Timing A 1985 Corvette
Thread Starter
Racer
Joined: Mar 2004
Posts: 252
Likes: 1
From: Troy Illinois
Timing A 1985 Corvette
I just got back from my mechanic and he was unable to pull a timing reading for my 1985 using his Snap-on data reader pluged into the terminal under the dash. I had set the timing, using a timing light, after installing an Edelbrock intake but wanted to check with a computer after reading so many posts concerning the moveing of the timing mark on the damper due to the rubber insulator in the damper. Can someone tell me if the timing can be set on a 1985 using the computer? If so what kind of reader is needed? My mechanic was able to pull many readings, TPS, Temperature, etc. but not the timing. I know the computers on the early C4 Corvettes changed every year, so maybe in 1985 timing using a computer is not an option. Also what hand held data reader would you recomend for a 1985.
Le Mans Master
Joined: Oct 2008
Posts: 9,758
Likes: 49
From: Houston Texas
I just got back from my mechanic and he was unable to pull a timing reading for my 1985 using his Snap-on data reader pluged into the terminal under the dash. I had set the timing, using a timing light, after installing an Edelbrock intake but wanted to check with a computer after reading so many posts concerning the moveing of the timing mark on the damper due to the rubber insulator in the damper. Can someone tell me if the timing can be set on a 1985 using the computer? If so what kind of reader is needed? My mechanic was able to pull many readings, TPS, Temperature, etc. but not the timing. I know the computers on the early C4 Corvettes changed every year, so maybe in 1985 timing using a computer is not an option. Also what hand held data reader would you recomend for a 1985.
Safety Car
Joined: Jan 2008
Posts: 3,939
Likes: 1
From: Vero Beach Florida
It's easy to check the timing mark on the harmonic balancer to check if it's slipped, just bring # 1 piston to TDC compression stroke see where the timing mark is in relationship to the timing tab. Should be around the 0* mark
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
I check mine using a standard timing light, unplug the EST plug by the firewall and start the car,, read or set the timing,, turn the car off and disconnect the negative cable to allow the ECM to clear the code set by unplugging the EST, reconnect neg cable and you are good to go.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Bill -
Most scanners out there will not read the 1985 computer since it has the 870 chip. I bought the Auto-X-ray only to find out after many false readings and attempts to check areas that were NOT the problem that they do not support the 85
...and there is nothing in their documentation that tells you that you are out to lunch with a 85. I had to call and they passed me around to several techs until they told me it would not work....never an option to exchange or return.
You might have to get something that will load on a laptop. I do know that the TECH1 from GM will read this....but they are EXPENSIVE unless you can find one on EBAY etc.
John
Most scanners out there will not read the 1985 computer since it has the 870 chip. I bought the Auto-X-ray only to find out after many false readings and attempts to check areas that were NOT the problem that they do not support the 85
...and there is nothing in their documentation that tells you that you are out to lunch with a 85. I had to call and they passed me around to several techs until they told me it would not work....never an option to exchange or return.You might have to get something that will load on a laptop. I do know that the TECH1 from GM will read this....but they are EXPENSIVE unless you can find one on EBAY etc.
John
Instructor
Joined: Sep 2004
Posts: 216
Likes: 4
From: Linton Indiana
You said you installed an Edelbrock intake...you didn't switch to a carburetor instead of fuel injection did you? If you did that you could just purchase an aftermarket distributor or a 1975 Chevy distributor and hook it to a hot wire from ignition and bypass the computer altogether!
Race Director
Joined: Jun 1999
Posts: 14,924
Likes: 9
From: Merritt Ils Fl
Going back a bit here but I don't think the 870 ECM reports timing as a data element. The reason the "standard"scanners will not work with the 870 is the slow BAUD rate. 870 is very slow compared to the follow-on 165. Again, if I recall correctly, Mark Mansure (sp) has a free program that will scan the 870 and the free version of Tuner Pro will also.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
with others, scanners will not read the 870 ECM. I hooked my laptop to it and got nothing. Hooked it up to my other car and it was reading everything.
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
??? TunerProRT works, so does WinALDL (both using a Toshiba laptop running Windows XP). My SnapOn MT8500 (aka The Brick) works. So where does the "no scan tool reads the '85" come from? Wrong... The '85 datastream is essentially identical to following years, just at a lower baud rate (GM did juggle the datastream information bits from year to year for about Every model year throughout the life of the OBD1 systems...)
NO OBD1 system reports anything to do with timing back thru the ALDL connector as serial data. This is not an '85 specific issue, it's just the way it works prior to OBD2. In reality the ECM doesn't Know what is going on with the timing, there is no information coming back to it from the secondary side of the ignition system to "tell" it that the advance signal the ECM is Sending is actually being executed.
If your "mechanic" (and I use the term loosely) thought he was going to check the timing on your '85 with a scan tool then you need to find another mechanic. Fast.
NO OBD1 system reports anything to do with timing back thru the ALDL connector as serial data. This is not an '85 specific issue, it's just the way it works prior to OBD2. In reality the ECM doesn't Know what is going on with the timing, there is no information coming back to it from the secondary side of the ignition system to "tell" it that the advance signal the ECM is Sending is actually being executed.
If your "mechanic" (and I use the term loosely) thought he was going to check the timing on your '85 with a scan tool then you need to find another mechanic. Fast.
Drifting
Joined: May 2002
Posts: 1,509
Likes: 3
From: Hazel Park MI
I have an autoxray also. Don't know what model as it's not in front of me. I can't get real time data from everything, but I can get some things. I can get BLM but not integrator, I can get O2 voltage but not cross-counts, knock sensor readings, RPMs, idle, coolant temp, but timing is not one of them. And I'm in agreement - I called autoxray and was told the same thing as John. To top it off, I bought it from TPIS....so I'm sure they don't know the scanning issues...
