Is something wrong here?

[indieaz]

There's no wires to swap. Just buy plugs. Of course I'm sure you knew that and it just traditionally came out of your fingers.

The stock NGK plugs are worthless IMO after 20,000 miles. I've changed them on 2 3.7Ls and at about 20k, that's when mileage, performance and smoothness starts going downhill. I can tell when KJs need tune ups at work, they run horribly.

Very strange...the only time i've had plugs last <30k miles was on a heavily modified LT1 engine (very aggresive cam = pig rich idle in closed loop).

Anyways, maybe i'll pull a plug a few plugs and see what they look like. Also, as for wires, isn't there at least a short wire from each coil pack to the plug?

 

[Marlon_JB2]

Very strange...the only time i've had plugs last <30k miles was on a heavily modified LT1 engine (very aggresive cam = pig rich idle in closed loop).

Anyways, maybe i'll pull a plug a few plugs and see what they look like. Also, as for wires, isn't there at least a short wire from each coil pack to the plug?

The coil is on the plug.

 

[LibertyFever]

245 70 16 tire, Airbox is clean and filter is changed, 60k miles

Have you had the Jeep's engine computer programmed for 245/70/16 tires?

 

[JeepJeepster]

Also, as for wires, isn't there at least a short wire from each coil pack to the plug?

Nope:

You must be registered for see images attach

 

[indieaz]

The coil is on the plug.

Well I'll be damned...never bothered to look before

 

[Marlon_JB2]

Well I'll be damned...never bothered to look before

Is GM still using coil packs or have they started using Coil-On-Plug ignition yet? heck even Kia has been doing that for a while... my mom's '01 Sportage is Coil-On-Plug!

 

[indieaz]

They may have started using coil on plug...i haven't worked on any of the ecotecs or the new 3.6 and some of the other engines. All the LS based engines are still using coil packs.

 

[indieaz]

OK, i pulled a few plugs finally this weekend. They didn't look all that bad...a bit of sulfur buildup but that's pretty normal. The gap was too large (about .055) so that would definitely have been affecting the spark. I went ahead and changed them anyways. The parts store only had autolites in stock which suck, but i figure @ $1.69/ea if i had to replace them again in 20k miles it'll be no big deal.

Also, this was one of the easiest plug replacement jobs i've ever done. The vehicle did seem to idle more smoothly afterwards (it was shuddering a tad before). Now to see if mpg improves back to old levels.

 

[scull20]

OK, i pulled a few plugs finally this weekend. They didn't look all that bad...a bit of sulfur buildup but that's pretty normal. The gap was too large (about .055) so that would definitely have been affecting the spark. I went ahead and changed them anyways. The parts store only had autolites in stock which suck, but i figure @ $1.69/ea if i had to replace them again in 20k miles it'll be no big deal.

Also, this was one of the easiest plug replacement jobs i've ever done. The vehicle did seem to idle more smoothly afterwards (it was shuddering a tad before). Now to see if mpg improves back to old levels.

Id be interested to see if there is any improvement, please keep us updated. Oh and how many miles do you have?

-Ryan

 

[JeepJeepster]

The parts store only had autolites in stock which suck, but i figure @ $1.69/ea if i had to replace them again in 20k miles it'll be no big deal.

Who told you they are not good plugs?

I used Auto-Lite double platinum plugs. Doing great so far.

 

[Marlon_JB2]

The vehicle did seem to idle more smoothly afterwards (it was shuddering a tad before).

Told ya.

 

[sevenhelmet]

x2 on the Autolite Double Platinums. Had mine in for about 12,000 miles now and it's running great.

 

[indieaz]

Id be interested to see if there is any improvement, please keep us updated. Oh and how many miles do you have?

-Ryan

32,000 miles.

I'll check mileage on the next tank of gas. What I can tell you is compared to 15,000 miles ago we were getting about 15-20% worse gas mileage.

@ 10k miles we consistently got: 24-25 highway, 18-19 city

Last few months we were getting 20-21 highway, 15-16 city.

We check mileage on every tank.

Told ya.

Where's the :bow: emoticon?

 

[indieaz]

No improvements in mileage. Thinking back, it seems like our mileage went to crap when we bought our new tires. But they are the same diameter as the stock tires I though. They aren't A/Ts or anything, so I can't imagine the tires could have dropped our mileage that much. They have been kept @ 40psi as well.

 

[Marlon_JB2]

No improvements in mileage. Thinking back, it seems like our mileage went to crap when we bought our new tires. But they are the same diameter as the stock tires I though. They aren't A/Ts or anything, so I can't imagine the tires could have dropped our mileage that much. They have been kept @ 40psi as well.

That explains it.

The main reason Chrysler used the Wrangler STs was because of that very reason. My sister's Jeep has also started using a bit more gas with her Fortera Silent Armors. Sadly, other than the extremely low rolling resistance (which increases gas mileage as you've noticed), the tire ***** and we'd both rather have a safer tire than better mileage.

Take these two road trips to Alabama for instance...

In 2004, I averaged about 23 MPG highway.
In 2006, I averaged about 22 MPG, and this time the engine was fully broken in too, but this time I had All-Terrains on the wheels.

 

[indieaz]

^ My new tires aren't all terrains though (Firestone Destination LEs). The tread is more aggresive thant he Wrangler S/Ts (what tire isn't?), but the S/Ts were kept 5psi lower than my new tires and I can't imagine the rolling resistance is *that* much higher.

We used to get 24-25mpg on the highway. Now we get 21mpg. You think the difference could be that much? Also, city mileage went from 18-19 down to 16.

I'm going to compare the odometer reading against google maps today on the Jeep and see if it's off any. In some ways i'm hoping it's about 5-8% off

EDIT: Agreed about safety...those Goodyear's did not feel safe. New tires grip considerably better, and despite this are FAR more quiet.

 

[Marlon_JB2]

I remember seeing up to 26MPG highway with my '04 on Wrangler STs. (But I think the fact that my rear end was higher than the front helped with aerodynamics maybe) I was only going 60MPH too.

Goodyear brags about the low rolling resistance as a positive to the Wrangler STs so I guess it has to be *that* good?

 

[indieaz]

Well, calculated the odometer is off by 4.5% (it's low). So that explains a portion of it...so our 21mpg highway was realyl 22, and the 16.5 city is really 17.25. Doesn't explain the whole difference, but part of it at least. I'm sure the tires rolling resistance is probably another 5% of the difference.

 

[tjkj2002]

Well, calculated the odometer is off by 4.5% (it's low). So that explains a portion of it...so our 21mpg highway was realyl 22, and the 16.5 city is really 17.25. Doesn't explain the whole difference, but part of it at least. I'm sure the tires rolling resistance is probably another 5% of the difference.

Just remember that your speedo was still off with your OEM tires.Also different tire company's may state a 235/70R16,but will be taller/shorter and/or thinner/wider then the next company's 235/70R16.And then tires are made different,so 2 tires of the same "size" can be vastly different in weight and height,that's your MPG difference right there.

When I was running the 265/75R16 MT/R's they measured a true 31.5" at 41psi,my current with my current tires(Truxus MT's,265/75R16) measure a true 31.9" tall and are noticeably thinner than the MT/R's.Also there was about a 10lbs difference between the 2 tires.

 

[indieaz]

Just remember that your speedo was still off with your OEM tires.Also different tire company's may state a 235/70R16,but will be taller/shorter and/or thinner/wider then the next company's 235/70R16....

That was my other thought is difference in actual diameter., I'll check this later when my wife is back home as our spare tire is still the OEM spare (it has about 2,000 miles on it). I haven't put them on a scale, but i didn't feel a noticeable weight difference between the tires.