Ad Radar
Item Posts    Sort Order

2001 GMC Yukon 8.1l P0300 Code

 
abrady28
I love my Chevy Chevette!
Posts: 1
Joined: 07/11
Posted: 07/12/11 10:33 AM

Hey Chevy Guys I'm to the end of my rope... I've got a P0300 code that knowbody can figure out. I've read all that I can with no luck. I started out doing all the over 100,000 mile stuff that I felt should be replaced then took it to the dealer to see if the "pros" could figure it out. They told me after 3 days they didn't have a good anwser for me. Maybe a fuel pump or a crank sensor. So this is the run down
2001 GM 8.1l 125,000 miles
Plugs 2 set (AC Delco) .065 clearance
Wires 2 sets (AC Delco)
Fuel filter
all 4 o2 sensors
Removed intake and resealed  
Crank Shaft sensor and relearn
MAF sensor
Cam Sensor
Fuel pump Delphi, (55 PSI), Fuel regulator, Injectors replaced.  
Compression check 135psi all 8
Ran a vacuum gauge inside the truck to watch for valve flutter had good in vacuum 19hg.
Back pressure test on Cats. good
All the freeze frame data looks good.
Ran a Tech2 shows all 8 cycl. misfire around 2500rpm. I can make the MIL light flash in the driveway it starts around 2300 and stops around 2700rpm I can make it stop when you disconnect the temp switch making the computer defalt -40 deg. and run super rich but with it hooked up the fuel trims are @ LTrim 0.0-3.0 on both banks. I starting to think a badly stretched timing chain.
abrady28@yahoo.com  

Post Reply
redneckjoe69
I mow my lawn and find Chevys
Posts: 2337
Joined: 03/10
Posted: 07/12/11 11:36 AM

http://www.obd-codes.com/p0300           this might help ya out?  

Post Reply
Pontiacman2
Moderator
Posts: 8956
Joined: 09/08
Posted: 07/12/11 11:48 AM

Good link Joe.  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

Post Reply
redneckjoe69
I mow my lawn and find Chevys
Posts: 2337
Joined: 03/10
Posted: 07/12/11 12:56 PM

thanx pman. Cool    just tryin to be helpful. Laugh       hows things going?  hot & about to rain here.  

Post Reply
Pontiacman2
Moderator
Posts: 8956
Joined: 09/08
Posted: 07/12/11 02:15 PM

It's Hot and Humid as He** and just finished raining here.

Hows things on your end?  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

Post Reply
chevelle83
I mow my lawn and find Chevys
Posts: 2280
Joined: 11/09
Posted: 07/12/11 07:17 PM

have you tried a junkyard computer?  

Post Reply
waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 07/13/11 07:41 AM

P0300 is a random misfire....

its usually either a vacuum leak.... or a ignition problem..

this is what the ignition coils look like...



i would take the coils off and examine them one at a time.....  look for signs of high voltage leakage...  dust circles between the inner winding and the inside of the outer frame....

this is a diagram for an earlier coil...

Coilhighvoltageleakareas


i have in a pinch removed the coils and  cleaned them with brake cleaner... then forced silicone sealer.. usually ultra grey .. between the gap ... adding to the insulation...    

the other problem is coil internal failure...  this is going to be a LOT easier with an under 10 buck tool at most parts stores...  part number 25069 at many parts stores

25069Sparktester

you can just use a screw driver.. or a modified spark plug. but this is adjustable...  so you can.. when its NOT sparking . . open the gap by twisting the screw ... then having somebody crank it again...   try not to run it for long with the wire disconnected...  these tests are usually done with the fuel pump fuse out.. and the injector power undone... usually by disconnecting the main injector connector..

you have to have a bright blue snappy spark.. that will jump about 3/4"    if you only get an orange spark and it will only jump a 1/4" .. you have a bad coil....

since you posted a code number.. i am taking that you might have a scan tool????? instead of just a code reader...

you will want to print this chart...  read it ONLY ONE line at a time..   start the engine.. get into the live data stream  on the scan tool....    the first line of data on the scan tool...   write it down on the proper line of the chart...  then write down the next line of data...   different scan tools show data in different orders...


Scandata

after writing down the info.. you can sit and review it.. post any thing that looks out of spec...

i don't think the 8.1 motors have the ability like others to tell the difference between which cylinder is misfiring..  i seem to recall reading that somewhere on a gm web site..  

i stop in several times a day.. post what you get...

if you don't have a scan tool that displays live data...   the best deal going is harbor freight 98614...  

Post Reply
waynep7122
I mow my lawn and find Chevys
Posts: 1130
Joined: 08/09
Posted: 07/13/11 07:51 AM

the other thing...   fuel pressure..  fuel volume...


do you have a fuel pressure gauge...???   can you swap on a new fuel filter and see if the old one was clogged by carefully blowing through it...   ( don't inhale)

it is totally possible that the fuel filter is bad.. and or the fuel pump is failing...  

monitor the fuel pressure..  as you bring the RPMs up...    you can also monitor the injection pulse width.. see if it goes way wide..   and or look at the short term fuel trims..   do they go crazy into the positive side as the ECM tries to make up for the loss of fuel...

you might also want to carefully watch or graph the TPS...   and the air flow meter also...


if you don't have a DSO .. and a low amp current probe to see the wave form of the amp draw from the spinning fuel pump armature...

there are these at HF stores.. there are 2 versions.. this one is for the smaller fuses... 20 Amp Automotive Fuse Circuit Tester ITEM # 67725

Image 10426

they also have one for the standard size plug in fuses...

Image 10425

30 Amp Automotive Fuse Circuit Tester ITEM # 67724

either one is 15 bucks..

on another forum.. a car that would shut down.. the owner plugged one of these into the fuel pump fuse.. watched the pump amp draw..  it was 6.8 amps.. until the motor started to stumble.. at that point the amp draw went to 19 amps as the engine stalled...  

Post Reply
TO TOP