P0300 with no other code

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Feb 5, 2021 | 10:15 PM

#11

tech2

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Joined: Mar 2011

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Quote:

Originally Posted by CitationX

Thanks hanky. I will check mode 6 data as well. Looks like I should look at A2-A9(TID 0C)

Found this GM site containing Mode 6 specs and diagnostic parameters that might be helpful for others.
https://gsi.ext.gm.com/gmspo/mode6/index.html

don't even have to go into mode 6 for gm misfire data. Any full functions scan tool will list it in special functions for gm. gm has a current and history misfire counter. go there to determine which cylinder is misfiring. If misfire history shows all on one cylinder...swap a coil and plug to a non-misfiring cylinder to see if the misfire follows the coil or plug...if yes...replace coil and or plug.
if the misfire are accumulating on one bank...look for things common on one bank...02 sensor, compression.

Sep 10, 2023 | 3:08 PM

#12

Freightmover1

CF Beginner

Joined: Sep 2023

Posts: 3

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P0300

Quote:

Originally Posted by CitationX

Hello everyone,

New member here. I shamelessly signed up to get some help with an engine problem that stumped me. I wanted to see anyone with experience could give me some advice on this.

2004 Chevy Express Van 6L V8. I can feel misfires, and P0300 DTC. Just P0300 without specific cylinder number. I know this can be a tricky one.. I guess I am lucky. The vehicle was unregistered and sat for a year - shame. Cleared out old fuels and fresh fuel in.

Work done so far-
Identified bad spark plugs for two cylinders and replaced.(ACDelco) All fuel injectors(GM) replaced. After reset, for 250+ miles no issues, no pending codes, but Catalyst and EVAP Monitor wouldn't set after several drive cycles. Then, one morning, P0300 DTC showed pending, then triggered the P0300 and Engine Check light.

Observations at idle

Upstream O2 Sensors voltages look good and fluctuating. i.e. 0.285, 0.085
MAF sensor reads 0.02 lb/s
Short Term Fuel Trim looks good fluctuating between +-3% on bank 1, -4% on bank 2
Long Term Fuel Trim high : 12.5% on bank 1, 16.5 on bank 2
Haven't done vacuum test yet.
Haven't done fuel pressure test yet
Hard start sometimes
P0300 DTC set and MIL lit

I was leaning toward the fuel system.. Fuel pressure low due to maybe the fuel filter being obstructed by sitting for a year, ECM compensating with trim. I guess it could be a vacuum leak too considering trim? If anyone has any pointers or ideas, I would appreciate it very much! Thanks!

i wend as Far as replacing the spark. And checking compression. I pulled the cat. Thinking that they may be Claude. I discovered That my front manifold was not heating up, that's exhaust manifold. To make a long story short, make sure that all coils are getting power. I had a blown fuse for the front bank. And the coils were not getting power and I. I was only running on 3. 3 cylinders

Sep 10, 2023 | 3:11 PM

#13

Freightmover1

CF Beginner

Joined: Sep 2023

Posts: 3

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P0300

Make sure to check fuse . To your coils. This engine will run on three cylinders

Sep 10, 2023 | 4:04 PM

#14

Freightmover1

CF Beginner

Joined: Sep 2023

Posts: 3

Likes: 0

P0300

Quote:

Originally Posted by CitationX

Upstream O2 Sensors voltages look good and fluctuating. i.e. 0.285, 0.085
MAF sensor reads 0.02 lb/s
Short Term Fuel Trim looks good fluctuating between +-3% on bank 1, -4% on bank 2
Long Term Fuel Trim high : 12.5% on bank 1, 16.5 on bank 2
Haven't done vacuum test yet.
Haven't done fuel pressure test yet
Hard start sometimes

P0300 DTC set and MIL lit

make sure your coils are getting power i had a blow fuse for the front bank and scanner was showing misfire on 2 4 6 the car would run but very little power only runing on 3 cylinders I was working on a 2011 chevy traverse

Last edited by Freightmover1; Sep 10, 2023 at 4:09 PM.