how to check dwell with CDI?
 

All,

I'm putting a new-to-me 2.2 E engine together, with MFI. I've got it running, but it still needs to get dialed in.

Just about the first thing in the "check measure adjust" sequence is dwell. So I hooked up my trusty old dwell meter . . . and I get no reading.

Is there something special to checking dwell on a CDI equipped engine ? do I need an updated meter ? my experience is limited to points type ignition.

Thanks.

You don't adjust dwell on a CDI system. There is no dwell. Skip that and go to timing.

Michel:

Try setting the point gap to .001 over spec. and then go to timing. Make sure engine is at normal operating temp. CDI does not care about dwell, but it is effected by gap.

Ok, thanks. So why does the "check measure and adjust" manual say that dwell needs to be 38 deg. +- 3 ? And I've read people saying that dwell needs to be "spot on".

Maybe I've got the names wrong. I've got the regular OEM ignition that came with the 2.2 E engine. Is that CDI ?

Michel

Dwell is important if you have the OEM distributor with points and the OEM CD ignition.

How are you connecting your dwell meter? Do not connect it to the coil as you would normally. Connecting it to the coil can knock out or damage your CD ignition. On my car (1972 T) there is a black/purple wire that connects to a spade connector on the side of the distributor, just below the distributor cap. This wire connects to the points inside the distributor. If your ignition is comparable to mine (highly probable), you will take your dwell reading from this wire. The way I do it is that I disconnect the black/purple wire from the spade connector on the side of the distributor and plug in a short jumper wire with exposed connectors. I plug the black/purple wire into the jumper wire and then connect my meter (Fluke 88) to the exposed metal connector on the jumper. Then, I ground the other lead to the engine and away from the fan. Next, I start the engine and take the reading.

I don't know what your specs are for a 71 2.2, but for the Bosch distributor on my car, dwell is 38 degrees +/- 3 degrees. I believe that the spec is slightly different for the Marelli distributor. Check your spec book, workshop manual, or your owner's manual for the correct spec for a 2.2. After you set dwell at your desired spec, next adjust timing.

Use distributor cam grease on the distributor cam and put a dab on the fiber block of the points. I have experienced excessive fiber block wear on the Bosch OEM points. In fact, the fiber blocks generally wear in as little as 700 miles. I notice the wear because as the fiber block wears, the points close up more, increasing dwell angle, and retarding timing. When timing retards, idle speed drops. So, it's a good idea to check timing after 500-1000 miles.

Good luck.

i use a real long, thin screwdriver, attach the dwell meter clip to the shank and reach in and touch the terminal on the distributor. quick and easy. jim was obviously thinking pointless distributor, like on an SC.

Indeed I was. This just goes to show you, you can't trust everything Superman says.

While we're on the subject of dwell....

How do you adjust dwell? I am thinking there has to be an easier way than I do it.

I:
1. Set the point gap
2. Hook up dwell meter
3. Start car
4. Check dwell
5. Stop car
6. Adjust point gap
7. Start car
8. Check dwell
9. Stop car
10. Adjust point gap
11. Start car
12. and so on until the dwell is dead on.

Please tell me there's an easier way!

Thanks!
BK

Thanks again. I must say that after my previous posting I did a search on this board and found posts by John and John that reflect their comments today. I'll try it tonite.

Sorry for the bandwidth, as we used to say a few years ago.

Michel

BK911
Sounds 'bout right to me. What a PIA. Years ago, I remember my dad adjusting the dwell on one of his GM cars by inserting a hex key in the distributor while the car was running and turning one way or the other. I believe that the adjustment with the hex key moved the plate on which the points were secured and thus caused the points to open/close. This way, he was able to set dwell right on the money in a matter of seconds with the car running and the dwell meter connected. That seemed to make a lot of sense to me. I wonder why Bosch never picked up on the idea?

PS-Nice to talk to a fellow Marylander!

Okay,

So I tried to check dwell by using the points wire or tab on the side of the distributor. Hooked the ground first, used a screwdriver as suggested above.

As soon as I touched the wire, the engine quit. No more ignition.

Does this point to a specific clear problem, with the meter or the car's wiring ? I suspect I'm going to have to dig into the wiring or the dist. itself to figure out what's happening.

All help/ideas appreciated.

Michel Richard

The simple fact is ... BK's procedure/process is required, unless you get the gap within the 0.012" to 0.016" 'window called for in the spec book! If you shoot for 0.014" to 0.016" ... your dwell <b>WILL BE CORRECT, as dwell and point gap are just different ways to express the same thing, i. e., how long the points are open/closed!</b>

As far as hooking up a meter like an Actron/SunPro CP7676 ... you hook the Negative (-) lead to engine ground, and the Positive lead to the Black-Violet/Black wire connection at the distributor output terminal. As most modern meters with the dwell function that need a direct electrical connection are expecting a trigger signal from a 12 Volt coil, and not a 6 Volt signal, the CDI-system trigger signal of approximately 5-6 Volts may present a problem for some meters!

If the engine dies when you connect the meter ... there IS a problem or deficiency in the meter, because they are SUPPOSED TO BE A HIGH-IMPEDANCE OF 1-10 MegOhms ... which doesn't/wouldn't affect the ignition system!

If you used the screw driver technique, you have to be VERY careful not to hit anything else with the shank. If you ground the shank the engine will cut out. How do I know? Not important!