adujsting the m/c solenoid

[capriceowns]

My caprice runs very rich after i rebuilt the carb. I have a haynes manual for the rochester but i dont get what its talking about.

Is there an adjustment I can do on my carb to lean out my mixture?

(its a 87 5.0 4bbl rochester, idk what version im sure its a feedback one)

[silicon212]

Originally Posted by capriceowns

My caprice runs very rich after i rebuilt the carb. I have a haynes manual for the rochester but i dont get what its talking about.

Is there an adjustment I can do on my carb to lean out my mixture?

(its a 87 5.0 4bbl rochester, idk what version im sure its a feedback one)

You need a dwellmeter. Once you get this, I will explain how this adjustment is performed. First, do you know where on the carb the adjustment for the M/C solenoid is?

You have a Rochester E4ME.

[capriceowns]

I probably could buy a dwell off ebay if it isnt too much.

I know where the m/c is, theres a plunger on it, i think its adjusted there.

[silicon212]

Originally Posted by capriceowns

I probably could buy a dwell off ebay if it isnt too much.

I know where the m/c is, theres a plunger on it, i think its adjusted there.

There's a screw plug on the air horn over the adjustment screw. You will have to remove this screw plug to get at the adjustment screw, which is under this screw plug (in the black circle).



You will need a special tool I believe - I don't think it's a regular screw (it's been two years since I've done this, and I've only done it once).

Anyways ...

[capriceowns]

So is a dwell meter required for this?

I have the tool to adjust that screw, it like a square head.

[silicon212]

Originally Posted by capriceowns

So is a dwell meter required for this?

I have the tool to adjust that screw, it like a square head.

Yes, you need the dwell meter to set the dwell on the M/C solenoid. You can't do it by feel, or by ear. The dwell reading on the solenoid has to be between 25 and 35 degrees on the 6-cylinder scale. These are not very expensive and you should be able to get one at any auto parts store.

If you look on the computer wiring harness on the right side of the engine, between the valve cover and fender and near the A/C evap coil, you will find a blade connector in a green plastic quick-connect housing. This is where you attach the dwell meter. You can see this in the image below:



It's the green thing below the A/C accumulator.

[capriceowns]

Ah, I see then. My connector is by my thermostat housing, but I got what you were saying.

Guess I have to get one. Got plenty of time, car currently isnt running

[capriceowns]

I was wondering, what does a dwell meter measure? Could I use a multimeter instead of a dwell?

[silicon212]

Originally Posted by capriceowns

I was wondering, what does a dwell meter measure? Could I use a multimeter instead of a dwell?

No, the dwell meter measures the amount of "on time" of the M/C solenoid, also called the dwell. If you put a voltmeter on it, you'd see the needle moving back and forth - not telling you anything aside from that the computer is pulsing the M/C solenoid. The dwell meter (as used for ignition point adjustment) measures the amount of time, in crankshaft degrees, that it's energized. It works a little differently for the M/C solenoid, but the principle is the same - it has to be "on" for a certain amount of time. Too long and the carb runs lean, too short and the carb runs rich. This of course can screw up the entire timing of the ECM - setting EGO sensor-related trouble codes and causing the SES light to light up, making the car run like crap and thirsty for $~3/gal. fuel.

[Blue Bowtie]

Originally Posted by capriceowns

I was wondering, what does a dwell meter measure? Could I use a multimeter instead of a dwell?

If your multimeter has a duty cycle scale (Like one of my Flukes does) you can use it. The desired setting is 50% duty cycle. On a dwell meter set on a 6-cylinder scale, that would be 30º.

Silicon covered it fairly well. You'll need a tool like an OTC 7667 adjuster set or equivalent.

MC SOLENOID ADJUSTMENT

• Connect a dwell meter or oscilloscope probe to terminal ‘B' on the enrichment solenoid connector;
  
• Start the engine and allow it to reach normal operating temperature. Start the engine and reset the base idle if necessary. The dwell meter reading should vary while this is occurring, or the oscilloscope square wave frequency (pulse length) should vary;
  
• Set the parking brake, block the drive wheels, and place the transmission in DRIVE for an automatic car, NEUTRAL for a manual car;
  
• The dwell meter reading should fluctuate between 10º and 50º on the 6 cylinder scale, the oscilloscope should indicate a 15-85% duty cycle. Adjust the idle air bleed valve screw (12) in 1/8th turn increments to obtain a dwell reading between 25º-35º. The optimum setting is 30º (50% duty cycle), so get as close to this as possible. Adjust the screw only a little at a time and allow the system to react between adjustments;
  
• If the desired reading is not attainable through this method, the idle mixture screws will have to be adjusted. This will require removal of the carburetor and cutting the throttle body away around the steel plugs. Then reinstall and adjust the idle mixture screws evenly , then adjusting the idle air bleed screw as described above to obtain the correct readings.

A "dwell" meter is basically a duty cycle meter that is graduated on degrees of distributor rotation for an engine. In Kettering (breaker point) ignition system terms, the duty cycle is the amount of time that the circuit is on (points closed) versus the amount of time the circuit is off (points open). The meter face is graduated in degrees of distributor rotation. A point dwell angle of 30º on a V-8 engine is basically a 66% duty cycle, or ON time versus OFF time. One cylinder fires every 45º of distributor rotation (90º of crank rotation), so if the points are closed for 30º of that time, they are open for 15º of that interval. 30º ÷ 45º = 2/3, or 66%.

A six cylinder engine is similar, but one cylinder fires every 60̊ of distributor rotation (120º of crank rotation). Typical specs for ignition point dwell on a six cylinder are 33º, and on a four cylinder engine 40º is common.

In terms of the mixture control solenoid on your carburetor, it is basically the same thing. The dwell meter is used to determine the amount of time the MC solenoid is ON versus OFF, or duty cycle. Since most automotive technicians have (or had) a dwell meter, the specification is presented in terms of dwell degrees. In reality, the measurement is the duty cycle percentage of the solenoid, but the common dwell meter is not graduated in those terms. Remember that 30º on the "V-8" setting on your dwell meter really means 66% duty cycle, and 45º would equal a 100% duty cycle.

Typical instructions for setting the solenoid are to set the meter on the six cylinder scale and adjust the "dwell" to an optimum of 30º, or in reality a 50% duty cycle. This means the solenoid is ON an equal amount of time that it is OFF. This is the optimum setting for fullest range of control by the MC solenoid.

If you don’t have a dwell meter, but do have an oscilloscope or better quality DMM with a duty cycle scale, just set the MC solenoid for 50% or as closely as you can get it. The typical instructions indicate that any reading between 10º and 50º and varying is acceptable (15-85% duty cycle), but “acceptable” isn’t good enough for most of us, or we wouldn’t be here.

Once you have it running correctly in stock form, you can begin the power tweaking and tuning.

[silicon212]

Originally Posted by Blue Bowtie

A "dwell" meter is basically a duty cycle meter that is graduated on degrees of distributor rotation for an engine.

Uh, yeah, that's what I MEANT to say.