Anybody good at reading plugs?

Just picked up an ‘08 access cab V6 A/T. The dealer said he had to replace a cat. I’m on 3/4 tank after very few miles. I’ll refill tomorrow morning and find out what the gas mileage actually is. It’s definitely poor. I figured I’d check the plugs and they were pretty eroded but otherwise look decent. If you can see anything obvious let me know. One is darker than the rest. I’m hoping just plugs perms it up, but at 208k I assume injectors might not be a bad play. I haven’t driven it long enough to know if it’s using oil, but the plugs are pretty clean and have clearly been in there a while.



I fill up in the morning and get a real mileage number, and then again next week and see how much it improved. Any other common issues that tend to reduce fuel economy on these? I usually drive 4-cyls.

 

They look to be about average. I'm not seeing any signs of concern, but yet again, I'm going solely based off of this photo. If you want piece of mind replace them and gap them to IIRC .040. I cant remember off the top of my head exactly but I think its in the range of .038 to .041 but double check your manual. Plugs are recommended to be changed every 30k, though some push the iridium plugs out to 60 to 100k. I change mine every 30k and they dont look as bad as yours do, but yet again, my vehicle is a 2012 with a hair over 60k miles. Additionally, you might want to get a can of MAF cleaner and spray your MAF sensor. Its delicate so treat it with respect. Take it out of your intake manifold before you clean it, some say you can clean it while it's installed but its easy to get to and remove. There's a few threads about it here. Also, you might want to look at running a bottle of fuel cleaner through your gas tank, pick your poison like STP but again, do your research. 208k miles and things are going to start acting funky. If you havent flushed your coolant, you might want to do a complete fluid replacement.

-J

 

I replaced them with Bosch Iridiums, and haven’t driven it yet. Gonna fill up 1mi down the road in the am, and compare next week to get real numbers. Hopefully that’s all it was. I couldn’t find my gapper or feeler gauges, but they look .090”+. I put a K&N AF in, changed the oil and put a can of SeaFoam in the tank before I drove it. The throttle and intake look quite clean. I removed the secondary AF when I changed the plugs. All tires are at 38psi. I plan to raise that to the 80psi the sidewalls say they’ll handle after I see what the new plugs do to the fuel economy. Checked fluid level in the diffs and they’re full. U-joints and CVs are tight. Tires are stock size. I plan on a drain and fill of the trans next weekend. I’m a M/T guy, but needed a back seat for a baby that arrived early and this was what I found in a hurry.

 

Pull the Iridiums. They are for 4 bangers. Put back NGKs or Densos. Your engine came stock with 3 NGKs on one side and 3 Densos on the other. Copper plugs, 30,000 miles work best with these engines.

Read, read, read the forums. Lots of excellent info here.

 

Just because the tires say 80 psi max doesn't mean you should run at that pressure. It will be a rough ride! Even 38 is on the high side. It's not going to make a noticeable difference in mileage. Under the best conditions you'll only get 16-18 mpg around town no matter what you do. You're driving a brick.

 

The iridium that “fits” that engine will actually cause problems? Why won’t it just do the same thing but last longer? Not saying I’m not wrong. I replaced the plugs because they looked eroded. I replaced them with iridiums because I assumed they would last longer. If they actually reduce fuel economy and performance I’ll be happy to toss them. I’ve just never heard that they decrease economy and performance, only that they don’t improve economy and performance.

 

I don’t mind the rough ride. One of my favorite trucks was a ‘94 Pickup. Nothing is rough after that. I’ve always run my tires at what they said was max, and that was usually 80psi. There’s less sway and any slow leak that ever develops is a problem far less frequently. Breaking takes a little longer, and you’ll wear the centers out on the tears if you don’t rotate, but with reasonable rotations I’ve never had a problem and have always preferred running 10plys at the pressure the tire will handle. Also, the thing is a crazy soft ride compared to my 2010 single cab. Im not sure why, but it is. Lastly, I won’t know a real number till I see how many gallons it holds on a fill, but it seems to be getting 10-14mpg if I was gonna guess. It’s used 3/4 tank and is at 180 miles. 16-18 wouldn’t bother me because that’s what I expected. Way under 16mpg just has me wondering what’s wrong with it.

 

I thought iridiums were the shiznit for almost everyone on here.

 

The 4.0 have a tendency to dislike some iridium plugs.
They seem to take well to the factory copper plug.

If you installed iridium and do NOT experience any problems (acceleration and idle) then leave it alone.
Others have used iridium in the past. They either have issues or do not at all.
You will not gain anything other than possibly extended plug change intervals. Which I won’t speak on.
If you have any issues, any at all, then Yes. Do revert back to the copper plugs.

Maybe @Jimmyh can come in and give his opinion on if you should or should not leave the iridium in?
He would know better than me.

 

^^^ all I wanted was a longer change interval. If they cause problems, I’ll be happy to remove them. I would expect some improvement from almost any properly gapped plug though because those were pretty eroded even if they were clean.

I’m no expert plug reader. I was glad to see that they were clean as it makes me feel like the engine probably isn’t burning oil. I haven’t had it long enough to tell if it’s using any, but at least the plugs aren’t filthy. I just wanted to know if they look good or if the two darker ones look like they were getting rich enough that those two injectors could be the reason the cat had to be replaced.

 

Not even about ride quality at this point, they won't behave properly. 80psi is for 11,000lbs+ load, not fuel economy. It's dangerous and you should see how high these small LT tires bounce at 80psi. Gas is cheap compared to burning tires up and driving a lumber wagon.

Max I would ever suggest unloaded is 40psi, and 44psi towing. 80psi is just dumb.

 

I guess I’m just dumb. I’ve never had a problem that I considered to be a problem. Got 83k from the first set of BFGs on my 2010, then 74k from GoodYear Wranglers, and then went back to BFGs cause I didn’t like the Wranglers in mud. They didn’t steer well. I ran BFGs on the ‘94 for many years and Pirelli’s on an ‘06 Chevy. I got over 70k from every set on both of those. All have always been run at max pressure and I’ve never had any issue. Maybe I just don’t expect a truck to corner and brake like a passenger car, but like I say I’ve always preferred it and never felt like it caused me any problems.

 

80psi? Forget the harsh ride, what about wearing out your tread in the center? Is your truck 4x4? I've got an 08 AC A/T 4x4 and the door jam says 29psi cold, so that's what I run. Yes, the suspension is a bit soft...yes, the gas mileage kinda sucks. I average about 17mpg and that's with 265/75R17 KO2's. It's also worth noting that the one and only time I dumped a can of seafoam in my tank, I got an increase of several MPG for that tank only.

 

Yes it’s a 4x4. The only time I’ve had worn out the center of the tires was on the rear tires only on the ‘94 when I got lazy about rotating. As long as I rotate around 15-20k there’s never been a real issue on that front.

I’d love 17mpg, but don’t expect it. I get 18-19mpg from my 2010 2.7L, so I have enough of a lead foot that I should be on the low end for this truck. I expected 15-16mpg. I may fill the truck in the morning and find out that 15mpg is exactly what I got. Just looking at the gauge and the miles though, it seems like that’s not even gonna be close.

 

Not trying to start a disagreement / argument.
But you may want to look in to the term “tire contact patch”.
Running a tire on maximum PSI almost never results in the best tire contact patch.
Only thing I can agree on is over inflation is usually better than under inflation.
Usually that is......

It’s your truck. Drive it how you like.

 

Nobody should run their tires at 80 psi on these trucks. I follow the manufacturer's recommendation of 29 psi front and 32 psi rear.

 

I’m not gonna tell you that it breaks as quickly or corners as sharply as it would with the recommended inflation pressure. It doesn’t. I’m just saying that uneven wear hasn’t been an issue with reasonable rotation intervals and total miles on a set of tires has been well beyond their warranty period, so life seems fine too. Discount Tire rotates and balances for free whenever I want and let air out till the tires match the door sticker every time, and every time after a week or two I drag the air compressor outta the shop and air them back up and like it better that way. Not saying everyone should, just saying it has never resulted in anything that I consider to be a problem.

 

Please put your tires to 30-35psi....

 

I think that 15-16 is attainable for you. I agree with others about cleaning MAF & TB. I did that this weekend; $8 for a CRC combo kit of both MAF & TB cleaner...I’m amazed at how much smoother my engine seems to run/drive. Also, checking diff/transfer case fluids couldn’t hurt. I changed those this weekend as well and every time I’ve done that, I swear I can feel it when accelerating. Those plugs look fine to me. The plug closest to the driver is always the dirtiest for some reason, but my attitude it to worry about it only if it gets progressively worse.

 

How I like my tires is not really the purpose of this thread. Two of the plugs were darker than the rest. Do they look like there was a problem on those two cylinders that may have resulted in the damaged cat and poor fuel economy or do they look A OK? If they’re good, and the plug replacemt still leaves me with 14mpg or less, is there a common issue on these trucks that I need to look at fixing, or do they usually end up around that range after 208k? My 2010 with 185k got about 18-19mpg when I got it 2010 and still gets 18-19mpg today.

I’ll update with the actual mpg when I find out tomorrow.