85 Corvette questions
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Cruising
Joined: Aug 2017
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85 Corvette questions
I have had my 85 about 25 years. Don't run like it did. Going to do some upgrades. But would like to fix what needs to be done. One thing is. It runs like a scolded dog when you first start it. But when warm it is not as strong. What is everyone opinion why it does that. What els do you think needs changed or done.before I start. I am changing heads,cam and exhaust first.
Last edited by Rocky Brian Lamb; Feb 27, 2019 at 03:38 PM.
Safety Car
Joined: Aug 2009
Posts: 3,752
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From: Melbourne, Victoria, Australia
I have had my 85 about 25 years. Don't run like it did. Going to do some upgrades. But would like to fix what needs to be done. One thing is. It runs like a scolded dog when you first start it. But when warm it is not as strong. What is everyone opinion why it does that. What els do you think needs changed or done.before I start. I am changing heads,cam and exhaust first.
My 85 runs the same hot or cold, sometimes the ecm can get itself in knots if it perceives a problem and tries to compensate.
I usually find when its not running quite right simply resetting the ecm, by unplugging the ecm lead or battery helps get her running as she should.
Do you have any check engine codes?
When the car starts from cold it is in open loop, at operating temp it will go into closed loop.and look at the oxygen sensor to enrich or lean out the mixture.
Also the TPS, MAF and spark retard are all looked at in closed loop.
Check the TPS should be 0.54vdc (i set mine at 0.6vdc for better off idle go) check your timing is good remember the ecm can retard the ignition heavily when sensing knocks. Retard will adversely affect fuel economy and performance.
I suggest a few simple checks and reset the ecm (disconnect battery for 10 seconds then reconnect) the auto learn will take a few minutes and performance will be good.
Good luck
Drifting
Joined: Mar 2017
Posts: 1,897
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From: Nashville TN
2017 C4 of Year Finalist
If it runs better cold than warm, that very well could be sensor issues. until 140 degrees, the ECM doesn't really pay attention to sensor data. So if that's when your problems start, you could have a issue with a sensor. Do you have access to data logging? That could help.
Otherwise, it's a 34 year old car. It may just need a little TLC, cleaning and tightening things up. I have no idea how you've handled maintenance up to now, but even just changing all the fluids on my '85 made it run much smoother.
Injectors could be a big one, too-if they're clogged or clogging, you could be not getting enough fuel. Having them cleaned or replaced could make a world of difference.
Just a few thoughts, would need more info to help further I think.
Otherwise, it's a 34 year old car. It may just need a little TLC, cleaning and tightening things up. I have no idea how you've handled maintenance up to now, but even just changing all the fluids on my '85 made it run much smoother.
Injectors could be a big one, too-if they're clogged or clogging, you could be not getting enough fuel. Having them cleaned or replaced could make a world of difference.
Just a few thoughts, would need more info to help further I think.
