Graham Sewell Posted August 16, 2009 Share Posted August 16, 2009 Took my usually trust steed out for the first decent run this summer after a few minor glitches early. Recent work included swapping the spark plug leads - which entailed resetting the dizzy as I couldn't get the cap on properly while the dizzy was in place. As the car was mostly stationary for 6 months with a nearly empty tank, I filled the car with petrol at the start of the journey. It became noticable that under hard acceleration above 5000rpm in 3rd or 4th gears that i was getting a major misfire. If I let up slightly, the misfire goes away and I can keep going to 6000rpm (in 3rd at least for obvious legal reasons). Now I can see a few options for causes: 1. a dodgy spark plug lead 2. a dodgy spark plug 3. dirty fuel has partially blocked a main jet or acceleration jet. 4. dying alternator leading to a flattening battery - although I would expect to be stranded before 100miles Point 3 and 4 are relatively easy to check, but 1 and 2 are a bit trickier. I am hoping that the dirty fuel is the cause as I can clean the jets easily enough and hope that it does not happen again. If it was dirty fuel, then I guess a new fuel filter will be in order.... Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
6speedmanual Posted August 16, 2009 Share Posted August 16, 2009 Hi Graham Is is possible to identify if it is a misfire on a single cylinder or if they are all cutting? Duff plug fairly unlikely but cheap to substitute. When you say swapped HT leads, was that for new ones? Try old leads again if that was the only thing you changed. Did you fit new coil to dizzy lead too? Could be this if you have an all-cylinder cut under load. Petrol unlikely to be suddenly dirty so blockage unlikely. Fresh petrol fill should have rejuvenated the old stale fuel in your tank from 6 months ago. Battery would be too dead to crank the engine long before it cannot power ignition system, so if engine will start then alt/batt not the issue. HTH Peter BRAWNGP green SUPERLIGHT FCITW 2009 😬 Link to comment Share on other sites More sharing options...
JampJ Posted August 17, 2009 Share Posted August 17, 2009 Something breaking down in the ignition system, coil, rotor arm, ignitor etc??? Cheers John JFDI (Just F*****g Do It) Edited by - johnjulie on 17 Aug 2009 09:01:20 Link to comment Share on other sites More sharing options...
virden Posted September 11, 2009 Share Posted September 11, 2009 Hi Graham, Did you trace the problem? My Super Sprint aw has suddenly started showing the same symptoms. Plus astrong smell of fuel, but I think this is due to the misfire. I went to Santa Pod and my world changed forever. Link to comment Share on other sites More sharing options...
elie boone Posted September 11, 2009 Share Posted September 11, 2009 Could be the auxhillary ventury ratling, i just replaced such a ventury because it was very loose and therefore was pitted and was pitch black due to back fire. Could also be fuel starvation due to dirt in the system. Link to comment Share on other sites More sharing options...
randybugger Posted September 11, 2009 Share Posted September 11, 2009 i had the same problem which turned out to be a dodgy coil to dizzy lead Tony Link to comment Share on other sites More sharing options...
Graham Perry Posted September 11, 2009 Share Posted September 11, 2009 Don't rule out a broken inner or outer valve spring either. I have had this twice over the years and it feels like an electrical misfire at high revs but doesn't show at low revs ☹️ Elie's suggestion is also a good one as this can also cause a misfire Edited by - Graham Perry on 11 Sep 2009 13:23:05 Link to comment Share on other sites More sharing options...
Area Representative Crudders Posted September 11, 2009 Area Representative Share Posted September 11, 2009 Hi Graham, I've had a merry time with my 7 trying to eradicate the exact same symptoms. I initially suspected your 1 and 2, and replaced plugs, leads, dist cap, rotor arm plus reset timing. Made no difference. I dismantled the carbs, blew everything through, sloshed around some Wynn's carb cleaner (a mix of Xylene and Naptha IIRC), found Elie's choke problem on no.2 which I remedied, balanced everything up, and that certainly made a difference but did not cure the misfire under load/revs. I then checked the power supply to the Aldon Ignitor and found that it was only seeing 4 Volts. With a slave battery this increased to 10 Volts and on a test drive the car flew - for about a mile anyway, then started misfiring and ground to a halt. Fortunately I had taken the booster pack with me so managed to limp home. Only then did it occur to me that I hadn't been seeing the charge light, and number one on the checklist for a non-charging alternator is a blown charge light bulb. By this time it was very late on a Sunday night and I haven't had a chance to get back in the garage all week, but first thing tomorrow morning I shall be back on the case. If it isn't the charge light bulb I shall run some tests on the alternator and repair or exchange. BTW, if you have a Lucas ACR type alternator there's an ebay seller by the name of JCR who sell a full overhaul kit, including just about everything bar the body and stator, for £19. Seems reasonable to me and their feedback is 100% positive. Cruds Link to comment Share on other sites More sharing options...
Mikey UC Posted September 11, 2009 Share Posted September 11, 2009 I had a worn cable under the dash in the ignition circuit, when I accelerated hard, the cable would move back slightly and short on the dash causing a miss fire. BAGPUSS 1600 Classic - a bit tatty around the edges Link to comment Share on other sites More sharing options...
millsn Posted September 11, 2009 Share Posted September 11, 2009 Sure it will just add another of someone else experiences that will no doubt be totally irrelevant but my typing fingers are itchy so here goes anyway! Recently replaced the HT leads on my zetec. Took it ot the RR and it had a funny misfire etc etc. Of the new leads from Ford, one was defective. It took a few weeks to own up to which one it was but it did start to misfire in honest fashion at tickover! Needless to say it chose to do this just as I was setting off for my MOT. Grr 😔 Link to comment Share on other sites More sharing options...
jonboylaw Posted September 11, 2009 Share Posted September 11, 2009 I had a similar problem that got progressively worse, turned out to be a failed coil.. Might also be a blocked fuel filter. Jon Link to comment Share on other sites More sharing options...
Peter T Posted September 11, 2009 Share Posted September 11, 2009 Could be a sticking valve, especially as you say that it was left idle for 6 months, gum deposits harden around the exhaust valve and are quite common with the use of additives if your are using them if you do not have an unleaded valve insetrs fitted. Compression/leak down test will verify this. Link to comment Share on other sites More sharing options...
Area Representative Crudders Posted September 14, 2009 Area Representative Share Posted September 14, 2009 Well, my problem turned out to be the same as Mikey's - I now have a fully functioning charge light, a rock steady 14 Volts at the battery with the engine running and no more misfiring. I think the Optimate had been masking the problem by giving me plenty of starting voltage, but the battery was obviously draining quite quickly with the engine running - a drawback of the compact racing batteries perhaps (mine is a Powervamp 625). I don't suppose the ignition and carb overhauls will have done any harm Crudders Link to comment Share on other sites More sharing options...
Graham Sewell Posted September 14, 2009 Author Share Posted September 14, 2009 I have not been around for the last week or two, and the car is booked in with Chris Wheeler on 2nd Oct. So hopefully a spirited drive home will ensue. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
bstark Posted September 14, 2009 Share Posted September 14, 2009 Mine did this, assumed it was electrical but turned out to need a de-coke ... Bob Stark Supersprinter Link to comment Share on other sites More sharing options...
Graham Sewell Posted October 3, 2009 Author Share Posted October 3, 2009 Well that was an interesting day..... If you recall, my symptoms started last May when I dragged the car out of the garage for the first time in months to get an MOT. It was starting to misfire slightly then (although that felt like a carb imbalance issue)). While trying to balance the carb, one of the ignition leads broke hence needing a replacement set. The fitting of the set required hours of messing around trying to get the dizzy cap off, leads swapped, dizzy cap on (which required unlocking the timing to get to the second clip, the leads to spontaneously leap off the cap and need to be put back on blind. Finally I drove the car a couple of hundred yards to the petrol station to fill with petrol. So which of these was the culprit of my major misfire?????? The most serious contender was the petrol. I know this as the tank was nearly empty yesterday morning, so I filled with super unleaded (usual Texaco brew) and two miles later my misfire could not be reproduced! So I turned up as Chris Wheeler feeling like a fool - to put it mildly. Chris then suggested that he put the car on the Sun engine analyzer (Krypton tuning of old) and pronounced that my timing was 4' retarded, I had a minor carb imbalance and my idle mix was too weak. So with these all corrected, I headed home with a car that pulls like a train and does not misfire. Cheers, Graham ------ Low tech luddite - xflow and proud! Link to comment Share on other sites More sharing options...
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