Killemall

Ok,
So i have had this 99 4.6 4x4 for 3 years now. It has been a great truck to me.
About a year ago the check engine light went on, and i got the codes pulled at AZ.

I dont remember the exact ones, but they were consecutive, and they all had fuel part related issues on them, but it said it it pulled them both, then it was the MAF sensor.

The only real problem its given me is that i am losing a few MPG. But i do a lot of long trips and it is making a a big difference per tank.

I cleaned the MAF sensor and got a new air filter. I dont think its actually the MAF sensor, because it still runs well.

I suspect a vacuum leak, or maybe an 02 sensor failure? those are the only things i can think of that would be relevant.

Any suggestions?

Ajaxs1988

Code would be helpful but if the light is back on again I bet it could be bank 1 and bank 2 running lean. I just got this code and it loves to rob fuel mileage! I found a vacuum leak on a hose running from the back of the intake manifold to the valve cover. With alot of tugging and prying and unhooking heater lines I came to the conclusion that the lioness never ment to he replaced and I sealed it with duct sealer which is the toughEST substance known to man! If your code is bank1 and 2 are running lean check everywhere for leaking vacuum lines cause it's the cheapest fix, cause after that what causes a lean run is a bad PCM, MAS, fuel filter or a fuel pump.
Godspeed

Ajaxs1988

That code was P0701 and P0704 I believe

Killemall

Thanks for the reply.
I am pretty sure its bank 1 and 2.
Any tips on actually finding the Vacuum leak? They are such a pain.

Ajaxs1988

I just stood there with the hood open and listened really hard and as I narrowed down where the whistling was coming from I just started grabbing all the hoses hoping i would stop the whistling or feel it sucking at my hand. Check that one in the back it seemed to be the biggest hose it comes from the passenger CRV

Killemall

Thanks for the suggestion. I'll check that out tomorrow.

Warspite

P071/P074 - Just 4 letter curse words. Is your idle high, or does it sputter when you let off the gas? And, do you have an aftermarket cold air intake (which over time can give you a lean mix without a vacuum leak). #1 source as reported here is that hose going from the back of the throttle body and around to the valve cover. If you detect a slight flat spot, chances are there's a pinhole leak there. Then, clean the sensors and change the fuel filter too. If that doesn't work, Google Vacuum leak. It will return a lot of YouTube videos that also include a smoke test (which one of them revealed a leak at the intake manifold).

Killemall

It doenst idle high or sputter at all. It does seem to rev even after i let off the gas when its parked though.

No aftermarket cold air intake.
Ok, i will check that hose. I hope its as simple as that.
I have already replaced the fuel filter as well with a wix.

Thanks for the reply!

Killemall

Also,
When this light first came on, it was literally a few gallons into a tank of gas that i had just put fuel injector cleaner in for the first time.
Would that have anything to do with it at all? I thought it was too weird to be a coincidence.

Killemall

Ok guys, i found it!
It was the one that went from the valve cover to the intake.
It looked fine at teh connector, but under the insulation it was completely gone and barley attached from either melt or just rot.

One last question that anybody can answer, will that check engine light go off instantly if its fixed, or will it take a while to go off?