just bought a 85 ta with a l69 engine and it has the check engine light on .. i checked and the code is 23 which says its a mat sensor .. i started looking under the hood and noticed it is unplugged .. i plugged it back in and the check engine light went off but it runs like crap .. with it plugged in and the check engine light on it runs fine .. should i just buy a new sensor ??

 

the sensor that is unplugged is the greenish blue one in the left front of the carburetor

 

Greenish blue connector at the RIGHT front of the carb is the mixture control solenoid. With that unplugged the carb goes to full rich and stays there. (might partially explain poor gas mileage?)

The connector sticking out the front of it at the LEFT front is the throttle position sensor. (which by the way, I STRONGLY recommend untwisting its wires and routing them correctly, UNDER the vent hose)

AFAIK the carbed motors don't have a manifold air temp sensor.

 

this is not a pic of my motor .. the check engine light code i get is 23 .. do you know what code that is on a l69 motor ?

 

heres a pic of my motor and whats unplugged .. again i just bought the car yesterday and it runs fine with it unplugged , just have a check engine light on .. when i plug it back in it runs like crap but check engine light goes off ..

 

That connector at the front RIGHT of the carb is the mixture control solenoid. With it unplugged the thing goes to full max rich 100% of the time. Surefire recipe for bad gas mileage and a clogged cat. However they re-used codes ALOT back then, so it's entirely possible that it means "MCS ckt open" in a carb setup.

If the car runs better with it unplugged, that probably means some of the carb's internal passages are plugged, or it's severely misadjusted. Given that it looks like somebody's been working on it REAL recently in terms of run time, and then it has sat around for an extended period of calendar time afterwards, could be any of the above.

23 is Intake Air Temp sensor low temp. Since all of the temp sensors are yerbasic generic RTD, i.e. very high resistance when cold (low temp) and very low resistance hot, if it's unplugged, the ECM will recognize it as low temp. If your car has one it'll be in the air cleaner. I'm not recalling there being one but then again mine is a 83 L69, 85 might be different. Computers came A LONG WAY in just a few short years back then; the 386 chip was introduced in 85, for example.

 

Anybody got any suggestions on what I should do ?

 

Well, leave the connector plugged in, that's for sure.

Unfortunately looks like they put the plug back in for the lean stop at least (can't see the one for the rich stop in the pic) as well as the cover, riveted in even, over the idle air bleed assy.

I'd suggest tearing the carb down and examining ALL passages carefully for foreign matter; then during reassy, setting those parts as follows: idle mixture screws 6 turns out; lean stop 2½ turns up from all the way down; rich stop 4 turns down from all the way up; and idle air bleed to wherever gives about 20 - 30° of dwell idling in gear on a dwell meter set to 6-cyl fully warmed up, and about 30 - 40° idling out of gear. If it's a T-5 (should be if memory serves) just set it to 30°. That should put it to within a range you can easily tune from.

 

cant plug the connector in , it wont run .. i just took it out for a ride with it unplugged and man does this car run good .. i just want the darn check engine light off .. thanks for your input

 

The Duke of Davenport is correct - Lots of codes were specific to the installation:

"23 M/C solenoid fault (Carbureted)"

Read Post #8 again. That will be the ultimate solution. Remember to address the main metering well Welch plugs and look over the throttle shaft bushings/bores when servicing the carb. Done properly, it may provide problem free service for another 20 years if used with good fuel filters.

If you want to TEMPORARILY get the SES light to turn off you can connect a 50Ω 5W wirewound resistor to the connector to fool the ECM into thinking the solenoid is connected, but the best results for mileage, performance, and reliability will be to clean and repair the Rochester.

 

you think it runs good now, try it after it's been fixed.

with the MCS disconnected it is running overly rich at idle and part throttle. not only will fuel economy suffer but it's going to run hot, and increase cylinder wall wear.

a 'rebuild' kit some carb cleaner and a few hours

 

So before going through the carburetor theres no chance its just that the mixture control solenoid went bad ?

 

of course it's possible the MCS is bad, although it is a fairly robust piece.

since the MCS and it's associated hat, springs and needles are inside the carburetor the question doesn't have any relevance.

 

Yup, a very VERY rare thing to go bad. Never seen it happen. Not saying it "can't" or "doesn't" or "won't"; only, in terms of "likely", it's REAL LOW on the list.

Plus, you ALREADY know it's working: if it was bad, nothing would happen when you plug it in. But something DOES happen, so, .... you can do the math from here.

There's kinda just no way around it. You're going to have to repair the carb properly if you want the car to work right.

 

Bought the carburetor kit and was getting ready to tear it down and found a vacuum off .. put it back on and plugged the Mc solenoid back in and it purrs like a kitten and no check engine light .. runs like a champ !! Thanks for all your input guys

 

Gotta love those easy fixes. However, save the kit. More than likely you will need it someday. We'll be waiting.