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Misfiring 1990 964

Lots of good advice there Ras62, thanks. I'll work through that lot in case I have a couple of things going on. Car is not misfiring at the moment. Car is also starting far better now with jump leads across the engine,so suspect earth strap on gear box is broken and was causing sluggish starter motor. Far better now.
 
Battery is 13V stopped and 13.25V when idling. Not too low, but not over 13.5V as you suggested.
 
If you're still on the original twisted earth wire that connects to the battery and frame change it. It might look OK but a new one is cheap as chips plus clean the brass connectors where it attaches with other wires to the body earth point.

My car had a bad earth that I diagnosed to the battery connector. I'd leave the car and go back and the electrics would be completely dead including the clock. Then it would magically re-connect. A new lead fixed it :thumb:
 
Flahp1 said:
Battery is 13V stopped and 13.25V when idling. Not too low, but not over 13.5V as you suggested.

That's a bit low but the battery is fine by the sound of it. Worth checking the battery at say 1500rpm to see if it rises. Ideally it should be 13.5-14.5v. Any less isn't ideal.
It's certainly worth checking the engine/gearbox straps and also the main +ve connector at the starter motor. This is the main connection point to the battery and they do get neglected and corrode. This may explain the low tick over voltage. Before getting any spanners up there pls disconnect the battery +ve terminal or sparks will fly!
Hopefully the cutting out will now be solved with the new O2 sensor installed. I tried all sorts before I changed it on my car and was getting desperate. The problem is they dont have defined fail modes so can appear fine on the hammer tester.

One issue I should have mentioned is the clock. The joints internally do go dry and cause all manner of issues for instruments and even running. Do a google search for further explanations. Worth removing the clock and resoldering the main contacts inside.
 
Thanks again ras62. I was out in the car this morning, couple of hours with no problems whatsoever. Stopped a couple of times, engine turned over very quickly and fired up every time. Went out again later and when I went to start car up, absolutely nothing there, almost like there was no battery connected. Couldn't find anything obvious, fiddled around with the jump leads from the engine to the frame, swear I heard a click, it then fired up as good as ever. Very odd, any ideas? Relay? Starter motor was changed last year.
 
Sounds like the DME relay to me although I know you've swapped it. Go round each item in the central electrics and reseat them all. This could be two unrelated problems, it sounds like the misfire issue maybe solved.
 
Flahp1 said:
Thanks again ras62. I was out in the car this morning, couple of hours with no problems whatsoever. Stopped a couple of times, engine turned over very quickly and fired up every time. Went out again later and when I went to start car up, absolutely nothing there, almost like there was no battery connected. Couldn't find anything obvious, fiddled around with the jump leads from the engine to the frame, swear I heard a click, it then fired up as good as ever. Very odd, any ideas? Relay? Starter motor was changed last year.

That was exactly the fault I had and a new earth strap from battery to chassis fixed it. :thumb:
 

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