What if you crossed your plug wires ?
08-18-2003, 09:56 AM
#1
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What if you crossed your plug wires ?
Just curious... Given that the car is twin plugged, what if you crossed up 2 plug wires on one distributor ? Would the engine management detect it and a warning light come on, would you even feel it ? Not that I did, the car runs smooth as silk since the distr. cap & rotor change, but it got me wondering, as with a twin distributor setup, there would always be one plug firing correctly.. Would you even notice ?
Anyway, I cannot recommend this strongly enough on a car with 45K miles! or less... I still acnnot fathom how on earth my plugs were getting a spark through this crud !
Anyway, I cannot recommend this strongly enough on a car with 45K miles! or less... I still acnnot fathom how on earth my plugs were getting a spark through this crud !
08-18-2003, 02:28 PM
#2
RL Technical Advisor
Hi Greg:
Any offending cylinder with a mis-timed spark from crossed wires will detonate and the knock sensors will crank back the timing far as it can. Its akin to having a broken distributor drive belt.
Now then, if left undetected this can result in a holed piston or some broken rings from detonation that cannot be prevented. The motor will feel rather "soft" if, and when this happens.
Any offending cylinder with a mis-timed spark from crossed wires will detonate and the knock sensors will crank back the timing far as it can. Its akin to having a broken distributor drive belt.
Now then, if left undetected this can result in a holed piston or some broken rings from detonation that cannot be prevented. The motor will feel rather "soft" if, and when this happens.
08-18-2003, 02:31 PM
#3
Whew, I feel lucky that I only have 6 wires instead of 12 wires! 
I must have check my plug wires about 15 times to make sure that I didn't get them crossed up. I was definately paranoid!
I must have check my plug wires about 15 times to make sure that I didn't get them crossed up. I was definately paranoid!
08-18-2003, 02:32 PM
#4
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The engine management could not detect that. Whether you felt it would depend on which ones you swapped. If you picked the cylinder that is 360 degrees out on firing angle it would most likely not be detectable, or at least no more than one plug not firing at all (some ignition systems fire twice per 720 degrees anyway, just means a spark happens on the exhaust stroke).
Re the state of distributor caps, "they're all like that guv". I have 84,000 miles on the original dist caps, rotor arms and plug leads with no problems. The spark erosion process generates particles inside the cap, they make it look dirty but are not a problem unless/until the contamination is so thick that an easier discharge path (than through your spark plug) is generated, that leaves pretty obvious discharge tracks inside the cap. Changing these parts may well be the answer for someone who has idle/misfire problems, but if you don't then it is likely to be unnecessary expense.
Re the state of distributor caps, "they're all like that guv". I have 84,000 miles on the original dist caps, rotor arms and plug leads with no problems. The spark erosion process generates particles inside the cap, they make it look dirty but are not a problem unless/until the contamination is so thick that an easier discharge path (than through your spark plug) is generated, that leaves pretty obvious discharge tracks inside the cap. Changing these parts may well be the answer for someone who has idle/misfire problems, but if you don't then it is likely to be unnecessary expense.
08-18-2003, 08:00 PM
#5
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I'm confused. I think what Greg was asking was what if the two wires from the same cylinder were swapped accidentally and ended up on the wrong distributor. This wouldn't alter the timing right? Don't the two plugs fire simultaneously?
Edward
Edward
08-18-2003, 08:24 PM
#6
RL Technical Advisor
Hi Edward:
If two plug wires (same cylinder) are swapped from one distributor to the other, the overall timing is not altered. Only the source of the spark is changed and since each pair fires simultaneously, its unnoticable.
If two plug wires (same cylinder) are swapped from one distributor to the other, the overall timing is not altered. Only the source of the spark is changed and since each pair fires simultaneously, its unnoticable.
08-19-2003, 01:54 PM
#7
I replaced my caps and rotors last night. I was amazed at the difference they made.
Like John says above, I used to think that dirty caps and rotors are not a problem on high energy ignitions like we have. I was not aware of any idle or misfire problems.
On a previous car, I replaced the cap and rotor at 90,000 miles and didn’t notice a thing. On the 993 I thought maybe, just maybe, I’ll be able to feel some slight difference. But I was proven wrong. I need to drive it some more to be sure, but I think this has made another major improvement to the slow speed bucking problem I’ve complained about so often.
My car has 66,000 miles and I’m pretty sure this is the first time they’ve been changed. They’re gonna get changed during the 30,000 tune-ups from now on.
I ordered them from http://www.bosch-auto-parts.com/ No affiliation. I’ll use them again, that’s for sure. I placed my order on the web on Friday, and they arrived on Monday. Total cost was about $140, tax included and free shipping. They are indistinguishable from the factor parts. In fact, the Bosch part numbers were the same. Well, the box for the rotor said “Bosch number X, replaces Bosch number Y” and my original rotors had Bosch number Y on them. I think the same is true for the caps. I’d have to take that black plastic cover of the new caps to be sure, and that’s not gonna happen.
As far as crossing plug wires, I thought about this as well. I used the “replace the old cap with the new one, and then move the wires from the old cap to the new, one wire at a time” method. The most likely cross-up to occur in this case would be to swap two wires that are next to each other on the cap, as follows. I believe the firing order of our cars is 1-6-2-4-3-5. It would be conceivable that you could pull the wire for plug 2 and replace it on plug 4, and vice versa with plug 4. You probably wouldn’t repeat the exact error on the other cap. This would mean that one plug in two cylinders right next to each other in the firing sequence wouldn’t fire. This is probably the case that Steve mentions, the case that would cause detonation. It would be in two cylinders in a row. Timing would be cranked back and I’d think the car would idle pretty lumpy. I think you’d feel this immediately.
Now on the other hand if you swapped a wire for an intake plug with an exhaust plug, e.g. plug 4 from one cap to plug 4 on the other cap, I don’t think it would matter.
Tom
’95 993
Like John says above, I used to think that dirty caps and rotors are not a problem on high energy ignitions like we have. I was not aware of any idle or misfire problems.
On a previous car, I replaced the cap and rotor at 90,000 miles and didn’t notice a thing. On the 993 I thought maybe, just maybe, I’ll be able to feel some slight difference. But I was proven wrong. I need to drive it some more to be sure, but I think this has made another major improvement to the slow speed bucking problem I’ve complained about so often.
My car has 66,000 miles and I’m pretty sure this is the first time they’ve been changed. They’re gonna get changed during the 30,000 tune-ups from now on.
I ordered them from http://www.bosch-auto-parts.com/ No affiliation. I’ll use them again, that’s for sure. I placed my order on the web on Friday, and they arrived on Monday. Total cost was about $140, tax included and free shipping. They are indistinguishable from the factor parts. In fact, the Bosch part numbers were the same. Well, the box for the rotor said “Bosch number X, replaces Bosch number Y” and my original rotors had Bosch number Y on them. I think the same is true for the caps. I’d have to take that black plastic cover of the new caps to be sure, and that’s not gonna happen.
As far as crossing plug wires, I thought about this as well. I used the “replace the old cap with the new one, and then move the wires from the old cap to the new, one wire at a time” method. The most likely cross-up to occur in this case would be to swap two wires that are next to each other on the cap, as follows. I believe the firing order of our cars is 1-6-2-4-3-5. It would be conceivable that you could pull the wire for plug 2 and replace it on plug 4, and vice versa with plug 4. You probably wouldn’t repeat the exact error on the other cap. This would mean that one plug in two cylinders right next to each other in the firing sequence wouldn’t fire. This is probably the case that Steve mentions, the case that would cause detonation. It would be in two cylinders in a row. Timing would be cranked back and I’d think the car would idle pretty lumpy. I think you’d feel this immediately.
Now on the other hand if you swapped a wire for an intake plug with an exhaust plug, e.g. plug 4 from one cap to plug 4 on the other cap, I don’t think it would matter.
Tom
’95 993
Last edited by tom_993; 08-19-2003 at 02:52 PM.
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08-19-2003, 03:02 PM
#9
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Yeah, my question was not about crossing wires between distributors, that would be pretty impossible to do if you did them one at a time, like I did.
I had a doubt for a moment about 2 wires (on the same cap) that I disconnected to reach the stripped bottom screw- before I marked them with the corresponding cylinder #s... But the shape, bend and length of the wire sort of indicated the most likely target. I thought I'd ask anyway, but the engine definitely runs smoothly and powerfully so I think I am allright...
IMHO, it would not cost anything to mold a cylinder # on the plug connectors just like it's done ont he caps, that would eliminate any errors!
no idea how you guys do the 2 caps and pluck the wires one by one, there was no way I had enough give in my wires to move the cap still attached !
On the usefulness of replacing the caps, I am no professional (in fact, as Bozo, I am the opposite) and therefore will not argue with the above. All I can say if take a look at my caps and look at the traces of arcing on the inside.... Almost like a screwdriver gouge... All I know is that my car had 45K on that set of caps and rotors, the rotor itself was very used...and now my idle is noticeably smoother with the 2 new caps. Trust me, i got RS mounts, I can feel my idle pretty good ! ;-)
It did not go from a tractor to a waterbed either, but it's smoother... For the money and admittedly the feel good factor, I figure it was worth doing, considering I will do the plugs soon - might as well have both ends taken care of...
I had a doubt for a moment about 2 wires (on the same cap) that I disconnected to reach the stripped bottom screw- before I marked them with the corresponding cylinder #s... But the shape, bend and length of the wire sort of indicated the most likely target. I thought I'd ask anyway, but the engine definitely runs smoothly and powerfully so I think I am allright...
IMHO, it would not cost anything to mold a cylinder # on the plug connectors just like it's done ont he caps, that would eliminate any errors!
no idea how you guys do the 2 caps and pluck the wires one by one, there was no way I had enough give in my wires to move the cap still attached !
On the usefulness of replacing the caps, I am no professional (in fact, as Bozo, I am the opposite) and therefore will not argue with the above. All I can say if take a look at my caps and look at the traces of arcing on the inside.... Almost like a screwdriver gouge... All I know is that my car had 45K on that set of caps and rotors, the rotor itself was very used...and now my idle is noticeably smoother with the 2 new caps. Trust me, i got RS mounts, I can feel my idle pretty good ! ;-)
It did not go from a tractor to a waterbed either, but it's smoother... For the money and admittedly the feel good factor, I figure it was worth doing, considering I will do the plugs soon - might as well have both ends taken care of...
08-19-2003, 03:14 PM
#10
Greg,
I think the plug number is written on the wires, but sometimes it's way back up the wire, or on the wrong side, and you can't see it. The intake and exhaust are distinguished with I and II, e.g I-4 and II-4. I don't recall which is which. Yes, a better location would be the connector.
Tom
'95 993
I think the plug number is written on the wires, but sometimes it's way back up the wire, or on the wrong side, and you can't see it. The intake and exhaust are distinguished with I and II, e.g I-4 and II-4. I don't recall which is which. Yes, a better location would be the connector.
Tom
'95 993
08-19-2003, 03:34 PM
#11
Burning Brakes
Actually it's very easy to check the correcness of wires. Just run shortly on first or second coil only. The coil with incorrect wiring will be easily identified.
