random code p0307 and p0300

joejoe1985 · 05-07-2008, 01:51 AM

i have a 1996 siveraldo 5.7l been having these check engine codes and went ahead replaced distributor cap rotor wires and plugs new coil new fuel filter and oxygen sensors still didnt fix it i noticed it runs fine as long as its idling or driving down the road it only hesitates if i stop at a red light and stomp on the gas to hard it cuts out like lack of fuel ran fuel pressure test and showed fuel pressure was fine and also noticed when im crusing down highway it kinda hesitates when im going off hill like its flooding but havent smell any gas leaks other than that runs fine and has plenty of power all the other times. could it be a bad computer or bad injector someone told me maybe burned valve since i had the convertors removed and drove it for about 6 months on open exhaust.

Case 7230 · 05-07-2008, 10:57 AM

p0307 is misfire cyl. No.7. You have replaced a lot of the things recommended, really only leaves Possible faulty fuel injector, burnt exhaust valve or faulty cat. p0300 is random/multiple misfire so in addition to above check for faulty EGR valve or faulty camshaft position sensor.

joejoe1985 · 05-07-2008, 01:32 PM

on these trucks how do u test fuel injector since its a 2 piece manifold?

Sneakysportsman · 05-07-2008, 08:19 PM

Sounds like a Clogged fuel filter in the tank or weak fuel pump, Because at idle it dosen't require the excessive fuel flow to maintain power, therefore the fuel pressure will show an adequate reading. Also the TPS will give the same symptoms as it also controls the flow of fuel. Even a bad mass air flow sensor will cause misfiring.
To check SFI model disconect the main injection harness at the fuel meter body and test voltages there. Check the oil for a gas smell, if the fuel spider inside the intake has a cracked fuel delivery line to the poppet nozzle it will miss on a cylinder and dump the gas into the oil. Get a set of noid lites to test the fuel system.

joejoe1985 · 05-07-2008, 11:19 PM

well i dont smell gas in the oil

joejoe1985 · 05-28-2008, 11:29 PM

ok i read and it said specs for fuel pump should be 60-66 psi but i did fuel pressure test and im getting 50psi could that be the prob?

Sneakysportsman · 05-28-2008, 11:32 PM

Most defanitely the problem, because a lower fuel pressure will not spray as much fuel as a highr fuel pressure. Remember there is a filter in the tank.

joejoe1985 · 05-28-2008, 11:59 PM

okay is it a filter for the pump?

joejoe1985 · 05-29-2008, 12:04 AM

if so do i have to get inside the tank if should would u reccomend going ahead and changing fuel pump while ur there even if the pumps good its orignal pump and truck has 150000 miles

Sneakysportsman · 05-29-2008, 10:10 AM

A tank removal is a pain in the A$$, since you are droping the tank with low fuel pressure problems a pump replacement is a sure bet that you have a good working pump. Milage means nothing, I know that the price of gas is too high but try to keep at least a 1/4 tank of fuel at all times, because the fuel in the tank cools the pump keeping the plastic gears from getting hot. I bought a Walbro in tank pump fro a High performance application and it didn't last a month and I paid $200 for it.

05-07-2008, 01:51 AM	#1
joejoe1985 Full Member Join Date: May 2008 Posts: 15	random code p0307 and p0300 i have a 1996 siveraldo 5.7l been having these check engine codes and went ahead replaced distributor cap rotor wires and plugs new coil new fuel filter and oxygen sensors still didnt fix it i noticed it runs fine as long as its idling or driving down the road it only hesitates if i stop at a red light and stomp on the gas to hard it cuts out like lack of fuel ran fuel pressure test and showed fuel pressure was fine and also noticed when im crusing down highway it kinda hesitates when im going off hill like its flooding but havent smell any gas leaks other than that runs fine and has plenty of power all the other times. could it be a bad computer or bad injector someone told me maybe burned valve since i had the convertors removed and drove it for about 6 months on open exhaust.

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05-07-2008, 10:57 AM	#2
Case 7230 Senior Member Join Date: Dec 2007 Posts: 547	p0307 is misfire cyl. No.7. You have replaced a lot of the things recommended, really only leaves Possible faulty fuel injector, burnt exhaust valve or faulty cat. p0300 is random/multiple misfire so in addition to above check for faulty EGR valve or faulty camshaft position sensor.

05-07-2008, 01:32 PM	#3
joejoe1985 Full Member Join Date: May 2008 Posts: 15	on these trucks how do u test fuel injector since its a 2 piece manifold?

05-07-2008, 08:19 PM	#4
Sneakysportsman Senior Member Join Date: Jun 2007 Posts: 296	Sounds like a Clogged fuel filter in the tank or weak fuel pump, Because at idle it dosen't require the excessive fuel flow to maintain power, therefore the fuel pressure will show an adequate reading. Also the TPS will give the same symptoms as it also controls the flow of fuel. Even a bad mass air flow sensor will cause misfiring. To check SFI model disconect the main injection harness at the fuel meter body and test voltages there. Check the oil for a gas smell, if the fuel spider inside the intake has a cracked fuel delivery line to the poppet nozzle it will miss on a cylinder and dump the gas into the oil. Get a set of noid lites to test the fuel system.

05-07-2008, 11:19 PM	#5
joejoe1985 Full Member Join Date: May 2008 Posts: 15	well i dont smell gas in the oil

05-28-2008, 11:29 PM	#6
joejoe1985 Full Member Join Date: May 2008 Posts: 15	ok i read and it said specs for fuel pump should be 60-66 psi but i did fuel pressure test and im getting 50psi could that be the prob?

05-28-2008, 11:32 PM	#7
Sneakysportsman Senior Member Join Date: Jun 2007 Posts: 296	Most defanitely the problem, because a lower fuel pressure will not spray as much fuel as a highr fuel pressure. Remember there is a filter in the tank.

05-28-2008, 11:59 PM	#8
joejoe1985 Full Member Join Date: May 2008 Posts: 15	okay is it a filter for the pump?

05-29-2008, 12:04 AM	#9
joejoe1985 Full Member Join Date: May 2008 Posts: 15	if so do i have to get inside the tank if should would u reccomend going ahead and changing fuel pump while ur there even if the pumps good its orignal pump and truck has 150000 miles

05-29-2008, 10:10 AM	#10
Sneakysportsman Senior Member Join Date: Jun 2007 Posts: 296	A tank removal is a pain in the A$$, since you are droping the tank with low fuel pressure problems a pump replacement is a sure bet that you have a good working pump. Milage means nothing, I know that the price of gas is too high but try to keep at least a 1/4 tank of fuel at all times, because the fuel in the tank cools the pump keeping the plastic gears from getting hot. I bought a Walbro in tank pump fro a High performance application and it didn't last a month and I paid $200 for it.