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| Misfire after 30 minutes | Rating: 
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| Posted: 05-06-2016 06:45 pm |
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1st Post |
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subwoofer Member
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It would seem I have an ignition problem... She runs very well for 30-ish minutes, then starts misfiring at low revs, dies at idle, can be started again if speed is available, but using the starter will not cut it. After a few hours, starting is easy again. There is spark when pulling a plug and looking, but not enough to trigger my timing light. Coil (Lucas, gold) is lukewarm. Dizzy is a 43D with a Pertronix Ignitor II. I'm more than ready to go crank fire with a Megasquirt now, but I would have liked to go to a GTG this weekend. Then it suddenly strikes me, it could be the tachometer at fault! I still run the original configuration.
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| Posted: 05-06-2016 06:56 pm |
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2nd Post |
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Frank Schwartz Member
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Well, the voltage to the coil runs through the tach...I, (opinion) suspect the coil...and is there a resistor in the circuit? If so, make sure it is correct..and that the red and black leads from the Pertronix unit are on the coil and not on the resistor... Now that sounds odd, but the Pertronix must be on both sides of the coil. If you have another coil, try it and see what happens...It seems obvious that something is breaking down and my first thought would be the coil..and second..the resistor... Let us know what you find. Frank
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| Posted: 05-06-2016 07:04 pm |
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3rd Post |
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subwoofer Member
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No resistor, AFAIK the gold coil is a 12V coil. Pertronix is correctly connected. I can't seem to provoke the problem standing idling in the yard and I don't have a spare coil. I may just try to patch another circuit to the coil and see what happens.
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| Posted: 05-07-2016 06:19 am |
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4th Post |
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answerman Member
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I doubt it's the tach (unless it's the actual bullet connectors on the tach itself just being dirty). The tach electronics proper don't actually have anything to do with the ignition circuit. I don't remember my wire colors offhand, but the way it works is that there is +12V coming into the one of the tach bullet connectors on a white wire (guessing on the color). The tach "connection" it attaches to just has a wire inside the tach that runs through a small coil (physically, not electrically) and then back out to the outside of the tach, with another connector. That connector is then connected to the wire which goes to the coil. There's no actual electrical connection between that +12v feed through the tach body to the coil and any internal tach components. What's inside the tach between those two connectors is basically just a jumper wire.
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| Posted: 05-07-2016 01:49 pm |
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5th Post |
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subwoofer Member
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I jumped the tach, and it seemed to be cured - for a little while... It is maybe looking like the alternator isn't all well, seeing only 12.4 volts at the battery at idle. It should have been a lot higher while running, even at idle?
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| Posted: 05-07-2016 03:56 pm |
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6th Post |
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Frank Schwartz Member
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Yes...it should be 13.6 or even better...maybe your battery is old or defective?? Most last about three years or four...if it is older, I would be suspicious. Most car parts stores can check it for you..they run a test and give you a computer printout. I'd start there..also have you checked the fuel filter back at the tank??? I had a similar problem with my Interceptor that turned out to be an alternator that was heat sensitive. It worked fine when cold but when it got all the heart from the engine (and it really gets hot under the hood of an Interceptor) it would fail and the ignition module would stop working when the voltage got low...took a long time to find that problem..but you do not have an ignition module, per se...however, I did personally have had a Pertronix unit that went bad. Just totally failed and would do nothing...Took it back to speed shop and they gave me another. First time I have ever had one of those go bad...but I don't think yours could be intermittent..could it? Or heat sensitive?? Have you tried a different coil??? So, let's start with the battery...and then the alternator ...after making sure the fuel filter is not getting clogged...and let us know. Frank
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| Posted: 05-07-2016 04:10 pm |
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7th Post |
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subwoofer Member
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I'm pretty convinced the problem is electrical, I pulled a main jet to check for fuel on the emulsion tube, and there was fuel to the ridge below the top holes, I think that is about right. Still no sign of life. It is clear that the problem is heat related, but there may be more than one fault. I just got a new battery, but even at the second attempt it didn't quite fit, some adjustment with a cutter and the welder required...
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| Posted: 05-07-2016 09:50 pm |
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8th Post |
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Tom Bradley Member
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I agree with Answerman that it is not likely to be the tach. It is most likely something in the engine compartment. I would check all the electrical connections to see if something is loose or corroded. A bad coil or resistor is also not likely, though possible. Sounds like the alternator may not be charging the battery, which would cause the battery to loose charge faster when driving than when sitting idle. Another possibility is the electrical switch on the steering column. I have had these go bad on me. This can be more of a problem when driving than when idling because there is more bouncing around which can cause the connection to go bad. Hot wiring directly from the battery to the + side of the coil will bypass everything, which will at least show you the general area of the problem. I also had a problem like this when I first started my car after several years sitting. In my case it finally turned out that the engine was running way too rich at speed so the plugs were getting fouled causing misfires. adjusting the carbs fixed it.
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| Posted: 05-07-2016 10:20 pm |
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9th Post |
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subwoofer Member
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I am more than a little confused, since it runs well under load and speed, getting stuck in traffic on the other hand is an absolute nightmare. As soon as I have modified the battery tray somewhat, a new battery will go in, it will be interesting to see if that changes anything. The Pertronix has adaptive dwell, so it would be strange if the coil overheats at low revs.
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| Posted: 05-08-2016 06:03 am |
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10th Post |
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Tom Bradley Member
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Cranking the starter takes over ten times as much current from the battery as does running the engine. So if the starter still cranks OK under conditions when the engine misfires, then the battery should not be the problem. Are you sure the engine is not overheating? Stop and go traffic is the worst for that. Possibly the gauge in the cabin is reading low? It could also be a vacuum leak or sticking weights in the distributor making the ignition timing when idling inconsistent. You might watch the tach to see if the idle RPM's are steady under all conditions. If you have the original tachometer setup (current drive rather than voltage), the tachometer reading in the cabin is probably not accurate with an electronic ignition. Mine was reading almost 30% high before I did a voltage-operation conversion. You might want to check the idle RPM's with a tune-up gauge from the auto parts store. If you are setting the idle RPM's using the cabin gauge, you may be setting it too low for reliable operation.
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| Posted: 05-08-2016 06:35 am |
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11th Post |
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Frank Schwartz Member
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You never told us if the battery checked bad or not...and if it was good, if the alternator was good. Frank
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| Posted: 05-08-2016 09:58 am |
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12th Post |
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subwoofer Member
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I have been shortish in the messages because I had to type on a phone and not a computer. Had forgotten the password to this site and the password reset doesn't work because it send to the email you initially registered from. That address was disused 6 years ago... Anyways: Battery: Functioning but getting old (mfg 06) and seems weak. I don't have too much cranking time left in it when the engine starts playing games. Alternator: It is only ten years old, just changed before I bought the car and looks good. The charge light goes out like it should after starting, but I haven't had time to investigate further. It is a suspect due to seeing that it is dropping the voltage down at idle when warm. Overheating: Doubt it. Electric fan directly on the radiator, needle rock steady. Due to a production error on the water pump I am measuring at the water rail below the carbs (Dell'Orto) but I think Lotus used to measure there. Tach: current drive, have the kit to make it voltage triggered. Trouble getting a round tuit... Jumped the coil feed off another circuit for testing, apart from seeing a lower voltage drop battery -> coil, no difference in behaviour. Idle speed: Principally set by ear, reading about 1k on the dial. Does not sound like a 700 RPM idle. Incredibly difficult to set idle speed when warm, either it stays where it is or it revs up to 1500-2000 (by ear), probably due to advance kicking in. Idle mix: 3 turns out to 4.5 turns out makes no difference to behaviour really, apart from the smell of the exhaust. Wideband lambda meter is on the todo list. Distributor: Mech advance only unit, true state unknown, but looked fine when installed 6 years ago when I changed the engine. Pertronix Ignitor II unit installed. Plug leads are blue silicon leads, probably installed just before I bought the car. Major PITA to get to the dizzy. :-( Coil: 4 year old Lucas Sport (gold) coil. No visible damage, estimated temp when I have problems ~60C (can hold it for about three seconds before it's painful). Ways forward: What I haven't done, but is worthwhile is to swap batteries when it is dying. Pull into the yard, wait for it to die (usually within seconds of falling into idle), attempt a start on the old battery, that failing - connect the new one and see if it fires. If it does, the voltage while cranking is too low to get reliable spark. A relay sending voltage straight from the battery to the coil is also something that cannot do harm. The end result is still that I have been having ignition trouble with this car since day one, it is time for computerized crank fire. But that takes some time to build, so that will be next season... -- Joachim
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| Posted: 05-08-2016 05:11 pm |
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13th Post |
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Tom Bradley Member
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Unless you are a musician, setting the idle by ear is probably not that reliable. The best way I found to check this is by recording and analyzing the exhaust note. I used a microphone connected to my lap top and Audacity software (free!). 1000RPM = 16.7 CPS or 60mS between pulses. An added benefit is that you can see the missing pulses when the engine misfires. If the missing pulses are always a multiple of 4 apart, then it is one particular cylinder that is misfiring. In that case it could be one unreliable spark plug, wire, Dellorto channel or even the distributor cap. The distributor cap in particular was not designed for the kind of voltages produced by electronic ignitions. Mine tended to go bad fairly often. I ended up coating the outside of mine with clear epoxy to get it more reliable. The jumper wire between the battery and the coil does not have to be anything fancy. I just used a test wire and alligator clips. There really is not that much current flowing in that circuit. Rather than switch batteries when the car dies, you might try connecting jumper cables to another car and see if that does the trick. Much faster.
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| Posted: 05-08-2016 06:11 pm |
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14th Post |
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Frank Schwartz Member
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On my son's JH, we found that replacing the distributor cap made a world of difference..we watched the engine in the dark and could actually see a spark on the distributor cap..replacing it worked great....also on another car I worked on recently (JH) I never could get the idle set right and it turns out that one cylinder had zilch compression and it turns out it had a burned exhaust valve...remove all plugs..check compression on each cylinder. And your battery was bought in 06?? or is six years old??? Try a new battery...just assuming it works even if it is old is useless... Let us know
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| Posted: 05-08-2016 06:13 pm |
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15th Post |
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Frank Schwartz Member
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Another thought...the vacuum retard unit on the distributor is usually bad , and if connected to the system allows air to be sucked in and is not good. Block off the vacuum line going to this appendage and it helps.
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| Posted: 05-08-2016 06:53 pm |
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16th Post |
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subwoofer Member
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There may be (probably is?) multiple issues here. The alternator needs a checkup, the battery replacement and so on so forth. Thanks for the reminder on distributor cap and rotor, they may well be heavily scorched by now. Note to self: Always the simple things first... My DD (a Vanagon on Megasquirt) eats rotors and caps, probably since it is running optimal coil charge at all loads and speeds. I don't know how old the cap is in this engine, but I have never changed it. Shame it's such a PITA to get to... The battery was made in 06, so ten years old, will be replaced as a matter of course. Thought of the jumper cables after I posted, whatever is easier is debatable, really depending on how many cars I have to move to get a battery within jumplead reach. The yard does not have much space left unused. I'm only a hobby musician, playing 15-20 gigs with a jazz big band every year. Is that musician enough for you? :-) Good idea on the sound analysis though, I can tell if all cylinders are running, but until it starts shaking I can't really tell they are running unevenly. Haven't sensitized myself to that sound pattern, I guess. To see the power of sensitizing, pick some artifact and have someone show you an example of when it is bad. Good candidates are end-of-roll markers on film shown 7 seconds before the end of the roll, and MPEG artifacts on TV. Once you start seeing them, you can never go back to not seeing them. But that was an aside. At least I know I don't have any vacuum leaks in the distributor. It has no vacuum connections, it's a 43D. Makes for lousy fuel economy, but at least it has mechanical advance. -- Joachim
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| Posted: 05-08-2016 07:29 pm |
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17th Post |
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subwoofer Member
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Well, some seller on Ebay just got an order for a tune-up kit. I don't need the points and condenser, but is was £9.50for the lot, can live with that. -- Joachim
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| Posted: 05-09-2016 01:27 am |
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18th Post |
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Jim Ketcham Member
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I had a similar problem in one of my JHs. When the car was warmed up it would die and not start again until it cooled. In my case I eventually found it to be a faulty rotor. It appears that their are substandard rotors on the market where the rivet is too close to the contact and eventually shorts out under high temp conditions. This has been documented fairly well (Google it). I bought a couple of rotors from the guy that sells "red rotor" and that appears to have solved the problem ( been running well for 2 years now). The good news is it's a low cost, easy thing to eliminate. I unfortunately did not discover it until I replaced my Petronix, Coil, plug wires, plugs... Good luck, Jim
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| Posted: 05-09-2016 06:32 am |
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19th Post |
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subwoofer Member
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Again, the simple things first, Jim. It's so easy to forget, one starts chasing the expensive bits before checking basics. Crossing my fingers here, having an intermittent runner is worse than a non-runner. -- Joachim
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| Posted: 05-11-2016 07:29 am |
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20th Post |
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subwoofer Member
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Got to the dizzy last night, as the adverts say "some (dis)assembly required"... Dizzy cap didn't look too bad, have seen a lot worse scorching than that. Not quite sure what that grey, greasy substance is, though.  Rotor, with a rivet. Could this be the smoking gun? Reviewing the history of my ownership, the ignition situation has been deteriorating since I first installed that engine. I was having problems with stalling, then restarting. Since I was running a resistor coil and points, and jumping the resistor made it start easily I assumed the problem was that the bypass circuit in the starter just had failed. The points and resistor coil were then replaced with a Pertronix and a 12V coil, and things were well again - for a while. -- Joachim
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