Strange starting problem - need some advice please
 

My 83 944 would not turn over at all & the battery checked out okay. So as soon as I disconnected the negative cable for a few minutes, it started right up. It has done this a couple of times & has also died once while driving around town. Fortunately it started back up then when I turned the key to the start position. Last night it ran fine & started right up with no problems. Could this be a bad DME computer? Please advice.

Does the starter crank when you attempt to start it and it won't start?

No, this is not the DME. More likely to be one of these things.

Poor connection on battery cables (you have to check both ends) or a bad battery cable.
Switch key
Poor connection on starter
Poor connection on one of several grounds. Search for a diagram of where they all are.

If you know how to work with a volt meter, measure the ohms between the negative battery terminal (with all cables connected) and the engine. Should read very close to infinite.

Check the voltage on the battery, then check the voltage on the big terminal of the starter solenoid.

Hook your meter to the small wire on the starter solenoid...check for 12V + during starting.

One of those tests will probably tell you what's wrong. It definitely will if the car is in that condition...if it's not, then the voltage or ohm will still be there just not measure what it should. In other words, you may find 14V at the battery and 6V at the big post of the starter..in that particular case the positive battery cable would not be making good contact or is bad.

I would try the ignition relay..before anything.... replace it with known good one.. they are not that expensive, and would be a good start.. everything entioned above by razorback is very critical issues as well.. good luck.. jc..

If the car sits for more than a week the starter won't crank over like a dead drained battery. When I disconnect the battery & charge it up it turns over fine & starts. However ; after I drove it to interstate batterries to check the condition on the battery , they said it checked out okay & it just needed a day more of charging. When I got home I hooked up the charger to the battery for about 30 minutes & tried to start it & got nothing. I disconnected the neg. cable & re-hooked it up & it turned over fine but did not start. This was the first time it ever did that. So I disconnected the cable again but for a longer time & then hooked it up & it started fist click. It died while I was driving the car to work & I was able to start it up right away & then it died again when I got to my works parking lot & i did the disconnect the neg. cable twice before it started right up again. It ran fine last evening & this morning.

Thanks for all your advice razorback, I will use the voltmeter & check all those cables you mentioned . You got me pointed in the right direction.

Okay , I will also check the ignition relay like you say & replace it with a known good one. Is that relay located by the fuse box? What about when the engine just died when driving down the street? What would cause that symptom? Thanks Jc924turbo.

yes. it is located in the fuse box.. but they change the locations for different year.. I think our site host has a good diagram.. but try the clark's garage site as well for your exact year lay out.. they have many other infos as well.. your cutting out issue may be other problem.. but.. try the relay first.. I have a 81 model that I'm constatly working on.. so .. I had many problems.. that I had faced.. in my 931 cutting out problem was involved with fuel delivery system... but again..many different problems can give you the same affects.. what razor had mentioned can possibly be closer sulutions to this problem.. good luck.. jc..

Okay thanks again for all your help. I will try to track down all those problems.

Sounds like you might have a slow drain on the battery. Could very well be a bad ground. I would take the battery and have it charged overnight. The charges the stores like Interstate or Autozone have are different then the usual home chargers.

Have them do a load test of it as well.

also make sure that your alternator is putting out a charge. Sounds like it is not since your car stops running while driving and then won't crank over afterwards. Maybe your alternator is bad and pulling juice from the fully charged battery as well even though the car is sitting for a period of time?

That's a good point on the alternator. I will also check it out when it is running.
The weird thing is the only way it will start is when I disconnect the negative cable for a few minutes & re-connect it. Like it is re setting the computer . So far the car seems to be okay but the problem may be intermittent?

If it were a bad battery, slow drain, or an alternator not charging problem, then disconnecting the battery cable and putting it back on would not fix the problem. Disconnecting a battery cable can't recharge the battery all of a sudden so having a dead battery is probably not the case. The problem is a bad connection through either a connect point, bad cable or bad electrical switch. Since moving the negative cable fixes the problem...most likely with the negative cable. DME has nothing to do with starter control so it can't be resetting the computer and fixing the problem. Starter works like this....power runs through the positive battery cable to the large post on the starter solenoid and is always hot. When switch key turns to start position, the small wire receives power from the switch key and engages the starter solenoid causing the starter to turn. Of course for the starter to turn after receiving power, there must be a connection from the negative post of the battery to the starter housing through the negative battery cable to complete the circuit. It's really that simple.

Old battery? Lead sludge accumulates at the bottom of battery cells and creates a current path and drain battery very shortly after rechargeing. I have eperience in two cases when trying to drive back from work. They started and ran beatifully in the morning, cranked really bad 8-10 hrs later and didnt start. Got them cable started from fiends car. New battery fixed all. This happend both in a Mazda and Volvo. BTW after recargeing those bad batteries acid density always read OK (green) on the density meter, funny enough!!!!!
Always check with an voltmeter on battery poles and running engine and read at least 14 Volts. Then you know alternator is OK . Next try is changeing the battery. Hope it helps.

Oh and.... DME has a voltage span meaning say 10 to 18 Volts. Like electronics DME works fine within this limits and does not work at all below 10 Volts. With a bad battery cranking is takeing all the juice in the starting attempt, voltage drops sharply and you will have no start.
With an old distibutor with breakers you would have a chance down to say 9 Volt and have start but not with a DME unit.

Also check on the DME/Fuel pump relay - my 1986 was doing the same thing before I changed out the relay.

Ed.

SmileWavy

The battery is 3 years old & I should probably replace it. I suspected it a couple of times but it always checked out good after charging it. Thanks again for all the helpful hints to everyone that posted.

larsz! Try to borrow a good battery from a friend and hook it up to your car. If the car starts up OK then measure voltage across battery poles. And again you should have minimum of 14 Volt on the meter with running motor. After that you can shut down the motor, break negative pole and measure between open pole and cable connector with an ampmeter and see if you have a current drain. If it is within few milliamps it is OK, is it amps there is an issue somewhere wich you have to trace down.
Good luck.
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Lapponia

Great advice Lapponia! Thanks for your input. I was just going to buy a new battery from Costco & also do the ohm meter checks. I already tried another battery from my other car & it started fine but it was a bit too tall. Have a good day.

The three positive cables attached to the battery terminal were loose. I have not tested the terminal yet for drain or driven the car yet but will tomorrow.