XJR6 failed emissions: overfuelling or dead spark plug?
Discussion
Some of you might remember back in October my car failed it's MOT with emissions being one of the problems. Hydrocarbons were up at over 900ppm. Then the car failed to start a week later and it was most likely flooded although a dodgy coolant temp sensor and code P1176 Banks 1 and 2 Long Term Fuel Trim too Lean (Fuel Mass Flow Rate) were found when the car was diagnosed.
I then replaced the badly cracked exhaust manifolds (for new) and the coolant temp sensor. I've also renewed the oil, oil and air filters.
Today I had the car booked in for an emissions test as I'd like to check that out before going straight to the MOT. Unfortunately, as I started the car to go for the emmissions test, it had developed a constant misfire. Just my luck.
Emissions test was done with the misfire and some fuel additive in the 1/2 tank of 97RON. I'd also taken the car out - with the misfire for a ten minute Italian tune up - naughty I know.
Hydrocarbons were around 880ppm this time. I spoke to the mechanic and we discussed the misfire. I said that during the test he was getting hydrocarbons down to 300 and advised me that if I cured the misfire added an additive and gave it an Italian tune up we might get emissions down. I informed him I'd already done the latter two suggestions (to a degree).
Once home I found that number 4 spark plug was fouled and all the others were a healthy colour. I replaced the spark plug and the misfire had gone. Car running sweetly again.
So, the questions are, will the car pass emissions now that the aforementioned problems have been addressed? Could one dead plug have caused emissions of hydrocarbons at 880ppm or have I still got a problem that was first detected in October (HC over 900ppm?)
Thanks in advance.
I then replaced the badly cracked exhaust manifolds (for new) and the coolant temp sensor. I've also renewed the oil, oil and air filters.
Today I had the car booked in for an emissions test as I'd like to check that out before going straight to the MOT. Unfortunately, as I started the car to go for the emmissions test, it had developed a constant misfire. Just my luck.
Emissions test was done with the misfire and some fuel additive in the 1/2 tank of 97RON. I'd also taken the car out - with the misfire for a ten minute Italian tune up - naughty I know.
Hydrocarbons were around 880ppm this time. I spoke to the mechanic and we discussed the misfire. I said that during the test he was getting hydrocarbons down to 300 and advised me that if I cured the misfire added an additive and gave it an Italian tune up we might get emissions down. I informed him I'd already done the latter two suggestions (to a degree).
Once home I found that number 4 spark plug was fouled and all the others were a healthy colour. I replaced the spark plug and the misfire had gone. Car running sweetly again.
So, the questions are, will the car pass emissions now that the aforementioned problems have been addressed? Could one dead plug have caused emissions of hydrocarbons at 880ppm or have I still got a problem that was first detected in October (HC over 900ppm?)
Thanks in advance.
In november...........
If you have a misfire on one cylinder your putting 1/6th of all your fuel straigh out the exhaust unburnt, so it does make a big difference. + 1/6th more oxygen than there should be, which will confuse the lambda sensors into thinking the car is lean.
Do you know what was the lambda read out this time. If its more than 1 then the misfire is the likely cause of all the problems. If your sure the misfire is cured, have them check it again.
If it starts to misfire again, and the new plug gets fouled, swap that plugs coil to a different cylinder. If then the different cylinder gets its plug fouled its the coil thats fauly.
If the same cylinder gets fouled there is somthing else wrong, like the injector stuck open or somthing.
If your sure the misfire is cured, then get them to test it again and it should be inspec. But it will never pass that test with a misfire.
Get a print out or right down as much as you can, both at idle and at 2500rpm.
Tame Technician said:
Was it runing on all 6 cylinders when it went for MOT.
I looked at your emissions printout and its harendous.
HC's (hydrocarbons) should be arround 30-50 although the limit is 200, yours are 900+, that means there is bucket loads of unburn fuel in the exhaust. (again overfueling)
But and here's the funny thing, the lambda reading is 1.04, anything above lambda 1 is considered lean normally, but lambda sensor can only sence oxygen, we know its actually rich from the HC's so the only way the lambda can be so high is if there is more oxygen in the exhaust than there should be, most likely cause for that is one of the cylinders isnt firing and just pumping air through, which would give you high lambda and high HC's, hence the question, was it running on all 6.
Glad to here the car is still alive.I looked at your emissions printout and its harendous.
HC's (hydrocarbons) should be arround 30-50 although the limit is 200, yours are 900+, that means there is bucket loads of unburn fuel in the exhaust. (again overfueling)
But and here's the funny thing, the lambda reading is 1.04, anything above lambda 1 is considered lean normally, but lambda sensor can only sence oxygen, we know its actually rich from the HC's so the only way the lambda can be so high is if there is more oxygen in the exhaust than there should be, most likely cause for that is one of the cylinders isnt firing and just pumping air through, which would give you high lambda and high HC's, hence the question, was it running on all 6.
If you have a misfire on one cylinder your putting 1/6th of all your fuel straigh out the exhaust unburnt, so it does make a big difference. + 1/6th more oxygen than there should be, which will confuse the lambda sensors into thinking the car is lean.
Do you know what was the lambda read out this time. If its more than 1 then the misfire is the likely cause of all the problems. If your sure the misfire is cured, have them check it again.
If it starts to misfire again, and the new plug gets fouled, swap that plugs coil to a different cylinder. If then the different cylinder gets its plug fouled its the coil thats fauly.
If the same cylinder gets fouled there is somthing else wrong, like the injector stuck open or somthing.
If your sure the misfire is cured, then get them to test it again and it should be inspec. But it will never pass that test with a misfire.
Get a print out or right down as much as you can, both at idle and at 2500rpm.
Thanks TT. Before I looked at the spark plugs I plugged one of those ignition lead/coil testers that flash between each coil and their corresponding spark plug. All coils appeared to function properly throughtout most of the rev range. it was only when I started to removed all plugs that I found number 4 to be wet and fouled. Replacing that one for a known good one curesd the missfire.
Back in October when the car had originally failed its MOT (emissions) I was not present with the car. So I had no way of knowing if there was a misfire present.
I've spent the last 6 months doing loads of jobs and had been looking forward to getting the car out on the road again. I was completely gutted with the misfire yesterday however we seem to have fixed it.
I'll keep an eye in that coil also.
Thanks again for your input - looks like you hit the nail on the head all those months ago.
Cheers.
Back in October when the car had originally failed its MOT (emissions) I was not present with the car. So I had no way of knowing if there was a misfire present.
I've spent the last 6 months doing loads of jobs and had been looking forward to getting the car out on the road again. I was completely gutted with the misfire yesterday however we seem to have fixed it.
I'll keep an eye in that coil also.
Thanks again for your input - looks like you hit the nail on the head all those months ago.
Cheers.
Got emissions checked again today with a full set of new plugs. HC level @2500rpm, which was 880ppm last week and over 900 in October is now just 39ppm. Needless to say I'm ecstatic as it's been an exspensive but educational journey. Thanks to everyone who has helped with this issue (and the non start), especially TT, as without you all I'd still be scratching my head.
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