QuestionDear HT:
I have a 1995 Isuzu Rodeo. (there are no Isuzu experts on the site, but this is a general question) It is a V6. For some reason it is
getting 10 miles per gallon. This seems a bit low. I've been thinking about changing the spark plugs and ignition wires. The factory wires are 7mm.
I've been considering getting performance wires, (either 8mm or 9mm) with a lower resistance than the factory wires. Should this make a difference in milage & performace, and is there a
point when the wires are too thick? or have too little resistance. the performace wires claim to have 8 ohms resistance. IE would 10-12 mm be too much Why or and would 8 ohms be too little resistance? why not?
Is there any truth to the claims that manufacturers of performace wires make with regard to better milage, acceleration, starting, etc?
Thanks Eric
AnswerHi, Eric. Most of what I'm going to give you is my opinion based on what I've experienced and observed, and isn't based on any type of scientific testing.
The difference between different thicknesses of wires is primarily the amount of insulation. All other things being equal, more insulation will better guard against arcing.
Using lower resistance wires could cause ignition system problems. Because the resistance on the secondary side of the ignition is lower, it'll induce a greater current on the primary side, which in turn can damage the coil or ignition module (or PCM, depending on what controls the ignition on your vehicle). Plug wires tend to have more resistance the longer they are. So, if you check the resistance of your shortest and longest wires and the new wires all have resistance values between those readings, then they should be okay. But if they vary too far one way or the other, it could cause the problems I've described above or unintended arcing.
Claims I've seen made by wire manufacturers seem to be nothing more than advertising mumbo jumbo. If your current plug wires are functioning normally, you won't be able to significantly improve economy or performance no matter what wires you use.
I don't know what type of driving you're doing, so I don't know whether 10 mpg would be normal. EPA estimates are around 15 city and 18 highway, so you're not really outside the believable realm.
If your vehicle isn't misfiring, then replacing plugs and wires will have minimal effect on fuel economy. It's still a good idea to do a tune up regularly as preventive maintenance, so if it's time for one, this is still a good idea for your car. I'm a firm believer in using factory parts, especially plug wires. I don't recall ever seeing an aftermarket wire that was of the same quality and durability of the factory wires. In most cases, you can purchase identical spark plugs (perhaps AC in your case) from a local parts supplier, rather than having to pay a much higher price for the same part at the dealer.
If you really wish to attack a fuel economy issue, I'd recommend checking things in this order:
1. If the check engine lamp is on, diagnose and repair that issue first.
2. If there's an engine performance issue, diagnose and repair that issue.
3. Check your tires for proper inflation. Higher tire pressures will give you less rolling resistance and increase your fuel economy, but exceeding the manufacturer's inflation recommendations by too much will cause you to wear the center of the tires and you'll need to purchase tires more frequently. And under no circumstances should you exceed the maximum pressure listed on the sidewall of the tire.
4. If you've got an automatic, drive the car and make sure it shifts normally and shifts into all forward gears. Also verify the torque converter clutch engages. If you don't know how to verify this, you'll probably need a professional to look at the vehicle. If you've got a stick, make sure the clutch is not slipping.
5. Check the suspension and alignment. If you have an excessive to in or out condition, it'll reduce your fuel economy because you're dragging your tires instead of having them simply roll.
