itchmay123

Hi All!!! I purchased an 81 with 7500 miles on it only to find out the emissions have been removed and the computer unplugged. I have all the emission parts including catalytic converter and smog pump, however the carb has been modified to remove the modules for ECM control of the mixture. I can overcome the carb, but what can be done to control the timing and smog pump so I can pass emissions???? Any constructive ideas would be greatly appreciated as I do not want to reconnect the computer and attempt to restore the control wiring!!!

stuck

It depends on where you live. No emissions checks for cars over 25 yrs old where I'm at in Tx. I've got an '81 and I'm just about about to bite the bullet and remove all the smog and ECM stuff. The ECM controls on the carb really suck.

TimAT

the computer cars had a different distributor. The module had 6 pins instead of 4 or something like that.

a1sensei

The ECM carb keeps the mixture ideal at cruise for ultimate fuel economy and will flow all the fuel you need for maximum performance at WOT. What sucks?

I'd get an E4ME and re-connect the computer. It is a good system and once you look into it, it is not at all difficult to work with.

God bless, Sensei

gingerbreadman1977

i hated that computer. i ripped it out with the carb, dizzy,tranny and the 2000 miles of wiring that connected it all and threw all of over the back fence .

1nicecorvette

so thats where that came from. i wondered what that was. hey my kid thanks you for all that "junk" . his go cart has never run better! and best yet... its emission legal now!

nate99

If you are trying to pass emissions with a partially intact emissions system, well, good luck. As mentioned, if you lose the ECM, you will have to get a new distibutor in addition to whatever you do with the carb, and the lockup on your torque converter will not work. I am looking in to a manual switch for that myself, but have not worked out the particulars.

CA-Legal-Vette

As some of the folks above have said, the first thing we need to know is where you are in the country. Different states, different rules.

Second, if you are trying to get it back to stock, you will need to do all or nothing. The carb is only part of the whole system. It does vary the mixture (except at WOT) but only has one other smog connection for the throttle position sensor. The distributor in this system controls the advance electronically. If the distributor is stock and the rest of the system is disconected, it'll run like a pig.

Last, there are a number of sensors including the MAP sensor and the O2 sensor as well as the temperature sensor. Besides the computer, all of the above will need to be working and hooked up correctly for the system to work.

Why don't you start by telling us where you are, what you still have and we'll go from there.

MN81C3

I agree with the previous posts. A lot will depend on where you live. Here in Minnesota we no longer do Emissions Checks and when we did, cars over 20 years old were exempt.

When I bought my 81, the Smog Pump, Dist, and sensors had been removed by the previous owner but was still running the E4ME carb. For me, it came down to the lesser of two costs. Obtain all the parts and pray the ECM still works or just pickup a pre 81 carb. I chose to pick up a Carb from a 1980 corvette and never looked back. I found that the secondaries were probably not opening on the E4ME carb as it sure runs great now.

I do agree with a1sensi - it would have been nice to have the ECM controlling things, but the cheaper path for me was the 1980 carb.

itchmay123

Here is what I have on the car now in Denver where all vehicles must pass emissions - trust me, I had to take my 67 Ford SWB Pickup back twice after tweaking timing and mixtures to get it to pass...Good news is obtain Collector Plates after emissions and never have to go back...

1. QJ carb must be pre-81 as the idle mixture and throttle positioning sensors are not present nor able to be installed in the top plate.
2. New smog pump, diverter valve assembly, hoses and electrical connectors. I have not put the drive belt on as the electrical wires that go to the ECM have been cut.
3. Catalytic converter has been replaced with a bypass pipe. O2 sensors are present and connected.
4. The EGR control module is missing.
5. ECM plug/s to Distributer have been disconnected but vacuum module is present.
6. ECM is present but unplugged.

Here is what I have in stock to install.

1. Catalytic Converter.
2. CC air line to smog pump.
3. Backflow valves to exhaust manifolds.
4. Spare connectors from used 81 wiring harnesses.

Here's what I am experiencing.

1. Car starts quickly and idles smooth.
2. Upon acceleration, feels and sounds like the engine is loading up - bogging down.
3. When hard accelerating, I hear what sounds like slight backfiring (popping) in the carb, but no flames when statically observing with air cleaner removed.
4. Occasional momentary knock and engine shake at idle.
5. Tranny works fine.

I believe I can deal with the carb and distributor to get close to passing emissions but I think the smog pump must be functional to dilute the exhaust at the manifolds and cat. Normally under ECM control the manifolds only receive air from the S pump until the engine is warmed up and then the valve diverts air to the Cat.

I appreciate all of your suggestions and opinions!!!!

CA-Legal-Vette

We'll need a CO member to chime in or perhaps you know the answers to the following.

If the distributor has a vacuum advance can, it isn't stock. This is probably good news, but maybe not.

To pass smog, do you just need to pass emmisions or do you have to have everything "as original?"

The "as original" part will be challenging. Given the cut wires, it will be hard to make the diverter work properly. The EGR was also controlled by the ECM via solenoids on the intake manifold (which I presume are gone). I'm not sure how you would make the above two systems work properly without the ECM.

I know that one of the standard requirements here in CA is that the "Check Engine" light, if present, needs to come on with the key and go off with the ignition. Without some clever electronic trickery, this is hard to do without the whole system being functional.

Oh and does your catalytic converter have the air input tube? If not,there is a pretty simply way to set the diverter so it only pumps air into the exhaust manifold. I doubt it will work as well as pumping air into the cat, but it'll be better than nothing.

itchmay123

The cat has the air tube connector and I have the original piping that runs from the exhaust manifold area to the cat. I believe just the presence of the smog pump and cat is all CO emissions physically look for so that should not be a problem as I will have everything connected and "looking" operational. I want to be able to have air from the pump going to both the exhaust manifolds and cat to dilute the exhaust as much as possible to help pass emissions. Normal mode is air to the manifolds only until the engine is warm and then it diverts air to the cat. The check engine light is not on because the ECM is unplugged. I believe I can optimize the timing and lean out the carb enough to help reduce the CO and Hydrocarbons, but I still need air from the pump....

CA-Legal-Vette

OK. If you're right, this should be workable. If you have a GM service manual, have a look at the vacuum hose diagram. If I recall correctly, there is a vacuum hose that goes from one of the carb ports through one of the TCS switches in the thermostat housing, through the vacuum switch (the one controlled by the ECM) into the diverter valve. If you bypass the ECM switch, it should accomplish what you're looking for and do the job adequately.

If you don't have the manual, I'll check it when I get home tonight.

LannyL81

If you need pictures of any of the emissions stuff on an '81 let me know. I have it all sitting in a box. I also have the AIR pump connector still in my car, even though I am not using it at this time, and can take a picture of that. One thing that I will not be able to provide is a picture of how all the vacuum lines are connected between the thermostat housing and the AIR pump.

Good luck,
LannyL81

itchmay123

Thanks Guys,

I have all of the manuals and a vacuum hose kit with diagrams. I think I can make the smog pump work to accomplish passing emmissions as long as I don't need the EGR controller module for the visual insection.

LannyL81 - Did you remove the EGR controller module? It is orange or red and mounted above the intake manifold, passenger side and closer to the rear of the engine?????

LannyL81

Yep, I removed it. Have it sitting in the box with all the other parts. Mine is cracked and not sure if it even works....have not tested it. Do you need a picture of it or do you need one? If I remember correctly, I could not find a replacment when I was looking for one.

itchmay123

Don't know if I am going to need it or not for emissions - I will do some research to see if I can find out the visual inspection requirements. I may need one, but also have not been able to find it anywhere!!! For all the time and money I have spent obtaining emission parts, I probably could have bought a trashed 81 vette engine with everything connected...