Chevy Silverado Has An Engine Misfire

1998 Chevy Silverado. Engine size = 5.3L. Work done to repair = changed plugs/wires and distributer cap and rotor.
Question = seems like a misfire when cold but ok when warm. Changed plugs seemed to cure for a couple of trips then started again. Changed wires and distributer/cap seemed to be cured then started again. Checked for trouble codes and there is none. Runs fine when warmed to operating temp. Stumped? If there is a misfire should get a code or pretty much any other problem but none show up?????

Answer:
This sounds like you may have a leaking intake manifold gaskets. These are know for leaking. They have been re-designed by GM to correct the problem of they shrink over time, do not seal when cold, then seal when warmed up. You can check this by spraying carb. cleaner around the bottom of the intake, and listen for any change in idle. Olds style intake gaskets have a green rubber insert around the intake ports. The new style gaskets have an orange insert. Can only be seen with the intake manifold off.

You may also want to clean the throttle bore and plate. When these get a little carbon on them, they can cause idle problems as well as a hard starting problem.

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Question:
2004 Silverado truck (5.7 Vortec) has an incredible amount of vacuum. Difficult to just remove oil cap..air is rushing through breather duct into carb, valve over through PCV. Engine has a high idle and is running rough. I was told to replace intake manifold gasket, not sure if this could be the lower intake gasket again. Truck has been an awesome truck, which i bought new. I have allot of miles on engine and sure allot more to go once this issue is resolved. Can you help me? Any help would be appreciated. Thank you for your time. 1999 chevy c 3500 crew cab. 5.7L V8. Repair done prior = replaced lower intake manifold gasket at 140,000 miles. Repair this problem = replaced distributer cap/button check vacuum lines and PCV.

Aanswer:
Yes, i would have to agree. Probably the lower intake gaskets have gone out, or the upper intake plenum has burned through somewhere. Inspect the upper during replacement of the lower gaskets.


Question:
Problem with my 1999 Chevy Silverado 1500. 5.3 L. Question = I have a 1999 Chevy Silverado that i bought about 2 months ago. Ever since i bought it has had a hard time starting except for first thing in the morning. I had the fuel pump replaced and have been using Lucas Injector Cleaner with every tank of gas. The problem never seemed to get better so i started to read online and i came across over 5 different cases where guys had the same exact problem and they replaced the fuel pressure regulator and the truck has fired great ever since.

I went out and bout a fuel regulator and put it on and now the truck starts great every time, but now the fuel pump is humming like it is running constantly while the truck is idling... ANSWER


Question:
I had it in a gm dealer. The mechanic said he doesn't know why the #4 cylinder has a misfire. Checked injectors. Engine is jerking when i let off of the gas peddle. Engine misses when i rev up the engine in park to about 2000rpm. Really noticeable when i drive in third gear. 2002 Chevy 1/2 ton truck. 4.3L V6. Warning lights: Service engine soon Codes P0300 misfire. Replaced spark plugs & wires cap & rotor cleaned egr,cleaned inside throttle body with Berrymans cleaner.

Answer:
Not sure why the dealer mechanic would say he couldn't find out what was wrong with it. Fuel injectors can fail two ways..They can fail electrically or they can be plugged up inside. If it is definitely not a fuel injector problem the next thing to check would be engine mechanical. Have a compression test done. Have a cylinder leaked down test done. This would show a problem in that cylinder with a valve or a valve seat.


Question:
Silverado 4x4 1998. Engine missing badly, hard starting if at all, very low idle stalling just sitting there. Showing codes:
P0405 exhaust gas recirculation
P0102 Mass air flow
P0336 Crankshaft position
I've changed the distributor cap and rotor button with new parts. I've changed the Mass air flow sensor. All cylinders have spark. I suspect a fuel injection problem, Anything else I should be looking at? Thank you for your time.

Answer:
Check for a vacuum leak. This can cause low idle, EGR coeds and stalling. Check for a leaking fuel pressure regulator (FPR). Check for excessive exhaust backpressure due to a plugged catalytic converter. These have been known to cause more that just acceleration problems. A plugged converter can cause missfires and other codes your have. Check for a loose ground wire on the rear passenger side of the top of the intake manifold, right near the fireall. 1 black wire. Give it a little tug while running to see if it changes things. Usually just the bolt is loose.


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