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Extra random injector firings

  • nzjagtech
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29 May 2020 01:10 #14036 by nzjagtech Other countries Jaguar XJ12 5.3, Jaguar XKS 5.3
Extra random injector firings was created by nzjagtech
I currently have a client's XJS that has an intermittent issue I'm seeking help with.
Lucas 3CU is 83477B
The car was parked up 8 years ago because of this problem. Now trying to recommission.
Owner's complaint = Drives OK for 1 hour or so, then cuts out and won't restart for some time.
I experienced this in the workshop and positively determined that the cutting out is flooding due to additional injector firings. Once stalled, the injectors would continue to randomly fire.
My first suspicion was trigger board or throttle sensor / trigger. I rigged the oscilloscope to test these. The acceleration sweep 10 firings still work OK and no extras from there. I tried to test the distributor trigger, but could not repeat the symptom.
I opened the distributor to inspect and found the board very cooked (I've seen many that look cooked but this by far the worst)
I've replaced the trigger board with the Hall effect unit currently recommended. Run it up and after warming, the symptom returned.
Tomorrow I shall be scoping the output channels directly from the ECU but I can't imagine anywhere else the extra, random pulses could come from.
What voltage pulse should I expect on pin 25?
Any other clues as to what could cause this?

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29 May 2020 07:19 #14037 by Obelix
Replied by Obelix on topic Extra random injector firings
...would be very nice if you could introduce yourself and sign with your Name !

Gruß
Christian

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29 May 2020 08:42 #14038 by Volker Europe Mercedes-Benz R107 450 SL, Mercedes-Benz W111 280 SE Cabrio
Replied by Volker on topic Extra random injector firings
Hi unknown,

can you please remove throttle switch connector and try without that. If that does not help, you must use a scope to monitor trigger board pulses and ECU pulses to amplifier and finally also amplifier to injectors. Pin 25 has 12V signals.

Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles über den Mercedes-Benz 107 SL/C in Sternzeit-107.de

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29 May 2020 09:07 #14039 by nordfisch Europe Opel Diplomat 2.8 E
Replied by nordfisch on topic Extra random injector firings
Hi,
I had suspected the trigger board as you did.

Can you try another ECU?

Regards
Norbert

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04 Jun 2020 00:25 #14094 by nzjagtech Other countries Jaguar XJ12 5.3, Jaguar XKS 5.3
Replied by nzjagtech on topic Extra random injector firings
Sorry. I just copied & pasted from an earlier email.
I am Ian Munford.
Jaguar specialist tech in Auckland NZ

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04 Jun 2020 00:31 #14095 by nzjagtech Other countries Jaguar XJ12 5.3, Jaguar XKS 5.3
Replied by nzjagtech on topic Extra random injector firings
I have another ECU that had been labelled "Faulty"
Most recent tests with both ECU's worked fine and symptom not present to test.
I'm now suspecting main relay contacts or power/ground connection but as symptom is elusive, I can't prove anything.

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04 Jun 2020 08:38 #14098 by nordfisch Europe Opel Diplomat 2.8 E
Replied by nordfisch on topic Extra random injector firings

nzjagtech wrote: ...
I ... positively determined that the cutting out is flooding due to additional injector firings. Once stalled, the injectors would continue to randomly fire.
...


Hi Ian,
we didn't know this problem up to this time but just recently had a 'client' with a Mercedes M110 that showed the same behavior. Here it is: Link extra firing

Seems to be a thermal problem.

Volker couldn't and cannot analyze the problem up to this time, because he faulty ECU is in Denmark.

I think, the only chance to get your ECU tested and repaired is to send it to Bosch Classic Service.

Regards
Norbert

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04 Jun 2020 09:18 #14099 by Volker Europe Mercedes-Benz R107 450 SL, Mercedes-Benz W111 280 SE Cabrio
Replied by Volker on topic Extra random injector firings
Hi,

so far I have not seen a single ECU with extra firings. I would be careful to be suspicious about an ECU in that direction.

But ground or power problems could well create that.

Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles über den Mercedes-Benz 107 SL/C in Sternzeit-107.de

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