Random sputter and backfire


#1

2000 Silverado 5.3
So I recently replaced my head gaskets due to the fact that they were ****. And I think I’m finally done working on this truck when I took it for a long drive and it did a little sputter and then backfired. I thought it was nothing since after the backfire it went right back to running perfect. Then again another day it did it again. Sputter. A loss of power and the BANG backfire and it was back to running like new. At first it was very rare. Maybe once every other day. Now its doing it 2-3 times on a normal drive to work. And it will idle rough during one of these spells as well now. When it starts to sputter and lose power I can throw it in neutral and rev it a few times. Once it backfires it’s back to running like new. Only codes I’m getting are o2 sensors but I have no cats. Just straight pipes from headers to a turn down exhaust. I was thinking maybe a fuel regulator but I had replaced that just a few months ago. Could it have already gone bad? I changed ymy fuel filter not long ago and cleaned injectors and rails when replaced head gasket. Can somebody please help? I’m stumped. :confused: thank you also new maf sensor and new intake gaskets.


#2

Backfires are often caused by misfires, which is why I think you get a stutter first, then a backfire. For some reason the fuel isn’t being ignited in the cylinder, and instead it gets pushed out into the exhaust, where it ignites there. So a problematic ignition system which doesn’t spark like it should be is more likely than the fuel system.

I’m puzzled by one thing you say. I don’t see how you can run a modern engine like this with no O2 sensors. The computer requires at least one O2 sensor for each exhaust bank, otherwise it has no way to adjust the fuel/air mixture. With no cat you could eliminate the post-cat sensor, but you still need the pre-cat sensor it seems to me.


#3

Have o2 sensors just no cats. Car was throwing a p0420 and p0430 code for cats operating below thresh hold or something along those lines. Sorry should have been more clear. When replacing my head gaskets I used a torque ratio chart saying 22ft lbs plus 90 degrees and I did it in the correct order. And after being done with the project I ran across another torque ratio charts saying heads should be torqued an additional 90 degrees. Has me worried to death my head gasket didn’t seal completely and the faulty ignition is from coolant leaking in to cylinder. I haven’t seen a loss of coolant yet, but its only been about a week or so…


#4

Plus 90 degrees minus the front and back inner bolts which I torque to plus 50 degrees


#5

Ok, I understand about the cats. You are right, the O2 codes are almost certainly b/c they are missing. BTW, folks have posted here that there are gadgets available for some engines – not sure how legal they are – you can hook up to where the rear sensors are supposed to go to turn off those missing-cat codes.

Coolant spurting into the combustion chamber could certainly cause misfiring. You could pressure test your cooling system I guess, if you think the new head gasket might be compromised. I can’t speak to the correct torque procedure for you head bolts. But I expect if you drop by a dealership shop during a time when they aren’t busy, somebody there will know the correct method. Not something to guess about, and no need to guess. It would be wise I think – since you seem willing to make major engine repairs on your own – to secure a factory service manual for your vehicle, either paper copy or an electronic version. Might save you a lot of grief in the future.

Since you notice no loss of coolant, I continue to think the most likely explanation is a problematic ignition system.

  • crank sensor
  • cam sensor
  • igniter
  • coil(s)
  • spark plug wires (if applicable)
  • spark plugs & gap
  • distributor cap and rotor (if applicable)
  • distributor could be worn out (again if applicable)

For the fuel pressure regulator, remove the vacuum hose and see if there is any gasoline in there. There shouldn’t be. You can verify the fuel pressure is correct by measuring it, if that’s in doubt. Suggest a thorough vacuum system check, including checking all the vacuum operated devices for leaks. You use one of those hand-operated vacuum pumps/gauge gadgets to do that. And double check that the PCV system is hooked up correctly, and if it has a PCV valve, that it is working like it should.

It would probably make sense to do a compression check too. How did the valves and seats look when you removed the head? Was the head surface planed for flatness as part of the head gasket job?