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Crank no start, then loud bang!

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Danny Wilde
Posts: 81
Joined: Wed Apr 18, 2012 8:44 pm
Location: Italy

Crank no start, then loud bang!

Post by Danny Wilde » Wed Jan 12, 2022 9:06 pm

Hi to all :D , as the title suggests I have an intermittent crank-no start issue, but it only happens when both these 2 conditions are in place, otherwise it always starts with no problem.

1) car hasn’t been used for around 2 weeks

…and

2) after no use for 2 weeks, car starts ok, brief 10 minutes ride then I park the car and of course stop the engine for a while (from 30 to 60 mins), then try to start again and the issue manifests itself.

Both conditions need to be present to get the issue, in fact, if I don’t use the car for 2 weeks but then make a longer journey say, like 1 hour and a half, then try to restart after 1 hour, all is ok.
Also If I frequently use the car and park it for an hour it also restarts ok.
The issue arised three times in total in the last 3 months, had to let it sit until the day after to get it to start again with no issues.

Symptoms:
Multiple attempts to crank give no start, with starter motor running smoothly but kinda momentarily "choking" every few seconds (one spin is slowed down every few spins), today after some attempts I got a loud bang with a little smoke from the engine :shock: , did not make more attempts after the bang of course...

Already replaced both main and fuel pump relays with new ones but no joy.
Also fitted new distributor cap, rotor, ignition wirings, spark plugs and ignition coil 5 years ago but never replaced the alternator. Could the alternator be the culprit? Would like to buy a new one but can’t figure which of these two could be the correct one: 12311718983 or 12311713450 ?

Any ideas? :-?

Thanks for your kind help guys :D
D
9/1986 euro 635CSi manual Diamantschwarz

marc79euro645
Posts: 33
Joined: Tue Feb 11, 2020 12:31 am
Location: pensacola

Re: Crank no start, then loud bang!

Post by marc79euro645 » Thu Jan 13, 2022 11:06 pm

I would suspect crank position sender-cps. If you get a noid light from an auto parts store to plug into an injector, that makes a quick easy way to see if your getting a pulse. Plug it into an injector lead when it won't start, it should flicker when cranking. if not your cps is probably the problem. If it does flicker, then your getting a pulse. I would then check fuel pressure. If you have pulse and pressure, I would check ecu next for corrosion, or cracked board. good luck!

User avatar
Danny Wilde
Posts: 81
Joined: Wed Apr 18, 2012 8:44 pm
Location: Italy

Re: Crank no start, then loud bang!

Post by Danny Wilde » Sun Jan 16, 2022 3:39 pm

thanks for your kind input mark89euro645 :D , as a matter of fact I replaced with oem new ones both the position and the speed sensors around 5 years ago along with the fuel pressure regulator, while the fuel pumps are about 10 years old (when I got the car), but will get them all checked, the ECU is probably still the original one.

So you would rule out the alternator? Would it be a good idea to get a new one all the same since it’s probably 35 years old, in order to avoid getting stranded one day in the future? Or do new alternators have a history of being worse than the original ones?
Thanks again :D
D
9/1986 euro 635CSi manual Diamantschwarz

marc79euro645
Posts: 33
Joined: Tue Feb 11, 2020 12:31 am
Location: pensacola

Re: Crank no start, then loud bang!

Post by marc79euro645 » Mon Jan 17, 2022 11:16 pm

I would rule out alternator, if battery is charging when running (14vdc plus). Low cranking voltage can create slow cranking, which means slow to no pulse.

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