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Dwell Angle 1986 3.0L

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kountzelightdiesel

Contributing Member
I had a little problem start last year that I wanted to address before the season starts.
I have a 1986 3.0 that stumbles pretty bad when you accelerate from idle to wot. I tune it up every year before season but I don't really understand dwell angle and point gap. Being a mechanic from the newer generation and diesels at that, electronics is more my speed.

I replace all of the tune up parts set the point gap and check the timing but I have never checked the dwell. My dad remembers this from back in the day as something that was important but can't remember why.

Any thoughts and advice is appreciated
Thanks
 
Re: Dwell Angle

Jeff, fair question, and I'll bet you're not alone on this. I'm verbose, so bear with me.

A 4 cylinder engine ignition distributor makes only one full revolution per two crankshaft revolutions.
This means that the ignition distributor is offered 360* in which to saturate and collapse the coil field, in order for all 4 cylinders to receive spark ignition.
Each cylinder (of a 4 cylinder engine) is given a 90* angle to create one spark cycle.
(360* divided by 4 = 90*)
The time in which the contact points are closed (as to create coil saturation), is referred to as "dwell".
In the case of the 4 cylinder engine, the dwell angle is subtracted from the 90*.

Let's say that dwell angle is to be 42*.
This 42* is the coil saturation duration.
The remaining 48* allow the contacts cooling duration. Much more than required, btw.

The 6 or 8 cylinder engine distributor is also offered the same 360* in which to fire all cylinders. However, the number of cylinders dictates that the dwell angle will be much less than that of the 4 cylinder engine. (there is still only 360* of distributor angle, in which to do this)


Basically, setting point "gap" is an estimate ONLY of correct or proper dwell.
Dwell is a more meaningful means of setting contact points.
Not nearly as critical on the 4 cylinder, however.

There ya have it!

Edit:
Now, I have a question for YOU.
2000 Dodge Cummins, the older school 24 valve engine.
Just over 100k miles. Runs perfectly. Starts with barely a turn over. Never over-heated, never over-worked.
I tow a rather large twin engine, 28' SDN F/B boat.
Is it possible that my injection timing could be off, or could be mildly tweaked, as to create a tad bit more torque? I know that, whether gasoline or diesel, BMEP or LPCP must be at/near 14* ATDC.
Any tips that you could offer me?
 
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Re: Dwell Angle

kountzelightdiesel said:
I have never checked the dwell. My dad remembers this from back in the day as something that was important
Click to expand...

If you are familiar with modern diesel electronics, then you know how PWM inputs and outputs work

Dwell is EXACTLY the same.

Only difference, instead of a digital PWM oscillator doing the switching, the points are an actual physical switch, bumped open and closed by the cam in the distributor. For the points to function properly, they need to be open and closed the right amount of time.
You can actually use the PWM measurement on most multimeters as a dwell meter. A dwell meter reads in degrees of rotation, instead of on time vs. off time, but you can convert.

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.
 
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Re: Dwell Angle

RicardoMarine said:
Jeff, fair question, and I'll bet you're not alone on this. I'm verbose, so bear with me.

A 4 cylinder engine ignition distributor makes only one full revolution per two crankshaft revolutions.
This means that the ignition distributor is offered 360* in which to saturate and collapse the coil field, in order for all 4 cylinders to receive spark ignition.
Each cylinder (of a 4 cylinder engine) is given a 90* angle to create one spark cycle.
(360* divided by 4 = 90*)
The time in which the contact points are closed (as to create coil saturation), is referred to as "dwell".
In the case of the 4 cylinder engine, the dwell angle is subtracted from the 90*.

Let's say that dwell angle is to be 42*.
This 42* is the coil saturation duration.
The remaining 48* allow the contacts cooling duration. Much more than required, btw.

The 6 or 8 cylinder engine distributor is also offered the same 360* in which to fire all cylinders. However, the number of cylinders dictates that the dwell angle will be much less than that of the 4 cylinder engine. (there is still only 360* of distributor angle, in which to do this)


Basically, setting point "gap" is an estimate ONLY of correct or proper dwell.
Dwell is a more meaningful means of setting contact points.
Not nearly as critical on the 4 cylinder, however.

There ya have it!

Edit:
Now, I have a question for YOU.
2000 Dodge Cummins, the older school 24 valve engine.
Just over 100k miles. Runs perfectly. Starts with barely a turn over. Never over-heated, never over-worked.
I tow a rather large twin engine, 28' SDN F/B boat.
Is it possible that my injection timing could be off, or could be mildly tweaked, as to create a tad bit more torque? I know that, whether gasoline or diesel, BMEP or LPCP must be at/near 14* ATDC.
Any tips that you could offer me?
Click to expand...

Rick, You can fool the Map Sensor into believing you are at full boost and it will fuel accordingly.

I have a 2001 Dodge 3500, 6 speed with the Cummins 24 valve. Just turned 300,000 miles.
 
Re: Dwell Angle

Thanks alot on the info that was along the lines I was thinking but was unsure.

Another thought I had the octane rating of our fuel is alot lower than when these engines were built are you guys making timing changes to compensate? If I run less than premium in mine it "diesels" have to drop it in gear to kill it


Rick I drive the same truck. The injector pump on that engine is not slotted to fine tune adjust the timing but the do offer offset keyways for the pump gear they are only like 1 or 2 degree advance. The automatics were 235 hp and the manual trans was 245 hp and I think that was the only difference.

What I would do is look into a programmer of some type I personally like the superchip because i think you get a nice little boost without too much black smoke and they keep the engine within its capabillities. I opted for the baddest I could find at the time its the quadzilla and I think turned all the way up it could do some serious damage but turned on a medium setting its sporty feeling very little black smoke and it gets about 26 mpg.
 
Re: Dwell Angle

I'm getting a nice spray everytime i pump it. The best way to describe it is... When I move the lever to wot it will speed up just a little and stumble there then I will pull out of it until it catches up once it is above about 1000 rpms it will take the fuel.
 
Re: Dwell Angle 1986 3.0

Ok to update my problem this is where I am...
This engine has run this way since I have had it in the boat. Last season when I installed it the needle valve in the carb was stuck flooding it. So I cleaned the carb and put a kit in it. cranked up runs about the same just no flooding. So I ASSUME (and yes I know what it means.) that it was in the ignition system but at the time it was prime season and I could live with it.

Fast forward to today... Over the weekend I set the dwell and the timing. The timing was a little fast about 8 btdc but that was where it ran best. I slowed it back down to 4. So ign. should be right on the money.

It still doesn't want to take the fuel so I start adjusting the idle mixture and this is where I find something odd. With the screws turned all the way in and seated it runs the smoothest. On the 4 barrels I have had in the past they would die if you did this. Would that be an indication of an air leak? Oh and I watched down the throat of the carb while accelerating the pump give a good spray pattern from about 1\2 throttle on from closed to 1\2 it just kind of dribbles.
 
Re: Dwell Angle 1986 3.0

The two screws control the amount of air being introduced into the low speed metering circuits.
Closed would mean NO AIR.
In order to have air with this fuel, you'd think that air would be supplied elsewhere.
Better take a closer look.

.
 
Re: Dwell Angle 1986 3.0

Rick thats what I'm starting to think either under the base plate or throttle shaft. Or maybe an intake gasket? Regardless with no air it should die not run better!
 
Re: Dwell Angle 1986 3.0

Ok get a can of throttle body cleaner, it's different then carb cleaner, wally world or any auto store like Auto zone has it.

With water going to the drive, start the motor, actually whenever the motor is running, water must go to the drive. Spray the cleaner around the base and body of the carb. If the motor runs different, don't worry you will know when it happens you found the leak.

Say you found no leak then continue around the other areas mentioned above. You will know it when it happens.

Post back the result we will go from there.

Heres a site give it a read if you have time:

THE CARBURETOR SHOP / Troubleshooting

This typing with 2 fingers is a b-yatch.
 
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Re: Dwell Angle 1986 3.0

to go with what Chief says, do NOT use it copiously, just short bursts, throttle body cleaner HIGHLY FLAMMABLE, one little arc and whoooooooosh. seen it, done it, been there, got the t shirt, should have had the fire extinguisher
 
Chief I ask you this only because I think you have told me before. When you swapped you 2.5 to the 3.0 which carb did you use? I thought you told me they were the same but they have a different part number. I am currently trying to straighten out the one for the 3.0 L
 
put the other carb on see if that fixs the problem.

Part number we don't need no stikin part number.

Just kidding. The jetting is exactly the same.

Maybe it's dirty or water in the bowl.

Maybe it't the accel. pump.

Maybe it's aliens that came down from mars living in the carb.

Just kidding.

Really no difference i swear exact same carb on the 2.5 and the 3.0.
 
Thanks I ordered another kit and between the two I should be able to make something happen I also ordered an intake gasket because when I sprayed it down with throttle body cleaner i couldn't get the bottom very well but the pieces of the gasket I can see look very rotten. I did have a little air leak at the base plate so it adjusted better. I think im on the right track
 
keep us updated glad your on track i did not even pull the tarp of yet.

I had a freekin lawnmower carb today give me the fits.5 years now first time out of the garage takes me all day to get the pos running good.
 
You're telling me that when you trained as a Mechanic, they did NOT teach you about Points? Thats the problem with todays teachers.....
Some figure if its "old school "...who needs it? WRONG !!!
 
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