I have an 03 silverado with a 5.3l vortec. I recently was driving and all of the sudden it started running like crap. It idles rough an excelerates rough. Throws a random misfire code.

Fuel pressure is ? Injectors all come back good on functional tests? And have power and ground, or flash an injector test light? Which bank has the lean ? find out your code definition for your intake. You may need someone with some test equipment if you cannot find a blockage or injector issue. Your computer could need some update, but you may have to ask the General.

Fuel system deposit build up, may require chemical treatment. Boroscope and part switching or substitution can be nec. if there is no help for this calibration. Have you already called GM and asked for direction or advice ?........does one or more of the plugs show evidence of a difference?

List your codes by number and definition again. Then your symptoms. Lets see if anyone reads this and already has your answer, thanks.

Are you using A/C delco parts?

earlier I mentioned fuel system deposits and the boroscope. left out valve deposits. There is chemical remedy available from dealers for concentrated valve deposit cleaning. But you need to know what cylinder(s) misfire. Idle air control can be cleaned. See what you can do with the reporting of codes and definitions and symptoms in a list. Then isolate what cylinder

I used ngk plugs and dura last plugs. I don't have crazy test equipment sadly. The code just says the misfire is random and isn't telling me anything. I don't know what causes it to run lean. And the intake code I dontunderstand.

When repairing automobiles it helps to define, isolate, validate. The parts must be high quality. not price driven. I very strongly suggest that you start with a set of the correct A/C delco spark plugs. you can get them at o'reilley's or wherever, but installing problems can be exactly why you struggle. A/C delco wires will last you 10 years plus, that's why they were used originally. Listing your codes allows me to look them up. Stating their definitions helps verify we are talking about the same thing. Having the symptoms listed nearby in the same paragraph on here gets you thinking and has facts nearby. to consider. Like a tech uses a repair order. I recently helped another guy with a truck like this. 30 times we had to correspond. he finally , did not say what fixed it, but selected the entry where I suggested he put his parts back on from GM, or go get some USED, GM parts from another truck. His aftermarket machine gunning of chinese made attempts had somehow kept it breaking down but he did not tell us.

If you have a plug or injector not firing, the evidence will be on the plug you remove. once you know which cylinder, you can trade parts between two cylinders to follow the failing part. if the engine has the problem, or the fuel, the air, the spark, the injector on-time, etc. we can find it. now I must suggest rereading all these entries to you.

Good guesses LtColumbo, Often intermittant unexplained problems come from aftermarket parts and the misdirection and throwing up of hands leads people down the path of losing their vehicle having invested 80% of the same money because of their avoiding skilled professional help. After the money's already invested in Junque, they comma cryin. I learned that with Mercedes parts vs. photogenic knock-offs on ebay They use the name of the fit but not the actual parts maker, then you get the item and it has a short unhappy life. But on the askers specific subject, I have a little thing that keeps bothering me.....since he has this system too lean code? Whatever code that was, we still have not received any true data, The idea of individual coil misfire would have been mentioned in his first entry as having a misfire code set. He does not say specifically, but he does not give weak or arcing spark symptoms. If he is not seeking pro help yet and low on cash, I would suggest public library search, as they have manuals and auto database info they pay $ for. It is free to look all these things up in, and it's all in one place. Since he was lost, that can get him a base of reference.

Very good analysis, but this asker has not told us any code, but some symptoms and in his own words, his memory of some indiscriminate information. I was attempting to get him to find his notes or rerun the test after his work so far.....the thing about having multiple misfires and or random misfires is that unburned fuel is the product, and in the event the plug fire burning the fuel from the last cycle, the exhaust would have no lean code............Since this inaccuracy exists, and no correct or verified data yet, you would hope to show the asker his cause of his main idea, which was reported as "I am so lost". Then when you can get the data verified.(Only then is it valid data.) perhaps he will respond by telling some actual current info, and see if the previous symptom repeats. Putting Chinese parts on his truck is not what I am trying to do because the intermittancy exists. Why the lean condition?

Whatever is occurring, is enough to be a rough idle and affect accelleration..........This is why I was saying the guesses were guesses. he did not report those codes as hard faults and his memory codes did not include them. That info came from you, thank you, and it is helpful that you have engines that compare. now we have some reason to understand where your ideas came from. Other people with same concern come behind later to read these things and guess that is their concern because it sounds similar. They say their mechanic is ripping them off because we wrote something. lets find out by actually finding out. That all I meant saying "guesses."

To reitterate your basis was that he had those codes, but he had not reported any verified codes yet.

He has replaced plugs and wires, did not describe the condition of the parts removed, and did not give resistance values for the wires. I am concerned he removed the good parts and installed some that last 1/5 of the life of his OEM. Some correct plugs makes sense if he wants a part to compare to. Since you gave your answer, lets see if we get any test readings or the results of a visual inspection at least.

Take to dealer and for around $100 they will hook it up and tell you what it is. It will save you lots of wasted money chasing different symptoms. My problem sounded similar and it ended up being the bad intake gaskets. I spent well over $150 replacing things I didn't need to, but in most places electrical stuff is not refundable once installed.

Seems to me there was an update service bulletin on those designs years ago. The updated parts, use of specific new age cleaning tools that do not marr, and the sealers, thread sealer and procedure make the sealing to stop the coolant going down to flatten the cam by displacing the lube of the engine oil. This goes way back. The problems can be external leakage too. But there has been much discussion lately of the cam sensor. You must research your vehicle knowing your vin ans all your info about your truck. Simply googling M.M.Y. and symptom can lead you into it. Searching every path can lead to the bulletin info, or component testing. An automotive database can speed things up for you if you do not trust Mr. Goodwrench for the right answer in a shorter number of minutes.

I reread the above posts from months ago, the concern and the codes are not fully known. The parts are suspect. he does not answer questions. 7 months now if you are reading this with a similar concern on yours. If it was lean, the intakes can be verified leaking simply enough without test equipment.

i have a 2005 chevy silverado 5.3lt its only firing on three cylcers anyone have ideal what it be be or any help