Discussion
Hi
I have been out driving with some friends today, covered nearly 200 miles, most of the time the car ran perfectly, but on 3 occasions i was getting a very heavy misfire, just enough power to keep going, maybe doing 50 to 60 at the time, on 2 occasions a friend was behind me and told me that there was a heavy smell of petrol in the air at the time i had the misfire, is it possible that overfuelling could cut my power so much, or must it be an ignition issue?, my rev counter stays reading ok and i have a light connected to the coil which stays lit up.
Any thoughts?
Paul
I have been out driving with some friends today, covered nearly 200 miles, most of the time the car ran perfectly, but on 3 occasions i was getting a very heavy misfire, just enough power to keep going, maybe doing 50 to 60 at the time, on 2 occasions a friend was behind me and told me that there was a heavy smell of petrol in the air at the time i had the misfire, is it possible that overfuelling could cut my power so much, or must it be an ignition issue?, my rev counter stays reading ok and i have a light connected to the coil which stays lit up.
Any thoughts?
Paul
Hi Pete
All of those have already been replaced earlier in the year, but this fault keeps coming back along with an occasional hiccup or sometimes a complete cut out, the misfire seems to happen only when its had a long workout, a lot of in town traffic seemed to make it worse than normal today, starts working properly again after 1 or 2 minutes, it splutters a few times and then goes back to normal, very frustrating.
All of those have already been replaced earlier in the year, but this fault keeps coming back along with an occasional hiccup or sometimes a complete cut out, the misfire seems to happen only when its had a long workout, a lot of in town traffic seemed to make it worse than normal today, starts working properly again after 1 or 2 minutes, it splutters a few times and then goes back to normal, very frustrating.
Hi
This is not a little misfire I'm talking about, it sounds and feels like it's only running on 4 cylinders, as such it won't Rickover so I can't get under the bonnet, it has been doing this since before I replaced the coil and amp, if it was a short on the injectors I guess they are all supplied individually, I think I have more problems than just one, similar thoughts on extenders, I suspect it's unlikely that several would play up together and then start working again after a few minutes.
So if we go back to the heavy smell of petrol, I guess it's over fuelling or not burning, can over fuelling when driving cause this? Any thoughts on how to check the ignition? I know I have power on the coil, maybe I need to measure the voltage, but I guess the 12v to the coil switches on/off for every spark, so I could just be missing some of those?, I guess this signal comes from the ecu?, any thoughts on how I could test this?, yes I have the rover gauge, is there a way to run it off a tablet?, my laptop battery doesn't last very long
I have made some assumptions on the function of the 12v and coil, please feel free to correct me if I have assumed incorrectly.
Paul
This is not a little misfire I'm talking about, it sounds and feels like it's only running on 4 cylinders, as such it won't Rickover so I can't get under the bonnet, it has been doing this since before I replaced the coil and amp, if it was a short on the injectors I guess they are all supplied individually, I think I have more problems than just one, similar thoughts on extenders, I suspect it's unlikely that several would play up together and then start working again after a few minutes.
So if we go back to the heavy smell of petrol, I guess it's over fuelling or not burning, can over fuelling when driving cause this? Any thoughts on how to check the ignition? I know I have power on the coil, maybe I need to measure the voltage, but I guess the 12v to the coil switches on/off for every spark, so I could just be missing some of those?, I guess this signal comes from the ecu?, any thoughts on how I could test this?, yes I have the rover gauge, is there a way to run it off a tablet?, my laptop battery doesn't last very long
I have made some assumptions on the function of the 12v and coil, please feel free to correct me if I have assumed incorrectly.
Paul
I have fixed my ecu up above the glove pocket to keep it located securely, I have opened up the connector and tested the pins one by one and sprayed them with electrical cleaner, still no change.
So the 12v coil signal is applied in 2 banks so the dizzy then distributes that to the correct cylinder, I assume one signal is for cyl 1,3,5,7, the other 2,4,6,8?, my rev counter stays stable so does that mean my 12v supply is good?, what would happen if the 12v itself dropped to 10v for instance?, or what if the 12v signal was received by the coil at the wrong time?
Although I have changed most of my ignition circuit I haven't actually changed the dizzy, any thoughts on this as a potential for my problem?
So the 12v coil signal is applied in 2 banks so the dizzy then distributes that to the correct cylinder, I assume one signal is for cyl 1,3,5,7, the other 2,4,6,8?, my rev counter stays stable so does that mean my 12v supply is good?, what would happen if the 12v itself dropped to 10v for instance?, or what if the 12v signal was received by the coil at the wrong time?
Although I have changed most of my ignition circuit I haven't actually changed the dizzy, any thoughts on this as a potential for my problem?
Hi guys, thanks for your thoughts, I have fitted an earth strap straight from the battery to the rear of the block, assuming the 6.8k resistor is one of the 2 near the coil then I have checked it and it's connections, all ok.
Thanks for the engine cycle map, I will study that in moor detail when I have something better than my phone to hand.
Going back to basics, what breaks the coil primary cct to give a spark?, any thoughts on what a week signal to the coil would do? Maybe not a strong enough spark?, I was originally thinking my misfire was fuel related, but my friends comment on a strong petrol smell maybe suggests the fuel supply is good and the ignition is where the problem is, but it's only the dissy I haven't replaced, can it cause this type of problem, switching between running perfectly and serious misfire?
Thanks for the engine cycle map, I will study that in moor detail when I have something better than my phone to hand.
Going back to basics, what breaks the coil primary cct to give a spark?, any thoughts on what a week signal to the coil would do? Maybe not a strong enough spark?, I was originally thinking my misfire was fuel related, but my friends comment on a strong petrol smell maybe suggests the fuel supply is good and the ignition is where the problem is, but it's only the dissy I haven't replaced, can it cause this type of problem, switching between running perfectly and serious misfire?
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
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
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
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
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
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
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
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