5 replies to this topic

[adcyork]

Right i've got a misfire problem with my 998 Stage 1 on cylinders 1 and 2.
It's most noticable below 2K RPM but does happen further up the rev range at very small throttle operations. If i floor the accelerator as its misfiring it smooths out and runs fine. This makes it very hard to just take it easy and save fuel as i have to be accelerating with the throttle pressed quite far just to make it run smooth.

The car has a lumenition electronic ignition inside the standard 59d dizzy, which i've timed up to 14 degrees BTDC according to the marks on the timing case as this was just before it started pinking.
I've changed the dizzy cap and rotor arm
Done a compression test and all cylinders were between 145 and 155psi and 175 and 185psi on the wet test.
Changed the plugs and gapped them at 0.68mm due to the lumenition kit.
Checked the lumenition HT leads and they are fine and leads 1 and 2 work fine on cylinders 3 and 4 so there's no problems there.
Checked for air leaks around the inlet and exhaust and the gaskets are sealed fine.
The coil is fairly old but i assume the problem doesn't lie with that as it runs fine on 3 and 4?

Something i have noticed is that the rev clock bounces which i know indicates an electrical fault but where does it lie?

Can anybody help me with this as i'm stumped

Edited by adcyork, 19 May 2008 - 12:40 PM.

[dklawson]

You've done a good job of summarizing what you've tried so far and it all makes sense. Please elaborate a bit on how you determined the misfire was/is on 1 & 2.

The tach bounce probably does indicate a problem with the low tension side of the ignition system. I don't know Lumenition so I can only make some general comments and suggestions. Most electronic ignition modules only have two wires exiting the distributor. They use the distributor housing as their ground/earth connection. On the 23/25 and 45 series distributors there is a high-flex ground/earth wire inside the dizzy that goes between the breaker plate and the dizzy housing. If that's missing, your coil current has to pass through the breaker plate bearing. This can lead to various ignition problems. Presumably the 59 series dizzys would have this also, so make sure that wire is in place and not broken (give it a gentle tug to check). I also remember an acquaintance who found that the crimp terminals supplied with his Lumenition unit gave him problems. He had a misfire problem that miraculously went away when he crimped new terminals onto the end of the module's wires.

Lastly, if you still have points to fit your distributor, reinstall them at least long enough for you to drive the car and see if the problem goes away. If the car runs well with the points you can assume there is something wrong internal to the electronic ignition module.

[adcyork]

Thanks for the answer dk. I've pinned it down to cylinders 1 and 2 by taking the plug leads off while it's idling and removing cylinder 1 or 2 plug lead or even both at the same time makes absolutely no difference to way the engine runs. Whereas removing either 3 or 4 almost immediatley stalls the engine.

I did put the earth wire back into the dizzy when i installed the EI kit and it was fine.

You say you're not familiar with the lumenition kit but there is a disc that fits over the dizzy cam which has 4 magnets on. The only thing i can think of is that causing the problems. Maybe magnets 1 and 2 aren't strong enough to activate the switch in the module and cause a sprak at the plug?

I don't know how likely that is though???

In fact now i think about it, i had this same problem intermitently with the points and condenser set up so i'm doubting wether it is at all related to the lumenition kit. The condenser used to blow quite frequently aswell. I don't know if that indicates anything as i could work out why they blew all the time.

I haven't got my points and condenser set up anymore because they were past it and got thrown away so i can't check to be sure now.

can you help me any further at all?

Edited by adcyork, 20 May 2008 - 01:41 PM.

[Ethel]

Swap your plug leads round to see if they're at fault, you could rotate the magnet on the dizzy shaft to eliminate any problem there. Could there be a manifold air leak since it's on one inlet port?

[dklawson]

plug leads off while it's idling and removing cylinder 1 or 2 plug lead or even both at the same time makes absolutely no difference to way the engine runs. Whereas removing either 3 or 4 almost immediatley stalls the engine.

disc that fits over the dizzy cam which has 4 magnets on. Maybe magnets 1 and 2 aren't strong enough to activate the switch in the module and cause a sprak at the plug?

i had this same problem intermitently with the points and condenser set up so i'm doubting wether it is at all related to the lumenition kit.

There is an additional electrical test you can try but I since you now remember that this problem happened with points it may not make any difference. Take the dizzy cap off and put a paint mark on the Lumenition magnet sleeve so you know where it was intstalled before. Remove the magnet sleeve, turn it 180 degrees and put it back on the dizzy cam. Repeat your spark plug test to see what cylinders are affected. If the problem is related to the Lumenition kit (more specifically its magnet sleeve) the problem should move to cylinders 3 & 4. The Pertronix/Aldon Ignitor module has been known to have occasional problems with their magnet sleeves. There's no reason to think Lumenition would be immune from this problem.

If the problem remains on 1 & 2, it may not be electrical at all. For example... do you have dual carbs? It could be that you've got a serious problem with the front carb and cylinders 1 & 2 are barely getting enough charge at idle to run.

[adcyork]

Swap your plug leads round to see if they're at fault, you could rotate the magnet on the dizzy shaft to eliminate any problem there. Could there be a manifold air leak since it's on one inlet port?

As i said in my first post: i have checked the leads like that and they're fine and there isn't any air leaks. I checked by spraying carb cleaner round the manifold. Am i right in thinking that an air leak would affect all 4 cylinders though?

There is an additional electrical test you can try but I since you now remember that this problem happened with points it may not make any difference. Take the dizzy cap off and put a paint mark on the Lumenition magnet sleeve so you know where it was intstalled before. Remove the magnet sleeve, turn it 180 degrees and put it back on the dizzy cam. Repeat your spark plug test to see what cylinders are affected. If the problem is related to the Lumenition kit (more specifically its magnet sleeve) the problem should move to cylinders 3 & 4. The Pertronix/Aldon Ignitor module has been known to have occasional problems with their magnet sleeves. There's no reason to think Lumenition would be immune from this problem.

If the problem remains on 1 & 2, it may not be electrical at all. For example... do you have dual carbs? It could be that you've got a serious problem with the front carb and cylinders 1 & 2 are barely getting enough charge at idle to run.

i'll have a go at that tomorrow and see what i find. I'm running a single HS4 so no twin carb problems.