2.5L MPG problems

[NIPs]

i have a 99 2.5l, ive had it for 2 years and only put 20k on it since ive bought it. when i first got the truck i would get 20mpg in the city, and 25-35mpg on the hwy, currently the truck has 200k on it and is only 15mpg hwy, i had an egr problem and i fixed it, no change, i did plugs and wires 2yrs ago or 20k miles ago( i checked 2 of the plugs yesterday and both looked fine and probaly have another 10k-15k miles left in them, i ran a digital bore scope into both cyl 2 and 3 they lookd somewhat ok, 3 had some type of sludge from what i could tell along the cyl wall that was only about an inch long if that, the only thing left i can think of is do the plugs again, im not really sure where else to look, any ideas are welcomed

 

[simpler=better]

15mpg is what yo ugen flooring it in 3rd all day

Timing belt stretched or worn?

Fuel injectors gummed up?

Are your MAF and O2 sensor working?

 

[NIPs]

15mpg is what yo ugen flooring it in 3rd all day Timing belt stretched or worn? Fue

im not getting any codes that would suggest o2 or maf, and i had already replace the maf, as far as i know the timing belt is original if that were stretched or worn than that would be jumping or i would have a misfire or rough idle which i dont have, injectors it could be those, but after thinking about it last night, im leaning more to my pcv, i havent changed the pcv on that truck, and ive had the truck for 2yrs, if the pcv had failed or stopped working it would explain the sludge in the cyl, the shitty mpg, and lastly i did notice a very small amount of oil leaking

 

[NIPs]

also its a 4spd auto not a 5spd manuel

 

[Mark_88]

Usual stuff like air filter and tire pressure would affect it too...as well as tire size and driving habits...shifting too high etc.

But the PCV should be replaced for sure...the oil loss could be the start of blow-by or just non-functioning PCV...it also greatly increases pressure under the pistons so it makes it harder for the motor to get the HP due to air resistance...not that there is much that small hose can release pressure wise, but it does have an impact all around...try just unplugging the pcv and driving it for a day...make sure to plug the intake inlet hose or you get too much air going in...like a vacuum leak.

Tire pressure can fluctuate due to air temp variances...as much as 5 psi in a single day with extreme temperature swings...

 

[NIPs]

my tires are slightly bigger than stock, but ive never had a problem b4 and my tire pressure in the front is always abt 30psi, and 35psi in the rear

 

[Mark_88]

OK...good tire pressure...so either swap out the PCV valve or unplug it and see if it makes a difference...the PCV valves are usually about $8 so it's an inexpensive part that can have a big impact and should be changed regardless of what the problem turns out to be.

You can also try a compression/leak down test to see if the problem is from valves or rings. You may have a dead or malfunctioning cylinder.

Another test you could do is to simply start the engine and pull the valve cover vent hose off while the engine is idling. If you see white vapour coming out of the VC vent then you have blow-by (if the air is cold when the engine is hot you could see steam also).

 

[NIPs]

i bought a new pcv but havent had time to put it in

 

[NIPs]

if i had a dead cylinder wouldnt my O2 sensor pick it up because of the unburnt fuel or extra air in the exhuast and wouldnt i feel a loss of power, but i dont have any of those issues, my o2 isnt picking up any saying i have that problem and idont feel like ive loss anypower, like i said i bought a new pcv which at the earliest i could do is monday morning in class, and while im there ill check compression

 

[NIPs]

i just rememberd i know i dont have a dead cyl cuz a couple weeks ago i was checking something else and i was using a infared temp gun and i went thru and check the exhaust manifold with it and checked each cyl exhuasty port and they all read between 590-620degrees and i checked each one 2-3 times to make sure i was getting the same reading across all 4cylinders, ps just so all u guys know and who do read this i amin school to be a mechanic, im still learning and i dont know everything and also have alot of access to Alldata and mitchellondemand, and tools and some of the most modern equiment, and my instructors incourage us to use our own vehicals, so when i say im gona do a pcv in my class now u know y

 

[Mark_88]

not sure what the variance between cylinders would mean...if anything...or what the actual temp should be...and if variances are normal.

Plug gap can certainly cause less efficient burning but you would also see lack of power...but may not actually notice it...sensors would probably catch that though.

Did you check the gas tank for leaks and pressure test the gas cap?

 

[NIPs]

gas caps only 6months old, plug gap is within spec, no leakes from fuel tank had this truck on hoist many times, never saw it leak or smell any gas that would cuz concern, the other night i took it on a drive a nice 1hr-2hr drive just driving around to let the truck go thru a full warm up been cold up here in michigan for the last 3 months, drove it on country back roads, some highway, and dirt roads,turned off the radio just listen to what the truck was doing, thinking maybe i missed something seeing how the truck never gets that kind of drive yeah it gets warmed up, but never a real long drive like that, so as im driving mostly doing between 55mph and 70mph on these snowy icy roads, seeing if anything changes basically looking for anything that missed, on the way back i was on a really bumpy section of hwy and i was about 10-15mins from at this point and suddenly the pitch of the engine changed, it went from normal sounding to kinda loud almost like an exhuast leak, so i get back with the engine still running i open the hood start looking at the manifold and flange and then i noticed it, so it hasnt been running any codes saying somthings up, and from the full warmup of the engine and getting to true operating temps for a consistant peroid of time the EGR line that i had welded back on had broken free, and that is the problem, well i could do a couple things and im already prepared to try one of the following, the 1st one is just buy the new egr feed tube(88.95 at the local Napa store) but the problem with that is theirs a good chance that whats left of the EGR tube on the manifold wont come off, 2nd i could weld the old hole on the manifold shut and relocate the egr downstream more where the rest of the exhuast has already been replaced, or my other option is to sleeve it which im not a big fan of using 1/4 inch or 1/2 inch copper flex pipe that has a melting point of about 1980F, so i should be more than ok , but what also could do is plug the old port on the manifold and run copper tubing downstream a lil bit not much it but the exhuast gases would be much cooler than before

 

[Mark_88]

If this got louder on your last trip then the pipe broke during that trip. It wouldn't have been the initial problem...unless there was a crack in the tube before and it just broke off completely.

I tried making a copper EGR pipe (still have it on the truck) but I used joints and elbows to piece it together since it just happened to work out well. Problem with mine is the joints are wonky because I didn't fasten them together...so I have a floppy EGR pipe...

But the important thing is to seal it once you get it made up and can install it without having to bend it too much...if it isn't sealed you would have essentially the same as a broken or cracked pipe and the exhaust gases wouldn't make it into the mix...

hopefully you're better at making things than I am...or have the proper tools which I don't...

 

[NIPs]

the orignal line could be pluged, with carbon, or it could just be the fact that its been such a cold winter this year, that that would kill my mpgs

 

[Mark_88]

The cold would definitely affect the MPG and this winter has been pretty brutal. Cleaning the EGR out when you replace the pipe would probably help a bit too...

Mine was packed full of gunk at one point and I thought that was part of my performance problem...after I cleaned it out the engine didn't run much better but I was getting a bit better MPG so...could well be a combination.

Guess you won't really know until it's done and you can test it!