Help! Carb replacement, can't get it running properly

[JohnnyGordo]

Guys, I know nothing of carbs for the most part. I have a 1981 Corvette with a Rochester E4ME Carburetor. I just replaced it because I was getting bad mpg, about 6. It was time to get one rebuilt, so I ordered a remanufactured one that was cleaned, rebuilt, and adjusted to OEM specs. Replacement was fairly easy.

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!!!! Is she running lean, or rich, thought about adjusting mixture, but don't know how, I see two screw holes in the front on either side, however, looks like it needs a special tool and I have no idea how to get in there= bad placement. Is the mixture my problem?

 

[Hib Halverson]

When's the last time the engine's oxygen sensor was replaced and has the check engine light been on?

 

[JohnnyGordo]

When's the last time the engine's oxygen sensor was replaced and has the check engine light been on?

The 02 sensor is about 3 years old. The car ran fine prior to carb replacement, it just had pitiful fuel efficiency. No check engine light at all, even now.

 

[lars]

If the carb you bought is a commercially rebuilt carb, the carb is likely to have a multitude of problems that will take significant effort to repair, if they can be repaired at all. I can guarantee you that this carb, if commercially rebuilt, is not "remanufactured, rebuilt, and adjusted to OEM specs." Many of us will not work on one of those commercially built carbs due to the terminal problems the carb builders build into them. You are much better off keeping the original carb and having someone like Henry out at Ole's go through it. Put the "rebuilt" one on the shelf for use as a book end for your service manuals. For further info, drop me an e-mail request for my "Commercially Rebuilt Q-Jet Problems" paper.

Lars
V8FastCars@msn.com

 

[JohnnyGordo]

If the carb you bought is a commercially rebuilt carb, the carb is likely to have a multitude of problems that will take significant effort to repair, if they can be repaired at all. I can guarantee you that this carb, if commercially rebuilt, is not "remanufactured, rebuilt, and adjusted to OEM specs." Many of us will not work on one of those commercially built carbs due to the terminal problems the carb builders build into them. You are much better off keeping the original carb and having someone like Henry out at Ole's go through it. Put the "rebuilt" one on the shelf for use as a book end for your service manuals. For further info, drop me an e-mail request for my "Commercially Rebuilt Q-Jet Problems" paper.

Lars
V8FastCars@msn.com

It was rebuilt by MountainMan Fuels inc., the guy has been rebuilding carbs for many years. He adjusted everythign to OEM specs. He is supposed to call soon and will give me step by step instructions on how to adjust it. The car starts just fine, however, it idles rough and low. If you put it in drive, the more gas you give it, the worse it bogs down it seems. If you give it a tad of gas, you may move a little. Pain in the but getting it up the hill to get into the garage. The carb has a warranty. Worse comes to worse, I'll put the old carb back on it I guess. It ran fine, just real bad fuel efficiency=6 miles per gallon.

 

[Peer81]

Alright, here a few things to check.

First check if your Check engine soon light is working at all. If not replace that first.
Second, is there a difference between running back cold and hot?
When cold the carb is running on its own and when the engine is at temperature the ECM will kick in. So how did the engine do when it was hot? To see what you're doing on these carb's you need to have a dwell meter.

And what is your spark base setting?

Greetings Peter

 

[JohnnyGordo]

Alright, here a few things to check.

First check if your Check engine soon light is working at all. If not replace that first.
Second, is there a difference between running back cold and hot?
When cold the carb is running on its own and when the engine is at temperature the ECM will kick in. So how did the engine do when it was hot? To see what you're doing on these carb's you need to have a dwell meter.

And what is your spark base setting?

Greetings Peter

I will check on the check engine light, but remember, the car ran fine prior to new carb install. So not sure if replacing other parts is the right way to go, I'm fairly certain it is a carb adjustment needed, don't know which one, or how to go about doing it.

When the car is cold, she fires right up and runs smooth at about 1100 RPMs, then within a minute, the idle drops and the bogging and hesitation starts and gets worse as the car warms. The idle will drop to about 400 RPMs, however, even when I give it gas up to 1000 RPMs it is still bogging (shakes the whole car). If I am able to keep it running, I put it into drive or park, and apply gas, the more gas I apply, the harder it bogs and the RPMs go straight down and the car dies. If I give it a little gas, it takes a sec, but I begin to move, too much gas and it bogs straight till the car dies.

Parts I've recently replaced:

Whole new ignition system (ignition coil, distributor, rotor, ignition module chip, spark plugs and wires)

New vacuum lines for entire emmission system. New PCV and now new carb, but ain't running right. All lines are good and there are NO vacuum leaks.

O2 sensor about 3 years old, planning on getting new one soon, but like I said, the car ran great except for bad fuel efficiency, ran really rich. I got a new carb just because I don't know when the last one was cleaned, rebuilt or replaced.

I do plan to switch out EGR valve soon as well.

 

[Wajulia]

But the car did NOT run fine. 6 MPG is not right. The carb will go open loop if the ECM is unhappy. Open loop is a full rich condition with no timing advance which may be the cause of the MPG issue and needs to be addressed for the 81 is to ever work well. You need to go through the debug procedures in the service manula for the CCC assuring there are issues and correcting the ones that exist.

Also, another possibility, if the car has been running that rich for a long period of time it could have melted the Catalytic converter, that would allow the car to run fine at idle and bog down during acceleration.

BUT -- I suggest you get the CCC sorted before changing any more parts.

 

[Peer81]

Like Wajulia say's. I'm not telling you to change more parts like you already did, first look for the problem and then see what needs to be done. Good change you're old carb is still fine!

With the sympthoms you have, as I read them. Look at the carb when it's doing this in idle and see if the carb isn't overflowing fuel. Mine did about the same and the fuel inlet stop was the problem.

Greetings Peter

 

[Wajulia]

The e4me carb (1981 OEM model) does not adjust like prior year Quadrajets. The computer measures the fuel mixture from the O2 sensor and then adjusts the carb appropriately. This works very well when it works -- it goes full rich when it doesnt (that is why people are telling you to see what the computer thinks of all of this, if you need help in the CCC diagnostics, there is a great section in the service manual. Let me know if you need a copy).

Any manual adjustments on this carb are basically setting the fuel mixture solenoid to the midpoint letting the computer take it from there.

IDLE -- The computer controls the idle mixture and it is controlled from the idle air adjustment screw on the top of the carb. This needs to be adjusted with the use of a dwell meter attached to the mixture solenoid test connector (green connector in front of carb) It is very sensitive, very fragile, and you should follow the procedures in the service manual. The two adjusters in the front and to the bottom on the carb are also idle adjustment, but are probably close already and are addressed only if you cannot make carb work using the prior adjustments -- BUT idle does not seem to be the issue so I would not change any of these

RICH and LEAN -- there is a rich and lean stop adjustment. Neither of these adjustments actually change the mixture of the carb, but in reality set the limits the computer can command. They basically set the solenoid in the center of the computers capabilities to adjust the carb. again it needs a dwell meter and you should follow the service manual procedures (I can send these to you if you would like) There are some tests that you can do to assure that the solenoid inside the carb moves the proper distance. If it does, the lean and rich stops are probably not causing your problem.

That is all there is to adjust (without discussing the choke), I am not sure that any of these adjustments will fix your symptoms. I do not think this is a carb issue. If it was running better with the old carb, put it back on and find out what is causing the mileage issue.

 

[JohnnyGordo]

Well, I don't have a dwell meter, and they are not cheap. The person who rebuilt the carb has contacted me and is giving me adjustment procedures. My slow idle is low: 400 RPMs and the car eventually dies. So I will adjust this and turn the idle screw half a turn clockwise.

Next, he told me to turn the mixture screws 1 full turn counter clockwise. Once that is completed, I am to start the car and report back to him what it is doing.

I was planning on changing my O2 Sensor, and it seems now is a good time. So I will order one of those and hope it is the problem in my CCC.

After reading about my emmissions and CCC. It really comes down to this: Carb, EGR valve and solenoid, O2 sensor, ECM, PCV valve and that's about it. I've already replaced the PCV valve, and now Carb, I think the next biggest thing is the O2 sensor because I've read they control a lot and are a big factor on how your car should operate. After that, I will order a new EGR Valve just because it looks old and there is some rust on the housing of it. Anyone know how I can check to see if the solenoid is still operating?

If my car does not run better after these adjustments, I will probably put the old carb back on it, just because at least I could drive it. I will do the adjustments soon, right now it's 28 degrees outside with snow...and I live in Louisiana. CRAZY weather.

 

[Wajulia]

The procedure that he gave you MIGHT make the car idle better, but only if the idle air valve is adjusted correctly as I described above. If not, they will probably make little difference, and your issue is not in the idle circuit in the first place.

You can get the CCC codes from the computer by removing the ash-tray. you will see a connector. with the key off, short the two pins on the connector that are not separated in the connector, on my car they are the two closest to the driver. Leave them shorted (I have used a screwdriver for this) and turn the key on but don't start the car. You should hear a chatter in the engine -- I think it is the mixture solenoid -- it is normal.

The check engine light should begin to blink. It will blink "12" three times (12 is one blink pause, two blinks, pause repeat this three times) It will then begin to blink the trouble codes. First number, pause, second number, pause (example 24 is "speed sensor error" and would be blink, blink, pause, blink, blink, blink, blink pause) It will blink out each code three times. When it repeats the code 12 it is done. Remove the short from the connector. If the car does not do this the light bulb or the ECM is at fault and you need to debug it.

The codes will tell what is happening with the carb, the o2 sensor and a whole bunch of other things. By replacing parts the way you are, you might get it to run better, but from my personal experience, you will never get an 81 to run correctly until you sort out any CCC issues.

Good luck

 

[Peer81]

Buy yourself a nice second hand analog dwellmeter for about $30, that ain't to much is it?

And (sorry to say) if you want to make this carb work it's easiest if you know how a E4ME carb works. Ones you know the system it's easy.

Greetings Peter