I'm having alot of trouble getting my 1969 250ce to run without the transistorized ignition switch (TIS).

This TIS started to overheat after 30minutes of driving, and car would just "shut off". New unit is very expensive, so I went about bypassing this TIS, using just the points distributor and coil (neg of coil to condenser, pos of coil to the pos which was used by the TIS).

Before starting the bypass, I had the car running well, but only for about 30 seconds, then it shut off abruptly.

Seems like I am getting too much fuel (long pulse time).

I have tested: Spark at distributor, spark at plugs, Fuel trigger points (for on/off functionality), pressure regulator, grounds, all injectors, timing.

I haven't tested: throttle position sensor or maniford pressure sensor.

I am wondering if there is something else that would cause the pulse time to change.

Cheers.

The temperature sensors affect the pulse time. They can easily be checked.

The MPS is hard to check. But you can check that the resistances are correct and that it holds vacuum (Per tests in manuals)

You should make sure the TPS is set up properly, but you can unplug it altogether and the car should run OK.

The original MB coil has different windings from a standard coil . Maybe get a cheap standard coil and try that.

But, as discussed before, make sure the trigger points are not staying closed for more than say 110-120deg.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

just had a quick glance as i am running! from what you say you are running the positive through the points, but points switch the negative to ground. the only reason they ran the positive was because the switch box switched positive. if you remove the switch box then as I remember you change polarity for points. hopefully someone else will comment on this before you try in case I am misreading what you are saying
cheers
barri

__________________
61 Austin mini
67 Lotus 7
74 450sl
76 Cadillac 8.2l (501 ci)

some new cars

megasquirt conversion on:
djet 74 450sl http://www.mercdjetmegasquirt.britautorepair.com/
cis 76 450sl http://www.merccismegasquirt.britautorepair.com/

the best view is always from the point of no return

You will need a coil for standard points. And the connections will need to be reversed from the original. The new coil will be marked +/-, the + is connected to 12V coming from the ignition circuit. The - is connected to the points. This is the cheap and dirty fix. An aftermarket transistorized ignition will serve you much better.

It is sooo much simpler to get a used box off ebay.
Also, make sure the box is well grounded to the chassis. That physical connection is a current path, not just a heat sink.

THx -CTH

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- cth350@gmail.com
http://www.111lakeside.com/

He's already got a used box.
These things were troublesome 30 years ag and they haven't improved.

If you have set up the old point set to work like cars did originally, did you remember to install a ground wire inside the distributor to ground the point plate to the distributor body? This is needed because this ground was not on the OEM set up. You car may have run for a bit with a casual ground and then abruptly stopped when the ground was interrupted. Install a proper internal ground for the point plate and see if that helps.

No, I didn't think to ground the points plate to the distributor body. I will do this. Thank you.

Looks like the points plate was already grounded to the distributor body. I took a picture:

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Mike

1969 250ce

You should be able to see a clear tac signal from the green wire and ground showing dwell "to spec" (41 degrees I believe). That's independent of the box being good or bad.

There's a post around someplace that talks about how to open one of these boxes and replace the transistor. Not that I can find it.

Thx -CTH

__________________
- cth350@gmail.com
http://www.111lakeside.com/