I was wondering if anyone has had this experience. I put a mild 350 (zz4 cam, edelbrock heads) in place of an L69. The cc qjet mc sol dwell at idle is 50 deg which is a full lean signal. Opening the throttle it goes to normal operation with varying dwell at about 30 deg. Its in a 84 Z28. Disconnecting the mc sol which causes full rich condition smooths out the idle. I get the feeling the computer just thinks the engine is rich.

Anyone experience this and know what the obvious solution is? thanks

Pete

 

Did the same swap, 84 L69 to a mild 350. Only change on the carb was to B hanger and CK rods on the secondaries. Runs great and never had a problem

 

during idle, what is the O2 sensor indicating?

 

Never checked, idles great and plugs are perfect.

 

Thanks for the replys. I did some more checking yesterday. It responded a little differently this time. Unpluging the mc sol made it worse. Maybe the first time it wasn't warmed up enough. I didn't think to check the O2 sensor output. I checked that the ECM was sending it the correct voltage. Its a new sensor and does seem to respond since unplugging the pcv hose (big vacuum leak) caused the dwell to decrease indicating a lean signal from the ECM to the carb.

From reading the service manual I may have the polarity reversed on the mc sol. I replaced it when I rebuilt the carb. I noticed yesterday it doesn't cycle all the time. The manual said reversed polarity could cause it not to function properly. It also set a code 23 once too which it the mc sol. I think I probably need to make sure the mc sol is operating correctly before I do anything else.

Thanks
Pete

 

I just went through a similar problem with my 350 swap. I think you need to make sure your TPS sensor reads 0.48V at idle.

In my case I found my float was too high and needed to set that too, but I had it rebuilt prior.

 

Actually, I finally figured it out recently. The engine really was running rich. The pressure was too high into the carb causing it to flood. It was very rich at idle but at higher speeds there was enough air flow to compensate. I put a new GM fuel pump on it and I suspect it was an LG4 pump which would generate the required 6 psi without the electric pump in the tank. Since L69's have the pump in the tank, the carb was seeing about 9 psi. Besides the rich behavior of the engine, there was also gas in the oil. So I knew it was running rich. My TPS sensor was properly adjusted BTW.

I put a fuel pressure regulator on it and that did the trick. Now it idles well and the mc sol dwell is normal at idle.

Pete

 

So the L69 carbed cars have in tank fuel pumps?

 

I believe that the LG4s had them in some years as well. The Electric In-Tank booster pump was not limited to just F-bodies either. I know the G-series used them in the tank, atleast in 1983 and 1984. IIRC, they were dealer upgrades to cure a vapor lock/fuel starvation issue.