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simon a-b

intermittent ignition fail

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Hi all

 

A while ago I had an intermittent ignition fail... I seated the HT leads and it went away.  All good for about a month.  Now it's back. 

So I loose ignition totally for a bit (tacho drops instantly to zero), then it's back but underpowered, not revving or pulling clean. 

 

Would low voltage on the 12v side of the coil give underpowered feel? 

 

For the tacho to drop to zero there are no spark pulses coming from the coil, am I right?  If so that coud be that there is no 12v supply to the coil, or it's not getting the signal from lumenition to spark...

 

I'll investigate the wiring to see if there's any evidence of issues around the lumenition and coil, and inspect in the dizzy... any other ideas?

 

Cheers,

Simon

 

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Upgrade today to remove Google ads and support TLF.

There's a thread on the Steven's engine forum titled "No Spark" that will be of interest (sorry can't paste link)  :thumbup:

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Ign switch???

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Once the fault is manifest, have a prod about with a multimeter and see where the volts are going! Work systematically through the wiring ... see if you have a 12v supply to the coil and lumenition...check the wiring to the distributor...that sort of thing. Make notes of what you find. Think!! I usually spend time staring at it and allowing the subconscious to work on the problem(!)  

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Thanks all... intermittent problems are the worst!  I guess I was hoping for a universal panacea...

 

I tracked down the stephens thread meantioned above, here's the best bit copied:

 

 

Ok, I think you need to go back to basics rather than just renewing everything you can think of. It is not money wasted of course because you will have new parts, but even then it may not cure your problem. First check is to pull back the rubber boot on the big fat ht lead that goes into the centre of the coil. Makes sure the metal end is pushed down as far as it will go into the coil tower as this is a common non-starting problem. Not fixed? Buy, or make yourself, a remote starter. A push button switch connected to 2 leads with a crocodile clip on each. Remove the large spade connector on the starter motor (red/white I think) and connect one lead to this terminal on the starter. Connect the other lead to a 12volt feed---battery positive is fine, press the button and the starter will turn the engine over (ignition does not even need to be on). With this bit of kit you can now conduct all sorts of tests in the engine bay without any assistance. With your multi-meter set to dc volts turn on the ignition, you should have 12v at both sides of the coil. No 12v means an ignition switch or ign. feed problem. To prove this you can make up a jump lead and connect 12v direct to the positive side of the coil. Be careful, ignition coils can work even if the polarity is incorrect. Make sure that the wires from the + on the coil do not go to the distributor which would mean it is incorrectly wired. If you feed 12v direct to the wires that go to the distributor you can fry the electrics, so take care. So with 12v fed to the + on the coil you will have dashboard lights. Spin it over by pushing the button on your remote starter. If engine fires, you have an ignition key/ wiring problem. If it doesn't fire check for spark. Pull out the big fat ht lead from the centre of the coil (the one that looks like a spark plug lead) and tape in a length of insulated copper cable (mains household cable is fine) Bare cable at each end, tape one end into the coil tower. Ignition on, hold the other end 1/4 inch from the engine block, spin over with your remote starter. Good fat spark means problem is in main coil ht lead going to distributor or rotor arm. You can prove this by doing the same test with the original ht coil lead replaced into the coil tower. Make sure this is pushed fully home well down into the coil tower. Remove the ht lead at the distributor cap and hold 1/4 inch off block. Spin engine (ign. on) with ht lead 1/4 inch off block. Good fat spark here means rotor arm problem Spark with the copper cable but not with the ht lead---replace the ht lead. If you take out the spark plugs it will make the battery last longer and be easier on the starter motor, but you won't know if it sounds like it is going fire up. Still no spark with the copper cable? This means removing the distributor. With the distributor out leave all the electrics connected. Attach an earth lead to the distributor body and then by spinning the dizzy by hand (ign on)as you check and change things you can see if you have recovered your spark at the coil ht lead held just off the block. At this stage you are left with an ignition amplifier fault or an internal distributor fault. I have also known new ignition coils to be faulty (1 particular make comes to mind) so you could repeat some of these tests with your original coil. Probably enough to keep you busy here. I think the pick-up assembly is the same on most Lucas '45' distributors as fitted to Metros so a visit to the breakers may help, the ignition amp. you may find on early Range Rovers or Jags. Good luck, Roy.

 

I've printed it out to go through next to the car...

 

Cheers,

Simon

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Hi Simon

Intermittent problems are indeed difficult solve.

I had intermittent ignition problems. Tacho dropped instantly to zero for a split second a time, and felt that the engine hesitated meanwhile.

It turned out to be an improper connection between the dizzy and power module.

There is a plug with three wires. One of the pines, or rather a spade, at the dizzy site was slit back a bit and seems just to rest next to the other part.

In hope that you will be able to source your problem.

Lars

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That little 3 pin connector is a bit of a "cause celebre"....the pins corrode and give poor contact and the sparks stop. Just moving it a tiny bit can make all the difference....of course, if it IS that, then you have to fix it properly once the diagnosis is done!

Liked the lengthy write up on ignition problems....very nicely done. 

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Intermittent ignition problems ie when engine was nice and hot turned to to be the dizzy pickup unit on my car. Fairly simple repair.

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Note that there should not be 12V on the coil unless the starter is cranking. It should be around 6-8 volts owing to the ballast resistor being in circuit.

 

If the voltage is 12 at the coil when the ignition is on but the engine is not cranking, this is a fault condition and will cause the coil to overheat and the internal thermal trip to cut the ignition until it cools down.

 

The later cars which the write-up applies to might have had 12 volt non-ballast coils.

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Thanks all

 

Finally got some time today to check it out.  I'm only getting 4.6v at the coil, the ballast resistor is marked 1.6 Ohms but tests 2 Ohms. 

 

My brain hurts when I try to remember grade 12 physics!  I'm getting 13v from the loom so there's no issue there.  This goes to a relay and loops out to the ballast resistor.  When the starter solenoid is on, the relay closes and bypasses the resistor giving full battery voltage to the coil.  When the starter is off, battery voltage goes through the resistor. 

 

I think I'm getting too low voltage to the coil (clearly)... If I bypass the lot and supply battery voltage to the coil it runs well.  This is not a permanent solution clearly!  But proves the logic I think/hope. 

 

I've had the pickup out of the dizzy, cleaned it, checked the wiring to the pickup which looks good.  I nipped closed the female end of the three wire plug and cleaned both ends with good electronic cleaner spray.   

 

Next I'll need to trawl the forum for ballast resistor ratings.  Not sure why this would become a problem after many weeks with no problems which still worries me slightly!

 

Cheers,

Simon

 

PS the relay setup is my addition... the car never had the pink wire while I've owned it

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Has the coil been replaced? 

 

Maybe it was replaced with a non-ballast resistor coil?

 

If the coil is the correct ballast resistor type and its run with the ballast resistor bridged across, it should run normally but the coil will overheat after a while. 

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Coil is new and definitely requires resistor

 

is 4.6v too low at the coil?  and if that is the problem, why is it intermittent!

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the resistor is a coil of wire in a ceramic heat sink.  I could undo the clamps and trim a bit off the wire, dropping the resistance... repeat until I'm getting 6-7v at the coil...

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That does not sound like the correct part. It should be a white ceramic block, completely encased.

 

Id you measure the voltage directly at each terminal of the resistor is it battery voltage at one end and the low 4.6 at the other? If so, either the resistor is faulty or the coil is drawing too much current ie faulty or the wrong type.

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I thought the voltage was supposed to be 9v approx at the coil when a ballast is used. As mentioned what is the voltage on the battery side of the ballast?

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I'll do some more testing tonight. 

 

This is a ballast resistor I fitted, a non standard part... my car should have had a pink resistive wire, it never had one and when I drove it prior to renovation job it blew at least one coil.  Since then I've done extensive renovation work...

 

The car has non standard ignition switch too so I made up a method of running a ballast resistor... the 12v (or battery voltage)  ignition supply loops through a relay to the ballast resistor mentioned, then to the coil. 

 

When the starter solenoid has power to it, the relay closes, taking 12v ignition supply direct to the coil.  Once the starter isn't on, the relay opens, supply only goes via the resistor. 

This has been working fine, nice low coil temp, easy start etc. 

 

Recently I've had the issue described in this thread.  So testing across the coil with the ballast resistor in circuit I get 4.6v.  Does anyone have an opinion on whether this clearly low voltage could be the source of my problems?

 

I'll next test to see what voltage is coming from the ballast resistor, there's only about 5cm of wire and two spade connections (that feel firm) between the coil side of the resistor and the coil so I don't think it'll be any different but it does need testing. 

 

Since it's been running well until now I think there must be a poor connection somewhere, the other concern is whether low coil voltage would give the symptoms I have, i.e. tacho dropping to zero instantly and poor running. 

 

I have heard the lumenition either works or doesn't but that the optical pickup is a more common fail point.  I've inspected the wiring and can't see any obvious strain/wear/issues but that's hardly conclusive. 

 

Cheers,

Simon

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So I did some more testing.  Battery voltage is hitting the resistor, and 4.6v is coming from it.  There is a bit of voltage drop through the relay so I'll redesign the circuit to avoid the relay on the way to the resistor. 

I bit the bullet and trimmed the resistor wire, a couple of times to get now 6v at the coil.  Engine starts and runs OK, I think I need more like 9v at the coil. 

Interestingly the coil shows 4v across it when the engine is running and 6v when ignition on but engine not running. 

Also I had a very low idle speed.  I wonder if I've knocked the timing somehow with all the distributor work I've been doing.  Airbox and cleaner are off the carbs but I'd have thought that this might lead to slightly faster idle rather than slower, due to restriction on airflow. 

I'll increase idle speed and check timing, and keep trimming the wire to the point I'm getting 9v at the coil and see how I go. 

Cheers,

Simon

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So you are using the ballast in series with the resistor wire? This would explain the low voltage. Ideally you would run a new non ballasted wire to your resistor.

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I dont think thats what he has. There is no resistor wire because he has the full 12V at the ballast. I dont think the S3 has this resistor wire, my 1982 turbo doesnt.  But I dont understand the reason for using this strange ballast resistor. A proper one costs around £2.00 and would have saved a whole lot of trouble. 

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Ah, I see what you mean! Yes that would suggest the resistor is too large.

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Thanks Gents...

 

No 'proper' ballast resistor available on the Apple Isle, so I used an alternative automotive ballast resistor, which worked fine for a couple of thousand miles of motoring.  Cost $8 vs a proper one taking a month to arrive and costing more like $40.  This one came from an auto parts place, I tried to find the ohms rating to use, can't remember where I found some detail but from memory 1.4 ohms was what is required.  So I used one with 1.6 ohms stamped on it... after all, it's just a resistor! 

 

Anyway with it testing between 1.9 and 2 ohms I've cut it down a bit. 

 

This is not necessarily the source of my problems, of course.  This problem is new... why the ballast resistor should suddenly change resistance and affect running I have no idea and don't find particularly likely.

 

So questions...

 

could someone test the resistance of a proper resistor? 

 

and does a good running car have a lower voltage across the coil when the engine is running than when ignition on but the engine not running? 

 

Cheers,

Simon

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Update... in digging around I found a big leak from the rear carb accelerator pump!  glad to have found that, new carb parts on their way to me now.

With the resistor 'adjusted' now to a reasonable voltage across the coil I get good running (not under load conditions), next thing to do is re-fit the carbs, rebalance them then test under load. 

I'm still suspicious though, if this hasn't cured the problem I'll try replacing the optical sensor next. 

Cheers,

Simon

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So new accelerator pump diaphragm fitted and no leak.  Went for a test drive, all good except for some hesitation under full throttle.  Balanced carbs again and that's gone too now. 

 

So I think I'm all sorted.  A question though:

 

The coil, lumenition etc is currently mounted to the boot wall (as opposed to being mounted inside the extra box part that is then mounted to the boot wall).  I did this so I could access the ignition parts while the engine is running.

 

Although I did a good 20 miles of spirited driving, full throttle at times, around 60mph fastest with no hint of an issue, I was a little concerned with the temp of the coil when I stopped.  It was hot, too hot to hold on to for any length of time.  5 seconds gripping it and it was getting uncomfortable.  The coil is getting a steady 6.5v now when running. 

 

Clearly there's a bit of extra heat from being exposed to the rest of the engine bay which would be removed if I re-mounted it into the separate enclosure, but when feeling the coil it seems hotter than the ambient temperature of the engine bay. 

 

Is this too hot?  I'm worried that it might overheat and fail, probably at the worst possible moment!

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Clearly there's a bit of extra heat from being exposed to the rest of the engine bay which would be removed if I re-mounted it into the separate enclosure, but when feeling the coil it seems hotter than the ambient temperature of the engine bay. 

 

Is this too hot?  I'm worried that it might overheat and fail, probably at the worst possible moment!

I'd have said yes, but not sure as to why, assuming it's in good condition & getting the right voltage. :o

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Thanks John, I'm confused too.  Would the voltage increase as revs go up?  I'll do a test tonight and give it a good rev... see if voltage goes up as the alternator spins faster.  The resistor is getting battery voltage now so I can't see how it could affect things but worth a look.

Coil is brand new...

Cheers,

Simon

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