I have a 02 excursion, i have owned it since 03. I have always used sae 5-20w oil. ans yes, it goes threw oil like most. i now have 155k on it but at 150k i decided to see if i could extend the life some. I put in full synthetic 5-20w, changed the plugs, replaced the air filter with a K&D.
500 miles later all of my trouble started. started poor milage, motor idled up and down, sometimes stalled when giving it the throttle from a stop. I changed the MAF & the TPS. it seemed to help for about 3500 miles but it was still using gas and idle was up and down.
Now at 5000 miles on synthetic the motor has no power, cant get it up over 2000 rpms while its parked in nuetral. I changed all 10 injectors, PCV, fuel filter. I have a theory that synthetic oil may be breaking down and not lubing the top end thus, cuasing to much friction. Shoiuld I switch back to SAE Oil?

 

I'm no expert, but I can't see how synthetic oil would create these problems. Is the truck throwing any codes? What about something clogging the exhaust?

 

Good advice, Onug. I believe that if the oil was causing issues then you would see it in the engine temps (just a thought).

I also had something similar issue happen to me. It ended up being a couple of bad COP's even though they were not reporting a misfire. You could also have a bad alternator. If the diodes are bad in the alternator then it will wreak havoc on the ECM (computer). Remember that just because the CEL is not on that does not mean that you don't have any codes.

 

Just ran a oil cleaner and drained the synthetic. replaced it with sae 5-20w. now i can get it up to 2800 rpms before it starts to misfire. when i drop down to 2500 or under it takes about 10 seconds to smooth out.
Trdltly, good suggestion regarding the Alt. Now that i think of it! when the motor started acting as if it was being flooded/misfiring and would not go over 1500 - 1800 rpms i noticed a squeel like a loose belt. it very well could be an alt not giving enough charge at high rpms to give to the coils and computer

 

the codes that i found where P0102 which i beleive (mass or volume Air, Flow curcuit low input) So i replaced the MAF and still get the code.
Also code P0113 which i think is (intake air temp sensor, curcuit high input). temp senor is part of the MAF unit.
Also code P0122 which is (throttle/ pedal, position senor)

I replaced all of these and still get the codes. no other codes have came up.

 

Try putting the stock air filter and housing back on and see if that helps.

 

It is more than likely that the oil-soaked (mpg increasing???) aftermarket X&Z filter messed up your MAF sensor (possibly CAI valve too) . If I were you , I would put the stock filter back , clean your MAF sensor with (CRC MAF Cleaner / Remove ( -)battery cable before you do that ) . Removal of battery cable also resets your codes . See where you go from there .
Good luck,

PS. I use full synthetic 5W20 without any issues .

 

I actully did place a stock filter back in and replaced the MAF again before this last rpm issue. I did not remove the cables though.

 

I would think that you may have a misfire, that won't always show up on the computer.
Have you checked the boots under the coils? Have you changed plugs?
Might be time to check on them, as the boots can be cracked and setting of all sorts of electrical shorts thru the engine.
Def unhook the battery for a bit to reset the computer after MAF cleaning and or replacing the air filter kits.

 

I did replace the plugs about 5000 mi ago. How do i chech the coil boots< what am i looking at or trying to find? and yes i will disconect the battery as soon as i finish my morning pot of coffee.
Someone had mentioned exhuast pressure. how do i check the cat to see if its partially closed. I cant disconect it becuz my hole exhuast is welded.

 

The boots were the rubber pcs with spring inside that connected the plugs to the coils. The coils are the first thing that you removed when changing the plugs.
You really should just replace them when replacing plugs.
Once out roll them in your fingers checking for cracks.

 

ok guys, i removed the battery cable for 1 hour. no fix. and now i have a misfire which sounds like 2 cylinders. and we know its not plugs or injectors so it must be coil boots. but this still does not cancel out the rpm problem

 

Two of your cylinders misfiring will cause the engine speed problems. I Would get new boots if it were me.

 

I do agree that i need to get new boots but the misfire of a couple cylinders will not hold the motor to 2500 rpms and die. i have a 2000 f350 with a v10 and it misfired on 3 cyls and still ran. This is something else. could a power steering pump be so bad that it is putting strain on the motor? i think my steering pump is going bad.

 

I would say no. I would lean more toward the exhaust. The engine could be trying to evacuate the air and it has nowhere to go.