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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4458
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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Chevrolet: code p 300 the fun misfire I have 1999 suburbanI

Customer Question

code p 300 the fun misfire I have 1999 suburban
I first replaced plugs wires cap and rotor
and it ran great. I driving down the highway heard a pop and check light came on. miss fire in cyl. 2 replace plug didn't fix it replace injector no luck. keep driving it. blow out the cat. replace cat, all 4 o2 sen. and feul injector spier and change out the coil.
Submitted: 1 year ago.
Category: Chevy
Expert:  Jerry Newton replied 1 year ago.
OK, what you need here is some diagnosis. I would start with a compression test, test all of the cylinders with all of the plugs removed. You have replaced fuel injector, plug, all of the ignition components, etc. but seem to have glossed right over the engine mechanical systems. Compression testing is the place to start here, you may find that you have low or no compression in cylinder #2.
Customer: replied 1 year ago.
I have done compression test on cyl 2 180 psi and 160 psi cyl 4 also did fuel presser of 50 psi
Expert:  Jerry Newton replied 1 year ago.
OK! Good deal. Fuel pressure is a little low, but if it runs, it's fine. Low fuel pressure won't affect one cylinder. It misfires at cylinder 2 all the time, even at idle while running in your driveway/garage? You can feel it running badly? Check engine light flashes when it's running?
Customer: replied 1 year ago.
yes the light flash at times. would the map sensor do this
Expert:  Jerry Newton replied 1 year ago.
Nope, whatever is causing this is specific to cylinder #2. You've replaced everything related to that cylinder, and still have trouble at cylinder 2. I would physically verify that it's cylinder 2 that's giving you trouble. Take a few steps backward, if you will. Cylinder 2 is the front cylinder on the passenger side of the engine. With the engine running, pull the #2 plug wire off (protect yourself from electrocution as necessary) and verify that the engine runs exactly the same whether the plug wire is attached or not, and also verify that you have spark present there. If it's definitely #2, remove the valve cover and check for a broken valve spring, bent pushrod, something of that nature.
Customer: replied 1 year ago.
ok did a complete comprehension check 180 - 170 psi. check no bend or broken vive train or right side. right side plugs are black from running rich. left side light brown
Expert:  Jerry Newton replied 1 year ago.
Ah, that's good info.Replace the right side oxygen sensor and see if the problem goes away.
Customer: replied 1 year ago.
ok I replace upper o2 sensor no luck. would you only have bank 2 run rich with cracked intake? and also you might have misunderstood me my problem started with a miss fire c0de in cly 2 and now I have code 300 random miss fire. its making the right side run rich. I do have a code reader that has live data the type to you
Expert:  Jerry Newton replied 1 year ago.
This is what I suspect: you have a faulty oxygen sensor that is giving a false lean indication, which is driving the computer to make the mixture richer. This is something I've seen a number of times, and typically swapping out the oxygen sensor solves this issue. The other variable is the fuel pressure regulator, but that tends to affect only the rear cylinders on the right side, due to its placement. Since you have a scan tool, let's get it running and look at some of the fuel trim data, and see what we can learn from it. Post some of the data up here if you like, and I will check it out for you.
Customer: replied 1 year ago.
here is my live data
FRAME 1 FRAME 2 FR-3 FR-4 FR-5 FR-6 FR-7 FR-8 FR-9 FR-10
fuel sys 1 OL OL OL OL OL OL OL OL OL OL
fuel sys 2 OL OL OL OL 0L OL OL OL OL OL
Calc load ( %) 6.7 6.7 6.7 6.7 6.7 6.7 6.7 6.7 6.7 6.3
ECT (*C) 26 27 27 27 27 27 29 29 30 30
STFT B1 (%) -1.6 -4.7 -6.3 -3.9 -4.7 -3.9 -5.5 -47 -3.9 -0.8
LTFT B1 (%) -2.3 -2.3 - 2.3 -2.3 -2.3 - 2.3 -2.3 -2.3 2.3 -2.3
STFT B2 (%) 1.6 10.2 - 15.6 20.3 24.2 29.7 34.4 39.1 43.0 0.8
LTFT B2 (%) 9.4 9.4 9.4 9.4 9.4 9.4 9.4 9.4 9.4 9.4
MAP (KPA ) 43 43 43 43 43 43 43 44 44 42
ENG RPM 798 844 851 857 837 845 799 774 823 830
SPARK ADV(*) 26.0 22.0 21.0 22.0 21.5 18.5 21.5 22.0 27.0 22.5
IAR (*C) 24 24 24 24 24 24 24 24 24 24
MAF(G/S) 15.18 15.12 15.08 14.94 15.08 15.08 15.08 14.91 14.86 14.63
TPS (%) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
O2SLOC B1S12___ B2S12___
O2S B1 S1(V) 0.790 0.245 0.040 0.045 0.495 0.040 0.085 0.055 0.745 0.785
STFT B1 S1(%) -3.1 -3.9 -5.5 -5.5 -4.7 -4.7 -2.3 -3.9 -3.1 -3.9
O2S B1 S2 (v) 0.690 0.600 0.500 0.565 0.645 0.625 0.410 0.580 0.495 0.840
STFT B1 S2 (%) 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2
O2S B2 S1 (v) 0.300 0.290 0.395 0.315 0.360 0.335 0.335 0.395 0.380 0.205
STFT B2 S1 (%) 3.9 12.5 18.0 22.7 27.3 32.0 36.7 41.4 45.3 3.1
O2S B2 S2 (v) 0.575 0.590 0.605 0.600 0.635 0.620 0.625 0.635 0.645 0.560
STFT B2 S2 (%) 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99,2 99.2
OBDSup OBD2
Expert:  Jerry Newton replied 1 year ago.
That is hard to read, but what I see is B2S1 not really doing anything, seemingly staying between .2 and .4v for those frames. During the same frames, I see B1S1 with a lot of activity, moving from .790 to .045 and back again. This is what you want to see. If the sensor isn't moving, it suggests to me that it's fixed lean, which would cause the computer to react by richening the fuel mixture.
Customer: replied 1 year ago.
sorry they are the first 10 frame off the live data playback they were all nice where you could read them. but I send them you got what you got. lol. the code reader is new to me I don't really understand what it s telling me
all the 02 sensor are new. I put in whole new fuel injector assembly with new regulator on it
Expert:  Jerry Newton replied 1 year ago.
I am able to mostly figure out what you posted there, 10 frames of each data line. Scanning through it, the one thing that stands out to me is that B2S1 inactivity. All sensors are new? Can you warm that up to operating temp, should be about 100C, and give me that data again? I want to see what it's doing when it's warmed up.
Customer: replied 1 year ago.
ok will do
Expert:  Jerry Newton replied 1 year ago.
Let me know what you come up with. I am getting ready to head out of here for the day, but I will follow up perhaps later tonight, and definitely tomorrow, so don't worry if you don't hear back right away.
Customer: replied 1 year ago.
here are the first 10 frames off live data after at operating temp
frame 1 2 3 4 5 6 7 8 9 10
fuel sys 1 cl CL CL CL CL CL CL CL CL CL
fuel sys cl CL CL CL CL CL CL CL CL CL
calc load (%) 4.3 4.3 4.3 4.3 4.3 4.3 4.3 4.3 4.3 4.3
ect(*C) 90 90 90 90 90 90 90 90 90 90
STFT B1 (%) -2.3 -0.8 1.6 0.0 -0.8 0.8 2.3 0.8 0.0 0.8
LTFT B1 (%) -4.7 -4.7 -4.7 -4.7 -4.7 -4.7 -4.7 -4.7 -4.7 -4.7
STFT B2 (%) 50.0 50.0 50 50.0 50 50.0 50.0 50.0 50.0 50.0
LTFT B2 (%) 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0 25.0
MAP(KPA) 46 44 45 45 45 45 45 44 46 45
ENG RPM 616 601 579 588 638 623 604 646 576 577
SPARK ADV 17.5 27 26.0 27.0 19.0 20.0 25.0 19.5 20.0 21.0
IAR (*c) 30 30 30 30 30 30 30 30 30 30
MAF(G/S) 10.04 9.92 9.85 9.75 9.91 10.08 9.88 10.03 10.07 9.92
TPS (%) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
O2SLOC B1S12___ B2SI2___
O2S B1 (V) 0.475 0.760 0.750 0.060 0.065 0.060 0.215 0.075 0.080 0.675
STFT B1 S1(%) 0.0 0.0 0.8 0.8 0.0 0.8 1.6 1.6 0.0 0.0
O2S B1 S2 (v) 0.070 0.140 0.80 0.060 0.065 0.060 0.065 0.065 0.065 0.060
STFT B1 S2(%) 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2
O2S B2 S1 (V) 0.030 0.025 0.815 0.015 0.015 0.030 0.010 0.075 0.030 0.010
STFT B2 S1 (%) 50.0 50.0 50.0 50.0 50 50 50 50.0 50.0 50.0
O2S B2 S2(V) 0,030 0.060 0.260 0.055 0.060 0.035 0.050 0.050 0.035 0.040
STFT B2 S2(%) 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2 99.2Jerry also check the battery voltage and that is reading 14V also over the top of my motor with the my stethoscope to see if I could hear a lead and the big no. and by the way my name is ***** ***** i didnt tell you sooner
Expert:  Jerry Newton replied 1 year ago.
Sorry for the delay, I was unavailable yesterday. So, let's see what we have here. Fuel trim is maxed out on bank 2, and bank2 sensor 1 is lean all the time. You either have a giant vacuum leak on bank 2, or you have a faulty oxygen sensor. A couple of things to note: I don't believe you have a vacuum leak or an actual lean condition, because your plugs are black. It's getting too much fuel, because the computer is being led to believe that it's lean when it's actually rich. Also, a "new" oxygen sensor does not equal a "good" oxygen sensor. All you have to do is drop it on the floor, and it's broken. It still appears that there's something wrong with your o2 sensor signal on that right side.
Customer: replied 1 year ago.
I have replace the front o2 sensor with a 2nd new one. Should I replace the back one to. Or could computer be bad in the truck. Would any other sensor send the motor I. To rich condition
Expert:  Jerry Newton replied 1 year ago.
It comes directly from the front O2 sensor for each bank. If this doesn't fix it, I would find a way to drive the sensor signal rich and see if the computer responds. It's possible that you have a bad computer, but I would want to prove it, not just throw a part at it.
Customer: replied 1 year ago.
should replace o2 sensor after the cat too? I have replaced the o2 sensor in front of the cat twice with new one.
Expert:  Jerry Newton replied 1 year ago.
The downstream sensor doesn't affect fuel trim, so no, there should be no point in replacing that one. What are you using for oxygen sensors, what brand?
Customer: replied 1 year ago.
jerry, I put all bosch o2 sensors and a walker exhaust. and when I put the new bosch o2 in the front right side. if the intake was cracked I would rich or lead on both sides? and to I do have some car knowledge I used to rebuild motor back in the 80's
and I have always drove a ford trucks. so the chevy has me stumped
Expert:  Jerry Newton replied 1 year ago.
it's not so much the difference between ford and chevy, we have a fueling issue. Based on the scan data, it's reading lean on bank 2, but you said the plugs were all black, so that tells me that it's actually running rich, but the oxygen sensor is reading lean. Unless the plugs just weren't really black, maybe I'm barking up the wrong tree on this. Let's put the black plugs aside for a moment. Yes, if you had a crack in the intake, you could be driving those cylinders lean and the oxygen sensor is reflecting that. So, if you take a little bit of carb cleaner and spray it on the cracked in the intake, does the idle pickup and smooth out?
Customer: replied 1 year ago.
I have stayed the intake 3 different times and it didn't change anything in the way motor ran
Expert:  Jerry Newton replied 1 year ago.
OK. I'm not clear on why you think there is a crack in the intake, whether you saw something or whatever. But if it's not leaking, it's not leaking. So, we're back to this lean indication on the scan tool. Left and right oxygen sensors are *usually* interchangeable. If the plugs are the same, swap them left to right, and see if the condition follows to the left bank instead.
Customer: replied 1 year ago.
Ok I will try that tomorrow . And if that doesn't work what do think I should try then
Expert:  Jerry Newton replied 1 year ago.
The misfire on bank 2 is related to the fact that it's also reading lean on bank 2. I definitely relate those two things because the fuel trim is maxed out. The computer is cranking up the fuel delivery on that bank in response to the O2 reading. If it's still doing it, unplug B2S1 and see what the oxygen sensor voltage is then. It should be .455V or very close to that when disconnected. If it's still lean when you unplug it (close to 0.0V), there is something pulling that signal low (short to ground) or the PCM is faulty.
Customer: replied 1 year ago.
Ok thanks Jerry, I will try that and get back to your enjoy your weekend
Expert:  Jerry Newton replied 1 year ago.
Likewise, let me know if you need anything else. I will be around on and off this weekend.

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