Troubleshooting acceleration/hp/mileage issue

[SwampFox89]

So I've searched the threads on here for days and decided to break down and start a new one to answer my problems.

First I will list my symptoms with my '99 Ex Sport, OHV. ~150k miles

1. Terrible mileage, about 13 mpg
2. Starting takes a hair longer after she sits for a couple days than when I drive every day.
3. Idling is rough when in gear at a stop sign or red light but not in park.
4. When I touch the pedal to go from said stop, she gets sluggish, then picks up.
5. CEL comes on for the occasional misfire, and frequent lean mix codes on both banks.
6. Going up hills, pressing down on the gas as much as I used to, it feels like she changes gears, the RPMs go to about 2200, like she used to, then drop to about 1250. Once it gets to about 1250, I lose about 60% of my hp and can't go more than about 45mph, until I floor it, and the gears change again. When it's down at that 1250, it also rumbles, like the engine is bucking and I can feel it straight through my steering wheel, into my shoulder.
7. In general, I've lost about 15% of my normal power.
8. Fuel needle seems to have a huge margin in a short period of time. Like when I'm facing downhill, the needle will drop, and when accelerating uphill, it goes up. The lowest to the highest can be about a quarter tank difference.
9. Replaced some injector o-rings that were getting bad.

Now let me throw in any relatively recent repairs I've done myself, regardless of relation to the problems.

1. Cleaned MAF sensor
2. Replaced TPS (I broke it once, derp)
3. Replaced the gaskets between the intake plenum and fuel rail and the gasket below the fuel rail. When I checked for vacuum leaks, this was the only place I found a leak, so I fixed it, correctly, torque to spec and everything.
4. Cleaned throttle body
5. Replaced IAC valve
6. Replaced fuel and air filters
7. Replaced PCV valve
8. Ran seafoam through the air intake (correctly through the vacuum line)
9. Ran 2 bottles of injector cleaner and seafoam through the gas tank (not at the same time of course)

So I'm thinking my next step is to take it to a trusty guy at a local family shop and him test vacuum pressure everywhere and if that doesn't work out, then I'm thinkin something with the fuel tank, the pump going bad, the pressure damper being clogged or something. I also haven't ruled out a bad DPFE sensor (even though I haven't had any codes for it) or the EGR valve, which should also throw a code...

Any help would be greatly appreciated, as I have a new job, with a long drive and money's tight right now.

Thanks fellow explorers...

 

[SwampFox89]

Bump

anybody out there?

 

[Dono]

Hows your coolant levels? Finding your coolant resevoir needs to be filled from time to time?

 

[Dono]

Think this could be it? Could possibly be fuel pump.
http://www.explorerforum.com/forums/showthread.php?t=190260

 

[my98nnj]

Sounds like it's misfiring. I'd lean more towards a fuel issue then spark being your getting lean codes. The MAF could be failing too and check the engine coolant temp sensor, make sure it's within spec when the engine is warm.
Have you looked at your spark plugs? They can give you clues as to whats going on.
When was the last time they were changed?

 

[Joe Dirt]

...and just to add some sad news, even if you do get it all fixed up, don't expect more than a few MPG's. But I agree it sounds like it might be a fuel delivery issue.

 

[SwampFox89]

So I gave in and took it to the shop (I left my spark plug socket at my dad's) I told him to check vacuum pressure and fuel pressure.

He did and found nothing wrong, and when he pulled my CEL codes, he saw a misfire on cylinder 3. I told him that those plugs had been replaced less than two years ago and they should be good. He said ok...

When I went to pick the truck up, he showed me my plug from Cyl 3 and the insulation on the post had been split clean in two. After I let a few expletives slip about how something so simple cost me so much money, he didn't charge me for the time or labor or tools fro getting that plug out. He only charged me for the diagnostics I asked for, the labor and tools associated with those, and a new plug. The moral here is that there are still good mechanics left in this world.

Thanks for your input folks!
Keep Exploring!

 

[Dono]

I hate to say this, but I kept cracking insulators on my spark plugs, and it turned out to be a cracked head allowing coolant to get sucked in to the combustion chamber cracking insulators.
If this happens again on #3 you know what the issue is.

 

[SwampFox89]

Thanks for the tip, Dono. The mechanic said that he checked the compression on that cylinder, and it came out to spec. Would that mean I'm ok on my heads or is this useless information?

 

[Dono]

Lets wait and see if another insulator cracks. Lets hope your good to go for another couple of years. I wouldn't do a thing unless you start chewing thru plugs.

Its good news that the compression up on the cylinder. Piston rings, and valves are working as they should.

 

[00meangreenXLT]

8. Fuel needle seems to have a huge margin in a short period of time. Like when I'm facing downhill, the needle will drop, and when accelerating uphill, it goes up. The lowest to the highest can be about a quarter tank difference.

I believe this is normal for these trucks, if I'm sitting facing down hill my needle moves (pretty rapidly like within seconds) towards E (the amount it moves varies on how steep the incline is, mine has moved more than a quarter before )...and vice versa when im facing upwards. There's lots of various hills and inclines on my daily drive to school and the needle hardly stays put lol

 

[joe doe]

I hate to say this, but I kept cracking insulators on my spark plugs, and it turned out to be a cracked head allowing coolant to get sucked in to the combustion chamber cracking insulators.
If this happens again on #3 you know what the issue is.

ditto on this quote here .i have had the same problem .if it keeps cracking the insulator then you have a cracked head on that side .

 

[97explorer sport]

My 97 sport does the same thing pulling out. Esp when my overdrive light is blinking. Idk why it blinks either and my mpg suck