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Post by philhart on Nov 22, 2021 16:31:31 GMT
Hi all
Wonder if someone can point me in the right direction. 1971 3.5 V8 saloon, always been a very good starter. Last week it would not start and established there was no spark. Fiddled about for a while and swapped the coil over for a spare, bypassed ballast resistor and still no spark, started testing the voltage in different places and the spark started ok again.
As a precaution i fitted a brand new ballast resistor and coil - all was well until I was in traffic yesterday and when revs dropped it started 'missing' quite badly again.
Not sure of next step here. HT leads a year old, distributor cap, rotor arm and points all new.
Does anyone have any thoughts please?
Many thanks
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Post by p5andrew on Nov 22, 2021 16:57:48 GMT
I would suggest the following checklist; - Begin by checking tightness of connections at starter solenoid, both the spade connectors (one of these provides a feed to the coil which bypasses the ballast resistor when cranking the starter motor), and the nutted connectors.
- Check tightness of all connectors to coil and ballast resistor.
- Check lead between points and coil. This lead is susceptible to failure due to constant flexing during operation of the vacuum advance/retard unit. If in doubt, replace this lead as it can often be responsible for an intermittent fault such as this.
- Check the tightness of the earthing strap between engine and body. It would also be worth unbolting the strap and cleaning up the areas to which it fixes to ensure first class connections.
There are many more possibilities but this should give you a starting point.
Good luck! |
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Post by eightofthem (Andy) on Nov 22, 2021 18:29:26 GMT
Sounds like the condenser is breaking down, will give those symptoms, but then again so will lots of other things.
Step by step process of elimination is required
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Post by Phil Nottingham on Nov 22, 2021 21:54:04 GMT
It will be something simple in the ignition - new parts can be more unreliable than the old so try again but poor distributor earthing or dirty cracked cap can cause sporadic misfires as can X tracking of old HT leads
Also try hot wiring as ignition switches can cause REAL problems
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Post by djm16 on Nov 23, 2021 1:54:41 GMT
Its worth taking off the distributor cap and have someone turn the engine over. Assuming you still have points, you should see the contact breakers opening and closing 8 times with a small spark each time they open. Incorrect points gap or worn distributor shaft bearings / bushings can prevent this even thought the contact breaker gap looks correct when stationary.
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Post by philhart on Nov 23, 2021 22:15:12 GMT
Many thanks for your all of your replies - looks like a busy weekend
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Post by Ken Nelson on Apr 4, 2022 17:06:21 GMT
Took my car (1966 P5 3-litre) out for the 1st drive this year. It started and ran fine down the road, and then just suddenly quit and won't fire at all again. Checked and it showed fuel present in carb and reservoir, good fuel pump action for both pumps, points opening and closing correctly, produced a spark from #1 plug wire shorted to engine block when cranking, points not shorted out in distributor when open, condenser not shorted. I filed points and cleaned spark plugs and car started and again ran fine down the road for another 3 miles and then quit suddenly again. Gave up and towed it to garage for them to check. It seems like it must be an ignition problem with an intermittent short perhaps? (spray ether didn't help either). No carbon tracking in dizzy cap, but wonder about a bad rotor? It's an old original Lucas rotor and looks fine but I didn't have another one to try substituting. I suppose it might have helped to try hot wiring the coil, but my patience was wearing thin by then at the side of the road. Somehow the Rover remains one of life's mysterious challenges more often than I'd like. Hope the garage is good with mechanical point ignition systems and carburetors and positive ground. We'll see...
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Post by MK IA Norway Viking on Apr 4, 2022 20:12:48 GMT
Hello Ken - indeed a mystery ! Normally I would suspect fuel issues, and I will share an experience I've had. The hinges on the bonnet have a very long travel. They can squeeze the fuel flexi hose so that when the bonnet is open the carburetter received fuel. When it is closed it will not receive any fuel - the distance travelled could be on the contents of the reservoir.
Another culprit could be the conically shaped wire mesh that is inside the carburetter, where the fuel inlet is connected to the reservoir. If this is not clean it will restrict the flow of fuel into the reservoir. When the bonnet is up and the pump running the carburetter will gradually fill up its reservoir and permit you to drive for 3 miles or so, until fuel starvation results.
Remember a VERY important matter - the pumps will stop pumping when the reach a certain backpressure. This backpressure has nothing to do with the level of fuel in the carburetter. If you have a clogged filter giving sufficient resistance you will arrive at the set backpressure and the pumps stop pumping.
If the fuel issues can be deleted, then perhaps the fault lies in the coil. A coil will get hot as it is used. When it gets hot it can fail. So try another coil that you know will be working to test the engine, and see if this will solve your riddle...
Best wishes and Happy Rovering !
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Post by enigmas on Apr 4, 2022 22:13:07 GMT
It will be something simple in the ignition - new parts can be more unreliable than the old so try again but poor distributor earthing or dirty cracked cap can cause sporadic misfires as can X tracking of old HT leads
Also try hot wiring as ignition switches can cause REAL problems
Although Phil's quote relates to a previous query I'm in agreement. if it's a points ignition system it couldn't get more basic. Jump a lead from a "direct power source" straight to the coil positive terminal bypassing the ignition switch. If it's still a problem after that then the issue is directly related to one of the ignition components and a careful investigation of the various components should identify it. |
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Post by Ken Nelson on Apr 4, 2022 22:43:03 GMT
Thank you both for the thoughts about fuel and ignition. I should have tried to hot wire the coil, but 3 miles is indeed about the distance it would run on just the reservoir bowl of fuel alone. I hadn't thought of that and will have to check fuel line routing. I'll keep you updated when I get to the bottom of this mystery!
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Post by djm16 on Apr 5, 2022 0:13:04 GMT
"but 3 miles is indeed about the distance it would run on just the reservoir bowl of fuel alone"
I would have thought half a mile would be about it. Is there really a 1/10th gallon of fuel in the bowl?
More plausible is the ignition switch heating up and going open circuit. Or some other electrical joint in the path.
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Post by MK IA Norway Viking on Apr 5, 2022 7:56:42 GMT
"but 3 miles is indeed about the distance it would run on just the reservoir bowl of fuel alone" I would have thought half a mile would be about it. Is there really a 1/10th gallon of fuel in the bowl? More plausible is the ignition switch heating up and going open circuit. Or some other electrical joint in the path. Good morning. I experienced the fuel strain and I too could travel 3 miles or so before engine cut-off. It could also be that fuel is entering the carburetter fuel box slower than the engine consumption so examine the fuel issue. Other than that I share member's thoughts that the issues are heat induced. It is so that when a coil or ignition switch gets hot, and cut power, it takes a little time for them to cool sufficiently to work again. Therefore, clock the time it takes from igntion failure to start and see if there is a variance between each time it happens. |
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Post by ray on Apr 6, 2022 8:04:22 GMT
Ken,
Have you tried changing the condenser in the points? Cheers Ray
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Post by Ken Nelson on Apr 8, 2022 0:12:28 GMT
Thanks for the suggestion Ray, but right now the car is sitting at a repair shop waiting in line to be looked at. When I was stranded at the roadside I was limited in what I could do to work on it. If it were home in my garage I would replace the points and condenser and try a different coil, but unfortunately the day after the breakdown I was scheduled for hand surgery, so I really had to get it towed somewhere for repair. I am at the mercy of the garage mechanics understanding something besides automotive computer repairs now, but I see old classics outside the shop frequently so I am hoping for the best and will keep all updated. I'm still at a loss though since it did jump a spark from #1 plug wire to block, and had a full reserve bowl of fuel and still wouldn't fire. Quite puzzling to me-perhaps fresh eyes will see what I missed!
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Post by Phil Nottingham on Apr 8, 2022 5:16:14 GMT
The cheap Lucas 25D6 distributor has a nylon "cushbush" for the drive dog. The nylon degrades and allows the cam to turn a few degrees altering the ignition timing. I replaced the drive dog from an earlier DMBZ6 distributor which is a solid drive. Later 25D6 distributors reverted to solid drive.
It is easy to check this as the cam will turn further than the centrifugal advance
I did mine 20 years ago and its been fine since
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Post by djm16 on Apr 8, 2022 6:26:08 GMT
The rubberised cushbush is a PITA.
I tried to re-make mine with medium grade urethane 2-pack. So far so good.
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Post by Ken Nelson on Apr 12, 2022 0:17:35 GMT
A little further update on my P5 running problem. The garage didn't get to my car for 4-5 days after I had it towed there. When they looked at it they didn't see any obvious problem, and wouldn't you know it-it started right up! They kept it for another 3 days starting it from cold and from hot (30 minute idle and drive) and it ran fine for them each time. So I drove it home today and it's never run better. But it had cut out on me 2 separate times a week apart, and refused to restart before I brought it in. So now I'm a bit stuck, since I don't know if I can drive it further than 20 feet from my garage with confidence. My plan now is to replace plugs, points, condenser, and coil. Then I'm going to replace the original plastic fuel line with ethanol resistant rubber fuel hose and check the fuel pickup in the tank. I'll carry a jumper wire with me to hot wire the coil if it stalls, and pray to the automotive gods to let me find the source of the cause. Fingers crossed as they say...
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Post by enigmas on Apr 12, 2022 10:07:16 GMT
If it's running points ignition Ken, then my best guess is that it's either the coil or the condensor.
I'd also want to hot wire it bypassing the ignition switch and anything between it and a direct positive feed from the battery to the coil. Literally just keep driving it and circling your block until it malfunctions or it doesn't, after you swap out those 2 items.
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Post by Ken Nelson on Apr 12, 2022 13:08:47 GMT
Thanks Vince, I'll try it and hope for the best either way.
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Post by Ken Nelson on May 4, 2022 17:51:09 GMT
Well, hopefully this will be the final update on my problem. It was not the coil or the condenser, although those were still the most likely options. Turns out that the points were shorting out somehow. Fortunately it acted up again in my garage and this time the points were not "breaking" even thought they mechanically separated properly on the cam. My guess is that the plastic sleeve insulator that fits over the post for the condenser and coil to bolt to without grounding out had partially worn out. It was the original set of points that came with the car, but they weren't pitted and had worked fine before. Anyway, a new set of points (and new condenser for safety sake) seems to have worked a charm and it started right on the button first time now, and I'm happy again!  |
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Post by 3litrekiwi on May 4, 2022 21:44:11 GMT
Great that you found the issue Ken. Now that you mention it, my car had a similar issue with the distributor base plate being slightly distorted. This wasn't apparent until the car was scoped and the advance and retard was erratic. The problem with mine and I suppose plenty of others is that varying degrees of skill have been applied to repairs and tuning over the years and small areas of damage, that possibly were not noticeable at the time can create curly problems later on. The point that a part goes from worn but functional to causing trouble is also tricky as our whole cars with a few exceptions are well worn in most areas.
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