HT4100 4.1, 4.5, 4.9 Discussion, Question about spark plugs! in Cadillac Engine Technical Discussion; I was thinking about changing out my plugs and wires since I dont know when they were last changed. I ...
Automobile(s): Ex:'92 ETC 4.9 Current:'91 Sedan Deville 4.9
Question about spark plugs!
I was thinking about changing out my plugs and wires since I dont know when they were last changed. I put 13,000 on this car since I bought it.
It doesnt hesitate, stall or misfire so am I good for a while or should I replace them anyway?
Also if anyone does recommend replacing them, I dont want to buy any uneccessary tools, so what exactly do I need to do the job(sockets, extensions, pivots, etc)
If it runs good I would just leave it alone. You could remove just one plug that is easy to access to check it for condition to see if it looks really old or worn. Usually you will do more damage trying to remove the plug boots, though, than you could prevent so I would just drive it unless there is an obvious problem. Plug wires and plugs are not the sort of thing that just fail without warning so you can usually predict, based on driveability, when they need attention.
If you want to check the condition of the wires park in a dark place at night, open the hood with the engine idling and warm and mist the plug wires with water from a spray bottle. Watch for arcs and sparks. If the wires are getting too old/brittle/cracked/etc. you can usually find any potential leakage of high voltage like this. If it is fine misting with water then they are usually very serviceable.
First of all, I agree with Chevelle--leave it alone, or take out 1 plug to examine it before doing the job.
In my opinion, if your car has high miles, and you're not worried about an extra 3-5 hp, I'd just install regular AC Delco plugs (not the platinum ones). These were standard on the 4.1, 4.5, and 4.9 engines through 1991, and provide great performance for a cheap price.
I don't like Bosch plugs as they tend to run cooler than Delcos, and sometimes the 4 electrodes can get in the way of the air/fuel charge. I'd never buy them. A single electrode is just fine.
I'm with awadecki on this. I actually tried the Bosh Platinum +4, and I couldn't get them out fast enough. The electrodes shroud the spark. The fuel/air mixture has to burn "around" them which does not help efficiency. It does provide a sort of "path of least resistance" for the spark, but that is not the best in many cases. The current is as important as the voltage.
The compression also has little to nothing to do with what spark plug you use. Higher compression means the fuel/air mixture is more likely to explode, so it surely does not require a "better" plug to ignite it. Sure, you still want the strongest spark possible, but this is not accomplished by decreasing the surface area of spark to contact.
These engines like the AC Delco plugs, so I wouldn't go aftermarket at all on them. I've heard RapidFires are the best if you want to buy something fancier, but I have no personal experience with those.
If you have a higher (or lower) compression, the theory says the ignition voltage depends on the gas pressure... But it is just a theory and in Real world with a commercially available car, I believe it will not affect much.
And, I agree with awadecki. I noticed that I get more deposit at the electrode of a certain plug in my engine when I use Bosch. I asked (at an Autozone shop) if I can get hotter plugs. They said it is not needed unless I have serious modifications. But what awadecki said makes sense to me!
Automobile(s): 1991 Sedan deVille 4.9L/1994 Lincoln Town Car 4.6L
Chatham, Ont., Canada
Re: Question about spark plugs!
From what I have read about wires, they don't just suddenly 'go' but lose their ability to conduct over time, making your car run less efficiently. My rule of thumb is to change them as soon as I get a car and then follow the manufacturer's recommendations afterwards.