Rough running and weak spark from coil
Discussion
Evening chaps,
Today i've finally got around to investigating a rough running problem i've been having which seems to be getting worse, initially it was just a bit lumpy but has now taken to intermittently cutting out at idle and stuttering badly during driving.
The car is a '98 4.0 litre
So far i have...
Plugged in Rover Gauge and checked fault codes. There were none.
Removed plugs and inspected, they were fouled up as is often the case, i have ordered a set of 6's as the plugs are fairly old now and i had intended to change to the hotter type anyway, particularly as i do a lot of short distance driving.
Removed HT leads (Magnecor KV-85) and inspected, visually they look fine and when tested with a multimeter don't provide any more resistance than would be expected for their length. I suppose they have been on the car since probably 2012 ish but haven't done a huge amount of miles, they were fitted by the previous owner.
Opened distributor cap and inspected, again it looks fine.
Removed stepped motor and cleaned, tested movement with Rover Gauge, the motorised arm pinged off with the spring but otherwise moved cleanly.
Then i took the HT lead from the coil to the distributor off and held it against the rocker cover whilst turning the engine over. There was a spark, but not a very big one. This isn't something i've done before so I'm not sure exactly what to expect but i would have thought that the spark coming off the business end of the coil should be pretty strong, is that the case?
So my questions are...
Should i be suspecting any kind of problem with the coil or condenser and is there any further testing i can do?
How can i identify a bad sensor reading which could be causing the ECU to over fuel?
Can i just ditch the plug extenders and protect the HT leads from the manifold or would i need to change the type of plug leads I'm using due to losing the resistance from the extenders?
And any other advice on what i should look into?
Thanks in advance for your help
Today i've finally got around to investigating a rough running problem i've been having which seems to be getting worse, initially it was just a bit lumpy but has now taken to intermittently cutting out at idle and stuttering badly during driving.
The car is a '98 4.0 litre
So far i have...
Plugged in Rover Gauge and checked fault codes. There were none.
Removed plugs and inspected, they were fouled up as is often the case, i have ordered a set of 6's as the plugs are fairly old now and i had intended to change to the hotter type anyway, particularly as i do a lot of short distance driving.
Removed HT leads (Magnecor KV-85) and inspected, visually they look fine and when tested with a multimeter don't provide any more resistance than would be expected for their length. I suppose they have been on the car since probably 2012 ish but haven't done a huge amount of miles, they were fitted by the previous owner.
Opened distributor cap and inspected, again it looks fine.
Removed stepped motor and cleaned, tested movement with Rover Gauge, the motorised arm pinged off with the spring but otherwise moved cleanly.
Then i took the HT lead from the coil to the distributor off and held it against the rocker cover whilst turning the engine over. There was a spark, but not a very big one. This isn't something i've done before so I'm not sure exactly what to expect but i would have thought that the spark coming off the business end of the coil should be pretty strong, is that the case?
So my questions are...
Should i be suspecting any kind of problem with the coil or condenser and is there any further testing i can do?
How can i identify a bad sensor reading which could be causing the ECU to over fuel?
Can i just ditch the plug extenders and protect the HT leads from the manifold or would i need to change the type of plug leads I'm using due to losing the resistance from the extenders?
And any other advice on what i should look into?
Thanks in advance for your help
Thanks WOO5IE,
The plugs i've ordered are BP6ES, so presumably non-resistant. Is that an issue?
I went out just now to test the primary and secondary resistance on the coil to see if i could get any closes to identifying it as being at fault. I couldn't find what the resistances should be specifically looking online but i measured the following...
Primary Resistance: 0.29 measured at range 200 Ohm
Secondary Resistance: 7.16 measured at range 20K Ohm
Does anybody know if that is correct before i replace it?
Im thinking that is a logical next step as the spark is present so therefor the ignition amp is switching the current to HT but the spark is weak so potentially the coil is on the way out.
The plugs i've ordered are BP6ES, so presumably non-resistant. Is that an issue?
I went out just now to test the primary and secondary resistance on the coil to see if i could get any closes to identifying it as being at fault. I couldn't find what the resistances should be specifically looking online but i measured the following...
Primary Resistance: 0.29 measured at range 200 Ohm
Secondary Resistance: 7.16 measured at range 20K Ohm
Does anybody know if that is correct before i replace it?
Im thinking that is a logical next step as the spark is present so therefor the ignition amp is switching the current to HT but the spark is weak so potentially the coil is on the way out.
Thanks Blitz,
Im aware that some people don't rate the Magnecor leads, personally i wouldn't have fitted them but as i know the problem is upstream of them at the moment they can stay for now. Im hoping TV8 will be able to help me out with a bit of diagnosis by substitution with known good parts but if not then i may well be in touch for a HT tester.
The car is currently not starting and I'm pretty sure the engine is a little on the flooded side, am i right in thinking the procedure is to remove the fuel pump fuse and turn the engine over to clear?
Im aware that some people don't rate the Magnecor leads, personally i wouldn't have fitted them but as i know the problem is upstream of them at the moment they can stay for now. Im hoping TV8 will be able to help me out with a bit of diagnosis by substitution with known good parts but if not then i may well be in touch for a HT tester.
The car is currently not starting and I'm pretty sure the engine is a little on the flooded side, am i right in thinking the procedure is to remove the fuel pump fuse and turn the engine over to clear?
Well, a bit more time spent on it today.
The 100amp fuse was fine and i have replaced the coil, the spark coming off the coil and at the plugs does seem stronger now and orange/blue in colour. But unfortunately when you turn it over you can hear it trying to catch and fire up every so often but still not starting. I've taken the new plugs out again to let the fuel evaporate overnight.
Not sure what the next step should be, ignition amp? The parts aren't mega expensive and the car hasn't had anything spent on it for a while so i don't begrudge it a few spares even if they don't turn out to have been absolutely necessary on the way, i'd rather spend the money on that and learn a bit more about the car whilst doing it myself than send it straight off to the garage and spend the same on labour. Up to a point anyway!
Tom
The 100amp fuse was fine and i have replaced the coil, the spark coming off the coil and at the plugs does seem stronger now and orange/blue in colour. But unfortunately when you turn it over you can hear it trying to catch and fire up every so often but still not starting. I've taken the new plugs out again to let the fuel evaporate overnight.
Not sure what the next step should be, ignition amp? The parts aren't mega expensive and the car hasn't had anything spent on it for a while so i don't begrudge it a few spares even if they don't turn out to have been absolutely necessary on the way, i'd rather spend the money on that and learn a bit more about the car whilst doing it myself than send it straight off to the garage and spend the same on labour. Up to a point anyway!
Tom
Gassing Station | Chimaera | Top of Page | What's New | My Stuff