Discussion
Just a small thing and not a problem as such but I wondered if anyone had experienced something similar. Recently I've noticed when my v8v idles, after a few seconds there is a slight 'thot' sound from the exhaust that punctuates the otherwise smooth hum, not a misfire but a definite momentary change in tone and sound as if the engine just missed a beat and recovered. Any ideas?, there are no active fault codes at present btw.
Jalfonse said:
Just a small thing and not a problem as such but I wondered if anyone had experienced something similar. Recently I've noticed when my v8v idles, after a few seconds there is a slight 'thot' sound from the exhaust that punctuates the otherwise smooth hum, not a misfire but a definite momentary change in tone and sound as if the engine just missed a beat and recovered. Any ideas?, there are no active fault codes at present btw.
Had it sometimes on my V8V and now on my V12V. Sounds like the idle is missing a beat. I think it is just the way the exhaust sounds as the revs stay constant so there is no choking or misfire. Jalfonse said:
Ed50 said:
Lee,
No worries I'll sort it when your round tomorrow night..............I've just found my big hammer....
.
Lol, let's hold back on the 'persuader' (hammer) and I'll go with your other suggestion of emailing Mike at BR the video clip ;-)No worries I'll sort it when your round tomorrow night..............I've just found my big hammer....
.
Went to Bamford Rose yesterday to diagnose the odd popping sound coming out of the tailpipe, I brought some cakes as I was advised this guaranteed good productivity.., nice set of chaps by the way and really helpfull
Down to the problem...
As soon as Bamford Rose team sat in the car and stood around it whilst the engine was at idle, it was clear to them the engine was misfiring and this was cause of the chuffing sound out of tailpipe. I'd came to the same conclusion as I had recently been 'tuning' into the vibrations rather than just the exhaust noice.
So why no emissions light was my question? and why no logged codes when I use my code reader?
Good question said BR, they plugged their diagnostic kit into the car and that too showed no misfire? At this point I started to worry about mechanical resasons for misfire which would have been bad news..
BR explained the reason for no codes was that the car had not been run through the required cycles necessary to learn misfire profile correction (or it had been wiped somehow from the ECU). Apparently the car has to 'coast down' in 6th gear with no electrical load from 70 to 30 mph to learn these adaptions. When complete the misfire detection diagnostic tool will be able to run real time measurement of misfire counts on each cylinder. Basically, once the coast down 'calibrates' a repeatable speed signal the diagnostic can then calculate the expect angular accelerration of the crank from each cylinder firing and look for abnormalities.
Once the diagnostic kit could measure misfire, cylinder 1 showed it was not firing at all, CEL came on, codes were logged and all started to make more sense..blood pressure started to return to normal and cakes were consumed.
The lesson here is that if you are relying on your emissions service light as the 'bible' to tell you if something is wrong, as I was - it won't if the car isn't set up with the necessary adaptive 'coast down' cycles.
BR then did a bit of old fashioned process of elimination detective work to find fault. Was not the spark plugs, although they looked tired and were changed for new ones. Was not coil packs, a coil was swapped from cylinder 1 to 2 and 2 to 1, the misfire stayed with cylinder. The engine was checked for compression and (thankfully) all was good in that respect (all read high and built pressure quickly). Sods law, last thing checked and it was the injector at fault. When the injector was plugged / unplugged, it was possible to feel the electronics 'clicking', but no fuel came out.
I could not believe my luck when BR said the RRP price of injector was only £25! BR had one in stock thanks to them building many race engines so with a few hours labour and a princely £25 for parts, my problem is now fixed.
I now have a V8 again and a bit more understanding of the car.....Result!
Down to the problem...
As soon as Bamford Rose team sat in the car and stood around it whilst the engine was at idle, it was clear to them the engine was misfiring and this was cause of the chuffing sound out of tailpipe. I'd came to the same conclusion as I had recently been 'tuning' into the vibrations rather than just the exhaust noice.
So why no emissions light was my question? and why no logged codes when I use my code reader?
Good question said BR, they plugged their diagnostic kit into the car and that too showed no misfire? At this point I started to worry about mechanical resasons for misfire which would have been bad news..
BR explained the reason for no codes was that the car had not been run through the required cycles necessary to learn misfire profile correction (or it had been wiped somehow from the ECU). Apparently the car has to 'coast down' in 6th gear with no electrical load from 70 to 30 mph to learn these adaptions. When complete the misfire detection diagnostic tool will be able to run real time measurement of misfire counts on each cylinder. Basically, once the coast down 'calibrates' a repeatable speed signal the diagnostic can then calculate the expect angular accelerration of the crank from each cylinder firing and look for abnormalities.
Once the diagnostic kit could measure misfire, cylinder 1 showed it was not firing at all, CEL came on, codes were logged and all started to make more sense..blood pressure started to return to normal and cakes were consumed.
The lesson here is that if you are relying on your emissions service light as the 'bible' to tell you if something is wrong, as I was - it won't if the car isn't set up with the necessary adaptive 'coast down' cycles.
BR then did a bit of old fashioned process of elimination detective work to find fault. Was not the spark plugs, although they looked tired and were changed for new ones. Was not coil packs, a coil was swapped from cylinder 1 to 2 and 2 to 1, the misfire stayed with cylinder. The engine was checked for compression and (thankfully) all was good in that respect (all read high and built pressure quickly). Sods law, last thing checked and it was the injector at fault. When the injector was plugged / unplugged, it was possible to feel the electronics 'clicking', but no fuel came out.
I could not believe my luck when BR said the RRP price of injector was only £25! BR had one in stock thanks to them building many race engines so with a few hours labour and a princely £25 for parts, my problem is now fixed.
I now have a V8 again and a bit more understanding of the car.....Result!
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