2000 gmc jimmy 4.3 other day it wouldnt start almost acted like it was flooded so i cranked and messed with most the day next morning same thing it would act like it wanted to start but just wouldnt so out of curosity i threw some fuel down the tb and it fired right up so i thought well its obviously the fuel pump so i threw my pressure gauge on the shreader valve and cycled the key and it had 65psi and maybe dropped to 58 cranking so know what i quit for the day came out this morning tried starting it and it finaly hit and started and had a dead miss and instantly threw the po300 code now it will start and run but misses all the time what might this be fpr messing up or the spider deal under the plentum bad any help would be so greatly appreaciated josh

 

are you sure there's no other codes stored?

Just for drill where have you bought your gas lately?

 

no that was it just the po300 code i buy my fuel at mfa never have had a problem i fueled my 4wheeler and wifes van same time with no issues also

 

65psi is quite high. How was the leak down rate after the pump shut off?

When was the last time a tune up was done (plugs, wires, cap, & rotor)? If recently, were AC Delco parts used? These trucks seem to prefer AC Delco caps & rotors.

Have you checked for any pending codes as well? Or history codes? Those could help to point in a direction for diagnosis.

 

yeah i just checked again it was between 58-62 i have a atd gauge and i dont think its hun percent accurate as far as leak down gauge never moved after keyed off i dont think any, when i unscrewed it the pressure relieved and about 3000 miles ago i did a complete delco tune up plugs wires cap rotor as far as history codes it has none stored everything has been prty well fine with this unit untill this happened

 

Then I too would suspect a fuel quality problem as 'fog was referring to.

 

yea i dont know whats going on its very frustrating

 

You could try a bottle or two of Isoheat to see if it might be water in your fuel causing the problems.

 

yeai mite give that a try

 

def not a fuel issue drained tank put fresh in sam misfire