2003 Chevy Silverado 1500 Runs Horrible

dewfpo · January 2, 2018

If you had a leaking intake gasket and you sprayed an ignitable fuel near the leak, the engine idle speed should have increased while you were spraying it in the location of the leak.

I would not have expected it to kill your engine unless your engine was already running ridiculously rich. In which case you choked off the additional air and made the A/F mixture even richer.

It could have been a fluke. Can you duplicate the engine dying. If yes, then I'd say you "at least" have a gasket failure.

Are you sparkplugs wet or black?

DEWFPO

Jacob11531 · January 3, 2018

I'll try again tomorrow more thoroughly. I have to admit I was kinda scared spraying that flammable stuff. Don't want to start fire. I'll look at a spark plug also.

Armo325 · January 3, 2018

I drove a 2005 Tahoe for 10 years with the same motor (I also added a Flowmaster 40 - it sounds awesome on that motor) you have. I didn't have the rough idle but I had all kind of codes for lean fuel condition. As txab already mentioned, the intake gasket is a VERY common culprit. In fact, I took the top of the motor apart and discovered that I had the newer, improved gasket and that was NOT the problem.

For me it was the mass airflow sensor. I know you said you cleaned it - I cleaned mine, too, but the problem didn't go away until I replaced it. It's a pretty cheap part (I bought mine here from Amazon - it's currently $79.50) and an easy swap. I don't know what the issue was but it was internal to the MAF sensor. Just another possibility to consider.

Good luck and keep us posted.

Jacob11531 · January 3, 2018

Thanks for the info. Forgot to mention this tho but when I got the codes checked for the third time 2 weeks ago it said to replace maf so it does have a new one now. It is either a intake manifold gasket which I will try again tomorrow or injectors. I will test injector resistance then do the screwdriver test to see if they fire constantly. Don't know what else this could be but this pos has caused me to go broke almost.

Jacob11531 · January 3, 2018

Just another question someone might be able to help me answer. I did a oil change about 7k miles ago with full synthetic high mileage oil. It is still golden and in good condition but I was going to go off when the computer tells me to change the oil. Should I change it when it looks dirty and bad or wait for the computer to tell me when? I also reset the system when I changed it. In essence my question is if the computer oil life monitor is reliable. Thanks again.

Armo325 · January 3, 2018

1 hour ago, Jacob11531 said:

Thanks for the info. Forgot to mention this tho but when I got the codes checked for the third time 2 weeks ago it said to replace maf so it does have a new one now. It is either a intake manifold gasket which I will try again tomorrow or injectors. I will test injector resistance then do the screwdriver test to see if they fire constantly. Don't know what else this could be but this pos has caused me to go broke almost.

Not that you want to spend extra money for no reason on the truck but, if you're going to replace the intake gasket, you may want to consider replacing the knock sensors while you're in there. It's easy to do with the intake manifold removed. Here is the valley with the new sensors and sensor wire installed when I did mine. Of note, the new intake gaskets are not yet installed in this photo.

I went to Amazon (again) for the parts - two knock sensors and the knock sensor wire.

26 minutes ago, Jacob11531 said:

Just another question someone might be able to help me answer. I did a oil change about 7k miles ago with full synthetic high mileage oil. It is still golden and in good condition but I was going to go off when the computer tells me to change the oil. Should I change it when it looks dirty and bad or wait for the computer to tell me when? I also reset the system when I changed it. In essence my question is if the computer oil life monitor is reliable. Thanks again.

There is some debate on this site (among others) about that. I know the owner's manual says the computer takes in to consideration "driving habits" to determine when it's time to change the oil but I have no idea what that actually means. I don't have access to a GM software engineer that could explain what data feeds the engine oil life display. I can safely say the computer has no idea what type of oil is in the motor but it likely assumes some base-quality motor oil. Not a great answer. Sorry.

Jacob11531 · January 3, 2018

At the moment right now I can't afford much other than the gasket. However don't I need to put silicon or something on top of or around the knock sensors? Seen it in someone's post. Thanks for info.

davester · January 3, 2018

It's not absolutely necessary, but if you wash your engine regularly, some water will run on that valley cover plate, and get into the two holes where the knock sensors are mounted, and then begin to rust the hell out of them. To prevent/reduce the likelyhood of that happening, people will either build a "dam" of rtv around the hole, or put rtv on the rubber plugs you see the wiring going through.

My truck is a work truck, so the engine pretty much never gets washed (but I don't know for certain, as I only bought it ~3 years ago), and when I replaced the knock sensors as part of doing the intake gaskets, both of them were rust-free and working fine, without any of that rtv present. I did replace them only because I had ordered all the parts from rockauto prior to disassembling the truck to see their condition, because the price of the parts was ridiculously cheaper than local parts stores).

I did put an rtv dam around the two holes, "just in case", but realistically they will never see water, short of a coolant leak spraying water there...

Jacob11531 · January 3, 2018

I will probaby do that since I plan on washing my engine bay regularly. Thanks for info.

Armo325 · January 3, 2018

davester nailed it. I have nothing to add except to say I did NOT use any RTV on mine. Short of driving in to a lake (something I have managed to avoid thus far), I was confident the valley would not be exposed to water so I chose to skip the sealant.

Jacob11531 · January 3, 2018

Ok so today I repeated the gasket and nothing happened this time so I think it was just a coincidence. Soooo, I am going to test the fuel injectors today. Also, when I have the truck in drive and I hit the gas and get to about 10mph the engine light starts to flash. If I hit the gas in park it wont misfire. This has been happening for the past week now. Anyone know what this could be? Thanks!

Jacob11531 · January 3, 2018

Ok so I tested the injectors resistance and they all seem fine with a resistance of 12.8-13.3

Armo325 · January 3, 2018

1 hour ago, Jacob11531 said:

Ok so today I repeated the gasket and nothing happened this time so I think it was just a coincidence. Soooo, I am going to test the fuel injectors today. Also, when I have the truck in drive and I hit the gas and get to about 10mph the engine light starts to flash. If I hit the gas in park it wont misfire. This has been happening for the past week now. Anyone know what this could be? Thanks!

I'm guessing it's a typo but is that supposed to say you replaced the intake gasket?

This is a bit of a guess only using the information provided so far but the vacuum system will have different pressures when under load as opposed to sitting in park, even at the same RPM. I'm guessing a vacuum leak or other air leak somewhere.

Jacob11531 · January 3, 2018

No I tried the starter fluid around the gasket today and nothing happened so it was just a coincidence. All the vacuum hoses are tight and I am going to do a 3 part sea foam cleanuing to see if that works. I' have also noticed that when i replace something the computer tells me to the code will not go away for example the maf sensor i replaced there is still a code saying to replace it. Maybe that can help some. Thanks for info.

Jacob11531 · January 3, 2018

Ran into a buddy of mine who is pretty good with mechanics and we found that cylinder 3 is not firing. We took out the plug and seen if it was sparking and no spark at all so no fuel issue. I replaced all the spark plugs today. I have all new coils and when i put on the new coil pack there was no difference in truck performance as there was with the old coil so i dont think its a bad coil. I think it is the wire that connects to the coil from the truck but i could be wrong. Any help on why this spark plug wont fire will be appreciated. (Also the spark plugs were gapped at .066 which was ALOT. I seen the correct gap is suppost to be .040 but have also read that .060 gives the truck better mpg and performance. what do you guys think) Thanks!