When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hello everyone, new to the forums and have been gaining lots of incredible info over the past few months on my recent '81 purchase. I have quite a few problems left to resolve but the most recent one I just discovered was that there is no ECM in my Corvette. Someone must have removed it in the past. I have had some hard starting issues and potential carb issues. (Albeit I did rebuild my '81 carb and it started up first try immediately but thereafter it takes at least 3-4 cranks in cold or hot weather unless I use starting fluid.) Would the ECM affect the starting of the vehicle in any way shape or form? I haven't seen much info on them or maybe I skipped over something. Thanks guys.
Without the ECM the timing will always be at base timing and primary rods will be at full rich which is the same as in a non computer control car while cranking. So other than that it should start.
Once its running it runs fairly well, sometimes it has a tendency to stall at lights unless I quickly put it in park and give it some gas. Since this car doesn't have an ECM; should I go about replacing it? If so, how would I go about getting the right "proms" or memory chips that the new ECMs do not come with?
Well if you can't find a replacement ECM the next best thing would be grab a ECM and harness from a 8 cylinder GM car with a feedback carburetor and wire it in. The in and outputs are all the same. Since the fuel side is only controlling mixture at steady state Cruise there's no fuel table. It's only going rich/lean off of the O2 sensor. The timing won't be the same though. You could always bump the base timing. Most guys here hate the feedback/computer control system and will tell you to dump it. It really not a bad system. The best reason to keep it is for the converter lockup.
Last edited by Fly skids up!; Jan 26, 2022 at 09:55 PM.
Can you post a photo of what is there, with the air cleaner assembly removed?
Perhaps a PO replaced everything already. A few photos will be easier than describing a rainbow in the dark.
Nice subtle reference.
Dio, are you trying to keep your 81 all original?
If so, there is an 81 ECM listed on the eBay right now for 125 - but no prom with it. You may have to piece it together.
If you are not worried about keeping it OEM, then there are better alternatives. Went through this with my 82.
Thanks for the replies everyone, I'm not too worried about keeping it stock; as long as I don't have to do anything crazy to it. (Although as a first timer I already rebuilt the carb, replaced weatherstripping, and installed the headlight conversion kit so I don't think any suggestions would be too hard.) I will try and post pictures tomorrow, I currently have the carb off because I forgot to buy and install a new float lol.
Thanks for the replies everyone, I'm not too worried about keeping it stock; as long as I don't have to do anything crazy to it. (Although as a first timer I already rebuilt the carb, replaced weatherstripping, and installed the headlight conversion kit so I don't think any suggestions would be too hard.) I will try and post pictures tomorrow, I currently have the carb off because I forgot to buy and install a new float lol.
I am actually in the process of ripping out all my 81 factory computer components; Computer, harness, carb, distributor, switches, sensors, modules, brackets EVERYTHING. I’d be willing to box it all up and sell it if it would be helpful. I can even sell the air injection system, I have the pump, manifolds, hoses, sensors and the goody thermostat housing… It’s off of a running car with less than 80k miles, just going to try the sniper EFI, it’s just stinking expensive … Let me know, I can make an “official” ad in the for sale section (forum mods do not like selling without and ad and price) …
Sorry for the late reply work has been very busy and I haven't had time to reassemble everything or take pictures. This current Vette has 89k Miles so that would be great. I will try my best to finally take pictures tonight and reassemble everything; and maybe you could tell me what else I might need electronic wise other than the ECM. I believe everything else is still on the car.
I also had no idea there was a Sniper EFI for the C3, I'm currently looking into it right now. Would this be a better (albeit more expensive) option reliability and long term wise over the ECM modules and related hardware?
Sorry for the late reply work has been very busy and I haven't had time to reassemble everything or take pictures. This current Vette has 89k Miles so that would be great. I will try my best to finally take pictures tonight and reassemble everything; and maybe you could tell me what else I might need electronic wise other than the ECM. I believe everything else is still on the car.
Originally Posted by RonnieJamesDio
I also had no idea there was a Sniper EFI for the C3, I'm currently looking into it right now. Would this be a better (albeit more expensive) option reliability and long term wise over the ECM modules and related hardware?
Let's see what you have first! For all we know, your ECM has already been bypassed.
I haven't heard anyone complain about the Sniper EFI who has installed it and set it up correctly. You still need an ignition solution (which could be as simple as a 4-wire HEI distributor, which you may already have, or want to get). But if you decide to LS-swap your car in a year, anything you do twice is wasted time and money.
FlySkids likes thes CCC system. I hate it like poison. kind of like people's attitudes towards Ozzy. is he one of the greatest singers of all time, or a fat stoner idiot who can't remember the words? anyway, first post uyou rebuilt the 81 carb. is it the 81 carb? does it have the 2 electrical plugs? if not, it is a non-ecm controlled carb.
Yes it is definitely a 81 Rochester Quad. It’s a solid carb but I believe I’ve just adjusted the float wrong (old was punctured by metering rods by previous rebuilder…) so no biggie. Here are some pictures under the hood. Warning: it’s not pretty but it’s a very solid car.
Thanks for the update and photos! Here are some quick thoughts/questions. Hopefully others will add theirs as well.
Your choke is open. Was the engine recently run and warm in this photo?
Can you get the part number off of the distributor, or check to see if it is a 4 wire, but missing a vacuum advance, or the 81's 7 wire HEI, which means your entire ECM-based system is likely intact?
You have a lot of open vacuum ports. I'm sure some were from removing the air cleaner, but notable are:
Port on carb (for fuel vapor system perhaps?)
EGR valve. Also, it looks like there is a blocking plate underneath the valve. Can you confirm that it has been disabled?
TVS switches on the water neck
The zip-tied distributor wires can cause cross-talk. It is better to use comb separators, and/or a wire loam.
That rubber hose line on the pressurized side (between fuel pump and carb) is a fire hazard.
If your ECM is really missing (it should be behind the seats), the carb and especially the timing will not be optimized, and could explain a lot of poor running. I know what I would with this car, but it is your car, so hopefully the Forum can help you get you running well, whatever path you choose.
with no ecm the carb and distributor are near useless. the q-jut uses a vacuum signal to set metering rod height which sets cruise mixture. your carb is waiting for an electrical pulse to cycle your metering rods for correct mixture driven by the ecm looking at oxy levels in the exhaust. and the timing curve sent to the distributor is never gonna get there either. so, old school. replace the carb and distributor with non-electrical control, or less old-school and Flyskids method. get an ecm and get the CCC up and running. the way you have it now is the worst of both worlds...
Just to be clear I'm not in love with the feedback carburetor system. However just to eliminate it because you don't understand it or just easier to replace it with a good old carburetor/distributor seem to be a bit of a bubba fix. Back in the day mechanics use to bad mouth electronic ignitions when they first appeared. It's bullshit, it's junk, it will leave you stuck on the side of the road, only the dealer can fix it, yada yada ya. Now a days how many guys would swap their HEI's for points?
Just to be clear I'm not in love with the feedback carburetor system. However just to eliminate it because you don't understand it or just easier to replace it with a good old carburetor/distributor seem to be a bit of a bubba fix. Back in the day mechanics use to bad mouth electronic ignitions when they first appeared. It's bullshit, it's junk, it will leave you stuck on the side of the road, only the dealer can fix it, yada yada ya. Now a days how many guys would swap their HEI's for points?
Because I can tune an 81’ Vette with 1980 Carb/HEI setup to walk away from a stock 81’ setup…..
The original CCC was Emissions mandated and extended across the entire GM line…..it is primitive and troublesome….it also does not support any mods…..has nothing to do with not understanding it….in fact understanding it is the reason for removing it….like Chrysler’s miserable Lean Burn and the Ford VVT carb….these all happened around the same time….a woeful, miserable era for automobiles I am afraid….
The 82’ was a ray of light because it was a stable EFI setup that used the pickup coil as a cam reference to fire injectors….the later 2 bbl TBI’s were stone reliable…..the feedback carbs mixture control solenoid was not nearly as reliable….
But saying to keep a feedback carb on a car because it is Bubba in your eyes is a stretch…..it is more reliable, and less to worry about on top of being able to tune it precisely….
I forgot how many of these cars and systems I have worked on…..and my statements come from that.
No ECM In 1981 Corvette
