andyrisso

I have a 1980 Corvette with the Calif 305 in it. (Don't hold that against me). The engine was rebuilt 3 years ago prior to my purchasing it so I do not know of any modifications made at the time.
Since I have purchased it, I have replaced the intake with an Elderbrock Performer intake manifold, a Rebuilt E4ME carb from Advanced Auto, Hooker Headers complete with side pipes which of course resulted in my removing the air pump since I felt there was no need for it.
I recently started having problems with some backfiring from the pipes, (no real noticable loss of power though), whenever I would get to an incline or gas on it heavily so I changed out the fuel filter last night and took it for test ride. In changing out the filter, I had to unplug the electrical connection to the Mixture Control Solenoid so that I could put a wrench to remove the filter from the carb. I had forgetting to plug it back in before the test drive and the engine worked great, even smoother than before the filter started going bad.
So this morning, I decided to leave it unplugged and come to work which is a 37 mile drive on the freeway, complete with 2 inclines and outside temp at about 38 degrees. It ran great with not a single issue. When I did the headers and the side pipes, I had the nub welded on for the O2 sensor and it is connected to the 3rd tube of the headr on the driver's side. It is the original O2 (with 2 wires).
My question is this. With regards to all that I have ready in the forums regarding the MSC, why is mine running great with no issues thus far with the MCS unplugged? Am I missing something or is this just a rare occasion?
I am really curious about this. The fuel milage seemed about the same this morning. I was advised by Summit Racing when I purchased the headers and side pipe that I should upgrade the O2 sensor to a 3 wire which would mean that I would have to run a resistor inline on one of the wires and so on to compinsate for the change in the headers from stock. The side pipes are 4" OD btw in case that matters.
Any input would be great to get some ideas on why and how. Also, in 1980, was the ECM really an upgrade or had it not been perfected enough to the point that simple changes as I have done made no difference in electronic stability even though you can feel in the increase in horsepower?

LannyL81

My thoughts:
With the MCS unplugged, the primary metering rods are at their richest position, which I would think would cause the engine to be rich all the time. So I am wondering why not????

Also, where do you have the two wire O2 sensor at? I also have the Hooker sidepipes and had the O2 bung welded in at the collector on the driver's side. I get the Check Engine lite all the time for O2 sensor error. I have to replace it with a three wire O2 sensor and so on to get the CCC to stay in closed loop.

Are you sure your computer is working? I assume the '80 CA model is the same as my '81 computer. Do you get a code 12 in test mode?

I am going to have to try to umplug the MCS this weekend and see what happens....sure has me curious.

jordan126

i also have an 80 from CA with a 305,no rust at all,great car

a1sensei

Check your trouble codes. As Lanny said, with the MC solenoid unplugged, it will run very rich and foul the plugs soon.

The carb is probably not adjusted correctly. Getting a re-manufactured one from a parts store, you can almost bet on that. Doug Roe's book "Rochester Carburetors" and the GM service manual have info on setting these carbs up. I'm betting this is where your whole problem is, especially if you are not getting any trouble codes.

A 3 wire O2 sensor is needed only if it is mounted far enough down the exhaust that it will never get to proper operating temperature. I have shorty headers with the bung mounted on the collector and I have no problems with the stock sensor. I'm not sure how well mounting it on a primary tube will work, but I suppose it could.

God bless, Sensei

andyrisso

Sorry it's taken so long to reply. I have the O2 sensor mounted about 10 inches down the tube on the number 5 cylinder. I still am running the original O2 sensor but think that it is going bad now. the symptoms are on heavy acceleration I am hearing a little backfiring, but it does not effect the power. It will also give off the sounds of backfiring through the side pipes at cruising speeds. It's not consistant, but it's there. I have since plugged the connector back into the carb, replaced the distributor and now cha nges, so my thoughts are that the O2 sensor has gone bad on me since now it's getting full heat and flow through the headers, unlike it was through the stock.

But all in all, it's still running liker a champ and am fine tuning it, which is one of the reasons that I had gotten it in the first place. The driving time in it far outways the occassional minor issues.