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post #1 of 15 (permalink) Old 04-04-2019, 04:12 PM Thread Starter
CEW
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What am I missing?

Hi all. Problem with the "Eight" a 1986 SU carburettor car. Please bear with me while I try to explain.
Took the car out on Monday for it's inaugural run this year after spending the winter months tinkering and tidying. It has been starting in the garage readily but not having been run anywhere since October last year it seemed a bit lumpy, so off we went and ,after filling up with premium UK fuel, it started and run very well with a 8 mile blast at legal A road speeds seemed to clear what I guess were slightly sooty plugs (newly installed). Made about half a dozen stops and started absolutely fine and after about a 35 mile round trip it was still a little bit lumpy at low speeds. I thought maybe carbs needed balancing so planned a trip to a RR independant specialist to get sme advice. This morning fired the car up and it ran for about 30-40 seconds before stopping and refusing to start at all. Now, the fuel pump was not making a sound so that was the first port of call, using a probe to feed the live side of the pump it ran fine,pump not engine,but not from it's own wire which is dead. Checked fuses all OK, I did check the carb filters after Mondays trip and, whilst needing to be renewed in the short term,they were not blocked, so I loosened a pipe to see if I had fuel flowing,I did but only when I fired the pump with the probe. Had a look to see if any wires had been disturbed and found nothing amiss. Next I thought I will check for a spark and lo and behold nothing, 12v at the LT ignition side of the coil switching via the key but nothing from the HT side,again all fuses OK and the car has a brand new battery and cranks over really well.
My question (s) are:-
Is it possible the spark amplifier has given up? It looks original and is a Lucas part. The car has 82000 miles under it's belt.
Does the amplifier incorporate a fuel cut off ? It seems odd that both ignition and fuel would give up simultaneously after running so well on Monday.
Are there any diagnostics that can be performed on the amplifier to ascertain it's status?

Any pointers or advice would be very welcome, thanks in advance.

Clive
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post #2 of 15 (permalink) Old 04-04-2019, 08:08 PM
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You may have 2 separate issues, (1) I would suspect fuel pump relay has failed and (2) check the spring loaded centre carbon contact (some folk call it a brush) inside the distributor cap, the part that makes contact with the rotor arm, they have been known to fall out. I can't help with testing the ignition module but hopefully someone more knowledgeable with electrics will chip in soon but I'm led to believe that it can damage the module if you disconnect a HT lead and then crank the engine to check for a spark while it is disconnected. I'm not familiar with Silver Spirits but on my Silver Shadow the fuel pump electrical supply is routed through the large oil pressure switch at the lower front of the engine so that (as a safety measure to protect the engine) the fuel supply will stop if oil pressure readings drop. It's possible or at least worth checking that the wire to the oil pressure switch hasn't become inadvertently detached as this might disable your fuel pump. Good luck.
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post #3 of 15 (permalink) Old 04-05-2019, 04:02 AM
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Ho I think on yours there is a resistor for the fuel pump near the nsr wheel, check the connections on it likely corroded.
Mike

chassis 27650
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post #4 of 15 (permalink) Old 04-05-2019, 04:31 AM Thread Starter
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Originally Posted by shadow 11 View Post
You may have 2 separate issues, (1) I would suspect fuel pump relay has failed and (2) check the spring loaded centre carbon contact (some folk call it a brush) inside the distributor cap, the part that makes contact with the rotor arm, they have been known to fall out. I can't help with testing the ignition module but hopefully someone more knowledgeable with electrics will chip in soon but I'm led to believe that it can damage the module if you disconnect a HT lead and then crank the engine to check for a spark while it is disconnected. I'm not familiar with Silver Spirits but on my Silver Shadow the fuel pump electrical supply is routed through the large oil pressure switch at the lower front of the engine so that (as a safety measure to protect the engine) the fuel supply will stop if oil pressure readings drop. It's possible or at least worth checking that the wire to the oil pressure switch hasn't become inadvertently detached as this might disable your fuel pump. Good luck.
Thank you Shadow 11, I think you may have given me hope as although I had not intentionally touched the HT leads the B4 lead was out of it's socket on the cap, which ,incidentally ,has not been removed prior to this weeks problem.

Mike, something else to check, thanks for that.
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post #5 of 15 (permalink) Old 04-05-2019, 03:10 PM
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To test the ignition module simply attach a test lamp to the negative side of the coil. Watch the lamp as you crank the engine over, if it flashes quickly that indicates the module is working to switch the coil on and off. If no flashing check for power to coil. If flashing check for spark at coil high tension lead to ground, no spark coil is faulty. If coil lead sparks check a plug lead, if no spark remove distributor cap and hold coil high tension lead 1/8th of an inch away from the centre of the rotor and have someone crank the engine over. If coil leads sparks to centre of rotor then rotor is dead shorted, a common fault with cheap aftermarket rotors.

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post #6 of 15 (permalink) Old 04-05-2019, 03:22 PM
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Also to safely test for high tension sparking get one of these and keep it in your car tool kit: https://www.ebay.com/itm/SPARK-PLUG-...UAAOSwFBRZbbWB

Or: https://www.ebay.com/itm/Auto-Car-Te...IAAOSwQcZboMe3

Either of these will allow one to determine quickly whether an FTP is spark or fuel.
Attached Images
File Type: jpg Spark tester.jpg (1.1 KB, 47 views)

SRH8505 SRC18015 SRE22493 NAC-05370
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post #7 of 15 (permalink) Old 04-05-2019, 03:56 PM Thread Starter
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Thanks for that Jim, the testing of the module is a great help and will determine whether a new one is needed.
I still have the issue of the fuel pump not working from the car electrics, it runs fine when an outside source is connected, but I think I may have stumbled across the cause of both faults, it being the after market alarm that has been fitted by a PO takes some of it's power from the B3 fuse that is labelled "start,ignition,fuel pump" and I am thinking that the alarm system uses these feeds to immobilise the engine and a fault has occurred within the alarm system. I am going to disconnect and trace everything next as I don't really need the alarm for the use I make of the car.
I have a spark tester in the toolkit albeit an older version of your suggestions,but it does the trick.
Thanks for the advice I will keep you posted.

Clive
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post #8 of 15 (permalink) Old 04-05-2019, 07:53 PM
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You may have found the solution to your starting and fuel supply problem. Test that fuse with an ohm meter for continuity or replace it, they can look good to the naked eye even though they have blown. Remove the fuse and clean the contacts on the fuse board with electrical contact cleaner and dab a little electrical contact grease on the contacts to keep moisture at bay. If you have a battery cut off switch cut the power while working on any electrics or disconnect the battery earth lead just in case you accidentally cause a short. Very often electrical problems in older cars are caused by corroded connections or poor earths.
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post #9 of 15 (permalink) Old 04-08-2019, 09:59 PM
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Any luck solving the problem yet?
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post #10 of 15 (permalink) Old 04-09-2019, 05:21 PM Thread Starter
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Not as yet. I have live feed to the ignition system and using Jims test have eliminated a problem with the module or coil but I am awaiting a rotor arm from Martin Jay "The Distributor Doctor" as he makes very good quality ones to the original spec and having had one fitted to my TR6 for more then eight years trust them implicitly. The fuel pump issue could be that I am assuming it runs constantly, having gotten used to fuel injected cars ,can you confirm that it does or doesn't?. Why I suspected the alarm system was that when I introduced power to the 20amp fuel pump fuse the indicators flashed and the alarm armed itself, I am still investigating that side of things but looking at the installation it has been done very professionally so I have left it alone for the time being.

Clive.
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