2000 Silverado Running Bad

[rat454]

i have a 2000 reg cab swb 5.3 2wd w 75K miles. About a month ago it started to running bad and my mileage went down about 2 mpg. It was an abrupt change not gradual. I service it regularly oil, filters, and take car of it.

The symptoms are:

it stumbles off idle in gear or park, not always though

it stumbles and bucks when load put on it at low rpms, example barely give it gas when cruising 45mph in overdrive.

it breaks up at wot and feels as it has lost power

 

It idles ok but not as smooth as before the problem started

there are no dtc

the engine light has not come on

 

I have checked fuel press 55-60psi

removed fpr and fuel press immediately went to 60

removed and cleaned egr valve, replaced gasket, egr not really dirty and valve moving freely, no change

I unplugged the egr, no change

I blocked off the egr with it plugged in, no change

ohmed all plug wires and all read very close to each other

the engine doesn't miss

pulled all plugs and all have a proper gap and seem to be burning evenly and clean

i cleaned the maf sensor with the proper cleaner, no change

i cleaned the throttle body bore with cleaner, no change

all gauges on the dash read normal oil press, volts, water temp

i have a diablo programmer and have been running a modified tune for the past 3 years with no issue, since having the problem I changed from the 93 octane tune to the 87 tune with no improvement

the diablo has a real time data feature so i reviewed readings from the sensors it monitors (iat, map, maf, fuel trims, tps, knock retard, spark advance, o2 readings, etc) and all seem to be responding according to engine rpm and load, I say all the readings are normal but i don't know the acceptable range.

I dont' have cats so they are not clogged

 

So i haven't got a clue what to look for. i think i have touched on all of the obvious easy things that may be causing the issue. Can anyone help???

[amtz.zero]

I may be way off here, but transmission maybe?

[rat454]

I may be way off here, but transmission maybe?

 

I dont' think so since it stumbles when revving the engine while the trans is in park

[Draenor]

Fuel filter?

 

Do you have a wide band? What are your fule trims when the engine stumbles?

[rat454]

Fuel filter?

 

Do you have a wide band? What are your fule trims when the engine stumbles?

 

I replace the filter about 15k miles ago, i know it could be dirty already but wouldn't good fuel pressure rule it out?

i can see fuel trims via my diablo but haven't looked at them while its running bad

will look at that

when i have looked at them the last few days long and short all range bet +6 and -2 % thats pretty normal right?

[rat454]

i have been told to clean the injectors. Would one or more injectors all of a sudden get dirty and start acting up? Would bad injectors cause a code to set?

[Xtremski74]

I would say fuel filter or fuel screen in the tank! I had a similar problem on my 2000 5.3 with 125k on it. Sometimes it's the obvious. Oh, yes you can have proper fuel pressure readings even with a bad filter. Because you are testing the fuel pressure without load on the engine so it wont be starved on fuel! When revving the engine is not the same as having the transmission in drive and trying to move a 5k lb. vehicle. It would need more fuel...which it is not getting! jmo good luck

[svensk]

you don't drive that truck enough...that's the problem. I still drive 70 miles a day in my 2000.

[Xtremski74]

Rat ....How you making out with the truck?

[ken1mod]

Does the fuel pressure hold when under load?

 

ken

[ml_electric]

Yank The bed off and replace the fuel pump, its going to go bad anyway. Had to replace the fuel pump twice in my 2000 w/5.3L. Also, over the course of 2-3 tanks of gas, run about 2-3 bottles of gumout fuel injector cleaner in each full tank of gas, that will take care of your fuel injector problem.

[rat454]

Yank The bed off and replace the fuel pump, its going to go bad anyway. Had to replace the fuel pump twice in my 2000 w/5.3L. Also, over the course of 2-3 tanks of gas, run about 2-3 bottles of gumout fuel injector cleaner in each full tank of gas, that will take care of your fuel injector problem.

 

I took the fuel filter off monday night and it was not the least bit clogged. I took it to a friend mechanic that has scanning ability. He has had it since last wednesday and still doesn't know what is wrong. He said he is picking up multiple misfires on no 4 cylinder. He swapped the coil out and the injector with known good ones and no change. This weekend he somehow tested the computers injector drivers thinking the comp may be going bad. He reported that the comp was good.