Dwell angle and rpm measurements

[Ruben911]

Can someone tell me how to measure the dwell angle on a 1976 911s Bosch distributor and how to measure the RPM using a dwell angle/RPM meter. Where do I connect the positive lead of the meter for these measurements. Also, does anyone know what the allen wrench size is for the rear toe and camber adjustment eccentric bolts?. Thanks

Ruben
1976 911s 2.7L

[tmctguer]

don't know if a '73 is the same as a '76, but here's how i do mine:

1). connect dwell meter ground cable to suitable ground. connect clip to non-ground terminal of the ignition coil. this is how i get my dwell measurement.

2). i use a separate measuring instrument for RPM (a gunisen gas tester with digital RPM display). i connect the positive cable of the unit to the one of the 3 fused connections in the rear engine compartment. i connect the ground cable to a suitable ground. i connect the remaining lead to the dwell meter clip connected to the non-ground terminal of the ignition coil.

3). usually, when i've got this rigged up, i have my timing light connected. spark plug clamp attached to #1 spark plug wire, positive cable connected to another of the 3 fused connections. ground cable connected to a suitable ground.

this gives me timing, tach and dwell at the same time.

actually, i am SUPPOSED to be able to use my dwell meter to read RPM. but for the life of me, i could never get it to work. the gunisen gas tester let me get the RPM reading i needed.

[Ruben911]

Thanks, I will try the setup this morning and try to confirm that the dwell angle is ok. I am going crazy trying to diagnoze a severe engine hesitation when the car is under load. I changed plugs, wires, rotor, cap during a recent tuneup and valve adjustment, and the performance has degraded instead of improving. Thanks

[T Bird]

Ruben
This works for me re: dwell. While my car is a 72T, I believe that the ignition system is the same. The positive lead from the meter gets its signal from the wire that is connected to the spade connector on the side of the distributor. This wire on my car is, I believe, black/purple. The way I tap into the signal from the points that passes through that wire is as follows. I made a short jumper wire, about 6" long, with male/female spade connectors. I disconnect the wire at the spade connector on the distributor and plug in the 6" jumper wire there, then connect the black/purple wire to the other end of the jumper. I then clamp the positive lead of the meter to the exposed spade connector between the black/purple wire and the jumper. I connect the negative lead from the meter to ground and presto, dwell can be read from the meter. The jumper just gives me a place to connect the positive lead.

I have followed this method for many years because, I seem to recall reading somewhere long ago that the dwell meter should not be connected to the coil on the Bosch CD system, as some meters can knock out the CD system if so connected. Whether this is true or not, I cannot say.

Good luck.

[Early_S_Man]

John is correct about the dist. location to pickup the dwell/tach signal at the points input trigger signal to the CDI-unit. A nice 6 Volt peak-to-peak signal is present there which will work with most dwell/tachs that don't use an inductive pickup coil.

Using the coil terminal 'A' would result in feeding 460 Volt pulses to your dwell/tach input circuits ... NOT a good idea! This applies to all Bosch CDI-systems produced from '69 thru '83 normally aspirated cars, and '76 thru '89 Turbos! For magnetic triggered CDI-units, the 'TD' signal to the tach on the dash can be used though dwell is not adjustable, and the wiring harness to the CDI-unit will need to be intercepted.