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.
Possibly heat related,could be injector wiring,
If you can get the bonnet open in time try putting a thin metal rod or your finger on the injectors each at a time, I've not done it on the Tvr but you should feel them pulsing, if one doesn't it's not working.
The injectors directly below the Power steering bottle ( if it's fitted there) can get a bit damp and often the bottle pushes down on the wiring,
It's intermittent by the sounds of it so a bad connection causing misfires when heat introduces resistance to your electrical supply, check the coil wires are tight etc, have you pulled the plugs out, you might find one black etc, I had a plug fail recently, could hardly notice it but every now and then a slight misfire, replaced it and all's well.
Could a spurious temp,sensor reading lead the Ecu to do some odd things with the mixture? Im asking aloud as I'm guessing !
Do you have Rover gauge.
If you can get the bonnet open in time try putting a thin metal rod or your finger on the injectors each at a time, I've not done it on the Tvr but you should feel them pulsing, if one doesn't it's not working.
The injectors directly below the Power steering bottle ( if it's fitted there) can get a bit damp and often the bottle pushes down on the wiring,
It's intermittent by the sounds of it so a bad connection causing misfires when heat introduces resistance to your electrical supply, check the coil wires are tight etc, have you pulled the plugs out, you might find one black etc, I had a plug fail recently, could hardly notice it but every now and then a slight misfire, replaced it and all's well.
Could a spurious temp,sensor reading lead the Ecu to do some odd things with the mixture? Im asking aloud as I'm guessing !
Do you have Rover gauge.
When was the coil last replaced? I'd replace it - it's a relatively cheap part, but it sits at the top of the pool of heat in the engine bay. And while you've got the coil off, that makes access to the ignition amp module easier so I'd replace that as well for exactly the same reasons. I'm going to do a full ignition refresh on mine every 30,000 miles or 5 years - iridium plugs, HT leads, distributor cap, rotor arm, coil and amp. You can always keep the ones you take off as standby spares.
Oh, and while you're at it, get rid of the spark plug extenders and fit a set of heat socks to the bottom ends of the HT leads instead. Getting rid of the extenders totally transformed my engine when I was having misfire problems last year.
Oh, and while you're at it, get rid of the spark plug extenders and fit a set of heat socks to the bottom ends of the HT leads instead. Getting rid of the extenders totally transformed my engine when I was having misfire problems last year.
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
The injectors are switched in banks of 4 from ECU pins 11 and 13.
I had a similar problem some time ago and found one of these connections in the ECU multiway plug was intermittent.
With the ECU normally dangling around the passenger footwell the loom into the ECU plug is subject to a lot of tension especially when moved, so not surprising faults occur. I moved mine to the bulkhead out of the way and the relays. No problems since.
I had a similar problem some time ago and found one of these connections in the ECU multiway plug was intermittent.
With the ECU normally dangling around the passenger footwell the loom into the ECU plug is subject to a lot of tension especially when moved, so not surprising faults occur. I moved mine to the bulkhead out of the way and the relays. No problems since.
Sorry can't help with the solution, but also looking for one as I have a very similar problem to yours - all is fine but occasionally get a very bad intermittant misfire.
I think it's something on the HT side, as the rev counter seems to work ok and not drop or jump during the misfire. Is your rev counter also working fine during the misfire?
I have also recently replaced most of the HT side - although think a new coil and amp is next..
I think it's something on the HT side, as the rev counter seems to work ok and not drop or jump during the misfire. Is your rev counter also working fine during the misfire?
I have also recently replaced most of the HT side - although think a new coil and amp is next..
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 Paul the only connection between the ECU and the ignition is the wire from the -ve on the coil that goes through a 6.8kohm resistor to the ECU. It tells the ECU that the engine is running. If you get a misfire the Lambda probes see this as a lean mixture and add more fuel so you get a very rich mixture on whichever bank the misfire is. You need to ensure that the engine block is well earthed . I have connected mine via a bolt on the back of the engine direct to the -ve terminal of the battery. It now runs much more smoothly. My intermittent cutting out issue was due to dirty connections to the 6.8kohm resistor and a corroded ECU main fuse. I have also ditched the stupid extenders and fitted Accell ceramic capped HT leads courtesy of Langys rod shop. You need to go through the electrics in a methodical manner, assume nothing, check and clean everything. Buy new old stock ignition parts in red Lucas boxes, if you can find them, they are genuine and good. modern Lucas parts are not good. Read Blitzracing's website and Chimpongas' posts. These guys talk much sense. PS fit BP6ES or COG's fancy ones if budget will allow. It's a rover V8 running a road tune not a full race motor needing short reach plugs. links: http://www.britishv8.org/Articles/Rover-14CUX-EFI....
http://www.g33.co.uk/fuel_injection.htm
http://www.g33.co.uk/fuel_injection.htm
Paulprior said:
....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?,
No.The ECU switches the injectors on in banks of 4 nothing to do with the ignition.
You could also check the plug/sockets to the injectors.
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?
As far as I am aware, if the tacho is still reading correctly when you are getting the missfire, then the problem is on the HT side of the ignition system - the coil amp and dizzy are working fine, switching the low voltage side of the coil correctly as the tacho is working. This is the stage I am at diagnosing my occasional missfire - my tch reads Ok during the missfire. I'm going to try a new coil next.
davep said:
Paul, I HTH here is the spark/ignition to injector firing relationship:
Basically, it is the coil spark or ignition pulse train that the ECU uses to control and time the odd and even injector bank firing pulses.
DaveBasically, it is the coil spark or ignition pulse train that the ECU uses to control and time the odd and even injector bank firing pulses.
This looks very useful. Is it possible to get it in an Excel file or similar?
Many thanks.
Paul
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, 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.
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
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