'86 305 running rich...

I had a similar problem and I bet the solution would have been buying a good carburetor. Instead, I experimented with an RC cirtuit to control the MCS and finally tweaked it so it has full power, no lag and is not as rich. I originally took the carb apart due to a heavy float.

I have set the idle to read between 30*-35* on the dwell meter's 6 cylinder scale when attached to the green test connector in front of the carburetor. Is this correct?

With that setting it still idles rich, and slightly rough. It idles better/smoother and less rich smelling when I advance the timing beyond the factory 0* specification. At the moment though it is set at the factory timing.

Cory

Find the (charcoal) canister control valve, it's a black plastic device with 4 hoses running to it, IIRC, it is usually mounted above and to the center of the alternator bracket, remove it from the car and shake it, if any gasoline comes out of it, replace it. Common failure part.

No gas came out, so I would guess gas isn't getting sucked in through there. What else should I check?? I'm really getting frustrated with this thing. I should work. I've got the lean and rich MCS stops adjusted like you said so at a higher RPM it reads 30*-35*. I have the idle mixture screws and air bleed screw adjusted so at idle it reads the same. Still though it smells rich throughout the RPM range and the idle is rough. I don't understand.

I tried pulling each plug wire one at a time to see that all cylinders were firing. They are all firing, though #8 is slightly weaker than the rest, but I can't imagine that should make such a big difference. Maybe a slightly rough idle if anything but shouldn't make it pig rich. The car runs nice and smooth and drives nice once you get going, but idle is rough and I can't get it smoothed out. If I unplug the MCS and the distributor plug it will idle more smoothly. I'm feeling like I've done everything I should for it to run well, but it still doesn't.

I check the voltage from the O2 sensor and it bounces around from .3-.6 and often bounces up to .7-.8 briefly before coming back down. Also, the air pump is not pumping air to the manifolds once it's in closed loop so it shouldn't be getting a false lean reading from the O2 sensor, and from the O2 sensor readings it is indicating rich if anything. I don't get it.

I suppose that is a possibility. It would certainly make setting the float level to factory specs inaccurate. The float is one of the solid rubber types. I never understood why they don't just use brass floats from the factory. I've never had a problem with them getting sunk/fill or otherwise out of whack like the solid ones sometimes do and like the plastic ones always do. I was getting desperate so today I set the float slightly lower than the specs called for. It didn't seem to make a big difference.

At least the car didn't stall today after my other adjustments. It's only gone 55 miles and it's already through half a tank of gas. That has included a good amount of idling in the driveway, but that seems ridiculous. I figure the tank is about 18 gallons, so assuming the sender is reasonably accurate that puts it at about 6 MPG. Let's say I burned a crapload of gas in the driveway and give it 10 actual MPG. That's awful. I've never even seen that bad of mileage in my Galaxie! The computer is setting the mixture to be so rich, and I can't for the life of me figure out why that is. If the float level was high or anything causing the mixture to be rich the computer should at least be reading a rather high dwell from the green test connector, but it is right around 30* which I understand to be a neutral point. More and it is attempting to lean the mixture, less and it is trying to richen the mixture. The O2 sensor trends up and down of the .45v stoich mixture reading, but often jumps to .7v-.8v which is rather rich.

I guess what I'm getting at is if the float were too high causing a rich mixture would the computer not be trying to compensate and give a high dwell reading?? Shouldn't it be giving a high dwell reading if for any reason the mixture is rich and it can't bring it back down to where it should be using the MCS?

I'm struggling to understand this thing. I thought I understood it before, but it is not behaving as I understood it to from the advice I have been given and from waht I have read. I think I may try pulling the carb off again and epoxying the fuel bowl plugs which are said to be prone to leak. I think I may be grasping at straws here. If I can't come up with something I'm tempted to pick up an older quadrajet and distributor. I'd really like to get it running properly as-is though. I was hoping for upwards of 20 MPG on the highway and about 15 around town. Unfortunately this damned computer is fighting me every step of the way.

Cory

If the MC dwell is varying at fast idle with a fully warmed up engine, the computer has control of the mixture based on O2 sensor input. I don't trust smell of the exhaust, rich and missfire are too easy to confuse. Plug color on the other hand, is trustworthy.

The EGR valve could be leaking, #8 is the closest to the EGR and will usually be effected soonest from a leaking EGR valve.

The O2 voltage -should- be rolling high to low.

Rich would be the O2 stuck high.

Check the EGR, check and make sure that the MAP sensor is properly connected, check and make sure that the TPS voltage is correct. Make sure that the magnet in the pole piece in the distributor isn't cracked, this could send extra RPM counts making the ECM 'think' that the engine is running faster than it really is.