DME Test plan help - 944S non start

[mhariush]

I have another thread, but with a bad subject line so I wanted to start a new one to address what I believe is the (or at least one of) the issues with my non start.

the other thread is here

History: I was driving the car when suddenly it died. I immediately tried to restart it, thinking I had choked it or something. Heard a click. No power at all.
Opened hood and found that the negative battery connector had popped off. I must not have tightened it properly.

I reconnect and try to start. Cranks but doesn't fire. No spark.

I have tried:
DME computer (2 spares)
DME relay (2 spares)
Ignition Control Unit/Final Stage (Bosch unit on the fender) (spare)
Ignition Switch (replaced)
Coil (spare)
Battery is fully charged
Bypassed alarm with clark's
Checked resistance on Speed Ref Sensor
Replaced Alternator (the old one was making noises anyway)

I have the 944S DME Test plan and I started looking at the test points.

Test point 3 b fail. I am not getting voltage. I tried this on my other (running) S and got voltage (but not through the 14 pin plug on either cars)



Ignoring the 14 pin plug test as I was getting no result on the running car or this car, I move on to the next point. But what do they mean here? "check power supply from ignition lock via the alarm unit to terminal 86 of the DME relay to the wiring diagram"?



Also, test point 4 fails. Fuel pump does not start when bridging 3 and 24 on the DME plug with ignition on.

[rhett]

Hi, just had a quick look at the wiring diagram, one thought...are you getting +12V at pin 30 of the DME relay?

[mhariush]

Hi Rhett, yes getting 13V at pin 30

[rhett]

OK, have you tried the two-way jumper lead? What you need to do is bridge pin 30 to both pin 87 (DME feed) and 87b (Fuel pump feed). This is outlined on Clarks. This should get you +12V to the DME on pin 37 if all the wiring to that point is good.

[rhett]

Interesting article on battery disconnection here:

Don't Disconnect the Battery with the Engine Running

[mhariush]

Interesting indeed, but I didn't do it on purpose

Also, I have replaced the alternator with a spare from another car. My alternator was making whining noises.

I'll go try the three way jumper now.

[rhett]

Originally Posted by mhariush

Interesting indeed, but I didn't do it on purpose

- I realise that my friend! Just an unfortunate incident...

Anyway, the jumper should get the battery voltage to where it needs to be. Once you have confirmed that you have +12V at the DME, you will have to try a known working one, along with a known working final stage. Another thing to check would be the continuity of the DME ground (pin24). Check this pin to the chassis. If open circuit then the DME will not run.

Its getting late here, so I will catch up on your progress tomorrow! Good luck with your troubleshooting

[mhariush]

hehe, I realized that you realized that I didn't do it on purpose

anywho, jumpered 30 to 87b and 87. No power on DME pin 37.

I also check pin 24 to the chassis. I'm a little green on electrics, so by continuity did you mean resistance/ohm? In that case I got the reading -1 (beyond the display) at 20M. Not sure why the - sign was there...

[djnolan]

First question: when you jumpered 30 to 87 and 87b is there 12v present on the jumper with ignition on, of course? If not you could have a supply problem to the main panel.

Did you check all of your fuses? check for any other unexpected electrical things not working when the ignition is in the accessory or on position, radio, lights, turn signals, blower, etc, etc - maybe power is not getting to the panel?

What is the battery voltage? Is it above 12v?

Some other observations:

-1 as displayed is open or infinite resistance. 0 ohms is continuity or a closed circuit. you may not have a ground to the dme if this reading is pin 24 to ground. hard to imagine how that would happen unless you smoked some major wires.

your earlier question about terminal 86 I interpret the book to say there should be 12v on 86 with the ignition in the lock position. probably needs to have this voltage from the alarm to start.

Does this car have a fusible link somewhere?

Did you say you had fuel on the plugs or not after cranking?

[mhariush]

I did not check if I had Voltage on the jumper when I jumped 30 to 87 b and 87, but I am getting 13V on 30 with ignition on

I checked all the fuses that are suggested in the different trouble shoot guides and steps. But I will double check ALL fuses just in case.

Battery is above 12V now I belive, I have been charging it. I was getting 11.5, but I got 13V on DME relay 30 earlier today.

So it displaying -1 is a problem... The car was driving fine until that negative terminal jumped off and I have not been playing with or around any grounds...

Regarding terminal 86, do you mean I should check for voltage at it with the ignition off? or ignition is the second position? Not sure I understand what you mean by "lock position"

Fusable link? As in if a wire has been spliced? Or melted? Not that I know of or have seen

I did not check the plugs after cranking, but I am not hearing the fuel pump and did not get it running when I jumped it without the DME relay or jumped the DME plug

[djnolan]

if there is voltage on 30 and you jumper pin 30 to 87 (dme) and 87b (fuel pump) there should be voltage on dme pin 37. if not there is a bad wire or connector... you can check continuity of the circuit with the ohm meter - remove the jumper and dme pin 37 to pin 87 should read 0 ohms...

[mhariush]

When I jump from 30 to 87 and or 87b I loose voltage. I also am not getting voltage on pin 37 with the three way jumper.

do you mean check resistance on pin 37 and terminal 87 (dme relay)? DME plug only has 55 pins.

[djnolan]

connect your volt meter as follows: positive lead to female pin 30 and the negative lead to ground. should read 12v with ignition on. add the jumper from 30 to 87 and the voltage should remain 12v.

[mhariush]

Got it, I thought you were talking about the DME plug

I get 12V from pin 30 with ignition on, but the moment I jumper it to 87 or 87b I loose the voltage.

[djnolan]

very strange indeed.

Try this: remove jumper.
Check the resistance from pin 87 to ground. should be infinite -1
Check the resistance of pin 87b to ground. same -1
Also check the resistance of pin 87 to dme pin 37. should have continuity - 0 ohms

if these don't check out suggest you remove fuse panel hold down screws, lift it up, and sniff around for some burnt wiring... you should be able to smell or see it if you fried something. also the small brown wire grounds on back of engine.

[rhett]

Originally Posted by djnolan

very strange indeed.

Try this: remove jumper.
Check the resistance from pin 87 to ground. should be infinite -1
Check the resistance of pin 87b to ground. same -1
Also check the resistance of pin 87 to dme pin 37. should have continuity - 0 ohms

if these don't check out suggest you remove fuse panel hold down screws, lift it up, and sniff around for some burnt wiring... you should be able to smell or see it if you fried something. also the small brown wire grounds on back of engine.

Hi DJ, just had a look at the wiring diagram and if you check from pin 87 to ground you will get a reading as you are measuring practically all the ballast resistors and injector coils, etc. as that pin feeds both the DME and the major engine electrics. Also pin 87b will have the fuel pump motor in circuit, so a reading will happen there too.

Otherwise I agree with all the steps you have taken above and definitely agree that this is very strange indeed!

The feed to pin 30 seems to come directly from the battery +ve term, it doesn't go through any fuses, etc. So, when you jumper it to 87 and 87b you are putting a load on what appears to be a 'floating' feed (one that has potential but cannot supply current due to high resistance or other failure). The injector coils and the motor coil are pretty low resistance loads that require a bit of drive current. Somehow this pin is incapable of supplying it, or.....a major ground has failed.

Again, I agree with your thoughts about burnt-out wiring, as when the -ve connection came off the battery, quite a lot of current had to flow elsewhere for a while and that could have taken out the wiring at a few places. It could be that the connection coming off did not immediately stop the motor, but a wiring failure did?

Checking the central electric and all the grounds for continuity seems like a good place to go at this moment.

[mhariush]

oh joy, fun days ahead then.

someone was very insistant that it might be the alarm, but i bypassed it as per clark's. but im going to tru again just for safety, with the alarm box removed and the connector jumpered.

would the alarm disable something that would kill voltage like that?

[rhett]

^^ I doubt it. Like I said..the supply to pin 30 seems to come directly from the battery +ve terminal, there is nothing inline at all.

Question: When you were connecting the jumper from 30 to 87 and 87b was the connector sparking at all, this would indicate a heavy load or short circuit? I am assuming not as the voltage is going totally and that would indicate a serious SC that would get wires hot, etc. and you are not getting that...

Suggestion, when you use the multimeter to measure continuity, set it down into the 2K range. 20M is way too high for anything on a vehicle.

[mhariush]

no sparks or anything like that when i jumpered, just the voltage going away. i'll set the meter down to 2K and i will do the tests again just to be completely sure

[djnolan]

since there are 4 positive feeds off of the batt, did we check some of the other circuits to see if they still operate? lights, blower, fans, rdio, a/c, etc? would it be helpful to isolate which branch of the electrical system won't carry a load if this is indeed what is happening?

Failure is not an option - Apollo 13