944 won't start, no spark from coil
 

A little introduction - this is my first post to the 944 board. I own a 1983 944 (daily driver) and 1982 911SC (racer). I have owned the 944 for about 6 months and have been able to fix and maintain everything on it based on info from this board found by a search (car had been stored for about 8 years and I did a few things to ensure it was good to go). This is the first time I've needed to post a question, in other words you people are good!

I have a problem with my 944 - currently the car won't start and there is no spark coming from the coil to the distributor (checked by grounded spark plug method). Some other symptoms and results from troubleshooting:

1. The car had been cutting out randomly, but not very often.
2. Tested the relay per SoCal Driver test method - both switches work - click, click
3. Jumpering the relay leads per SoCal Driver test method turns on the fuel pump - I have not checked fuel pressure yet (I will on Sunday)
4. There is 12V at both wires to the coil with the ignition switch turned on.
5. There is 12 V to both injector pins with the ignition switch turned on.
6. All leads at coil and distributor are in good contact.

I have not checked the reference sensor, but I am certain the sensors are placed properly.

Questions:
Anyone diagnose my problem right off the bat?
How do I ensure the coil is good (that is my first guess based on no spark from the coil to the distributor)?
How do I ensure the DME is good?
If DME is bad, what are my options and sources?

Thanks in advance and sorry to bring this up again if I missed this in my search,

Mike M
Davis, CA

You could get a high capacity voltmeter and check the output from the coil while someone cranks the car. Generally, from my experience in electronics, if it sits that long, there's a good chance it will have gone south. I don't think 944 coils are that expensive, so you could run down to your local parts store, buy one and try to fire the car with it.

Does your 83 have a factory alarm? All of my 944's have been later models that have had it, but I am not sure if it was an option in 83.

But I had a "cut-out" problem, both intermitten and then finally completely dead. It turned out to be a bad alarm control brain that was cutting the ignition system.

Also, you should check your reference sensors to make sure they are supplying the DME with a signal to fire the coil. These can also be checked with a multimeter.

Mike, Sounds like you've eliminated quite a bit of the electrical. The basic test for the injection is to jump the DME relay completely out of the circuit and see if it starts. If not then it's off to "Fase Too" of the testing procedure. I'll conjecture that the DME relay is working OK as you have power to the injectors and the fuel pump runs when you crank it.

Check the plugs to the reference and speed sensors. Could be loose or corroded. If not use an ohm meter between the center pin and one of the outer pins on each sensor. Should be around 1K ohms. Note the other side pin is an isolated ground shield. It will should show as an open circuit.

The rear most sensor, the one closest to the fire wall will show about 2 volts between the 1k'd pins during cranking. This is the speed sensor. The front of the two is the reference sensor and should show a 2 volt pulse. Might be hard to pick up on a digital volt meter. You can see the needle jump on an older analog meter.

There is a way to use a diode to see the pulses too. The Bosch/Porsche DME Test Plan has a part number of 171 919 081B with a 1/4 watt 220 ohm resistor on the negative side of the diode. Think any diode will work. Connected across the two active pins on the sensor you should see the diode flicker. Or you could get an injector pulse checker from Pep Boys or Kragen or ???? and check to see if the injectors are firing as the reference sensor is responsible for firing both the injectors and the coil.

So basically it's down to the reference sensor, fuel pressure or loose/corroded solder joints in the brain to get spark and/or the injectors to fire.

Just because the fuel pump runs does not mean you have fuel pressure. There is the filter and dampener in the way of the injectors and going out of the fuel rail the pressure regulator.

There are other poor running considerations but we will save those for;

Fase 3 !

Thanks for the replies - a couple of follow ups

The car has an alarm. It is situated next to the DME under the steering wheel. It is an UNGO with passive and motion, but both functions are turned off. How do I remove the alarm from the circuit?

How do you fix loose/corroded solder joints in the DME? Who refurbishes these things or where do you buy a new or good used one?

Thanks again,
Mike M
Davis, CA

Take the DME apart carefully and just start reflowing the joints. The DME is quite a sturdy design. Make sure to get it all back together the same way.

You haven't determined that the DME is the problem yet.

As you report voltage to the injectors and the coil the alarm does not seem to be the problem -- unless it's cutting off the fuel pump.

But....

Most after market alarms will ground out the trigger side of the coil. This is the same side that goes to the DME. I would take that wire off and with the key on spark that side to ground. NOTE: This is the opposite side that the power comes in!

If you get a spark then the alarm is grounding that side or DME is not triggering the coil properly.

Before you do all that stuff - check the resistance across two of the three pins of the speed and reference sensors. About 900 - 1040 ohms. Nothing at all means it's bad. It's the easiest test to do without getting bent out of shape or getting greasy and I wish I'd done that on my own car which recently displayed ALL your symptoms and checks.

Thanks for the guidance - I will be busy on these checks tomorrow. I'll report back on fuel pressure, alarm circuit and sensors.

Mike M
Davis, CA

Bingo - I hit a dead reference sensor
 

Many of you advised to check the reference sensor for resistance and sure enough no resistance. The speed sensor checked out good at 1010 ohms. For good measure I checked the fuel pressure and it hit the spec at 40psi.

I will replace the sensor tomorrow and hope she fires up. But, you now have me worried about the alarm circuitry. I can not figure it out nor trace it. I will post another topic on this one.

Thanks for all the help,
Mike M
Davis, CA

sounds like you're getting 1st class advice.....just food for thought....I had a similar problem which turned out to be a dead fuel pump...it was turning ( making noise )....but no fuel was being pumped!

PS - my car also sat ( 3 yrs or so) before I bought it!

Varoom! The 944 runs again. It was a dead reference sensor. I plan to take the old one apart - I understand they are magnetized by a coil of very thin wire and the coating or sheild can break, shorting the coil - thus no resistance. Anyone know for certain?

Thanks to all for the great guidance and expert advice on my no spark problem. I hope to able to return the favor some day (and I'm sure this won't be the last time you bail me out)

Mike M
83 944
Davis, CA

You should use it to make a simple adjusting tool for when you need to replace / adjust the speed sensor.

Here's how:

http://forums.pelicanparts.com/showthread.php?threadid=98754

There's a metal insert with a tightly coiled copper wire in the stainless tube and a permanent magnet in the plastic body - they make excellent bolts pickup tools if you glue them into the end of a piece of plastic washer hose You'll be glad of it if you ever have the misfortune to drop a bolt in one of the little holes (huge holes when Mister cockup pays a visit ) next to the sensorts.

Cool tool - will do.

Thanks

FYI, only reason to adjust the ref. mark sensor bracket is if it has been removed or moved.

Whilst on the subject of reference sensors ... I've not actually seen a new and unused sensor fresh out of the packet as I've only bought them from breakers yards. Is the bottom of the stainless tube originally completely flat? All the sensors I've seen have a feint impression of the metal round bar within - I've assumed that slight play in the tube allows the metal insert to hammer a slight dome. Is that right?

I have ruined 3 such sensors in my travels, and, not coincedentaly, I have 3 such pick up tools!SmileWavy

Just had similar prob. on my '87 944S. Turned out to be the ignition module ($108 part)

I have two new sensors right out of the box and they have flat ends. I still have no spark and there is a clicking noise (sounds like signal light flasher) coming from the alarm control unit.

Porsche dealer wants me to tow car into them and they said they will get it going for me. But, I have done all of the rebuild by myself so far and pride will not let me give up, yet.

I've seen them both ways, some flat and some rounded on the bottom. do they all come flat new?

btw...what's your year/model

is it a factory or aftermarket alarm

and best of all, why don't you 'liven-up' this forum by starting a new topic (and wake up Todwic!)

'86 944 non-turbo (sunroof, leather).

Alarm control unit has porsche part number on it, so I presume it's factory. It's attached to bracket holding DME to bracket under passenger side footrest (floor area). There is also a "Viper" brand control unit hanging down from beneath dash on drivers side?