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99 Silverado P0300 Misfire

Rick99

By Rick99
in Ask A GM Technician

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Rick99 New Member

Rick99

Posted
Posted

I am having repetitive problems with my 99 Silverado with the 4.3 engine developing a misfire and producing a P0300 trouble code. Based on the number of similar posts, this appears to be a fairly common problem with this engine. Has anyone figured out a permanent fix for this issue? I bought the truck approximately two years ago and have replaced the distributor cap three times and just finished cleaning the corrosion from the cap terminals about a half hour ago. I've also replaced the rotor, ignition coil, coil wire, spark plug wires, and spark plugs. As an extra measure, I've also replaced the fuel filter and EGR valve. The last two distributor caps I installed were high quality NAPA units with brass terminals, however it didn't seem to matter much - I still end up having to tear into the ignition system every couple of months or so. Another post on this website recommended making sure that the ventilation screens on the bottom of the distributor were clear, however my 99 model does not appear to have any. Any advice is greatly appreciated. Thanks -

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted
recommended making sure that the ventilation screens on the bottom of the distributor were clear, however my 99 model does not appear to have any.

 

The vent screens are very tiny and recessed into the holes (2) in the base of the dist. You might be overlooking them.

ricobeach Enthusiast

ricobeach

Posted
Posted

Rick99,

 

I have a 2000 Silverado with the 4.3l that threw the same code a few weeks ago. However mine started having trouble starting (longer than normal crank times). I changed the dist. cap, rotor, plugs, etc but nothing helped. I took it in after Christmas and it turned out to be a bad CPI (central port injection). The poppet nozzles and lines were going bad and didn't hold fuel pressure anymore. $900 later my truck works well again. You might want to check the fuel pressure to see if yours is OK. You just connect a fuel pressure guage to the schrader valve on the fuel line located near the distributor cap. It just screws right onto the connection.

The fuel pressure when the pump primes should be about 61 psi. (don't start vehicle yet, just turn key to the on position)

After the pump primes, the pressure should hold steady. If it drops, you have a leak.

When you start the engine, it should read about 5-10 psi lower then the prime pressure.

Hopefully this test can give you a little more insight into what is going on with your fuel system. I had hoped that mine would just be the fuel pressure regulator but when it was tested further at the shop, the poppets and lines were no longer holding pressure and leaking. This is a somewhat common problem with our engines. In California they even got an extension of their warranty for this problem.

 

Rico

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