Coil + Test Light, Glow or Blink?

tfranko29 · 07-02-2005, 08:05 AM

Hello Friends,

1983 944 drives great, but this morning it killed during idle. I checked the usual suspects already and I am down to a "no spark", yes I checked the timing belt, it okay. Should the testlight results on the + & - posts on the coil, during cranking, glow continuously? Or should one of the posts blink and the other one glow. Please help!

Thanks
Frank

tfranko29 · 07-02-2005, 09:18 AM

Hello Again Friends,

I attempted to open my hood and now the cable broke, anyone know how to open a hood that doesn't want to open the old fashioned way?

SoCal Driver · SoCal Driver's Garage

If the cable is broken at the hood you have to reach up from under the front with a long screw driver and lever the latch.

The cable may be broken in the car. Use vice grips and give it a pull.

tfranko29 · 07-02-2005, 06:16 PM

I got the hood open, thanks to SoCal Driver, Regarding the coil, I took it out of the 944 and put it in a '72 911T and it worked great. I put it back into the 944 and still no ignition, what's doing that. I also checked the fuel injector plugs and they aren't lighting up my test light. Does this mean bad reference sensor?

SoCal Driver · SoCal Driver's Garage

With the key on you should have 12 volts at the coil and 12 volts at one side of any injector plug. If you don't have voltage at the coil it's the ignition switch. If you have voltage at the coil and no voltage at the injuectors then it's the DME/fuel pump relay.

If you have voltage at the coil and at the injectors and no spark then first thing to check is the connections to the reference and speed sensors on the back side of the engine intake manifold. The reference sensor is what triggers both the injectors and the spark/coil. These could be reversed if you have had them off recently or just not making contact inside the connector. Also the plastic around the connectors will crack from age and cause the wires inside to seperate.

SoCal Driver · SoCal Driver's Garage

You can bypass the DME/fuel pump relay by running a jumper from the battery to the coil (black wire) and jumping from fuse 2 to fuse 3 on the 8 fuse block. Count from the door.

tfranko29 · 08-05-2005, 10:53 AM

SoCal,

A) Thanks for all the previous help! I have done all the tests you prescribed and some of your other 'no start' posts. I bought a new DME Relay and installed it, with the key on, I light up my test light at the coil, and on both sides on the connectors to the fuel injectors. Next step, pull a spark plug boot and stick a plug into it and lay it on intake manifold and crank, no spark. I fiddled with the reference plugs and reinserted them and jiggled the wires and no spark. I don't have a dig. multi meter, can I test for signal on the ref. sensors with my 12V test light?
B) This is an anomaly, but if I let the car sit for a period of time, 3 hrs. or perhaps 3 days, and try to start it, it might start and it might idle for approx. 5 sec. or 30 sec., but then it kills like a light switch. Then it won't start anymore.

SoCal Driver · SoCal Driver's Garage

The R&S sensors are a PITA sometimes. You can use a diode/resistor to check them. The speed sensor should be putting out about 2 volts when you crank the car. The reference pulses at about 2.5 volts. You need an oscilloscope to see this.

Should also check the adjustment. Clearence to the flywheel teeth is .8mm or about 1/32" at the speed sensor. Usually a very cold environment will play heck with the sensor adjustment.

tfranko29 · 08-06-2005, 04:02 AM

Thanks SoCal,
I don't think I can wrangle with an oscilloscope. My friendly neighborhood Porsche mech. is going to make some $ on this one.

SoCal Driver · SoCal Driver's Garage

Should be able to find the diode and resistor at a Radio Shack. Basically the same setup as the noid lights. It will show the 2 volt pulse as the engine is cranked. Here is what the DME Test Plan states:

Zero10 · 08-06-2005, 03:29 PM

I don't know where you got that idea from SoCal, but it's brilliant. In my head I figured it wouldn't generate the current required to light an LED, but it sounds like it will. I think you just gave me the diagram to another tool to always keep in the car. Given that it's a 220 ohm resistor, you wouldn't want to use it to check for +12V unless you had a very tolerant LED, but for speed/reference sensors, I bet it would work great.

If you get a super-bright LED you would be able to see it even better. Particularily a blue LED since our eyes are most sensitive to wavelenghts of light that we percieve as blue.

I have all the pieces to make one, I think I will and just keep it in the car...

tfranko29 · 08-07-2005, 09:35 AM

Thanks SoCal,

I will try the tool, it looks great. Tried again today 8/7/05 to start the car and it started on the first pull, ran for 1 full minute and then killed. Next, tested coil green wire with 12V test light, no blinking at coil when cranking. When I took out the S & R sensors to clean and I removed some rusty metal filings from the front sensor, right in the middle of the magnetic little barrel, reinstalled. No start. If you read this post, the car always seems to start when its stone-cold, runs for 30 secs. to 1 minute and then its done for the session.
Next step is the tool. Thanks.

Frank

tfranko29 · 08-07-2005, 04:12 PM

I went to Radio Shack this afternoon and purchased my rig, $3.16