p0300 help

[Gregs]

hey guys i'm having a little trouble with my truck. Leaving a parking lot the truck starts sounding weird and the check engine light comes on. It starts shuddering and the check engine light is flashing so i know that its misfiring. i wasn't able to get up over 20 mph so i pulled to the side of the road. everything looked ok so i started it up again and drive home without any problems. Scanned it and all it has is p0300. watching misfires at idle i have about 4 per cylinder that go away if i make the engine idle up. i'm thinking the misfires at idle are because of my cam. it doesn't have cats so its not like that could be the problem. What do you guys think? I didn't have my v2 with me so i didn't get anything caught on a log. plugs and wires are pretty new and fpr is ok. thinking possible fuel injector hung up? freeze frame showed stft bank 1 at -25 and ltft bank 1 were -3 when the code set. bank 1 is an lc1 simulated nb

i also checked crank angle sensor cal and it was ok

[joecar]

The LTFT at -25% indicates there is too much fuel if the fuel was being burnt properly...

if the fuel was not being burnt properly (as in a misfire) then the NBO2 would see excess oxygen and would cause the PCM to drive the LTFT grossly positive;

so we can say that there is too much fuel on that bank...

[ assuming it is the truck in your sig, it would have a manifold referenced FPR ]

check these:
- remove reference hose from FPR and check for fuel in the hose or fuel coming out of the FPR (if it is then FPR is bad);
- with referenced FPR, rail pressure should vary as MAP or MANVAC vary (i.e. measured rail pressure minus MAP should yield a constant);
- key on engine off (cycle key several times to prime fuel rail), you should see rail pressure maintain steady (if not, the something leaks: injector(s) or FPR).

It's on one bank so it probably isn't FPR... it maybe leaky injector(s) on that bank.

Of course, check plug wires, coils; also check for loss of coolant and do pressure test on cooling system;

how old are the NBO2 sensor(s)...?

[Gregs]

The LTFT at -25% indicates there is too much fuel if the fuel was being burnt properly...

if the fuel was not being burnt properly (as in a misfire) then the NBO2 would see excess oxygen and would cause the PCM to drive the LTFT grossly positive;

so we can say that there is too much fuel on that bank...

[ assuming it is the truck in your sig, it would have a manifold referenced FPR ]

check these:
- remove reference hose from FPR and check for fuel in the hose or fuel coming out of the FPR (if it is then FPR is bad);
- with referenced FPR, rail pressure should vary as MAP or MANVAC vary (i.e. measured rail pressure minus MAP should yield a constant);
- key on engine off (cycle key several times to prime fuel rail), you should see rail pressure maintain steady (if not, the something leaks: injector(s) or FPR).

It's on one bank so it probably isn't FPR... it maybe leaky injector(s) on that bank.

Of course, check plug wires, coils; also check for loss of coolant and do pressure test on cooling system;

how old are the NBO2 sensor(s)...?

yeah i checked the fpr and its fine, bank 1 is a wideband if that matters. wires and plugs are very new. will do a coolant pressure test tonight at work, but i'm not missing any coolant.

the freeze frame only showed
bank 2 stft = -3
bank 2 ltft = -3
bank 1 stft = -25
bank 1 ltft = -3

it runs ok right now. i was thinking that since only bank 1 was very rich that an injector was bad on that side but if it were one bad injector i shouldn't have gotten a random misfire right? shouldn't it have been cylinder specific?

[joecar]

Check also your ground connections.

[nevinsb]

It runs fine with STFT disabled? Looks like you got a 266 cam in there, which isn't all that hot of a cam. Could also be a valve train failure.

[Gregs]

i had the code pop up again, i didn't feel the truck misfire but i saw the light turn on. I got a freeze frame shot and i was scanning when the light turned on. I'm very confused because i don't see anything grossly wrong. Help!


[PCM INFO]
VIN=2GCEK19T531248207
OS=12579405
Stream=LS1B

[PCM CVN]
12579405=A583
12577861=D700
12579437=23F6
12572447=FFD4
12570845=7739
12578354=82D4
12572573=78D8
12572533=C012

[System Readiness Tests]
MIL=ON
DTC_CNT=1
MIS=Ready
FUEL=Ready
CCM=Ready
CAT=Pending
HCAT=N/A
EVAP=Pending
AIR=N/A
ACRF=N/A
O2S=Pending
HTR=Ready
EGR=N/A

[DTCs EPA Current]
P0300=PCM,--------

[DTCs EPA Pending]
P0300=PCM,--------

[DTCs Enhanced]
P0300=PCM,MF-HX--I

[PCM Freeze Frame 0]
<0002>=0x0300
FUELSYS.FUELSYS1=CL
FUELSYS.FUELSYS2=CL
LOAD_PCT=10.2%
ECT=91°C
SHRTFT1=0.8%
LONGFT1=-2.3%
SHRTFT2=7.0%
LONGFT2=0.0%
MAP=54kPa
RPM=1434rpm
VSS=16kmh
MAF=25.3g/s
TP=21.2%
STATE02.TCCPWM=Inactive
STATE02.EBPSW=Inactive
STATE02.LD=Inactive
STATE02.CBPSW=Inactive
STATE02.TCCSOL=Inactive
STATE02.VATFD=Inactive
STATE02.TRACSTAT=Inactive
EGRS=0.000V
FTEMP=63°C
FTPS=1.647V
EGR=0.0%
ECT1ST=86°C
IDLEDES=5rpm
EGRDES=0.0%
BARO_B=98.9kPa
<119E>=0x92
RUNTIME=29600s
MFCSTAT.MFC2ND=None
MFCSTAT.MFC1ST=None
ODOFIRST=15km
ODOLAST=15km
FFCOUNT=1Count
FFPASS=0Count
FFNOTRUN=0Count
IBPW1=5.7ms
IBPW2=6.2ms
ETCPED=5.9%
ETCTP=21.6%
E85PCT=0.0%
TPDES=22.0%
APP=19.9%
<139C>=0x00
<139D>=0x0000
TSTATE33.GEAR_X=No
TSTATE33.GEAR_P=No
TSTATE33.GEAR_R=No
TSTATE33.GEAR_N=No
TSTATE33.GEAR_D=No
TSTATE33.GEAR_3=No
TSTATE33.GEAR_2=No
TSTATE33.GEAR_1=No
TOS=409rpm
GEAR=Second
<0002>=0x0300

[PCM Freeze Frame 1]
<0002>=0x0300
FUELSYS.FUELSYS1=CL
FUELSYS.FUELSYS2=CL
LOAD_PCT=10.2%
ECT=91°C
SHRTFT1=0.8%
LONGFT1=-2.3%
SHRTFT2=7.0%
LONGFT2=0.0%
MAP=54kPa
RPM=1434rpm
VSS=16kmh
MAF=25.3g/s
TP=21.2%
STATE02.TCCPWM=Inactive
STATE02.EBPSW=Inactive
STATE02.LD=Inactive
STATE02.CBPSW=Inactive
STATE02.TCCSOL=Inactive
STATE02.VATFD=Inactive
STATE02.TRACSTAT=Inactive
EGRS=0.000V
FTEMP=63°C
FTPS=1.647V
EGR=0.0%
ECT1ST=86°C
IDLEDES=5rpm
EGRDES=0.0%
BARO_B=98.9kPa
<119E>=0x92
RUNTIME=29600s
MFCSTAT.MFC2ND=None
MFCSTAT.MFC1ST=None
ODOFIRST=15km
ODOLAST=15km
FFCOUNT=1Count
FFPASS=0Count
FFNOTRUN=0Count
IBPW1=5.7ms
IBPW2=6.2ms
ETCPED=5.9%
ETCTP=21.6%
E85PCT=0.0%
TPDES=22.0%
APP=19.9%
<139C>=0x00
<139D>=0x0000
TSTATE33.GEAR_X=No
TSTATE33.GEAR_P=No
TSTATE33.GEAR_R=No
TSTATE33.GEAR_N=No
TSTATE33.GEAR_D=No
TSTATE33.GEAR_3=No
TSTATE33.GEAR_2=No
TSTATE33.GEAR_1=No
TOS=409rpm
GEAR=Second
<0002>=0x0300

[PCM Freeze Frame 2]
; Freeze Frame Empty.

[PCM Freeze Frame 3]
; Freeze Frame Empty.

[PCM Freeze Frame 4]
; Freeze Frame Empty.

[PCM Freeze Frame 5]
; Freeze Frame Empty.

[MODE05]
; Mode $05 data could not be retrieved.

[MODE06]
;ID MinLimit Value MaxLimit Units Result
;----- -------- -------- -------- -------- ------
0204.L= 0, 0, -, ,OK ,"EVAP Canister Loading Test"
0266.H= -, 1.3, 7.0,inH2Ov ,OK ,"EVAP Excess Vacuum Test 1"
0236.H= -, 0.0, 0.0,s ,OK ,"EVAP Excess Vacuum Fail Test 2"
0206.L= 0.0, 0.0, -,int-s ,OK ,"EVAP Excess Vacuum Pass Test 2"
0250.L= 11.0, 1.5, -,inH2Ov ,LOW ,"EVAP Weak Vacuum Pass Test 1"
0260.H= -, 35.0, 35.0,int-s ,OK ,"EVAP Weak Vacuum Fail Test 1"
0230.L= 0.0, 0.0, -,s ,OK ,"EVAP Weak Vacuum Test 2 Vacuum"
0240.L= 0.0, 0.0, -,s ,OK ,"EVAP Weak Vacuum Test 2 Vapor"
0211.L= 0.0, 0.0, -,s ,OK ,"EVAP Purge Leak Pass Test"
0221.H= -, 0, 0,s ,OK ,"EVAP Purge Leak Vapor Fail Test"
0271.H= -, 0.0, 0.0,inH2Ov ,OK ,"EVAP Purge Leak Vacuum Fail Test"
050A.H= -, 461, 1450,Samples ,OK ,"Post Catalyst Sensor Open Test - B1S2"
054A.H= -, 0, 1450,Samples ,OK ,"Post Catalyst Sensor Open Test - B2S2"
0A09.H= -, 0.000, 0.000,:1 ,OK ,"EONV NV .020},Test"
0C60.H= -, 0.000, 0.035,s ,OK ,"Catalyst Test Bank 1 (Using OSC Compensation Units)"
0C70.H= -, 0.000, 0.030,s ,OK ,"Catalyst Test Bank 2 (Using OSC Compensation Units)"
0E11.H= -, 9, 8,Samples ,HIGH ,"Oxygen Sensor Heater X/Y Samples Test - B1S1"
0E12.H= -, 9, 8,Samples ,HIGH ,"Oxygen Sensor Heater X/Y Samples Test - B1S2"
0E21.H= -, 0, 8,Samples ,OK ,"Oxygen Sensor Heater X/Y Samples Test - B2S1"
0E22.H= -, 9, 8,Samples ,HIGH ,"Oxygen Sensor Heater X/Y Samples Test - B2S2"

[Gregs]

Tested fuel pressure and its good, injectors ohmed out good, pressure tested coolant and it was good, and chemical block tested it and it was good too

[Motorzane]

Check for a vacuum leak. Possible intake gasket.

[Gregs]

Tested intake gaskets and ther're good. Engine compression is also good. I dont know where to go from here

[joecar]

What is rail pressure with reference hose removed...?

What is rail pressure with reference hose attached (subtract MAP from this, do you get the same value as above...?)...?

Check spark plugs and wires again... is the ground connection at the rear of the driver side head good and connected...?

Check that each coil body has zero volts compared to engine block (i.e. are coils grounded good)...?

Check coils for cracks or external carbon tracking.

Check that wires click onto plugs and into coils securely.

Does it get worse with heat...?

[Gregs]

What is rail pressure with reference hose removed...?

What is rail pressure with reference hose attached (subtract MAP from this, do you get the same value as above...?)...?

Check spark plugs and wires again... is the ground connection at the rear of the driver side head good and connected...?

Check that each coil body has zero volts compared to engine block (i.e. are coils grounded good)...?

Check coils for cracks or external carbon tracking.

Check that wires click onto plugs and into coils securely.

Does it get worse with heat...?


i don't remember what the fuel pressure reading were, i know it was over 50 psi.

for the grounds the back groundstrap is good but i have a question about the grounds for the coils. each coil gets a ground from the wiring harness, but they also get a ground from the coil bracket right?

most of my coils were getting a grounds through the coil bracket to some degree. but not all of them were that great

[Taz]

Hello Greg,<o:p></o:p>
<o:p></o:p>
The ICs do not ground via the mounting brackets.<o:p></o:p>
<o:p></o:p>
The left bank (IC 1, 3, 5, 7) ground pin A of each coil via G102 (ground at left front of engine block). Pin B of each coil ground via PCM C2 pin 60.<o:p></o:p>
<o:p></o:p>
The right bank (IC 2, 4, 6, 8) ground pin A of each coil via G104 (ground at left rear of engine block). Pin B of each coil ground via PCM C2 pin 61.<o:p></o:p>
<o:p></o:p>
<o:p></o:p>
Regards,<o:p></o:p>
Taz

[Gregs]

Hello Greg,<o:p></o:p>
<o:p></o:p>
The ICs do not ground via the mounting brackets.<o:p></o:p>
<o:p></o:p>
The left bank (IC 1, 3, 5, 7) ground pin A of each coil via G102 (ground at left front of engine block). Pin B of each coil ground via PCM C2 pin 60.<o:p></o:p>
<o:p></o:p>
The right bank (IC 2, 4, 6, 8) ground pin A of each coil via G104 (ground at left rear of engine block). Pin B of each coil ground via PCM C2 pin 61.<o:p></o:p>
<o:p></o:p>
<o:p></o:p>
Regards,<o:p></o:p>
Taz

thanks for the reply Taz

will it cause problems if the coils are also grounded through the coil brackets?

i just got back in from checking out the grounds. i pulled the plug off each coil and tested through the wiring harness and it all checked out. i checked each coil for resistance between the the pin on the coil and the outer metal strap and none of them would flow electricity. From what I've read in the Haynes manual you aren't supposed to be able to test them in that way.

[Taz]

Hello Greg,<o:p></o:p>
<o:p></o:p>
Pin A of each IC may be connected to any GOOD ground. If you have connected these to the coil brackets, then ran ground straps to the coil brackets from the block or frame, you should have a good ground.<o:p></o:p>
<o:p></o:p>
Pin B of each IC must ground via the appropriate PCM pin.<o:p></o:p>
<o:p></o:p>
P0300 is a random misfire … which could be caused by many things … finding the source will take a methodical approach and often a lot of time.<o:p></o:p>
<o:p></o:p>
I have had a defective (let still functional) O2 sensor as the route cause of this code.<o:p></o:p>
<o:p></o:p>
On one of my own trucks the route cause of a very random and intermittent P0300 DTC was a defective injector connector. It passed visual inspection, passed continuity check, and connected positively to the injector – but under the right circumstances the connection could become intermittent.<o:p></o:p>
<o:p></o:p>
Good luck with the search ….<o:p></o:p>
<o:p></o:p>
<o:p></o:p>
Regards,<o:p></o:p>
Taz

[Chevy366]

I have seen a low battery make this code throw as well , not to mention a engine idling to low a RPM at a lope can cause it as well .
Hey Taz , route , is a way of travel , root , as a root of the cause . :hihi:

[Taz]

Thanks ... working too much and responding to posts in a hurry ... is the ROOT of all grammatical errors.


Cheers,
Taz

[joecar]

Yeah, that root takes you down a route. :doh2:

[Gregs]

Well i got it figured out, it was the MAF. i guess it wasn't dirty enough to set the check engine light but i cleaned it off and the misfire counts went to zero. I've been driving around for a few days now and the light isn't coming on so all's good!:rockon:

[Taz]

Nicely done ... thanks for posting the results ... may help others with future diagnostic efforts.


Regards,
Taz

[joecar]

Thanks for posting back.

You may want to check for leakage past the air filter (why did MAF get so dirty...?).

[Gregs]

Thanks for posting back.

You may want to check for leakage past the air filter (why did MAF get so dirty...?).

i couldn't see any dirt on it but i am running a k&n filter and they are well known for messing maf sensors up. I feel stupid for not realizing it sooner.

[Chevy366]

Ah , the old K&N oil on the MAF .
I have a Vararam VR-6 on mine uses same type filter as K&N , worry about this every time I clean the filter .

[Gregs]

so everything's been fine since i cleaned the maf but today it started to misfire really bad again and was flashing check engine light. I pulled over and disconnected the maf but its continued to misfire with it unpluged. i was wondering about the posibility of the maf diagnostics not failing the maf after it was unpluged because the check engine light was flashing. what do you guys think?

funny thing but it only stumbled in the 1800-2500 rpm window, still pulled hard like normal over 2500 rpm

on a side note i must have jinxed myself because as i was walking out the door this morning i thought about taking my v2 which was on the counter with me but i told myself "oh you're not going to need that" :bash:

[Rich Z]

Were you able to resolve this misfire problem?

[Gregs]

Were you able to resolve this misfire problem?

yeah it was a dirty maf all along

[natsuto]

My truck on a very random and intermittent P0300 DTC routes reason of a defective fuel injector connector. By visual inspection and continuity check, and actively connected to the injector.

[joecar]

Did you fix the injector connector...?