Discussion
Hi Bruce.
Unfortunately changing my amp and coil has not changed anything for me, along with leads, plugs, dissy cap and rotor arm, I have taken apart the ecu plug and checked all the connections, stripped the loom back from the ecu, but all the cables look good, I do feel it's still possibly a cable as sometimes after checking things I get slightly different problems between a hiccup, misfire or cutout, at the moment I only have the misfire issue, I suspect they are all connected and the differance is in the severity of whatever is causing the problem, I will let you know when I find it, but it may take time as the problems often disappear for several weeks.
Paul
Unfortunately changing my amp and coil has not changed anything for me, along with leads, plugs, dissy cap and rotor arm, I have taken apart the ecu plug and checked all the connections, stripped the loom back from the ecu, but all the cables look good, I do feel it's still possibly a cable as sometimes after checking things I get slightly different problems between a hiccup, misfire or cutout, at the moment I only have the misfire issue, I suspect they are all connected and the differance is in the severity of whatever is causing the problem, I will let you know when I find it, but it may take time as the problems often disappear for several weeks.
Paul
Tobs said:
Hi, yes you could be right - I really need to look into it more, but from memory the spark is generated when the ignition amplifier goes open circuit (triggered by a magnetic switch in the dizzy I think), causing the field in the coil to collapse and induce a current into the secondary windings generating the HT spark.
Its not that straight forward- when the coil is switched off you get a massive spike created in the coil primary as the magnetic fields collapse. The size of this spike is mostly controlled by the resistance in the HT leads and combustion chamber conditions, and is typically 150 to 300 volts. Its this spike that the rev counter and the ECU pick up, and the dropper resistor in there to protect the ECUs electronics.Paulprior said:
Hi Tobs, I don't think I would rule out some components just because the tachometer works ok, I believe this signal is used by the ECU to know that the engine is running and at what rpm, the resistor reduces the 12v down to maybe 5v that the ecu might use (I am guessing here) , but if the 12v at the coil reduced by 10% down to 10.8v would that cause a misfire?, the ecu signal would drop from 5 to 4.5v, maybe that's within range and works ok, the ecu signal is also maybe not too bothered about the timing of a spark rather than having a signal from the coil or not.
I'm hoping someone will come along soon and just update me on what creates the spark, points in the dissy maybe?
Paul
I'm hoping someone will come along soon and just update me on what creates the spark, points in the dissy maybe?
Paul
More generally HT faults can be difficult to pin down without some sort of test gear to measure the HT voltages or look at the waveform shape. The old style crypton tuners with a oscilloscope had this facility, but you would need a classic car garage to find one these days. Gunson used to do a great HT tester that gave a bar graph display of the HT voltage down each plug line, but have long since stopped producing them.
Hi Paul,
On paper your problem appears similar but mine happens more frequently . Occasional hiccup followed a few miles later by missfire usually between 5 and 10 miles from home on most journeys. Not absolutely convinced it is missfire as when it clears say within a mile it does so progressively and not with a surge that you normally associate with plugs clearing.
Admittedly at this time the engine is rough as though on 4/6 cylinders but it is reluctant to rev even in lower gears.
Could this be the engine going into limp mode temporarily? Rev counter continues working , no faults on Roverguage
Worry that persisting while in missfire/limp mode will damage the engine. .
Most of the ignition consumables have been replaced including coil and amp as per Dods recomendations.
Will clean up connections to the ECU but do not hold out much hope.
I will be following your progress with interest
Bruce
On paper your problem appears similar but mine happens more frequently . Occasional hiccup followed a few miles later by missfire usually between 5 and 10 miles from home on most journeys. Not absolutely convinced it is missfire as when it clears say within a mile it does so progressively and not with a surge that you normally associate with plugs clearing.
Admittedly at this time the engine is rough as though on 4/6 cylinders but it is reluctant to rev even in lower gears.
Could this be the engine going into limp mode temporarily? Rev counter continues working , no faults on Roverguage
Worry that persisting while in missfire/limp mode will damage the engine. .
Most of the ignition consumables have been replaced including coil and amp as per Dods recomendations.
Will clean up connections to the ECU but do not hold out much hope.
I will be following your progress with interest
Bruce
It wont be limp home, RoverGauge would throw an error code. If you can have RoverGauge running when it happens (or use the logging facility for just the short term fuel trim (turn all the other sensors off in the options menu), a miss fire will show high positive fuel trim on either bank.
Bruce
I have had a period where mine also seemed to have the misfire fairly early on after starting, I have been looking into this since I first bought the car in Jan this year, I also had a period of over 1000 miles without any issue, I don't see the point in taking it to someone else to try and fix because the chances are that they will not see a problem, I was thinking it was fuel related until my friend following me in a Caterham mentioned the heavy fuel smell, so now I'm thinking it sunburnt fuel rather than not enough fuel, I have recently had lights fitted to my dash so I can see if the pump is running and I get a signal at the coil, last time I had the misfire both lights were OK, showing a coil signal and the ecu signal to the pump was ok.
Blitz racing - I'm not sure where you measure the voltages you mention, I thought the coil primary circuit - LV would be 12v, the HT secondary 20,000v plus?, last weekend I thought I would replace the LED light I had connected across the coil with a Voltmeter so I could check for a reduced voltage during a misfire, but when I tried to start the car it wouldn't start, when I disconnected one of the meter leads then it started ok, I tried this twice to prove the problem, it would appear that the resistance of the meter was too low and reducing the voltage?, the meter didn't light up or display anything, I then put my normal multimeter on the connection to the new meter ( I reconnected it after starting the engine) but could only read less than 1 v, I find this rather strange, but ran out of time, I will try again at the weekend.
You have mentioned before in other threads about not guessing at the problem but try to prove it instead, I fully agree with this, but running low on ideas on what to try and test, I am quite proficient at troubleshooting electrical or mechanical issues but need some guidance on how this part of the circuit should work and how to test, so any thoughts are very welcome.
Can I run the rovergauge on a tablet or something with a longer battery life than most laptops?, if so what parameters should be monitored?
Thanks
Paul
I have had a period where mine also seemed to have the misfire fairly early on after starting, I have been looking into this since I first bought the car in Jan this year, I also had a period of over 1000 miles without any issue, I don't see the point in taking it to someone else to try and fix because the chances are that they will not see a problem, I was thinking it was fuel related until my friend following me in a Caterham mentioned the heavy fuel smell, so now I'm thinking it sunburnt fuel rather than not enough fuel, I have recently had lights fitted to my dash so I can see if the pump is running and I get a signal at the coil, last time I had the misfire both lights were OK, showing a coil signal and the ecu signal to the pump was ok.
Blitz racing - I'm not sure where you measure the voltages you mention, I thought the coil primary circuit - LV would be 12v, the HT secondary 20,000v plus?, last weekend I thought I would replace the LED light I had connected across the coil with a Voltmeter so I could check for a reduced voltage during a misfire, but when I tried to start the car it wouldn't start, when I disconnected one of the meter leads then it started ok, I tried this twice to prove the problem, it would appear that the resistance of the meter was too low and reducing the voltage?, the meter didn't light up or display anything, I then put my normal multimeter on the connection to the new meter ( I reconnected it after starting the engine) but could only read less than 1 v, I find this rather strange, but ran out of time, I will try again at the weekend.
You have mentioned before in other threads about not guessing at the problem but try to prove it instead, I fully agree with this, but running low on ideas on what to try and test, I am quite proficient at troubleshooting electrical or mechanical issues but need some guidance on how this part of the circuit should work and how to test, so any thoughts are very welcome.
Can I run the rovergauge on a tablet or something with a longer battery life than most laptops?, if so what parameters should be monitored?
Thanks
Paul
Um- The coil consists of two coils, a primary and a secondary. When the coil has 12 volts in the primary a magnetic field is built up in the core that passes over both the primary and secondary windings. When you remove the 12 volts from the primary the magnetic field collapses rapidly, cutting through both the primary and secondary windings, so you get a massive voltage in the secondary as it has lots of turns of wire, but also the primary but it has fewer turns so the voltage is only hundreds of volts, not thousands. Its called ringing, and is an AC signal seen at the coil terminals as the DC is removed. This is why you had a condenser in the days of points to mop this spike up and not burn the points. You cant use a DVM on DC to measure any coil primary voltages on the switching side as its all over the place with the AC spike, and even on AC the DVM is not fast enough to read the spikes, its a no winner. You need an oscilloscope to do anything meaningful on the coil primary on the switched side. On the secondary side there is a wealth of data if you can monitor the HT as it goes down the plug lead (like some engine analysers can) as open circuits show up as extra high HT voltages, or coil / Amp issues will show up as low HT voltages. Get a trace of all 8 cylinders and if there is a fault on one it will be clearly visible due to the change of waveform. Even without the fault being present to the point of misfire the wave forms will still show something is a miss. Its just guesswork otherwise.
If its an ignition fault, the only thing RoverGauge will show is very high or fixed levels (as in 100%) of short term fuel trim (adding fuel) when the misfire is present, as a lambda probe cant tell the difference between a lean mixture or unburnt mixture, so the ECU adds load of additional fuel to try and fix the issue.
If its an ignition fault, the only thing RoverGauge will show is very high or fixed levels (as in 100%) of short term fuel trim (adding fuel) when the misfire is present, as a lambda probe cant tell the difference between a lean mixture or unburnt mixture, so the ECU adds load of additional fuel to try and fix the issue.
Edited by blitzracing on Sunday 21st August 17:23
Just an update - note that i'm not the OP but had a similar problem of an intermittent misfire, and after replacing HT leads Dizzy cap, rotor arm & plugs still had the issue.
I've now replaced the ignition amp with an original lucas one (red box) and coil with a genuine bosch one and all seems better than it's ever been (i've owned the car almost 10 years now)! I've always had the odd occasional hesitation when accelerating - however this is now gone, so must have been either the coil or ignition amp ( in hindsight I should have change one at a time so I could work out which it was!)
I've now replaced the ignition amp with an original lucas one (red box) and coil with a genuine bosch one and all seems better than it's ever been (i've owned the car almost 10 years now)! I've always had the odd occasional hesitation when accelerating - however this is now gone, so must have been either the coil or ignition amp ( in hindsight I should have change one at a time so I could work out which it was!)
Blitzracing - thanks for the explanation, as you say, to trace the fault with proof will be difficult on the LT or HT side of things, i have looked on the net for portable scopes and they are available, just not in the right voltage range, maybe i can look for some resistive leads to reduce the voltage signal. after all i am looking for a change rather than needing an absolute figure, have you ever needed to go down this route to find an intermittent misfire problem?
Before i look to obtaining a scope do you think that there is any chance that excessive fuelling could cause this problem?, can there be to much fuel to ignite? also i guess there are 2 possibilities for the misfire, either all 8 misfiring, or some working ok and the others maybe not at all, does anyone have any idea how many cylinders you would need to loose so that you can only maintain speed, say at 50mph in top, dropping down a gear or 2 doesn't help.
Tobs - Congratulations, i hope you have completely cured your misfire now
Before i look to obtaining a scope do you think that there is any chance that excessive fuelling could cause this problem?, can there be to much fuel to ignite? also i guess there are 2 possibilities for the misfire, either all 8 misfiring, or some working ok and the others maybe not at all, does anyone have any idea how many cylinders you would need to loose so that you can only maintain speed, say at 50mph in top, dropping down a gear or 2 doesn't help.
Tobs - Congratulations, i hope you have completely cured your misfire now
You cant go anywhere near the HT without a special probe designed for the job, but the LT side can be done with a potential divider with a couple of resistors, but if you spike a scope with 300 volts its likely to kill it (yes I did it with copper HT leads before I knew about the spikes). If I was in your shoes, id be looking for an old time garage who can use a Crypton still, far better than buying a cheap nano scope that will just confuse the issue. I cant say if its anything else- its simply a case of removing unknowns by proving what bits are working OK with the right tools.
I was hoping that my 3 intermittent issues, hiccup, misfire and cutout would all be from the same cause, unfortunately it doesn't look that way, today I had 3 very short hiccup episodes, I have been trying to track my issues with some LEDs as below.
During the hiccups the bottom red light went out, this is the 12v coming out of the pump relay contacts, the green light at the bottom which is unlit in the pic came on, this measures from the pump relay coil negative to earth, I believe this line is controlled through the ECU, so it appears that the ECU was switching the pump off, any ideas on why this might happen?.
During a previous misfire session I only had these bottom 2 lights connected, but they didn't change, so it appears these issues are not related unfortunately
Paul
During the hiccups the bottom red light went out, this is the 12v coming out of the pump relay contacts, the green light at the bottom which is unlit in the pic came on, this measures from the pump relay coil negative to earth, I believe this line is controlled through the ECU, so it appears that the ECU was switching the pump off, any ideas on why this might happen?.
During a previous misfire session I only had these bottom 2 lights connected, but they didn't change, so it appears these issues are not related unfortunately
Paul
If the 0 volts (request to run) from the ECU is intermittent and your ignition amp is OK have you checked the ignition amplifier plug/socket? They are not the most substantial item and have been known to cause problems in the past.
If you are ever up near the Lakes I have a Crypton that displays the 8 HT traces in fact I have two.
Crypton tuners frequently crop up on ebay but generally need some detailed work to get them running (tantalum capacitors are a weak spot) but I suppose as they are 30-40 years old this is to be expected.
If you are ever up near the Lakes I have a Crypton that displays the 8 HT traces in fact I have two.
Crypton tuners frequently crop up on ebay but generally need some detailed work to get them running (tantalum capacitors are a weak spot) but I suppose as they are 30-40 years old this is to be expected.
I Loubaruch
Yes I have swapped amps over 2 or 3 times, no change with any of the faults, connectors all look ok.
Unfortunately I'm not so close to the lakes, but as my problems are intermittent it wouldn't be so easy to have a Crypton analyser connected full time, if memory serves me correctly they were so big I would need to attach a trailer
Paul
Yes I have swapped amps over 2 or 3 times, no change with any of the faults, connectors all look ok.
Unfortunately I'm not so close to the lakes, but as my problems are intermittent it wouldn't be so easy to have a Crypton analyser connected full time, if memory serves me correctly they were so big I would need to attach a trailer
Paul
Paul, hi
Just a random thought from a non-mechanically minded numpty.
You mention running at 50 mph and not being able to accelerate.
That is exactly the symptom I had 1.5 miles before grinding to a complete halt with a blown 100 amp fuse.
Prior to that the car had been running on 7, then 6, then 5 etc
As you probably know, the fuse lies electrically between the alternator and the battery, thus stopping the battery from charging and more importantly, you are running on battery until the circuit is restored. Often the fuse merely cracks and doesn't completely blow, giving intermittent performance, and of course when it is allowing a flow of electrons things recharge and make the car seem fine again.
The fuse is under the car, roughly directly under the alternator, and can be found in a black fuse holder by following the thick lead down from the alternator. Takes a small socket (?8 or 10 mm?), and do take it out completely to see if it is broken but still making intermittent contact.
5 minute job to check if you haven't already.
Just a random thought from a non-mechanically minded numpty.
You mention running at 50 mph and not being able to accelerate.
That is exactly the symptom I had 1.5 miles before grinding to a complete halt with a blown 100 amp fuse.
Prior to that the car had been running on 7, then 6, then 5 etc
As you probably know, the fuse lies electrically between the alternator and the battery, thus stopping the battery from charging and more importantly, you are running on battery until the circuit is restored. Often the fuse merely cracks and doesn't completely blow, giving intermittent performance, and of course when it is allowing a flow of electrons things recharge and make the car seem fine again.
The fuse is under the car, roughly directly under the alternator, and can be found in a black fuse holder by following the thick lead down from the alternator. Takes a small socket (?8 or 10 mm?), and do take it out completely to see if it is broken but still making intermittent contact.
5 minute job to check if you haven't already.
The ECU keeps the fuel pump running when it gets the ignition pulse from the coil- typically it will keep the power on for about 2 seconds per pulse, ie you would have to miss multiple trigger pulses to get to the point it turns the pump off. Id expect to see the rev counter blip if this was the case. You could try earthing the pump directly just as a test, but it will remove the safety bit where the pump stops if the engine stops, so dont do crashing the car!
Edited by blitzracing on Monday 12th September 16:25
QBee, that's an interesting thought for my misfire issue, I have this which I fitted while looking for my slow start problem, but didn't think to look at it when I last had the misfire.
It just plugs into the cigarette lighter socket.
Blitz racing, I saw the pump cut out from my lights, probably only a second each time to get a hiccup, I didn't specifically look at the Rev counter but I would think I would notice it drop off while looking at the lights, we discussed that I can't easily measure the coil signal, but could I measure the signal from the coil to the ecu after the resistor? If so would it be measured as AC?, for the misfire maybe it's better to see a voltage, for the hiccup maybe a light to monitor just on or off?, do you know what pin this signal goes to?, is this the only signal that tells the ecu to switch the pump?
Paul
It just plugs into the cigarette lighter socket.
Blitz racing, I saw the pump cut out from my lights, probably only a second each time to get a hiccup, I didn't specifically look at the Rev counter but I would think I would notice it drop off while looking at the lights, we discussed that I can't easily measure the coil signal, but could I measure the signal from the coil to the ecu after the resistor? If so would it be measured as AC?, for the misfire maybe it's better to see a voltage, for the hiccup maybe a light to monitor just on or off?, do you know what pin this signal goes to?, is this the only signal that tells the ecu to switch the pump?
Paul
Have you run the car without the plug extenders as suggested.
I had similar intermittent issues especially when the car got hot after sitting in traffic.
I changed amp,leads coil etc and thought it improved it , but ithe problem was still there intermittently. All the original parts are now back on the car and the final fix was changing the plugs . The plugs were changed to resistive and putting some cheap EBay heat socks on.
Cars been perfect for months now
I had similar intermittent issues especially when the car got hot after sitting in traffic.
I changed amp,leads coil etc and thought it improved it , but ithe problem was still there intermittently. All the original parts are now back on the car and the final fix was changing the plugs . The plugs were changed to resistive and putting some cheap EBay heat socks on.
Cars been perfect for months now
WOO5IE said:
Have you run the car without the plug extenders as suggested.
I had similar intermittent issues especially when the car got hot after sitting in traffic.
I changed amp,leads coil etc and thought it improved it , but ithe problem was still there intermittently. All the original parts are now back on the car and the final fix was changing the plugs . The plugs were changed to resistive and putting some cheap EBay heat socks on.
Cars been perfect for months now
That was my misfire cure too.....a new set of extenders were fitted during service in Feb 2015, and I had six of the new ones fail within six months. Four failed electrically, two were prone to popping off the plug. I now have resistive iridium 6 plugs and high temp fibre glass socks and have never had a misfire since.I had similar intermittent issues especially when the car got hot after sitting in traffic.
I changed amp,leads coil etc and thought it improved it , but ithe problem was still there intermittently. All the original parts are now back on the car and the final fix was changing the plugs . The plugs were changed to resistive and putting some cheap EBay heat socks on.
Cars been perfect for months now
On Thursday I was at a friend's rolling road session and a misfire was detected. I had a spare set of old extenders with me, the problem turned out to be no 7 extender. Replaced, misfire gone.
On Saturday I popped in to help a PHer with constant misfire problems, despite changing loads of stuff. Looked and listened, and tested exhaust manifold temps. No 1 and no 8 extenders faulty, nice shiny set only two years old. Replaced them with two of my old set, problem appears solved.
So all I can say is that extenders do seem to be a problem for some, new sets are definitely a problem, even when marked Beru, Germany and bought from a TVR source, and deleting them for good quality socks (rated over 1000 degrees) seems to solve the issue permanently.
Well done Anthony. Before going Mbe I had the odd misfire, part of the upgrade included removing the extenders, no misfires since 
I've put resistive plugs in but apparently it buggers up my neighbours free view box on his TV !
Mine does the same when motor bikes pass the house but not when running my car which seems at odds, hmm!
I've put resistive plugs in but apparently it buggers up my neighbours free view box on his TV !
Mine does the same when motor bikes pass the house but not when running my car which seems at odds, hmm!
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