P0300
04-17-2017, 10:48 PM
#1
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Thread Starter
Join Date: Mar 2002
Location: Lafayette, California
Posts: 275
P0300
My first question is, would running the stock fuel injectors cause my problem?
It is a 1997 SS with a 383 with a stock cam and 1.6 crane roller rockers, LT4 Knock module and an MSD Opti. Idle fuel pressure is at 41 lbs. it has had a slight tapping sound since start up but I can't figure out what it is. it sounds like it's coming from the lifter area. I readjusted the valves but it is still there.
Rough Idle, when I pull the power to the fuel injector on cylinders 2,4,5,7 there is little to no change in the engine. When I pull the others there is a dramatic change.
The car set for a long time and so did the injectors. The fuel was removed from the tank and new fuel was installed for the startup. The car ran fine for over 1500 miles and now with over 2500 it developed the P0300. I changed the plugs and the #1 and #2 were black (#2 was Very bad). All the others appear to be normal. I changed the opti, TPS,EGR and the #2 Injector. The wires are Taylor and there is no arcing or damage so with 2500 miles I figure they are ok. I checked for vacuum leaks and all of the intake bolts are properly torqued.
It's been raining the last two days so I will hook my computer up tomorrow when I get home to give fuel trim info. Last time I hooked up to it was as follows.
STFT B1 34.4%
STFT B2 50%
STFT B1 S1 34.4%
STFT B1 S2 99.2%
STFT B2 S1 50%
STFT B2 S2 99.2
It is a 1997 SS with a 383 with a stock cam and 1.6 crane roller rockers, LT4 Knock module and an MSD Opti. Idle fuel pressure is at 41 lbs. it has had a slight tapping sound since start up but I can't figure out what it is. it sounds like it's coming from the lifter area. I readjusted the valves but it is still there.
Rough Idle, when I pull the power to the fuel injector on cylinders 2,4,5,7 there is little to no change in the engine. When I pull the others there is a dramatic change.
The car set for a long time and so did the injectors. The fuel was removed from the tank and new fuel was installed for the startup. The car ran fine for over 1500 miles and now with over 2500 it developed the P0300. I changed the plugs and the #1 and #2 were black (#2 was Very bad). All the others appear to be normal. I changed the opti, TPS,EGR and the #2 Injector. The wires are Taylor and there is no arcing or damage so with 2500 miles I figure they are ok. I checked for vacuum leaks and all of the intake bolts are properly torqued.
It's been raining the last two days so I will hook my computer up tomorrow when I get home to give fuel trim info. Last time I hooked up to it was as follows.
STFT B1 34.4%
STFT B2 50%
STFT B1 S1 34.4%
STFT B1 S2 99.2%
STFT B2 S1 50%
STFT B2 S2 99.2
04-18-2017, 07:02 AM
#2
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Join Date: Jul 2005
Location: Okemos, MI
Posts: 9,479
Re: P0300
Interesting. P0300 is a random misfire, affecting several cylinders. I would have expected P0302 (misfire in cylinder #2), maybe some others. Is P0300 the only code? Is there both a set code and a pending code?
Have you done a compression test?
I'm not an LT1 guy. I'm betting Fred will have much more useful advice.
Have you done a compression test?
I'm not an LT1 guy. I'm betting Fred will have much more useful advice.
04-19-2017, 12:48 AM
#3
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,646
Re: P0300
Let me understand this.... you are running stock 24 #/HR GM Multec fuel injectors, in a 383 stock cam.... hopefully not with the ProCharger in your signature? What heads? I generally avoid S/C applications because I have limited experience with them.
Stock injectors should be adequate for at least 360 HP at the flywheel. More HP than that and they can be too small.
To assess the fueling system, you first need the long term fuel trims (LTFT) for both banks. While I believe the scanner will give you an average for all the operating cells (0 through 18), you need a left and right LTFT for each cell. The STFT's are confusing to some extent because you give individual values for the pre-cat (S1) and after-cat (S2) O2 sensors. Have never heard of that before, and virtually all the A/F ratio control is via the pre-cat sensors. The after-cat sensors are just checking cat performance (do you even have cats?). 99.2% on a STFT would indicate the STFT is maxed out at the largest possible value of 255 (8-bit field). The STFT's are supposed to be moving up and down cyclically from a bit above 128 to a bit below 128. But as noted I have no idea why you are getting a reading for STFT on the after-cat O2 sensor.
Do you have the capability to run a data log? That would be more useful.
While P0300 is "random misfires" it still a generic indicator of misfires. What you really need is a scanner with GM Enhanced Parameters so you can pull up the misfire count for each individual cylinder.
You indicate your fuel pressure at idle is 41 PSI. Is that with or without the vacuum compensation line attached to the fuel pressure regulator?
Stock injectors should be adequate for at least 360 HP at the flywheel. More HP than that and they can be too small.
To assess the fueling system, you first need the long term fuel trims (LTFT) for both banks. While I believe the scanner will give you an average for all the operating cells (0 through 18), you need a left and right LTFT for each cell. The STFT's are confusing to some extent because you give individual values for the pre-cat (S1) and after-cat (S2) O2 sensors. Have never heard of that before, and virtually all the A/F ratio control is via the pre-cat sensors. The after-cat sensors are just checking cat performance (do you even have cats?). 99.2% on a STFT would indicate the STFT is maxed out at the largest possible value of 255 (8-bit field). The STFT's are supposed to be moving up and down cyclically from a bit above 128 to a bit below 128. But as noted I have no idea why you are getting a reading for STFT on the after-cat O2 sensor.
Do you have the capability to run a data log? That would be more useful.
While P0300 is "random misfires" it still a generic indicator of misfires. What you really need is a scanner with GM Enhanced Parameters so you can pull up the misfire count for each individual cylinder.
You indicate your fuel pressure at idle is 41 PSI. Is that with or without the vacuum compensation line attached to the fuel pressure regulator?
04-21-2017, 11:10 PM
#4
Registered User
Thread Starter
Join Date: Mar 2002
Location: Lafayette, California
Posts: 275
Re: P0300
Thanks for your time. I have removed the super charger and engine and installed an NA 383.
I have Auto Tap so I'll see what the capabilities are.
It did bring up a P0303 and P0307.
The fuel pressure test was done with the vacuum line on.
Jake, that is my next move.
I found the intake gasket blown down into the engine at cylinders #2&4 which must have happened during the back-firing. these were the two plugs that had burnt oil on them. That's what told me to change the intake gaskets.
Today I changed the wires with no change.
I have Auto Tap so I'll see what the capabilities are.
It did bring up a P0303 and P0307.
The fuel pressure test was done with the vacuum line on.
Jake, that is my next move.
I found the intake gasket blown down into the engine at cylinders #2&4 which must have happened during the back-firing. these were the two plugs that had burnt oil on them. That's what told me to change the intake gaskets.
Today I changed the wires with no change.
04-22-2017, 10:03 AM
#5
Administrator
Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,646
Re: P0300
You may have a leak in the FPR vacuum line. Spec for pressure with the line OFF the FPR is 43.5 PSI. GM accepts anything between 41-47 PSI. When you reattach the vacuum line, pressure should drop proportional to intake manifold vacuum. With a stock cam the drop is typically about 8 PSI, putting the pressure in the mid-30's at idle. Might want to check the pressure again.