SPONSORED LINKS

Sets a P0300 code at idle

Tiny
GARY THRESHER
  • MEMBER
  • 2003 CHEVROLET AVALANCHE
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 216,200 MILES
This is a customers car under 1500 rpm cylinders two and seven misfire. Above 1500 rpm the engine runs smooth and misfire stops. Ignition coils and wires are okay, new plugs, new injectors, intake gaskets, replaced fuel pressure with in spec. Any insight on this problem?
SPONSORED LINKS
Monday, February 5th, 2018 AT 7:51 PM

16 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning.

Have you tested the compression?

What is the fuel pressure?

Roy
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 3:39 AM
Tiny
GARY THRESHER
  • MEMBER
  • 9 POSTS
Compression 150 to 140 on all cylinders. Fuel pressure at idle is 57 psi.
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 7:43 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay thanks.

Sounds like it is running lean.

Can you read the long term trims with a scan tool?

Roy
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 8:09 AM
Tiny
GARY THRESHER
  • MEMBER
  • 9 POSTS
That is what I thought. Scan tool shows 5% on bank one and 2% on bank 2. Tested for vacuum leaks cannot find any. Had original manifold gaskets replaced them still same thing. O2 sensors are old but seam to be working properly.
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 10:41 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
They are reading good.

What are the mass air flow readings?

Roy
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 11:08 AM
Tiny
GARY THRESHER
  • MEMBER
  • 9 POSTS
Air flow at idle it jumps around between 4.5 and 5.7 gpm as for the voltage I do not remember. Working on other things at the moment can get that if you need it, but will take a while.
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 11:35 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, got time. Make sure there is no leak on the hose from there to the throttle body and the connector is clean and tight.

Roy
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 12:39 PM
Tiny
GARY THRESHER
  • MEMBER
  • 9 POSTS
I know the hose is good and connections are tight. I will get those numbers now.
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 3:58 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay.
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 4:02 PM
Tiny
GARY THRESHER
  • MEMBER
  • 9 POSTS
Right now cold 1.2.
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 4:18 PM
Tiny
GARY THRESHER
  • MEMBER
  • 9 POSTS
As the idle came down.8.
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 4:20 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, that looks good.

All readings are good. I am wondering if it is a valve related issue. The cam and lifters on these engines are common for failure. Removing the valve covers and inspect the rockers for any damage. I would also look at the movement in the affected cylinders.

Roy
SPONSORED LINKS
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 4:25 PM
Tiny
GARY THRESHER
  • MEMBER
  • 9 POSTS
I have looked at the action of #7 valves both moving same amount as the rest on that bank and there the same height. Have not checked bank 2. There is one lifter ticking a little on one bank. Is it possible for one cylinder to disrupt the air flow of another on the opposite bank? I have seen it on adjacent cylinders.
Was this
answer
helpful?
Yes
No
-1
Tuesday, February 6th, 2018 AT 4:40 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Yep, very possible. I would check for the source of the noise.

Roy
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 4:41 PM
Tiny
GARY THRESHER
  • MEMBER
  • 9 POSTS
I will thanks.
Was this
answer
helpful?
Yes
No
Tuesday, February 6th, 2018 AT 4:52 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Keep us updated.

Roy
Was this
answer
helpful?
Yes
No
Wednesday, February 7th, 2018 AT 2:48 AM

Please login or register to post a reply.

Related P0300 Content

Sponsored links