Another misfire thread (sorry!)
Discussion
Ok - enjoyed reading all the misfire threads, but want one of my own now!
Have been using the Griff regularly since February after 12 week lay up. Most of the time its great but suffered nasty misfire a few weeks ago (sorted with new HT leads). Have noticed since an intermittent misfire - just now and again, very slight but enough to make me wary...
No real pattern, happens at different revs, sometimes when warm/hot sometimes on startup.
Changing the crispy old HT leads definitely made the major problem go away, at the same time I did the rotor arm, amp and distributor cap (all looked a bit past it anyway). Plenty of fuel pressure, all LT and HT connections solid as far as I can tell.
Busy busy at work so time at a premium (and too mean to pay a garage), so... Before I pull the plugs I had a thought;
I can borrow one of those fancy laser/IR thermometers from work. If I got a temperature reading from each exhaust port, presumably the misfiring cylinder should be cooler than the rest, thus narrowing down the search.
Anyone tried this?
Of course, the other thought was that I might have fouled up the plugs driving home with the original misfire problem and I should stop being a lazy git and change the plugs anyway. This would however deny me the chance to play with a new gadget, plus I'd really like to see just how hot the manifolds get!!!
Have been using the Griff regularly since February after 12 week lay up. Most of the time its great but suffered nasty misfire a few weeks ago (sorted with new HT leads). Have noticed since an intermittent misfire - just now and again, very slight but enough to make me wary...
No real pattern, happens at different revs, sometimes when warm/hot sometimes on startup.
Changing the crispy old HT leads definitely made the major problem go away, at the same time I did the rotor arm, amp and distributor cap (all looked a bit past it anyway). Plenty of fuel pressure, all LT and HT connections solid as far as I can tell.
Busy busy at work so time at a premium (and too mean to pay a garage), so... Before I pull the plugs I had a thought;
I can borrow one of those fancy laser/IR thermometers from work. If I got a temperature reading from each exhaust port, presumably the misfiring cylinder should be cooler than the rest, thus narrowing down the search.
Anyone tried this?
Of course, the other thought was that I might have fouled up the plugs driving home with the original misfire problem and I should stop being a lazy git and change the plugs anyway. This would however deny me the chance to play with a new gadget, plus I'd really like to see just how hot the manifolds get!!!
Yes it should give you a clue however how hot does your gadget read ? If you spent a lot on it you will probably be ok however if you were a cheapskate the manifolds will fairly quickly get beyond the range it will measure. Also it is difficult to get a consistent reading because the exposed area of pipe differs between each cylinder.
...see your point - the gadget isn't mine it'll be borrowed, its industrial spec and goes from -20 to +500 deg c with a stated accuracy of +/-2% range so it aint going to be particularly accurate at the sort of temps we'll be seeing and I guess it'll be off scale fairly quickly. Hadn't thought about the variation between manifold pipes, suppose I could minimise the effect by measuring at the same point, (joint between the pipe and the flange..?) but thermodynamics was never my strongest subject!
- time for some experimenting.
- time for some experimenting.
Sorted! Number 8 cylinder ht lead (brand new) not making a connection at dizzy cap. Adjusted the internals with long nose pliers, job done.
Temperature probe was fun to play with but went off scale within 5 mins once I started running up and down the revs!
Narrowed the misfire down by unplugging leads one at a time and seeing which one made no difference.
Slightly worryingly I've now found 3 very similar set screws on the floor under the car, but can't see where they're from...
Suppose I'd better take a photo and start a new thread!
Thanks for the help all.
Temperature probe was fun to play with but went off scale within 5 mins once I started running up and down the revs!
Narrowed the misfire down by unplugging leads one at a time and seeing which one made no difference.
Slightly worryingly I've now found 3 very similar set screws on the floor under the car, but can't see where they're from...
Suppose I'd better take a photo and start a new thread!
Thanks for the help all.
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