my ecm question.....does my prom id number identify in any way by manufacturer or exact type of programming on it? anyway....thanks for all the input so far....maybe I should track down the grounds for all the computer stuff....car had sat like almost forever....just seems like this happened right after tranny swap.....Have a great day all.......Geoff

The original PROM chip should say something like "DELCO ABTT 4773." That's what my chip says. The chip is located behind the "breadbox" in the dash. You can access it by taking off the panel where the passengers shins and feet would be. I think there are 3 or 4 screws that hold that panel on. The chip itself is located in that metallic box up there. You have to take off the two hex bolts and unplug the computer things from the back of the box. Make sure to disconnect the negative battery cable before you start this work.

After you get the box down, you unscrew the two little screws that hold a thin metal cover for the PROM. Then you just push the sides of the PROM to pop it out.

Trouble codes can be pulled by jumping the top two terminals on the right of the data link convertor. Turn the key on but don't start the car. The codes flash 3 times until it goes to the next code. The first code is always a code 12.

 

[Edmond]

and I think it heats up a bit faster at idle than it did before...I have a 180 degree t stat and it cruises at just about 180 +/- 5 drgrees or so....just climbs faster at stop lights it seems....no coolant leaks or low fluid

That is actually normal for it to climb that high; GM had it climb that high for emission purposes. If you want the fan to come on earlier, a PROM reprogram and some Water Wetter will help you out. Stock, the coolant can run up to 230 if you've sat at the light long enough.