Peter R Shaw Posted April 23, 2005 Share Posted April 23, 2005 Getting a missfire at between 5 and 6 k under load ...... also the rev counter doesnt seem as steady as it used to be i.e. it flickers up and down instead of being steady .... any ideas ? Road7runner S7S.1.7 X flo here Link to comment Share on other sites More sharing options...
greg Posted April 23, 2005 Share Posted April 23, 2005 [wild guess]Bad earth?[/wild guess] Link to comment Share on other sites More sharing options...
Bradbys Posted April 23, 2005 Share Posted April 23, 2005 How long has your alternator been on the car? Best place to try 1st IMHO. Link to comment Share on other sites More sharing options...
chrisd Posted April 23, 2005 Share Posted April 23, 2005 Had the same symptoms last year with my x/f, it also felt like I was hitting the rev limiterat about 4K revs - turned out to be the wires connected to the alternator. They looked OK at first glance and were securely connected but had 'cooked' and fractured inside the insulating plastic. Hope this helps Link to comment Share on other sites More sharing options...
DW Posted April 23, 2005 Share Posted April 23, 2005 Coil might need replacing David 1700XF Link to comment Share on other sites More sharing options...
Peter R Shaw Posted April 23, 2005 Author Share Posted April 23, 2005 alternator is less than 3 months old ... it started on the last session of the last track day .... the dizzy cap is a bit worn so will try replacing that ... any other tests for the coil ? Road7runner S7S.1.7 X flo here Link to comment Share on other sites More sharing options...
Graham Perry Posted April 23, 2005 Share Posted April 23, 2005 Mine has done this in the past just as the leads were about to drop of of the alternator. make sure they are tight and have not worked themselves loose Link to comment Share on other sites More sharing options...
JampJ Posted April 23, 2005 Share Posted April 23, 2005 Could be so many things, plugs, leads, coil, distributor, ignition, fuel. If it is something that happens everytime, maybe a good idea to put it on an engine analizer, Crypton etc. Should be able to pin point the problem. You could spend a lot of money changing things that are OK. Cheers J&J Link to comment Share on other sites More sharing options...
Peter R Shaw Posted April 23, 2005 Author Share Posted April 23, 2005 new dizzy cap and rotor arm ... a little better ... but still an odd miss ... Road7runner S7S.1.7 X flo here Link to comment Share on other sites More sharing options...
Joe 90 Posted April 24, 2005 Share Posted April 24, 2005 Sounds like you're in the right area then. Coil and condenser (if you have points) next I think. SEP field working, not spotted in 103,300 miles. Some photos on webshots, updated 25 Jan Link to comment Share on other sites More sharing options...
Peter R Shaw Posted April 24, 2005 Author Share Posted April 24, 2005 no point ... aldon .... still an odd misfire but not always at the same revs .... Road7runner S7S.1.7 X flo here Link to comment Share on other sites More sharing options...
JampJ Posted April 24, 2005 Share Posted April 24, 2005 Check all the electrical connections on the coil etc, make sure they are a good tight fit. What coil are you using? Cheers J&J Link to comment Share on other sites More sharing options...
Robster Posted April 25, 2005 Share Posted April 25, 2005 Had the same symptoms last year, in the end it was a plug breaking down. I changed the plugs and the HT leads and it cured it! The leads should be changed every couple of years anyway as the performance will drop off. Chasing odd misfires under load from leads/plugs is SUCH a pain that the small price of new ones is well worth it. Link to comment Share on other sites More sharing options...
JampJ Posted April 25, 2005 Share Posted April 25, 2005 If you're going to change the plugs, you could try: NGK B8EVX, expensive, but very good! Cheers J&J Link to comment Share on other sites More sharing options...
Tim_H Posted April 25, 2005 Share Posted April 25, 2005 Had the same symptoms last year with my x/f, it also felt like I was hitting the rev limiterat about 4K revs Me too. - at the moment - doesn't always do it either Watching with interest. L7 EVN Link to comment Share on other sites More sharing options...
Peter R Shaw Posted April 25, 2005 Author Share Posted April 25, 2005 I put new plugs in first ... the leads were new last yr so dont think they are worn out yet ( especially at the price I paid ) Road7runner S7S.1.7 X flo here Link to comment Share on other sites More sharing options...
J A T Richardson Posted April 25, 2005 Share Posted April 25, 2005 I had the same experience as ChrisD, and had the wildly swinging tacho - except mine eventually stopped altogether - just outside Spa... Riding home on a low-loader was great - NOT. You can't see that the wires are cooked, but it is worth while re-routing them as far from the exhaust as possible. My local motoer facto had an alternator plug which allowed me to re-route the (repalced) wires straight down to a bottom chassis rail. No probs since Link to comment Share on other sites More sharing options...
Tim_H Posted May 27, 2005 Share Posted May 27, 2005 mine's still doing it - (getting worse now) - where do I start ? - more of a DRRRRRRRRRRR when you are under full load, at any revs 2500 ., but of course, a few seconds later - it might not do it again for 5 minutes! Oh - and to add, when it's doing this, the tacho needle jumps too! Like someone's flicking an on/off switch very rapidly. L7 EVN Edited by - Tim_H on 27 May 2005 07:43:28 Link to comment Share on other sites More sharing options...
Nigel Riches Posted May 27, 2005 Share Posted May 27, 2005 Try disconnecting the lead to the tacho, easiest at the coil end, and see if the problem continues. 1982. 5 speed, clamshells. B.R.G / Ali. The True Colours. Link to comment Share on other sites More sharing options...
Tim_H Posted May 27, 2005 Share Posted May 27, 2005 *arrowup*the problem isn't the tacho AFAIK, it's just that the tacho 'bounces' when the engine's misfiring. Also noticed that it does it either when the engine's hot or cold. I'm moving away from the breaking down coil / plugs / leads theory, and thinking more broken wire theory, that sometimes contacts and sometimes doesn't. L7 EVN Link to comment Share on other sites More sharing options...
Nigel Riches Posted May 27, 2005 Share Posted May 27, 2005 Is the tacho bounce the effect or the cause of the misfire? it's not unknown for the transistors in the tacho to fail. 1982. 5 speed, clamshells. B.R.G / Ali. The True Colours. Link to comment Share on other sites More sharing options...
Tim_H Posted May 27, 2005 Share Posted May 27, 2005 it's not unknown for the transistors in the tacho to fail. But would that cause a misfire? It seems that the 'bounce' is an effect of the misfire, and like I said, it comes and goes. (might not do it for 1/2 an hour) I'm erring towards a bad connection - somewhere..... L7 EVN Link to comment Share on other sites More sharing options...
Nigel Riches Posted May 28, 2005 Share Posted May 28, 2005 Hi John, the transistor in the tacho could be failing in a partial manner, they don't necessarily work or not work (go, no go), if the supply side (+ve) is being shorted to ground by this device, in a partial fail mode, then some of the volts will get to the coil, to do the job of running the motor, and tacho, the rest will be lost to ground via the shorted side of the device, this will give unstable tacho display, as the signal is present / not present, and the same will be reflected in the ignition circuit, and the symptoms you describe of working erratically would fit with a transistor breaking down, very intermittent, and very difficult to pinpoint, as I said earlier, isolate the tacho and see how it goes, if it continues to run poorly, well you know it's not the tacho, if you do isolate the tacho, I would recommend removing all electrical connections from it, ie. both sides of the coil, as if it's shorting from +ve to ground through the transistor, and you remove the negative from the coil, this will have no effect on the fault, as it will find a path via the ground in the tacho, sounds like you've got a curly one there, but the collective wisdom on BC should be able to see you right, regards Nigel. 1982. 5 speed, clamshells. B.R.G / Ali. The True Colours. Link to comment Share on other sites More sharing options...
Tim_H Posted May 28, 2005 Share Posted May 28, 2005 er, to add to this, my horn has started sounding all by itself. so, I was driving home yesterday pm, beeping at everyone, making a complete knob of myself. The wiring´s certainly gone dicky somewhere! Tim (In Menorca)! Link to comment Share on other sites More sharing options...
Peter R Shaw Posted May 28, 2005 Author Share Posted May 28, 2005 I too have a mis fire on my x flow .. red ignition light comes on and a mis fire at hight revs ... sorry for the high jack Road7runner S7S.1.7 X flo here Link to comment Share on other sites More sharing options...
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