If I am not mistaken, those codes will be 1537 & 1538.

 

Correct.

I would do the Techron or if you can get your hands on a can of BG44k. I recommend Techron though, but have had good luck with the BG44k.

I still have a feeling it is your plugs causing the issues...

Also, when you do replace the plugs, put a very small amount dielectric grease on the terminal nut and plug boot. Keeps any moisture out, and provides good connectivity. I do this with all of my gasoline engines and hardly do I have a corroded terminal. It's not a required thing to do, but it certainly doesn't hurt, especially if you live in a salty or humid environment.

 

BG44K is 3 time the price of Techron, and it's not what it used to be due to VOC regulations.

Actually, these days dielectric grease *IS* pretty much a requirement. Try to keep it off the contacts, just grease the inside of the boot.

 

I got about 15 or so cans of the old good stuff that I bought from my dealer 2 years ago before all of the eco emissions stuff. They gave me 5 cans free, and I bought the rest, or something like that. I drop a can in once a year. The new can says "VOC Compliant".

That's why I agreed with Techron being the best. I guess if you can get your hands on a old can of 44k, then that'd work ok too.

With the dielectric grease, I must be doing something right. As I've seen people/service depts. not use it. Maybe I have pride and common sense in my work.

I haven't heard about keeping it off the contacts, as many put it on the contacts to keep the corrosion off. At least I do, and never really had an issue. Maybe because I'm conservative with it and not use the entire tube in one boot.

 

Well I cleaned those valves in the intake manifold, real shiny. Tried the MC plugs.......still no difference.

 

With the LTFT number being high, I'm starting to think there's a crack in the intake manifold somewhere that I can't see.

 

You might be on to something. I'd take it off and look at it under some good light. Clean it up if you need to.

If it's a small crack, you should be able to fix it with some high temp epoxy.

If you want to buy a new one, you are looking at around 600 bucks from Tasca.

 

I'll try the Techron next.

 

Gumout for high mileage engines available at Walmart has the same chemical cleaner as Techron. It works great!

 

If you buy Gumout, you have to look for "REGANE" on the bottle.

 

First the details; 2004 F150 Heritage, 4.2L, Auto, 4X4, 3.55 gears, 158K on motor, isolator bolts and air box gaskets changes at 118K (Green Ones), O2 sensors (sensors 1) swapped at 115K (Bosch), CAI at 125K. Truck runs well but about 3-4 months ago the gas mileage dropped from 17 to 18 mpg to 12-14 mpg. There are no CEL's and no pending codes. I replaced the plugs (MotorCraft) and all plugs were properly gaped and silicone grease on the plug terminals, wires are MotorCraft and were changed at 111K. I got the following readings with engine at 190 deg F operating temp and at 3 specific constant rpms, idle, highway at 65 mph in OD and 65 mph not in OD. I did remove and cleaned the MAF with MAF cleaner and some of the readings did improve like the diff between the LTFT bank 1 and LTFT Bank 2 was reduced from 10% to 5% on the highway. Has anybody got ideas on where to go now?

LTFT Bk 1 / LTFT Bk 2 / STFT Bk 1 / STFT Bk 2 / RPM / Timing Advance #1 cylinder
18.71 / 17.4 / -2.11 / -3.12 / 801.51 / 14.16
9.68 / 4.22 / -3.59 / -1.77 / 1667.3 / 27.47
3.12 / 1.56 / -3.12 / -0.52 / 2598.75 / 33.46

 

Get rid of the intake, put the stock intake back on with a dry paper filter and Gotts mod, then change the MAF.

 

glc, good eye!! I read this last night... and I didn't see CAI.

Yes, do as glc said, do the Gotts mod with a paper filter or revert it back to stock and replace the MAF sensor. Those CAIs, especially the oil based ones are notorious for fouling up the wire on the MAF sensor giving poor fuel trims and gas mileage.

 

Well, the CAI has been on there for almost 2 years without incident. I routinely clean the MAF with the cleaner generally every oil change. Is it the CAI itself that's the concern or the K&N filter as there are alternatives to the oiled filter?

 

It's both - not only can the oil foul the MAF, a K&N does not filter well at all. Also, it shouldn't be an issue with the 4.2, but any aftermarket intake can have issues with proper MAF metering. Intakes look and sound good, but don't help with performance one bit unless your engine has a lot of other mods - and can actually HURT performance due to drawing in warm underhood air instead of cool fenderwell air.