NathanLewis

I'm not a genius at all, nor do i completely understand how these electronic feedback quadrajets work.

My thought has been that they are simply a regular carburetor just sending back info to the ecu.

But my question relates to the 02 sensor. How much of a role does this play on this carb? If it were contaminated, or worn out, would it cause the ECU to run the carb in rich mode, making the car run poorly?


My friend bought a camaro with the 305 and it runs like crap, even after the wires, dist cap, plugs. We can't figure it out, possibly the choke has failed, or the float. I really don't know.

five7kid

iTrader: (14)

The O2 sensor is vital. The carb has what is called a "mixture control solenoid" (MCS) that pulses to control the fuel that is allowed through the primary jets. The ECM uses the information from the O2 sensor (along with engine speed, throttle position, and manifold vacuum) to determine the pulse duty cycle.

When the O2 sensor gets weak or fails, the signal it sends to the ECM is toward lean, meaning the ECM will richen the mixture. If no signal is received by the ECM from the O2 sensor, it goes full rich.

You may or may not have an O2 sensor problem. If it isn't connected, then obviously that is a problem. If it hasn't been replaced, then it may be the problem.

When you first turn the ignition to "on" without starting the engine, do you hear a clicking from the carb? If you do, that's the MCS. It should go for 15-20 seconds then stop if you don't start the car. It can be heard with the engine running if you listen close enough. If you don't hear it, then you probably have some problem with the MCS or its circuit. The "default" or failure mode is for the MCS to go full rich.

The choke is fairly easy to check. It should open as the engine warms up (easily seen by removing the air cleaner lid). Is the "Choke" light coming on?

A failed float would flood the carb. You'd probably know that as well.

Is the SES light coming on while the engine is running? If so, you need to retrieve the codes from the computer and go from there.

NathanLewis

Yeah, The ticking happens when you turn the key on run position.

I took the car to my school(automotive institute) and we used a scanner on it. It won't read the ecu, and its a snap on scanner, so its not a cheapo scan tool. The check engine light just blinks rapidly and dims like its shorting out.

I might try using a paper clip and touching two of the terminals to blink out a code for me.

And i guess we'll get the o2 sensor out tomorrow and have a look at it.

five7kid

iTrader: (14)

Not all that common, but it sounds like an ECM problem.

NathanLewis

I'll have to find out.

ocpmann

I had a 84 caprice classic that the snap on scanner would not read. The new computor fixed that. computor was around 100 to 150 bucks, and kragen orielly's

ZF6camaroZZ4

Theres a Diag connector on the passenger side, by the blower motor. White connector lt/blue wire.(can get it right off the mc solenoid too).
Connect + lead of a Dwell meter to that, - side of dwell meter to ground.
Have dwell meter on 6 cylinder scale.
Engine at idle should read 30, engine at cruise should read 30.
Put your hand over the carb, should lean out to like 50-55.
Towards 0 is rich.

Use a combo of the airbleed, rich stop, to get those to be 30. Of course you should have them set to factory spec's, along with the mixtures to start off. Also check your tps for .63v at idle.

Little edit:
Sometimes I take things for granted.. So I just wanted to add:
To do the above, car needs to be warmed up in Closed loop. When you first start the car there will be a fixed dwell in Open loop. When you get into closed loop for feed back, your looking for those 30's.
If it's not getting into closed loop, look at the O2 and temp sensor for sure.
And if your getting feedback, but its in the high number 40's 50's. You know the carb is running rich and the ecm is trying to lean it out. And on the other side, if its in the low 10's 20's... the carb is running lean and the ecm is making the mixture richer.
Setting for the 30 gets the car running real crisp, someting you can really feel driving.

anyway, GL

Camaro305SB

I don't know if it would affect talking to the ECM, but do you have an electronically controlled distributor in it? Without that your codes will just keep coming up 12 or 21 (I forget but its for no pulse from distributor).

NathanLewis

everything is stock.

checked the code, and it flashed back 32, which would be the egr valve. I'm guessing its gone bad or clogged up.