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TOPIC: Non starting, with difficulty

Non starting, with difficulty 05 Mar 2019 18:30 #20749

  • pheigho's Avatar
  • pheigho
Hi, I wonder if anyone can help.

I own an s4 with 80k miles on the clock which I have owned for the last 15 years or so. Just lately (in the last 2 or 3 months or so).

Starting from cold, starting is almost instantaneous, from hot, the same, once hot, if I leave the car for 2 or 3 hours, it starts after 7-10 seconds on the key, when it does start, (a) only 3 or 4 cylinders come online for two or three seconds (b) a large puff of dark smoke comes out of the back (c) there’s a very strong smell of petrol in the cabin that clears after a minute of so after which, it settles down well and runs smoothly and pulls cleanly.

I’ve changed all of the plugs, HT leads, both distributor caps and rotor arms yesterday......but the problem is still there.... can anyone make any suggestions please.

Thank you, Peter
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Non starting, with difficulty 05 Mar 2019 22:44 #20751


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  • Rich928's Avatar
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Hello Peter,

The Porsche 928 S4 has two independent 4-cylinder spark systems. It sounds like when the engine is warm one of the spark systems is going off line. It could be caused by a corroded connection, of failure of a coil/coil wire to distributor, final stage amp, or even the EZK spark controller.

I sugest that you DO NOT drive the car. When the engine is only running on one spark system, the unburned fuel from the dead 4 cylinders flows into the hot catalytic converter and a fire can start! Many 928s have burned from this kind of problem.

If you're not a mechanic, please find one who can diagnose and fix this potentially dangerous problem.
Rich
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1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast
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Non starting, with difficulty 06 Mar 2019 14:43 #20754

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  • pheigho
Rich, thanks for your advice.

I’m not sure if it’s a single bank of cylinders causing the problem, it seems to be churning on the key for several seconds, then fires up badly for only 3 or 4 seconds before settling down to an even running.

It’s both the starting issue, along with the strong smell of fuel in the cabin as well as the blast of black smoke when the engine starts that’s concerning me.

Starting cold or hot, there is no smell or smoke and indeed it starts on the button, it’s seems to be only after being allowed to cool for two or three hours.

But thank you for your advice, I think this maybe beyond my ability, so I’ll book it in..
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Non starting, with difficulty 06 Mar 2019 15:30 #20755


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You mention "banks" of cylinders. The two spark systems control "both sides" of the V.

Ignition circuit 1 is cylinders 1, 4, 6, and 7
Ignition circuit 2 is cylinders 2, 3, 5 and 8.

The actual spark firing order is 1, 3, 7, 2, 6, 5, 4, 8

I have a detailed PDF document that illustrates the concept of the Porsche 928 spark and fuel system. If you'd like a copy, send me a note to info (@) electronikrepair.com

Other possibilities that can cause symptoms that you describe are leaking fuel injectors and leaking fuel pressure regulator or fuel dampeners. However, these items usually cause rich running all the time. Your LH fuel injection module could also be in the early stages of failure, though it sounds like your problem is quite repeatable, so that lowers the odds. If your mass airflow sensor has never been inspected, I suggest checking the calibration (no way to do it at home). I can provide that service as well as checking out your LH fuel injection unit.

I recommend starting with a fresh tune up and see if the problems go away. If your spark plug wires are original, they may need to be replaced. Do not install "cheap after market" types, the BERU OEM type are expensive but fit and have the proper zero ohm cables with resistors in the plug caps.
Rich
Membership Chairman
Charter Member
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed rescue
1979 928 5-liter track beast
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