P0300 CODE ON 99 GMC YUKON

[ACEINTHEHOLE]

  I HAVE 99 GMC YUKON WITH 72000 MILES ON IT I WAS PULLING A MOUNTAIN GRADE TRIED TO ACCELERATE AND THE TRUCK FELL ON ITS FACE. I FOUND THE PLUG WIRES TO BE BAD SO I DECIDED TO CHANGE THE PLUGS,WIRES,CAP AND ROTOR STILL SAME CODE, TRIED SEA FOAM IMPROVED A LITTLE STILL MISSING ON #6 AND #7 AND CODE P0300 KEEPS POPPING UP TRUCK IS RUNNING VERY ROUGH, ON A PREVIOUS DISCUSSION I HEARD ABOUT AN OEM UPGRADE FOR THE INJECTORS BUT NO PART# SEARCHED AND FOUND NOTHING PLEASE HELP?

[Transman]

Here is the tsb # and the parts numbers
TSB# 00-06-04-003b
CSFI  to MFI Conversion Parts:

Part #                                          Desc.
12568332                                 V-6 MFI Assy.
88894355                                 V-6 Bracket
17113215                                 V-6 Seal kit

93441235                                 V-8 MFI Assy.
17113206                                 V-8 Seal Kit
93442096                                 V-8 Bracket
* The bracket is required to convert the system however, I have gotten some V-8 kits with the bracket inside.
Hope this helps, Transman

[ACEINTHEHOLE]

I forgot to mention my fuel Pressure is at 58# I'm going to do a compression test in a minute.Are there any other tests I should try before I modify?

[ACEINTHEHOLE]

When I do comp. Test can I pull all 8 plugs at Once or should I do it 1 at a time? My miss goes away at 2800 rpm using a snap-on 2500 Scanner.

 

[crunch]

What engine?

What kind of spark plugs are you feeding it?

[ACEINTHEHOLE]

It's a 5.7L and I put AC delco plugs in.

[crunch]

You need to get the fuel pressure up to specs.
How is the camshaft retard setting?

Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

[ACEINTHEHOLE]

Cam retard is at 0 degrees
Key on engine off fuel Psi hits 62 drops to 58 in 2 sec.
Engine running 58-60 bouncing.
@1500RPM 56# steady.
With return Pinched off key on engine off 96#

[ACEINTHEHOLE]

Oops After shut off psi 58# and goes up to 62# After 15min.All Readings in Park did not drive.

[crunch]

If the gauge is on the money you fuel pressure is low.
Should be 60/66. 65-66 under laod and drop back to 61-62 full vacuum or no load.
Can you feel the miss on 6 and 7 cylinder or noitce it on a cylinder balance test?

[ACEINTHEHOLE]

Yes you can feel the miss the truck Runs very rough, shakes at an idle and doesn't want to accelerate unless you get on it then it goes but it's not pretty. How do you do a Balanced cylinder test? This started pulling a mountain grade and has been running Poorly for the last Week. I drove aprox. 70 miles to get home and been limping to and from Work all week.

[ACEINTHEHOLE]

At an idle my Scanner Shows misfire on 5,6 and 7 if I hold it at 2800 rpm in park it Stops Misfiring on the Scanner but the ses light Keeps flashing .when driving it Shows misfire on 6 only, I Never get any Code except P0300
 

[ACEINTHEHOLE]

Can the pressure be adjusted to me the fuel pump sounds good if it Pushes 96# with return pinched, where is the regulater, is it in the intake?

[crunch]

The pressure regulator controls running pressure.

[crunch]

Cylinder balance test can be doe pulling one plug wire at a time and watching rpm drop.
Did you get a chance to run compression test.
I would run it and switch plugs and check for good hot fire to the missing cylinders.
And also check firing order on plug wires.