Fixed dwell over 50 degrees

[Clone TIE Pilot]

The fuel/air dwell mixture is stuck at over 50 degrees not moving. I tried causing a vacuum leak by disconnecting the PCV valve which did drop the dwell by 20 degrees, indicating the O2 sensor is operating. This seems to be pointing to an over rich condition, I don't what would cause this as the motor was running fine before with correct dwell and this problem came out without warning.

A couple years ago my motor was running lean, turned out to be a vacuum leak which I fixed. Then I set the dwell to the 30-35 degree range, I remember when I took the air cleaner lid off the dwell would go rich. Now when I take the lid off there is no change in dwell.

 

[tetomas]

Re: Fixed dwell over 50%

High dwell indicates a rich mixture, and mcs is trying to lean it out. Look at float level, or a canister purge valve gone bad. Is it running good or does it seem too rich? You might be able to just make a small adjustment with the mixture screws on the base of the carb and get it back in line. What engine, what carb?

 

[Clone TIE Pilot]

Re: Fixed dwell over 50%

Chevy L69 305 and E4ME Qjet that was rebuilt by SMI a couple of years ago, dwell was fine then. I disconnected the vapor line from the carb and plugged it, no change in dwell. I just hope the floats or the needle valve didn't go bad from E10. The motor also diesels a little after shutdown, it never did that before.

 

[tetomas]

Re: Fixed dwell over 50%

Are you still running the mechanical fuel pump? High fuel pressure could be a culprit, but not likely with a mechanical pump, unless the pump has a return line and it is stopped up.

 

[techg8]

Re: Fixed dwell over 50%

youre on the right track.

heavy float would raise fuel level, making the mix go a bit rich

Check for nozzle drip at idle - both on primary and secondary sides

spray the bleeds/passages out with some carb cleaner, could be one is varnished up, making the carb pull more fuel.

 

[Clone TIE Pilot]

Re: Fixed dwell over 50%

Still using a mechanical fuel pump. The car has sat for awhile so maybe a bleed is gummed up.

 

[Clone TIE Pilot]

Also my voltage light is on very faintly. Can a failing alternator make the ECM not work right? Throwing the voltage for the signals off?

 

[Clone TIE Pilot]

Took the airhorn off today. The float seems to be floating ok. I tested the needle valve with a Mityvac and it held vacuum so it doesn't leak fuel. However the accel pump is shot, the seal is swelled up from E10, even the little seal in the airhorn for the pump shaft went bad.

 

[techg8]

Took the airhorn off today. The float seems to be floating ok. I tested the needle valve with a Mityvac and it held vacuum so it doesn't leak fuel. However the accel pump is shot, the seal is swelled up from E10, even the little seal in the airhorn for the pump shaft went bad.

Never seen a seal in the airhorn for the pump shaft. maybe a SMI modification?

 

[Clone TIE Pilot]

Took the airhorn off today. The float seems to be floating ok. I tested the needle valve with a Mityvac and it held vacuum so it doesn't leak fuel. However the accel pump is shot, the seal is swelled up from E10, even the little seal in the airhorn for the pump shaft went bad.

Never seen a seal in the airhorn for the pump shaft. maybe a SMI modification?

I have a couple of old non rebuilt Qjets for parts and they have the seals too, they are pretty hidden since they are held in by a washer that is staked in, seems like the TPS plunger has a staked in seal too. So I just took a seal from the airhorn of one of my old part donor Qjets to replace the swollen one. The bad seal swelled so much it popped the staked washer right out. Ordered a new E10 proof accel pump and airhorn gasket, just sucks to wait.

I tested the needle valve with a Mityvac like Cliff Ruggles says to do, and it held vacuum so it doesn't leak. The float seems to be floating ok, no signs of sinking. Guess I may have a bad sensor somewhere, the TPS checked out ok with a multimeter.