I’m having trouble getting a stable dwell and I’m not sure if it’s an issue with my multimeter, a sensor, or the carb.

The car cranks and runs with a strong idle but I’m getting a smell of fuel. Dwell will read very inconsistently. For instance, it might jump from 0 to 4, or 5, then 28 and finally a reading in the 50s…

I recently installed a new heated o2 sensor, tps and changed the baseplate to throttle body gasket so I’m not sure where to begin with diagnostics. Car was running great before I replaced the tps (was reading 5v at idle).

Here’s my settings: mixture screws are about 4.5 out from lightly seated. Lean stop is 4 out from lightly seated and rich stop is set so I get 1/8 travel from mark to mark I made on a screwdriver inserted/depressed into the IAB slot. TPS is set to .5v at idle. IAB is about 3.5 out from seated. I can hear the MCS clicking/see it moving when the car is running. There are no trouble codes.

This isn’t the stock engine - 350 with a healthy cam and headers. However, the car was reading my dwell fine before I made these changes and was just suffering from nozzle drip.

 

I might be on to something - the o2 sensor is reading .8v-.9v at idle. From my understanding that should be a rich exhaust condition, however, the computer seems to want to make the mixture richer. I'm also smelling fuel while it's running.

 

Second update: carb is not responding to any changes. It makes me think it’s either stuck in closed loop or for some reason trying to go full rich. The mcs is clicking. Possibly unrelated but the upper radiator hose is not pressurized when warmed up.

 

Ordered an Alltest 3226 to get a better picture. However, I pulled my spark plugs and they're all flaky/white. Appears to be running super lean despite the 02 reading. Any ideas?

 

until the O2 sensor reads a signal that crosses the rich/lean threshold the system will continue to try to adjust from its 'last known good' setting.

might be time to plug all of the vac lines and work your idle mixture screws and IAB until you get varying dwell

start around 2 1/2 turns out on the mixture screws and 2 turns out on the IAB. adjust the IAB 1/2 turn out while watching the dwell, waiting about 30 seconds between each adjustment. go to about 8 turns out then start again at another 1/2 turn out on the mixture screws. Repeat.

in the end you hope to be near 4 turns out on each..

this assumes everything is working correctly.

reconnect the vac lines after you get somewhere and see if one of them changes anything.

 

Thanks, NAF. Not sure if this just isn't a popular thread but I was starting to feel like I was talking to myself... Anyways, I got my "new" Brainmaster scanner in and with the KOEO the dwell is fixed at 30 degrees. Out of curiosity I tried to check the dwell with my multimeter and got a varying reading between 12-24. Something must be up with multimeter, the dwell connector, or possibly the way I'm making the connections. I do have an extra cooling fan relay grounded to the battery so I'm wondering if that's affecting the reading.

This weekend I'm going to toss in another set of spark plugs, reset the timing, idle, tps and then adjust dwell with the scanner.