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They call me, Hugh Huffner
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Discussion Starter #1
Okay, just went through the engine on my 81,

went to 10.0:1 compression, .060 over (had had a previous bore to .040) have quadrajet on top, new cam (50 state legal) 700R$ tranny, and a set of 3:54 gears, same exhaust, no other mods except roller rockers. (valve sizes same)

Okay, here is problem, when we start it, it shoots immediately to about 2000 rpm and stays there. If we unplug the distributor, she will drop to 1500 and stay there. Mess with the idle, and she dies. Check engine light is on and stays on. Does not flash codes. (has not been touched either!)

Books are telling me nothing. Zero. Nada. The dealer knows not about a C3.
Has anyone had problems with the ECM after a rebuild? Emission system is on car, everything is functional (car smogged when we started! It also ran correctly, and was completely jacked inside.)

Really need some help here. Anybody have some good knowledge? I found another guy with an 81, and took a picture of his label under the hood, so we know everything is plumbed right, and all the sensors are new and wired.

Really need someone who KNOWS about troubleshooting an 81 after a rebuild. Corvette 101.com was garbage, so was everyother website I have been to. You are my last hope! Call if you need to! 805-340-6388
My mech, and I cannot figure this out, and no one here in the valley seems to be reliable with vettes, one "tuner shop" told me my car did not even have a computer!
PLEASE PLEASE PLEASE help!:WTF
 

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Ok try this,
disconnect the battery leave it disconnected for about 5mins,reconnect the battery and start the car let it run.
This should reprogram the comuter.
Hope it helps.
Mike
 

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Your modifications should not cause any problems. Do you have the factory service manual? I have been running a fairly modified (much more than yours) with the stock CCC system and know the system pretty well. The check engine light might be showing a "soft code", which is basically something minor and it resets when turned off. If the RPMs are high for whatever reason, the ECM will advance the timing. If you unplug it, the RPMs will drop. I'd check for vacuum leaks. Did you rebuild the carb? Let me know as much as you can and I will try to help. God bless, Sensei
 

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They call me, Hugh Huffner
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584 Posts
Discussion Starter #4
We got the old girl running! We are still low on vacuum, which we are tracing.
Found a couple leaks, and repaired them. I am now Idling at 850 rpm.

We are getting code 23 from the ECM, (Mixture control open or grounded) have not as yet been able to figure that one out. She starts, runs, and idles, does not seem too rich, or lean.

We did rebuild the carb that was on the car. We tried two other rebuilt carbs, and no dice, wrong ones. We reset the computer and put the original (which was not throwing codes before) back on. Idle settled down and she ran well. I think the mixture control doomahickey is on the right front (top) of the carb, am ordering a new engine harness to eliminate any possible faulty wiring. Any ideas on the Mixture Control?
Steve
 

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Replacing the engine harness sounds like a whole lot of work that is most likely not needed at all. I'm at work right now, but I'll try to give you some stuff to start checking later on. This will probably be a fairly easy fix. God bless, Sensei
 

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First thing to do: Check the connection at the MC solenoid (yes, it is the plug on top of the carb). I always recommend using Caig Labs Deoxit on all connections. The car is a quarter century old, those electrical connections need cleaning. This stuff is good! I get it on Ebay (just search for "Deoxit") If you are in a hurry you may be able to find a source locally. Radio Shack has it, but only in tiny bottles and they are expensive! Then disconnect the battery to reset the computer and see if it still throws the code. If it does, Check the plug at the ECM and clean those terminals (especially terminal 18). Reset the ECM and check for codes again. If there is still a problem, Disconnect at the ECM and MC solenoid, use a multi-meter to check the wire for continuity or short to ground. (This is easy to do, if you don't know how, let me know and I will explain). God bless, Sensei
 

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Well, I will throw in a thought. When you set the dizzy timing mark at idle, did you unplug the dizzy harness?
 

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They call me, Hugh Huffner
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584 Posts
Discussion Starter #8
Okay,
Let the computer reset, still throwing code 23.

Going to try to find the product you mentioned today. Only ordering top harness (The one that goes from main to the carb and that pot on top of the smog pump) two of the connectors are messed up so want to replace them. It is like $200 from Mid America or Ecklers.

Car fires immediately with no backfire and no stumbling. runs well, though very lopey, (some is cam, some I think is low vacuum, a bit of idle adjustment, and a bit of break in needed)

Car was timed first with dist disconnected from harness(dead timing), then adjusted with dist connected. We had carb harness hooked in during timing. Idle is smooth, and engine revs well up and down, Oil press and temp normal, volts normal, coolant temp does not spike up super quick. She does not seem to run super lean or rich. No dark smoke when you stomp on her, no smell of unburnt fuel when idling or revving.

And on the last post what exactly is a "dizzy?" :smack

Really appreciate your guys help. I know it is pobably a simple tweak, just pulling my hair out trying to find it. I am praying you guys can help. Wont pass smog with the check enging light on, lol.
Steve
 

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This may sound dumb, but is your cruise control diphram in the correct place? I had the same problem after I did my top end. I had it installed it wrong and it wouldn let the carb close all the way.
 
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