Moorron
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 posted on 22/9/08 at 09:15 AM |
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misfire help
Argh will it never end.
Someone please give us some tips on this problem I have.
Rebuilt engine and ran it on the road for 50 miles, everything was fine even when I got stuck in traffic, put the car away and on Sunday (2 days
later) started it up and let it warm up on the drive. After about 2 minutes the idle changed and sounded like it was running on 3 cylinders so I
thought I would take it up the road and see if it clears. 2 miles later and it was still there so I took it back home to check some things over,
cylinder number 3 was not working as taking the plug lead off did nothing so I removed the plug and I could see it was dry black not like the other 3
which were the normal light brown. I turned the car over with the plug in its lead and earthed to the chassis and couldn’t see a spark. I thought the
coil had gone but it has 2 coils which 2 cylinder share and the other cylinder is fine. Checked the lead and this is also fine.
After a few tries it suddenly ran fine, took it up the road and it was ok for about 1 mile. Then it came back, so I drove round a mates to see what he
thought. When I tried to start it up to show him as soon as I flicked the starter the dash lost all power, tried it again and as soon as I flicked the
started it did it again. This time I turned the head lights on and this caused power loss so when I tried to draw some amps it cut the power. now i am
right in thinking are the 2 related? It was like an earth or contact problem so I need to check all wiring from the battery, but I would like to know
if the engine would run on 3 cylinders if there was an earth or weak contact and thus limiting the power to the coils?
When driving at a constant speed the engine hunts like the misfire is intermittent. Other possible info that might help, I checked the compression and
all is fine, I drained the carbs to see if fuel was in them and this is also fine.
ideas?
Sorry about my spelling, im an engineer and only work in numbers.
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Moorron
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| posted on 22/9/08 at 09:42 AM |
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sorry for the repeat posts, the works pc is pap.
Sorry about my spelling, im an engineer and only work in numbers.
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adithorp
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| posted on 22/9/08 at 12:01 PM |
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2 problems don't sound related to me.
If it was earth/bad connection related then you'd expect generally effect all, not just one cylinder. How did you check the leads? Try swapping
leads to to another cylinder and if the missfire moves its the lead. If not it's probably the coil (yes, they can still fire on one and not the
other) or the plug. Have you tried another plug?
adrian
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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Moorron
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| posted on 22/9/08 at 01:05 PM |
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Hi, i took the lead off and measure its resistance and compaired it to a good working one.
No it did change the plug, i will try this tonight and see if the problem moves cylinder.
£50 for a new coil ...ouch!
Sorry about my spelling, im an engineer and only work in numbers.
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Moorron
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| posted on 23/9/08 at 07:48 AM |
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Just an update on this which has got me confused and I thought I knew a bit about wiring too.
With the ignition turned off if I turn the headlights on they work fine, use the flash button to get main beam on and as soon as I touch the switch
the car looses power. With a volt meter on the battery the volts drop from 12.5 to 5. If I leave the button down it stays at 5 volts, if I let go the
lights slowly come back up from a very dim light. IF I flick the lights off and on again they work at full until I hit the flash again. But its not
the lights, if turn them off and switch on the ignition all works fine, I can hear the fuel pump working and my dash lights up, if I then try to start
the car as soon as I flick the toggle starts switch all power goes off again and the fuel pump slowly turns and creeps back upto speed over about 10
seconds. If I flick the ignition off and on it suddenly goes back to normal.
I have checked the earths around the car = did nothing
I have unplugged the dash to remove any question of the wiring for the dash = did nothing
I have unplugged the alternator = did nothing
I have unplugged the front and rear loom and dash = nothing
Battery is fine and to remove any other strange problem I have connected my jump start batter across it and still nothing.
Now I am starting to scratch me head as i am lost. Why would drawing a lot of amps cause a sudden sharp drop in power just like a short would, yet no
fuses are blowing, no wires heating up and no smoke!
I am using a bike engine so the main power lead enters the car and goes to the remote starter solenoid, here it goes into the bike loom and also goes
off into the car loom and fuse box. With the starter lead disconnected from this solenoid you can here it click when the starter switch is press and
power remains fine, even with the lights on????
Is it the starter? How can this affect anything when the starter switch is left off?
Is it the solenoid?
Sorry about my spelling, im an engineer and only work in numbers.
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Spyderman
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| posted on 23/9/08 at 11:07 AM |
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Where are you testing the voltage from?
Try it at the battery when doing the load tests. If it is still dropping then it has to be a bad cell on the battery. If not then move the test point
further away from battery until you find the drain point.
Don't just assume the battery is fine, they can fail at any time and in many ways.
Battery problems can cause many seemingly unrelated symptoms.
If this doesn't help then just test everything in sequence and try not to assume any part is OK until proven.
As you are finding electrical problems can be very frustrating and time consuming.
Good luck!
Spyderman
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Moorron
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| posted on 23/9/08 at 12:31 PM |
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Hi, im taking the reading from the battery posts. I have bypassed the battery with my starter battery and it does the same so its not the battery im
very sure.
Im going to check the wiring to the ignition switch tonight and also the bike solinoid and bypass both to see what happens. Whats got me confused is i
have never seen a battery be dragged down to 5 volts and not have some smoke. To drop a 38AH battery to 5 volts it must be drawing a silly amount of
amps yet the cables are cool?
Sorry about my spelling, im an engineer and only work in numbers.
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