Dwell does not go down

Hi all,

I have a problem with my car. I hooked up a dwell meter and noticed my dwell was at 55. Book says 41. Regapped it to 0.012 dwell as still 55. Went out got a new set of point and regapped it 52. Played around with it and went from 0.006 to 0.026 and it was always between 51-55

What would cause the dwell to stay that high?

I'm taking my reading from the positive side of the coil while the engine is running.

Thanks for any help.

Reply to
No body
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You're connected to the wrong side of the coil.

Reply to
aarcuda69062

You should be taking the reading from the negative side of the coil (that's assuming the coil polarity is correct). The wire on the negative side of the coil should be going to the points.

Larry

Reply to
Larry Webb

Yes you're both right Positive. That's what I hooked it up to. Sorry.

Negative did not give me anything.

Reply to
No body

Ok. I re read your posts. & I went out to the car. It's hooked I can get a reading from the + side and nothing from the - side.

Could it be the coil is on backwards?

Reply to
No body

We could get a lot farther if you tell us what you're working on...

make model engine

Reply to
aarcuda69062

Oh, Sure,

It's a:

72 Benz Model 250 (gas) Chassis W114 Motor M130 2.8L dual zenith carb
Reply to
No body

Then you've definitely got a problem if you can get a reading by hooking your dwell meter across coil + and ground, but no reading by hooking the meter across coil - and ground. The former will read on a voltmeter between 6 and 11 volts, depending on your ignition system's primary-side specifics. The latter (and only the latter) will give you dwell readings.

Coil - should be connected via a wire to the breaker points.

Reply to
Daniel J. Stern

primary-side

72 benz? Could it be a positive ground system?
Reply to
Steve W.

No, Mercedes cars were negative-ground beginning *decades* before that '72 was built.

Reply to
Daniel J. Stern

Bad dwell meter. Try a SUN.

Reply to
wws

I'd first verify the connection with an ohm meter or test light. Connect either the same way you connected the dwell meter, and manually operate the points to see if the meter reading changes (ignition switch off) or the light blinks (ignition on but engine off). Your connection is wrong if you see no changes. Otherwise, what kind of dwell meter do you have? Any digital type or an analog meter that either contains its own battery or connects to the positive terminal of the car battery should be accurate. But some cheap analog meters connect only to the chassis ground and the coil negative (may be considered the positive for the points) and don't actually read dwell but simply averages the voltage across the points. It may be possible to test the dwell meter by connecting it to a 6-9V source of AC (not DC), such as a filament transformer or plug-in power adapter. The meter should read 45 degs. for 8 cyls., 90 degs. for 4 cyls.

Reply to
do_not_spam_me

Does he really need something that good? Actron makes decent automotive test equipment, including Sears Craftsman, that costs much less.

I'm not knocking Sun, and I have an old Sun tach/dwell with a very well dampened analog meter movement that can move an unusually wide 120 degrees. The movement alone is probably worth much more than the $50 I paid for the whole thing over 20 years ago.

Reply to
do_not_spam_me

Ok,

Found the diagrams. Reversed the coil it was on backwards, Traced the condenser wire and put the Craftsman dwell meter to that point & I was able to get a proper dwell out of it.

There are pre-resistors that are prior to the coil. Could these interfere with the coil?

Thanks for your help everybody.

Reply to
No body

You should verify your coil is a resistor needed type. Some run best on

12 volts, lots run best on 9 volts. Mixing them leads to short coil life and short points life. I for instance have an aftermarket Accel coil on my Jeep and it will run on both no trouble.

The resistors can interfere is worn out. Normally they blow open, but sometimes can fuse short. You use a multimeter to see what voltage is present at the coil with the key in run position. You have power so likely they are ok.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

No body wrote:

Reply to
Mike Romain

Probably not. A dwell meter is fairly simple instrument. He fixed it. The coil has three connections: +, -, and high tension lead. I should have recalled that, but it's been long time since I built a rod. I'm into OBD II, and air con these days, Trans are next. Wish me luck.

wws

Reply to
wws

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