Help! 81 Corvette idle rough/low, 5 mpg, little smoke

[JohnnyGordo]

Please help. I needed a hobby. I like muscle cars and mechanics so I bought a project. Actually, it's not much of a project. It's an original 81 Corvette with 38K. Everything works except for power antenna and cruise control. With this mileage, it's never been driven very often. It fires right up, however it idles rough, sometimes hesitating to where is slightly shakes the whole car. It smokes a little and I smell gas = it's running rich. I'm getting a pitiful 5 mpg and the car is supposed to get up to 15. I've replaced the entire ignition system, so any other ideas for the very slight hesitations, running rich, slight smoke. I've also replaced the PCV Valve. There is no check engine light either, so I have no codes to go off of. The car's been pampered and has sat for a long time. I thought the carb might be clogged, so I've used two bottles of SeaFoam to unclog and that hasn't really helped. Any ideas to get me started would be much appreciated. Thanks in advance.

-John

 

[Peer81]

It could be a couple of things.

I would first begin with the carb. Buy a dwell meter and connect it to the green connector near the carb and to ground. See with the engine idling if the dwell is around 30 degrees at 6 cilinder scale. You can adjust a couple of things to the carb to make it run richer or leaner.

Good luck with the 81, very nice Corvette to have

Greetings Peter

 

[Vettehead Mikey]

Do what Peer81 suggests, and throw away the Seafoam, it's a waste of money. Most likely you have a serious vacuum leak and a carb that needs rebuilding.

 

[JohnnyGordo]

How do I check for vaccum leaks and where? Do I use soapy water and spray on it while it is running. I'm limited in my mechanical knowledge, which is why I'm here. Learning as I go.

 

[JohnnyGordo]

Do what Peer81 suggests, and throw away the Seafoam, it's a waste of money. Most likely you have a serious vacuum leak and a carb that needs rebuilding.

Thanks. But how do I check for leaks?

 

[Alan76]

Try some carb cleaner and spray around the base of carburator if rpms increase theres your leak also check the vacum in the headlight system
pull the line off and plug see if it smooths out vacum line dry rot over time

 

[LannyL81]

Yes, pull the vacuum line off the intake behind the carb, plug it and see if the engine runs better. If it does, then you have lots of vacuum connections to check.

Check to see if the choke plate is open all the way after a few minutes. Put a long screwdriver to the front of the carb with the engine running and listening for clicking. This will tell you that at least the mixture solenoid is working. It may not be as your mpg is so low. That part costs about $40 or so. If you have a DMM, you can check the TPS operation. It is just a variable resistor.

The carb settings requires a few special tools. If the plugs over the idle air mixture screws or idle air bleed valve have not been removed, then the carb is going to have to come off the car. Then might as well just rebuild it.

In fact I will offer to rebuild it; you buy the carb kit and pay shipping both ways and any parts that it needs. I cannot clean it like the various carb rebuilding companies do though. All I have is a can of carb cleaner and a brush, no tank to dip it in. But I do have the tools and I follow the GM manual settings.

The E4ME carb has alot of very good qualities about it.

LannyL81

 

[JohnnyGordo]

Yes, pull the vacuum line off the intake behind the carb, plug it and see if the engine runs better. If it does, then you have lots of vacuum connections to check.

Check to see if the choke plate is open all the way after a few minutes. Put a long screwdriver to the front of the carb with the engine running and listening for clicking. This will tell you that at least the mixture solenoid is working. It may not be as your mpg is so low. That part costs about $40 or so. If you have a DMM, you can check the TPS operation. It is just a variable resistor.

The carb settings requires a few special tools. If the plugs over the idle air mixture screws or idle air bleed valve have not been removed, then the carb is going to have to come off the car. Then might as well just rebuild it.

In fact I will offer to rebuild it; you buy the carb kit and pay shipping both ways and any parts that it needs. I cannot clean it like the various carb rebuilding companies do though. All I have is a can of carb cleaner and a brush, no tank to dip it in. But I do have the tools and I follow the GM manual settings.

The E4ME carb has alot of very good qualities about it.

LannyL81

I think I found something. As I was removing everything, I noticed that the vacuum switch, which connects to the upper radiator hose housing area where the thermostat goes, was broken off. It had two tube lines into it. One came from the carb and the other went around the car, I think it hooks into the EGR valve. It was broken, therefore, a huge vacuum leak. There are two sensors on there. It was a pain to find the part, but I found it and ordered two new ones (I figure change one, change them both.) Also, I have no idea if the carb has ever been rebuilt, there are so many things that could be wrong in there, so I ordered a remanufactured/rebuilt carb (Rochester Quadrajet E4ME. It has been rebuilt to OEM specs. Hopefully, I have enough know-how to switch out the carbs. After inspecting all the lines, they all look new, so the previous owner must have did this. I've already replaced the entire ignition system. I pray and hope she runs better after replacing carb and sensors. If not, the only other idea I have is O2 sensor and EGR valve. Any advice? or am I on the wrong path? Thanks for all the help and thank you for offering to rebuild the carb.

 

[JohnnyGordo]

I think I found something. As I was removing everything, I noticed that the vacuum switch, which connects to the upper radiator hose housing area where the thermostat goes, was broken off. It had two tube lines into it. One came from the carb and the other went around the car, I think it hooks into the EGR valve. It was broken, therefore, a huge vacuum leak. There are two sensors on there. It was a pain to find the part, but I found it and ordered two new ones (I figure change one, change them both.) Also, I have no idea if the carb has ever been rebuilt, there are so many things that could be wrong in there, so I ordered a remanufactured/rebuilt carb (Rochester Quadrajet E4ME. It has been rebuilt to OEM specs. Hopefully, I have enough know-how to switch out the carbs. After inspecting all the lines, they all look new, so the previous owner must have did this. I've already replaced the entire ignition system. I pray and hope she runs better after replacing carb and sensors. If not, the only other idea I have is O2 sensor and EGR valve. Any advice? or am I on the wrong path? Thanks for all the help and thank you for offering to rebuild the carb.

So, I put in a new carburetor in (remanufactured, rebuilt, and adjusted to OEM specs), the same as was in the car. Followed everything to a T. Once completed, she fired right up and was idling very well...I was so happy...until I put it into gear. She bogs down so hard when you give it gas, she barely moves and will die, even when I give it gas. HUGE hesitations. When idling in park, the car is very responsive to gas, but once in drive or reverse, she runs terrible. I drove it a block and it died on me four times trying to get it home. I had to give it lots of gas in park, then slam it into gear to keep it running and to get it moving. ad I'm about to put the old one back on if I can't get any help. PLEASE HELP!!!!

 

[Alan76]

Ibought a rebulit carb from on line supposed to rebulit bench tested all I had to do was bolt it on!!!!! Yea right so after calling said rebuilder and getting run around they tell me to return I put my intials on it sent it back days later they send same one back said they did this and that still not good wound up read Lrs Paper on problems he found with commerically rebuilt carbs My friend Jack who is ase certifird and been a mechanic since 1971 fixed and now runs like a charm

 

[Wajulia]

With all of this going on, are you getting an check engine lights and codes?

 

[terry82]

i have a 1982 vette .if my car was doing what you have said, i would look at the coolant sensor in front of the motor .that sensor talks to the ecm.when it goes bad it tells the computer to add fuel .

 

[Wajulia]

Retrieve the ECM codes, it will tell you what senso ro actuator is at fault and you can debug the problem to the correct part. True that the coolant sensor can cause the ECM to go open loop, but there are many other things. Learn about the 1981,82 ECM, it is not that scary and can give you tons of info to debug these problems. THe service manual has fantastic isolation procedures based on the fault codes

 

[JohnnyGordo]

Aha!!!!

i have a 1982 vette .if my car was doing what you have said, i would look at the coolant sensor in front of the motor .that sensor talks to the ecm.when it goes bad it tells the computer to add fuel .

BEST ADVICE I GOT YET! Yes, you were right, the plastice male connectors on the sensor that the vacuum lines connect to, was BUSTED and Broken. Therefore, the sensor was not functioning properly. Good call and thanks for helping me find a possibility for my gas consumption problem.

 

[JohnnyGordo]

Alrighty then.

Retrieve the ECM codes, it will tell you what senso ro actuator is at fault and you can debug the problem to the correct part. True that the coolant sensor can cause the ECM to go open loop, but there are many other things. Learn about the 1981,82 ECM, it is not that scary and can give you tons of info to debug these problems. THe service manual has fantastic isolation procedures based on the fault codes

Come to find out, my check engine light is not working so I can't get the codes read to me, so I am working on trying to fix the check engine light, then will begin diagnostics check to see if I can get some error codes.

 

[HammerDown]

...The E4ME carb has alot of very good qualities about it.
LannyL81

Providing EVERYTHING in it and around it is operational 100%
Personally, I'd rather have the option to tune the engine myself IE fuel mixture-engine timing.
Considering deleting both the E4ME and the computer controlled dizy for non-computer quad carb and HEI.