No tach bounce/ignition switch

[GostRidr]

Hi All,

Running down the list of issues for a no spark no start. I have no volts to 86 slot under the DME relay AND I have no tach bounce. Does the tach bounce come alive only after the 12V or will that be a separate issue once I replace the switch?

Thanks!

[mytrplseven]

Typically, a no-bounce of the tach is traceable to the ref/speed sensors or their connectors. They are magnetic induced, low voltage outputs.

[Lapponia]

Most likely, the ignition switch. It provides 12V to 86 when turned to On and Start and 12V to pin 5 at tachometer (that is why tach jumps a little). Also, check grounding at 85 and crown shaped ground far up above the DME. This ground is probably the most neglected in fault findings and is often very corroded.

[944 Ecology]

Originally Posted by mytrplseven

Typically, a no-bounce of the tach is traceable to the ref/speed sensors or their connectors. They are magnetic induced, low voltage outputs.

Actually, no... it is an indication that there is no ignition signal getting to the coil (it's a parallel wire to the coil wire). The causes for that can include either of the sensors, but can also include the DME/ECU, the DME relay, or the wiring harnesses involved.

[911tracker85]

unless it turns out your tach does not work....

[dgcantrell]

Make this jumper wire and put it in the DME socket. If the car runs, you have a bad DME relay or bad ignition switch. This bypasses the ignition switch and puts power directly on the DME and Fuel Pump (as would the relay if it were working properly) and if it runs, you know everything is ok so no need to be throwing more parts at it.



When you plug it in, push the terminal 30 contact in last. Terminal 30 is the terminal that is hot all the time from the battery. You will hear the fuel pump come on and possibly the fuel injectors will click. Do not leave it plugged in once you are finished testing. It WILL run your battery down.

[GostRidr]

Thanks All,

DG, this is the Clarks jumper for 87 87b and 30 right? I've used this before. No go just now. So I understand, I would still turn the key correct (this is close but not completely hot wiring the car right?)? Also, this should then light up my spark tester when placed at one of the wires right? Failing this test means the ignition is NOT the issue then right, or rather, MAY not be the issue. Damn, it seems I am getting farther away!

In the meantime, I already ordered a new ignition switch that should be here tomorrow.

Thank you!

[dgcantrell]

Yes, you still have to use the key to crank the engine and it will turn off with the key. If the car does not start and run with this jumper, you have several possibilities that could be the issue. Do you hear the fuel pump running with this jumper installed.? You should. You should also hear the airflow meter and the injectors "click" once as the jumper is installed. If you are not getting spark with this jumper, you probably have a bad or mis-adjusted reference sensor. Could be a number of other things like the coil, distributor cap, rotor, etc. Put your spark tester on the coil wire to see if the coil if putting out spark. If so, your issue is downstream (plug wires, distributor cap, rotor, or the those damned resistor ends that Porsche uses on the spark plugs. I eliminated mine with Magnecor wires. Not had an issue with plug wires in the almost 15 years (or more) that I've run them.

[Jfrahm]

Hey I prefer the resistor ends. Makes for very robust plug wires.

Also check the alarm/disabler.

[GostRidr]

Thanks for all the feedback. Still trudging through.

I understand through the 944S DME test plan that these may be my remaining issues:
-Ground/Plug connections (can't find the crown shaped one Lapponia mentioned above, haven't gotten to bell housing one yet)
-DME Power supply
-Speed/Ref Sensor
-Ignition and Final Stage
-Engine temp sensor (don't think that is a no spark issue)
-Idle speed control activation


Others have added these:
Alarm (old Clifford Tasor II was previously disabled but may be causing some trouble?)
All the appropriate wiring

Fuel pump does run.

If the tach does work (think the no spark is new issue and hoping tach is reliable) then the no spark issue is pre spark right? Clark's says the next thing to check is the ignition but DG taught me that the jumper bypasses this. I did find a test somewhere to run a DVM to the starter solenoid to confirm ignition switch good and voltage good to the starter. Does this line up with where I am next?

As for the alarm, it is a rats nest and I am saving it for last as the car ran for 6 years in the previously disabled state. The reference sensors on the S can only be accessed by removing the intake manifold or having elven hands and arms. When I did do this 9 years ago the sensor was replaced at that time so I am saving that for second to last. I do not have an oscilloscope and will be using the DVM to check for continuity.

My plan is to do what I can with the DVM and then start removing the intake manifold to get to the main ground and the sensors. This will be a slow project but I should be able to get more updates this weekend. Thanks for the assistance!

[GostRidr]

Hey JFrahm, did you mean you prefer the stock resistor ends or seconding the Magnecore?

[dgcantrell]

The Magnecor wires are pretty robust. Plus 4 less parts to break. Porsche wires cost almost twice as these and last half as long. I bought these in 1999.... Still going strong and no break down in the jacket whatsoever. The factory set looked like a damned Christmas tree at night when I replaced them.

[S ECU Repair]

GostRidr,

Just overlooking this thread and didn't want you to do extra work when checking your Reference Sensors

The most effective and easiest way to check your sensor is at the ECU / DME harness.

How to test a Porsche 944 RPM and TDC sensor

Hopefully this will save you time and you won't have to worry about not having 11 hands!

[GostRidr]

Fantastic! Thank you! Been dreading removal of the intake manifold to check the sensor. Fingers crossed that I can get to this tomorrow.

[Mr_John111]

Ghost rider,

Yours is a 16valve 'S' model?

If it is, whilst the principle is correct the Pin numbers in the link are different.

You need 47 and 48 for the reference sensor and 8 and 30 for the hall sensor

John