P0300 and Stumble

[swimaway]

Hey guys,

I've been searching for this for a while... like 2 weeks. SO I figured I would make a post to see if you guys could help me.

2005 Suburban - 5.3L - 200k

I picked this thing up for a song... literally. Exterior is awesome, interior is awesome. Had a P0300 code and the guy didn't know what to do... so I got it for about $1000.

I already have a 2004 Tahoe and a 2002 Tahoe... both with around 100k on them... so this was more of a challenge car for me and I like the suburbans.

The problem. Obviously it's throwing a P0300 code, and will occasionally flash the CEL while driving. That being said.. while driving, I don't notice anything. It pulls great, drives great, no hesitation, no shaking, nothing.

Upon slowing to an idle at a stop light, the stumbling beings. It has a rough idle. Never dies, but it's rough.


So far, I have replaced

Plugs
Wires
Coils

Checked for vacuum leaks. I hear what I think might be a vacuum sound coming from the driver valve cover... that being said, I have sprayed starter fluid all around the intake, the vacuum lines, and basically the whole engine. No changes. I have removed the driver valve cover and searched for cracks. Nothing.


Where should I go to next?



Thanks

 

[osiris94ej]

Use a scanner of some kind to monitor misfires, it will tell you which cylinder or cylinders are misfiring. Going from there you can narrow it down further. There are tons of things that can cause that random multiple code.

Sent from my SM-N920V using Tapatalk

 

[swimaway]

Use a scanner of some kind to monitor misfires, it will tell you which cylinder or cylinders are misfiring. Going from there you can narrow it down further. There are tons of things that can cause that random multiple code.

Sent from my SM-N920V using Tapatalk

So, I tried that. I can't really figure out how to read that data. I have a pretty decent scanner, but I can't figure out how to monitor that data

 

[sumo]

You need a scanner that can monitor live data. One that built in misfire counters. It will show you exactly what cylinder is misfiring and how frequent. P0300 is random misfire detected while p0301 -p0308 the last number indication what cylinder is misfiring

 

[osiris94ej]

Scroll down when monitoring the real time data. Look for the misfire counters. The ones that are counting up consistently are the active misfires. I've seen some strange things happen through the shops I've worked at. Had a truck with misfires all on bank 1 (LH) ended up monitoring o2 data and it was dead. Replaced o2 and gone. Have had others misfire because of worn lifters and/or cam lobe. Also seen weak valve Springs cause a small missfire.

Once you can narrow down which cylinders you can dig deeper.

Sent from my SM-N920V using Tapatalk

 

[swimaway]

Should I post the live data here?

 

[swimaway]

DTC_CNT 1
FUELSYS1 CL
FUELSYS2 CL
LOAD_PCT (%) 7.1
ECT (F) 186
SHRTFT1 (%) -21.9
LONGFT1 (%) 8.6
SHRTFT2 (%) -19.5
LONGFT2 (%) 7.8
MAP (PSI) 5.1
RPM 538
VSS MPH 0
SPARKADV 18.0
IAT (F) 123
MAF (LB/S) .02
TP (%) 11.8
O2SLOCB1S12--B2S12--O2B1S1 (V) .064
SHRTFTB1S1 (%) -1.6
O2B1S2 (V) .875
SHRTFTB1S2 (%) N/A
O2B2S1 (V) .850
SHRTFTB2S1 (%) -2.3
O2B2S2 (V) .805
SHRTFTB2S2 (%) 99.2
OBDSUP OBSII

 

[swimaway]

DTC_CNT 1
FUELSYS1 CL
FUELSYS2 CL
LOAD_PCT (%) 7.8
ECT (F) 190
SHRTFT1 (%) -3.1
LONGFT1 (%) 0.0
SHRTFT2 (%) -2.3
LONGFT2 (%) 4.7
MAP (PSI) 4.6
RPM 1908
VSS MPH 0
SPARKADV 44.5
IAT (F) 123
MAF (LB/S) .04
TP (%) 19.6
O2SLOCB1S12--B2S12--O2B1S1 (V) .455
SHRTFTB1S1 (%) 3.1
O2B1S2 (V) .235
SHRTFTB1S2 (%) N/A
O2B2S1 (V) .255
SHRTFTB2S1 (%) 2.3
O2B2S2 (V) .040
SHRTFTB2S2 (%) 99.2
OBDSUP OBSII

 

[swimaway]

This was taken from my 2002 Tahoe

DTC_CNT 1
FUELSYS1 CL
FUELSYS2 CL
LOAD_PCT (%) 2.4
ECT (F) 195
SHRTFT1 (%) 2.3
LONGFT1 (%) 14.8
SHRTFT2 (%) .8
LONGFT2 (%) 15.6
MAP (PSI) 6.1
RPM 548
VSS MPH 0
SPARKADV 18.0
IAT (F) 123
MAF (LB/S) .01
TP (%) .4
O2B1S1 (V) .765
O2B1S2 (V) .775
O2B2S1 (V) .0485
02B2S2 (V) .765
OBDSUP OBSII

 

[swimaway]

Crap, I just realized I posted this in the wrong forum. Can someone please move this to the 2000-2006 one.

Sorry guys. It's been a long day