lean fuel

rickysilverado · June 16, 2002

sup guys love the site. My truck is giving me a hard time. Its a 99 4.8L silverado. Every time my truck passes the 60km or 4th gear until 110km or so, the truck starts rumbling like its not getting enough fuel. I had my fuel pump changed and had this problem with my old fuel pump. Im thinking maybe its the fuel filter thats clogged since i never had it changed and started getting this problem in the 86000km range. Its really bad in the highway and i have to pump the gas pedal quickly in order to stop the rumbling. The truck runs perfect at full throttle but at cruising it can become really annoying. You guys seem to know your stuff so i would apreciate your help. Later by the way i have catback and a intake installed nothing major

Shaners · June 16, 2002

Welcome to the site!!!

It sure wouldn't hurt to change the fuel filter. I'd check the air filter too, while you're at it.

There has been an issue of the tranny going into OD early. When I had my '00 Silverado, I had the dealer reprogram my tranny so that it wouldn't lock up the torque converter in OD until I was going at least 45-50 MPH. This solved my drivabillity problems. With the stock programming it seemed as the the motor was lugging too much when it went into OD.

rickysilverado · June 16, 2002

I think you are right cause it does seem to go into od very early. What if i get a shift improver kit like the one from jet or b&m? Would that also solve the tranny isue?

Shaners · June 16, 2002

I know the Hypertech HP III will allow you to change shift points along with all kinds of other fun things.

However it is pricey....

If your truck still has some warranty left you should talk to your dealer. There was a TSB about this problem and the dealer should know about it. Even if you are out of warranty, they may still do the update to your computer for you... it's worth asking.

June 17, 2002

I agree with the tranny theory. If your truck was lean on the fuel mix, you would see a degrease in performance, increased detonation, and skipping at high rpm and heavy acceleration.

Partial throttle and cruising would be least affected.

July 9, 2002

MINE DID THE SAME FOR A WHILE.. PROBABLY FROM 14,000 MILES TIL IT FINALLY BURNED UP 2ND BAND AND STARTED ON FIRST AT 16000 MILES... NEW TRANNY WAS PUT IN UNDER WARRANTY OF COURSE AND IS SO FAR DOING FINE.. I PLAN ON GETTING A HYPERTECH TO FIRM UP MY SHIFTS AND CHANGE MY SHIFT POINTS NOT ONLY TO SATISFY ME BUT TO ALSO HOPEFULLY HELP MAKE IT MORE DURABLE AND DEPENDABLE...

CMNTMXR81 · July 10, 2002

If it's not the tranny, you can always have an injector cycling pressure test done with a TechII at a dealer to verify that all you injectors are firing.

Essentially you hook up a fuel gauge to the fuel rail, pressurize the system, then have the TechII cycle each injector. As each injector cycles, fuel pressure in the fuel rail should drop a couple psi. If not, you know that injector isn't firing or isn't firing sufficiently.