Hi,
I've got two OEM ignition wire sets for my M30B35 engine at the moment. I removed the first one from my Shark and I think it's been in use since 1988 when the car was made. The other set is unused, but has been sitting in storage since 1987.
I measured the resistances of the wires:
ORIGINAL WIRE SET (kOhm) UNUSED WIRE SET (kOhm)
Lead 1 5,49 6,07
Lead 2 5,98 6,06
Lead 3 5,60 6,06
Lead 4 5,95 5,94
Lead 5 5,77 6,04
Lead 6 6,00 5,98
Average: 5,80 6,03
The average resistance of the original wire set is lower than that of the unused wires. But the original is also more "uneven" when it comes to the difference between the highest and the lowest resistances of the leads (9,29% versus 2,19% with the unused wires). Does this affect anything?
Which set would you guys use, or are the differences so small that it's all the same? And what is the specific resistance of my engine that the leads SHOULD have?
Thanks!
- KNude
Ignition wire sets, which one should I use?
Moderators: GRNSHRK, ron, bfons
Ignition wire sets, which one should I use?
1988 635CSiA
You can't ignore my techno.
You can't ignore my techno.
If I was to decide, I would continue running the original set, and keep the unused (new) one in the garage as a spare.
I believe you will hardly (if at all) find a new set of wires which fit perfectly and have the same quality as your unused 1987 set.
Although the original set shows a bit its age, the resistance is quite consistent and I don't believe it has any negative impact. However, if the engine misfires (due to the ignition wires), or there are other signs of a failed ignition wire set, then the story is different.
I believe you will hardly (if at all) find a new set of wires which fit perfectly and have the same quality as your unused 1987 set.
Although the original set shows a bit its age, the resistance is quite consistent and I don't believe it has any negative impact. However, if the engine misfires (due to the ignition wires), or there are other signs of a failed ignition wire set, then the story is different.
'94 E32 730i, M30B30
'06 E86 Z4M (sold)
'86 E28 535i, Euro (sold)
'06 E86 Z4M (sold)
'86 E28 535i, Euro (sold)
Thanks for the input! I'll do as you suggested and continue using the original wires.
By the way, I measured the resistances of my ignition coil. The resistance between terminals 15 and 4 was a little under 6000 Ohms, so according to this site it should be OK: http://www.hiperformancestore.com/Motronic.htm
However, the resistance between terminals 1 and 15 was about 1,1 Ohms, which is more than twice the 0,5 ohms it apparently should be.
Could this cause the engine to run unevenly? It now seems to be running a bit rough, which is especially obvious when idling. The engine shakes the car about once every second or every two seconds. It's not too bad but noticeable. I've just adjusted the valves and installed a new cap, rotor and new spark plugs (NGK ZGR5A).
By the way, I measured the resistances of my ignition coil. The resistance between terminals 15 and 4 was a little under 6000 Ohms, so according to this site it should be OK: http://www.hiperformancestore.com/Motronic.htm
However, the resistance between terminals 1 and 15 was about 1,1 Ohms, which is more than twice the 0,5 ohms it apparently should be.
Could this cause the engine to run unevenly? It now seems to be running a bit rough, which is especially obvious when idling. The engine shakes the car about once every second or every two seconds. It's not too bad but noticeable. I've just adjusted the valves and installed a new cap, rotor and new spark plugs (NGK ZGR5A).
1988 635CSiA
You can't ignore my techno.
You can't ignore my techno.
well probably you will measure around 0.6 ohms if you just touch your ohm-meter connections together. So you should allow for that when taking readings of low resistance components. You should also try and allow of the contact resistance onto the component being measured, so arguably touching both leads onto the same contact on the test part gives a more accurate 'zero' reading.
Re the plug lead resistance; IIRC the resistors are in the plug caps. Your readings are well within spec.
What will throw the ignition system out of kilter is not the resistance per se, it is the breakdown voltage of the leads. You can't test for this but you can see if a mysterious misfire changes when you move the leads around (out of the plastic tube) or when you change plug leads.
If the leads are breaking down very badly, you will be able to see it happening if you look carefully when it is dark. Don't worry about a little corona discharge, that is normal; worry about obvious sparks, especially if they coincide with dark marks on the insulation.
cheers
Re the plug lead resistance; IIRC the resistors are in the plug caps. Your readings are well within spec.
What will throw the ignition system out of kilter is not the resistance per se, it is the breakdown voltage of the leads. You can't test for this but you can see if a mysterious misfire changes when you move the leads around (out of the plastic tube) or when you change plug leads.
If the leads are breaking down very badly, you will be able to see it happening if you look carefully when it is dark. Don't worry about a little corona discharge, that is normal; worry about obvious sparks, especially if they coincide with dark marks on the insulation.
cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~