are these codes associated with a dirty EGR valve or a marginal O2 sensor ?

 

it's fuel delivery...put a f.i. fuel pressure guage onto your shrader valve on the fuel rail. wrap a towel around the line run it up by the windsheild close the hood down to the safety latch and take it for a short drive.
should be 38ish at idle and ramp up under load going down the road.
after you determine if it's low fuel psi or not; you'll be dropping the fuel tank to repair/replace the rubber lines that run from the plastic Y connector to the 2 fuel pumps.
perfect opportunity to replace the stock pumps with a dual 255 set up. i did . got'em from sal

fyi...this happened to mine shortly after i changed to a garbage can lid sized lower pulley.

good luck,
pat buchanan

p.s. other than that it could be a massive vaccum leak.

 

I take it you have a'99 (twisted99) what MAF sensor do you ahve on it.

 

Fuel pump.

 

I say vacuum leak, tune, or maf.

good luck.

later,
chris

 

agreed... maybe a bad O2 sensor, but that would lead to a different code.

is the truck shifting differently? If not, you can probably rule out the MAF.

check all the black plastic hoses for a crack or unpluged. odds are this is your problem

 

my truck tossed that code when i did the dime mod
pulled the dime and all was fine

 

i assume you do have a new fuel filter too right?

 

i thought that our trucks read 32lbs at idle??????

 

NO Ihave a 01...had 2 99's..The first one was....Twisted..as in totaled.....

Just installed a new fuel filter....

stck MAF....RWTD Predator Dyno tune....
making 410 RWHP and 500 FT pounds
SAE

shifts fine.....

Autometer Fuel Gauge shows good idle and
otherwise fuel presure...

did a quick check of the intake boot lines seem fine..guess I'll start looking harder....

thanks for the input....

truck has 89000 miles.....

ported eaton...4 pounder...BR7EF plugs @.036 gap..JLP intake....160 degree hypertech.... E-Fan ..FTVB..stock fuel pumps m
I have reset the codes...drove several miles and no code yet.....

 

Put your stock breather cap back on, assuming you have an aftermarket one.

 

Nope..stock breather with upgraded PCV ...

just pulled the EGR and cleaned..it was dirty but not nasty..

 

Clean your MAF... should make your problem go away. My dad's truck had this same issue, and we found it to be the MAF sensor was dirty. I would clean that, then check it to see if the problem clears up. He had this happen around 125,000 miles or so.