davidimurray
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| posted on 14/3/14 at 01:43 PM |
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Pinto Misfiring
Further to my previous post here -
http://www.locostbuilders.co.uk/viewthread.php?tid=189530
I was wondering what thoughts people had around my misfire?
Car has done 300 mile since being put on the road. Wideband has been on it the whole time and AFR has been good. On the way back from work noticed a
few pops and bangs and noticed that she was running a bit lean.
Checked when i got home and there was a definite rough missfire and the AFR had gone up by about 1.3 throughout the range - i.e. 12.7 to 14 as an
example.
Missfire generally seems to be barely noticeable at idle, quite bad at light throttle openings and less noticeable at higher throttle/rpm.
Car is running megajolt, ZX6r carbs and has always popped on the overrun
Whipped the pilots out, quick spray with carb cleaner no difference.
As per advice I rebalanced the carbs, which were out and it is much better, but still has a missfire.
Put a new set of plugs in and no change.
Have soaked around the inlet manifold and carbs with WD40 and no change in RPM.
Current thought it is it could be exhaust manifold leak?
Any ideas/thoughts much appreciated
[Edited on 14/3/14 by davidimurray]
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zammobhoy
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| posted on 14/3/14 at 03:04 PM |
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Need to find out if it's related to one particular cylinder mate.
Pull of all the plug caps one by one. They will all make a difference but if the misfire is down to one cylinder, when you pull that cap, it will run
evenly on three pots without misfire. If they're all the same then it's a general fueling/ignition thang.
cheers,
Paul.
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ash_hammond
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| posted on 14/3/14 at 05:16 PM |
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These have helped me out in the past when my pinto has developmed a miss fire:
Link
.: www.mac1motorsports.co.uk | www.m1moc.com :.
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gregs
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| posted on 14/3/14 at 05:22 PM |
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Worth checking valve stem seals if it's one cylinder - they can (and did on mine) come up and then leak oil into the cylinder snuffing the
spark.
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ash_hammond
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| posted on 14/3/14 at 05:25 PM |
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quote:
Originally posted by gregs
Worth checking valve stem seals if it's one cylinder - they can (and did on mine) come up and then leak oil into the cylinder snuffing the
spark.
+ 1 mine has done this once.
.: www.mac1motorsports.co.uk | www.m1moc.com :.
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davidimurray
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| posted on 14/3/14 at 05:59 PM |
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quote:
Originally posted by gregs
Worth checking valve stem seals if it's one cylinder - they can (and did on mine) come up and then leak oil into the cylinder snuffing the
spark.
When you say come up I take it you mean raise up the stem away from the head? Would never have thought of that one! Did you get any smoke when that
happened?mine is lovely and clean from the exhaust.
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ash_hammond
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| posted on 14/3/14 at 06:11 PM |
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When mine did it I got smoke on over run and adle.
.: www.mac1motorsports.co.uk | www.m1moc.com :.
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gregs
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| posted on 14/3/14 at 06:53 PM |
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quote:
Originally posted by davidimurray
quote:
Originally posted by gregs
Worth checking valve stem seals if it's one cylinder - they can (and did on mine) come up and then leak oil into the cylinder snuffing the
spark.
When you say come up I take it you mean raise up the stem away from the head? Would never have thought of that one! Did you get any smoke when that
happened?mine is lovely and clean from the exhaust.
Yes - they lift off the head and work up the valve.
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jacko
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| posted on 14/3/14 at 07:06 PM |
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Could it be spark plug leads [HT]
could it be one of the coils breaking down
Valve burnt ? do a compression test
Just a few ideas to think about
Jacko
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old_timbo
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| posted on 14/3/14 at 11:36 PM |
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As I suggested on your other thread I recon you are running too weak at below 2000 rpm and at light throttle openings. My Pinto does similar things
with an AFR much more than 12:1. You can just about get it to idle at 14.7, but it is totally undriveable. I have also discovered it makes things a
lot worse if you run a high octane slow burning fuel like Optimax which is needed for full throttle, high boost etc. when you are trying to avoid det.
Guess it is down to a relatively unsophisticated combustion chamber, designed in the days of leaded petrol, and when fuel economy and emissions
wern't the holy grail they are now.
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davidimurray
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| posted on 15/3/14 at 12:06 PM |
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quote:
Originally posted by old_timbo
As I suggested on your other thread I recon you are running too weak at below 2000 rpm and at light throttle openings. My Pinto does similar things
with an AFR much more than 12:1. You can just about get it to idle at 14.7, but it is totally undriveable. I have also discovered it makes things a
lot worse if you run a high octane slow burning fuel like Optimax which is needed for full throttle, high boost etc. when you are trying to avoid det.
Guess it is down to a relatively unsophisticated combustion chamber, designed in the days of leaded petrol, and when fuel economy and emissions
wern't the holy grail they are now.
Timbo- the car was running around the 12s and did so happily for 300 miles then suddenly started running around the 14s with no changes made to the
car- hence why I suspect there is a problem. I don't want to mess with the fuelling as it was set nicely.
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jacko
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| posted on 15/3/14 at 12:51 PM |
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valve tappets adjustment to tight ?
jacko
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davidimurray
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| posted on 15/3/14 at 02:49 PM |
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Issue seems to be cylinder no 2, couldn't detect an issue pulling the plug leads, but at certain rpm it is spitting back through the carb on no
2 only.
Checked the cam belt hadn't slipped, but all looks OK.
Just been out to get a compression tester so that's the next check.
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rusty nuts
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| posted on 15/3/14 at 04:01 PM |
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Check the valve clearances
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davidimurray
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| posted on 15/3/14 at 05:16 PM |
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Compession a good 13.5 to 14 bar on all cylinders. Time to whip the cam cover off and inspect.
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zammobhoy
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| posted on 15/3/14 at 05:50 PM |
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Have a look in the mouths of the carbs whilst blipping the throttle and make sure that slide on no. 2 is lifting. If not, suspect the diaphragm.
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davidimurray
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| posted on 15/3/14 at 07:38 PM |
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Whipped can cover off. Checked valve clearances and all seemed OK bar cyl 3 and 4 inlets which were a smidge tight, I reset just in case. Also checked
all the stem seals and they were all there and correctly seated.
Fired her up and as expected still misfiring 
All the carb slides are raising properly, inc no 2.
Also tried richening up the carbs at idle to give me an AFR of 12 again and the burble was still there.
Think it might be exhaust off next to check and reseal.
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davidimurray
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| posted on 16/3/14 at 02:03 PM |
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She lives 
Whipped the diaphragm assemblies out of 1 and 2 and noticed that no2 needle was sticking out further than the other. Stripped the needle and found the
spacer washer under the circlip missing. Found one in my box of spares, fitted and all good.
Mystery is how has it been fine since I last touched the carbs 200 miles ago?I can only think I missed refitting it and the circlip has been sat on
the ledge all this time until it dropped down?
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