Coil-on-plug advantage

[rationull]

Originally Posted By: TallPaul
There are some advantages, but on the whole I think they suck (there is a T-shirt that says "Front Wheel Drive Sucks and shows a picture of a tricycle--hahaha). But on balance I feel the consumers were sold a bill of goods by the manufacturers and the auto media. Notice the really nice muscle cars are RWD like Mustang and Corvette.


Yeah I've seen that shirt, pretty good. Honestly though, for most consumers who don't push their cars to their handling limits it really doesn't make that much difference. For those applications IMO an easier to assemble, more lightweight drive train is superior. Ideally "easier to assemble" would translate to "cheaper for the customer" but whether or not that's the case really isn't about FWD vs RWD anyway. Of course there are also maintenance headaches related to bigger V6 engines set up for FWD in cars with tight engine bays but that's really a different packaging problem I think.

Now this isn't saying anything about the performance market, and of course most muscle cars and sports cars should continue to be RWD, because presumably the purchasers intend to have some fun with them. I'm looking forward to the next few years when hopefully all the new small RWD coupes that have been talked about for years will actually be built. Hyundai's Genesis Coupe looks promising and I'm looking forward to getting some details on the Toyota/Subaru combined venture and the alleged Nissan 240sx successor. I just wish Honda would make one too but the CR-Z is supposed to be FWD.

 

[mpvue]

FWD is what most people need (but don't know it): good traction, lightweight, economical, more interior room.
don't bother mentioning mustang/corvette/any other high perf RWD car as proof of superiority; different needs/wants/requirements. a minivan is a better people mover than a 2/4 seater RWD performance car.
however, I qualify that by saying that there are bad parts to FWD: timing belt change and CV joints being the standout problems.
as for coil on plug: it's simple. less parts. more accurate timing, no wasted spark.

 

[javacontour]

Originally Posted By: rationull
Originally Posted By: exranger06
Originally Posted By: Rabbler

Greater reliability.

Gonna have to disagree with you there. I work for Napa and we sell a lot of ignition coils for Ford vehicles with COP systems.


But when one of the coils fails, you still get spark in your other cylinders. If a manufacturer chooses to use cheaper coils for COP systems then sure, they'll fail more but with equal quality parts it seems like COP systems (or really 1 coil per cylinder no matter where it's mounted) would be statistically less likely to suffer complete failure.


The more parts you add to a system, the lower the MTBF of the system. So while the failure of a single coil may not leave you on the side of the road, more coils means more frequent repair, not less.

Of course if failure is measured in 100's of thousands of miles, it may not matter to the average consumer.

http://www.techworld.com/opsys/features/index.cfm?featureid=1944

The same would be true for coils. Say the coils have a MTBF of 1 million hours.

If you had 250K cars, each with four coils, or a million coils in the marketplace, you would expect to replace a coil for every hour of vehicle operation. If the typical car travels 12K miles/year or about 200 hours of operation, or 800 coil operation hours/year for each car, then one would expect 200 coils will fail over the course of a year in that population of 250K cars.

It's not my vehicle will go a million hours before a failure.

The question is, in any given hour, is my car going to be the one that has a coil failure? The odds are low, but even lower if I have only one coil that has the same MTBF.

 

[javacontour]

Oh, and the odds are every one of the 200 failures will be on an enthusiast forum telling the other 249,800 owners that their cars are crud, LOL

 

[rationull]

Understood about MTBF and the fact that more coils means more frequent repair. But I think the earlier point still stands that the system as a whole can be more reliable when you've got more coils. With a single coil feed a distributor, when that coil goes you're stranded. With a coil per cylinder, when a single coil goes you can most likely still drive (although particularly if you're talking about a 4 banger, the drive might be pretty rough).

 

[Rabbler]

Originally Posted By: rationull


But when one of the coils fails, you still get spark in your other cylinders.


That was my point, a single failure only effects 1 cylinder as with a single coil system if the 1 and only coil fails, while they your walkin' home.

I didn't mean to infer that a COP system was of superior quality.

On a side note most of the coils I have replaced were damaged by faulty engine controllers or improper servicing (cracked housings)

 

[meep]

It's been 21 years since I rebuilt my first V8 myself. Assembled my first small (tecumseh) engine from parts 24 years ago. In those 24 years, I have encountered _1_ automotive single-coil coil that went bad (VW bug) and _1_ single coil magneto ignition that went bad.

A single Lincoln LS I've known lost 3 of 6 in its first couple years of life.

CPs are a common failure item on BMWs per MSN-auto's reliability ratings. CPs seem to be damaged on a number of engines when oil leaks into them from valvecover gasket failures. I certainly hear of a lot more COP failures today than single coil failures yesterday.

BUT, my COP jeep drives great, gets good mpg for what it is, and if it can help emissions, GREAT. I want my individual coil packs. Wasted spark is OK too!

M

 

[javacontour]

I think in the past 5 or so years, VW had some coil issues.

I wasn't saying it was bad. I was just saying more parts increases your odds of needing a repair. That's all.

 

[SHOZ]

Ford misfire detection comes from calculating engine speed difference between cylinders via the CPS sensor. As they use the PCM to trigger the coils through the ground circuit and all the COPs have a common B+ source there is little that can be told from the electrical signal

 

[PandaBear]

Originally Posted By: javacontour
I think in the past 5 or so years, VW had some coil issues.

I wasn't saying it was bad. I was just saying more parts increases your odds of needing a repair. That's all.


That makes a big assumption that the parts you need to use and the parts you provided are the same qualities and have the same statistical reliability rating.

MTBF represent infant mortality (new units), not long term durability. A distributor coil that needs to last 200k miles and fire 4x as fast (for a 4 cylinders) will be different than the coils used to last 200k miles and fire 1/4 the speed. When you need to lower the design spec, it could be cheaper than 1/4 of the original. Of course, if a manufacture cuts corner you end up getting poo poo parts in either case.

 

[Kestas]

Interestingly, my 18-year-old Marquis has a single ignition coil and an EEC-IV with self diagnostics to determine which cylinder isn't firing (no need for a scanner). The only advantage with a COP over my setup is that self diagnostics can tell whether misfire is from the ignition or fuel injector.

 

[brianl703]

Originally Posted By: rationull
With a coil per cylinder, when a single coil goes you can most likely still drive


That would be pretty bad for the catalytic converter.

 

[brianl703]

Originally Posted By: Kestas
Interestingly, my 18-year-old Marquis has a single ignition coil and an EEC-IV with self diagnostics to determine which cylinder isn't firing (no need for a scanner). The only advantage with a COP over my setup is that self diagnostics can tell whether misfire is from the ignition or fuel injector.


With EEC-IV..on my 1988 Mustang GT..there's an "ignition diagnostic monitor" (IDM) connection from the coil primary to the EEC-IV unit. EEC-IV can determine if the coil isn't firing when it's supposed to be. (Usually that would be due to a failure with the TFI-IV module).

 

[rationull]

Originally Posted By: brianl703
Originally Posted By: rationull
With a coil per cylinder, when a single coil goes you can most likely still drive


That would be pretty bad for the catalytic converter.


Maybe. I thought about that too but I wonder if the PCM would shut off fuel to the misfiring cylinder if it detected the coil was bad, in order to protect the cat. That would be logical given the required warranties on emissions equipment. I'm not sure if it works like that, though. If I remember I'll take a look through my car's FSM when I get home and see if it says anything about it.

In any case I'd rather be able to choose to sacrifice the cat and get where I'm going than not have the choice.

 

[Rabbler]

Originally Posted By: brianl703
Originally Posted By: rationull
With a coil per cylinder, when a single coil goes you can most likely still drive


That would be pretty bad for the catalytic converter.


Better to drop only 1 cylinder than say 2 cyl on a waste spark system.

A COP coil is also required to produce more than 4x the voltage compared to an older single coil system. That could account for increased failure.

 

[rationull]

Originally Posted By: Rabbler

A COP coil is also required to produce more than 4x the voltage compared to an older single coil system. That could account for increased failure.


Why's that?

 

[OVERKILL]

Originally Posted By: Kestas
Interestingly, my 18-year-old Marquis has a single ignition coil and an EEC-IV with self diagnostics to determine which cylinder isn't firing (no need for a scanner). The only advantage with a COP over my setup is that self diagnostics can tell whether misfire is from the ignition or fuel injector.


Yup, the 'ol cylinder balance test. EEC-IV was a very advanced system for it's time. That's why the MAF implementation (A9x ECM's primarily) is still so popular and there are a number of chips and tuners (twEECer for example) available to work with it.

 

[Rabbler]

Originally Posted By: rationull
Originally Posted By: Rabbler

A COP coil is also required to produce more than 4x the voltage compared to an older single coil system. That could account for increased failure.


Why's that?


I believe it's for emissions. While you certainly don't need 80,000 volts to light the A/F mixture that voltage potential greatly reduces the chance of an ignition related misfire. With these premium long life spark plugs and low quality fuels I doubt an engine would be running very well after 80k with an older round coil conventional ignition system.

 

[Jim 5]

Originally Posted By: rationull
Originally Posted By: brianl703
Originally Posted By: rationull
With a coil per cylinder, when a single coil goes you can most likely still drive


That would be pretty bad for the catalytic converter.


Maybe. I thought about that too but I wonder if the PCM would shut off fuel to the misfiring cylinder if it detected the coil was bad, in order to protect the cat. That would be logical given the required warranties on emissions equipment. I'm not sure if it works like that, though. If I remember I'll take a look through my car's FSM when I get home and see if it says anything about it.

In any case I'd rather be able to choose to sacrifice the cat and get where I'm going than not have the choice.


I had a failed ignition coil on my BMW, and I didn't run it like that for more than 30 seconds. I had a number of concerns. Catalyst, wear from fuel wash on the cylinder wall, and fuel dilution. I later found out in my bentley service manual that the computer on this car shuts fuel off to the cylinder in which the ignition coil has failed.

In short, I could have driven it to the dealership for a replacement with little to no adverse effects. Not knowing this, I had it loaded up on a flatbed and taken to the dealer. It was not on my dime anyway as the repair was under warranty.

 

[mechtech2]

I am not a big fan of COP systems, but they DO eliminate spark plug wires. This eliminates a big cause of misfires down the road.