CIS dwell meter question

[rgmrgm]

I have read the many posts on the subject of using a dwell meter to test the efficiency of CIS but i cannot get the right numbers. hot engine O2 voltage was fluctuating .4 to .7 volts, dwell was fluctuating between 48 and 51 degrees on an 8cyl scale. i assumed it was too rich so i turned the mixture screw counter clockwise in 1/8 turn increments until it reached 37 to 41 degrees fluctuating. one more 1/8th turn ccw and the dwell read 40 degrees with no fluctuations. i returned the mixture screw to the previous position which gave me 37-41 degrees fluctuating. i just checked it with a cold start and the dwell reads 40 degrees no fluctuating. why would the dwell stop fluctuating on a hot engine as i enriched the mixture? does it reach a point that it just assumes a 50% duty cycle and in my case is that 40 degrees on an old analog dwell meter 8 cyl scale. or am just witnessing more cis voodo

[psalt]

My advice would be to reread those posts, you seem confused. First, the quoted meter readings are on a 4 cylinder scale. Next try to understand when and how the system goes from open to closed loop. Cold engine, open loop, the duty cycle is fixed . Once the engine is hot enough to trigger the temperature switch, it should go into closed loop and the duty cycle will fluctuate. If you determine that the mixture needs adjustment after the car has been driven and reaches operating temperture, make one small adjustment, then drive the car to see where it settles.

[rgmrgm]

let me ask my question differently. I am trying to get my 82 sc smog tested. hydro carbons are way up 660 ppm CO a little high.. when i lean out the mixture the hydrocarbons go further up. i have retarded the timing and checked that the vacuum retard is working. put in a new O2 sensor. hot engine-the O2 sensor is putting out .4 to .7 volts fluctuating- dwell meter reading about 40 degrees on the 8 cyl scale (no 4 cyl scale on my meter) not fluctuating. if i lean it out i can get the dwell down to 37 to 41 fluctuating but the hydrocarbons go way up, 750 ppm if i enrich the mixture i can get the hydrocarbons down to 120 ppm but the dwell goes to 40 degrees on the 8 cyl scale and does not fluctuate.

[Joe Bob]

Is the cat functional?

[rgmrgm]

it has a cat but i dont know if it is working properly. i am not understanding how the HC can go down by making the mixture richer. the car runs fine plenty of power, smooth idle. if i lean it out i have a HC problem

[Joe Bob]

HC goes up, CO goes down and vice versa. A functioning cat is needed to convert CO....2CO + O2 => 2CO2. 2CO2 is Carbon Dioxide.....

The O2 sensor helps to control unburned hydrocarbons (HC).......

So, good O2 sensor, good cat, adjusted mixture with an analyzer and allen wrench.

The typical 3 stage cat controls NOx, HC and CO. It sounds like the cat may be the culprit. Not all parts burn out at once. How many miles are on it? You don't mention the NOx level.....

[psalt]

My advice would be to stop making mixture adjustments until you understand the system. In closed loop, you are viewing the correction factor, so the statement,

"if i lean it out i can get the dwell down to 37 to 41 fluctuating"

makes no sense.

When you lean out the mixture, the system responds by increasing, not decreasing, the duty cycle. A low duty cycle closed loop means the system is trying to lean out a too rich mixture. This setting gives better WOT performance when the O2 sensor is ignored.

I think you can convert the 8 cylinder scale to 4 by doubling the reading. HC is usually too much ignition timing or a lean misfire. If it is still high after you set the mixture to 50% fluctuating on the 4 cylinder scale and the timing to 5 BTDC, both vacuum line disconnected, I would be looking for leaks at the injector sleeves and boots.

Paul

[rgmrgm]

perhaps i should take it one step at a time. Cold engine, dwell meter attached to CIS test port green and white wire. turn the key,starts first turn,dwell meter reads 40 degrees on the 8 cyl scale. if i double that i am at 80 and if i convert that to duty cycle i get 88% duty cycle. that number is wrong How do i correct it

[trond]

if you lean it out too much you can get misfire and unburnt fuel. Also if ignition is not 100% misfire can give high HC

My car too smelled of HC even as it was running so lean it was surging at cruise, popped occasionally and exhaust tip was light grey/white. When we installed the EFI system and got the fuelling right, my friend commented on how the exhaust no longer reeked of fuel and he was right.

Later when checking with a strobe the ignition was flickering around the mark. Combined with lean mixture setting this too would contribute to misfire and high HC.

All must be in tune. And catalytic converter must work

[psalt]

Cold engine, dwell meter attached to CIS test port green and white wire. turn the key,starts first turn,dwell meter reads 40 degrees on the 8 cyl scale. if i double that i am at 80 and if i convert that to duty cycle i get 88% duty cycle. that number is wrong How do i correct it



The cold, open loop, warm up duty cycle should be above 50%, this is making the mixture rich for warm up and all you care about is drivability. Emissions, and 02 feedback loop, are irrelevent at this stage. It is not adjustable, but you should not care if it runs well, unless you want to replace the ECU. Check it again with a know good meter. Test the main temperature switch at the left side chain case and confirm that it triggers the ECU into closed loop when the engine warms up. When it goes into closed loop, the dwell meter needle should drop and fluctuate in the middle of the 4 cylinder scale. If it reads too high in closed loop, the K basic mixture is too lean, and it is bleeding off lower chamber pressure to richen up the mixture. If the reading is too low, the basic mixture is set too rich and it is raising lower chamber pressure to lean out the mixture. If you are trying to pass an emissions test, set it so it fluctuates around 50%. If HC is still too high after setting the timing to 5 BTDC and reconnecting the retard, you may have other issues. How old are the plug wires, plug, cap, and rotor and when did you change the oil last ?

[rgmrgm]

i had been making some progress but did not trust my fuel pressure gauge so i borrowed a known good one and rechecked the fuel pressure, system pressure was 58psi which is a low, i removed the system pressure regulator from the fuel distributor to check the number of shims and the condition of the O ring. It has three shims and the O ring was in good shape, as i loosened it to remove the residual fuel pressure dropped to zero. when i replaced it and turned on the fuel pump, no pressure. pump is running but no pressure. i removed the regulator again to make sure i didn't screw up the O ring, small trickle of fuel came out O ring was fine and wet. re installed it still no pressure cracked open one fuel injector line slight trickle of fuel but still no pressure reading on the gauge, what have i done now?

[Joe Bob]

Sounds like you killed Kenny.....new pump time.

[rgmrgm]

i can hear the pump running. dont they usually quit running when they go out

[rgmrgm]

left it overnight. today i activated the fuel pump, sounded normal, produced only 5psi. i guess my next step is to make sure the tank is providing fuel and then remove the pump and try another one.