Failing fuel pump
2000 S-10 V 6 with 255,432 miles. Check engine light on with code PO 300
(random misfire) and PO 171 (system too lean)
Replaced fuel filter ,checked for vacum leak with gage (needle steady at idle)
changed MAF sensor . While driving at about 70-74 mph tach at about 2100
rpm the engine will stumble and the tach will show a slight drop in rpm's. Not
continuously.The fuel pump was replaced in 2007 that was 113,000 miles
ago.Could the out put from the fuel pump be decreasing causing this type of
sure..but under a load or a nice steady cruze??? also check...wiggle any/all elect conections you can find.
The injection spider was replaced back in july of 2015
nice steady cruzz
first things first.. is the filter new??
I'd check the fuel pressure at the schrader valve, it should be 56 to 63 lbs. just to be sure. The common thing for the random miss-fire, and a lean condition is a intake manifold leak. Try taking some carburetor cleaner and spray along the intake gaskets, plenum , base of throttle body, If the rmp's increase, then there is a vacuum leak.
Make sure there is no air entering the tubing after the maf sensor. All clamps are tight, the pcv hose is in good shape. No cracks anywhere and the plenum is seated good and tight on the top of the throttle body.
I did notice that the "O"ring that seals the top of the throttle body was flat from age.Think I should start with a new "O" ring. That would produce a lean mixture.
Anywhere there is vacuum. Spraying carb cleaner would have picked this up. Increase in RPM's...
Yes, it will cause a lean code if air enters there because of that o ring. The problem with the carb cleaner test is there isn't vacuum there. It doesn't always work for the plenum before the throttle body.
Update: Used starting fluid and sprayed areas of possible vacuum leaks. No leaks where found. Sprayed area around base of intake and throttle body. Still no increase in RPM's. Did notice that the "feeling" of the engine stutter is at 2000 rpm's. Highway speed of about 70 -74 mph. Could my throttle position sensor have a bad spot at that point?
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