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

 

[osiris94ej]

You need to find the misfire data

Sent from my SM-N920V using Tapatalk

 

[SLCHOE]

Clean your MAF sensor and throttle body.

Pull out the MAF sensor (like out of the car and unplugged) and hit the hot wire elements with MAF or Carb cleaner. Dry with compressed air (be careful with air pressure if using shop air). You just want to dry it off and evaporate any solvent afterwards.

Pull off the hose going to your throttle body. Turn the key on with engine off and either have someone hold down the gas pedal or use a prop rod to hold the gas/accelerator pedal to the floor.
Go to the engine bay and spray a rag with carb cleaner. Get it wet. Then wipe down the throttle body plate on both sides and also the throttle body bore.

IT may hesistate to start after this so crack the throttle open a little with the gas pedal and crank it. Let it idle 10 minutes and repost your data.

Don't brush the sensor filaments if you've never done it. They are fragile and will break if too much pressure is applied. Spraying them with Carb cleaner gets almost all of the grime off. Just blow through it a few times and make sure that it's dry.

At the end of all this your PCM has to adapt to the new sensor readings so either just start it up and let it idle for 5-10 minutes or disconnect the negative battery cable for 15 seconds. Judging by the data from your scan tool, that tool most likely cannot clear PCM memory by a button push so those are the easiest ways to do it.

Judging by the data you provided this will either help or completely fix your issues. Good luck!

 

[swimaway]

Hey guys, thanks for the help.

I have now tried all of the above. I still have the P0300 code. I even went as far as replacing the MAF.

Sometimes the idle feels a bit better, sometimes a bit more rough. It seems the more I drive it the worse it gets. If I drive it for a bit, shut down, and go again, it's worse.

 

[sumo]

Have you tried spraying brake cleaner around the base of the intake or around hoses? If the idle changes, you can get a better idea where the leak is, that is if there is one

 

[swimaway]

I have tried that as well. No idle changes. Tried the Seafom thing. Lots of smoke, no improvement

 

[swimaway]

Fuel pressure is 42 at idle. Goes to about 50 @ 2000 rpm at load.

 

[sumo]

No misfire data? That what we need to see

 

[osiris94ej]

Fuel pressure is 42 at idle. Goes to about 50 @ 2000 rpm at load.

What is the KOEO fuel pressure at?

Sent from my SM-N920V using Tapatalk

 

[osiris94ej]

No misfire data? That what we need to see

... what he said.

Sent from my SM-N920V using Tapatalk

 

[swimaway]

I have a Centech 60794 - I don't think I can pull misfire data. I'll have to wait until tomorrow to take it over to a shop to have it read