Hello all,
This is my first post and I look forward to seeing what everyone has to say.
BLUF: 2003 Suburban 5.3L Flex has Cylinder No. 6 Misfire. Check engine light is off until accelerating and then the check engine light blinks. Check engine lights turn off when slowing down.
Background:
This is my first post and I look forward to seeing what everyone has to say.
BLUF: 2003 Suburban 5.3L Flex has Cylinder No. 6 Misfire. Check engine light is off until accelerating and then the check engine light blinks. Check engine lights turn off when slowing down.
Background:
- The truck would not start, it would crank but would not turn over until after several seconds cranking. I tested fuel pressure. With key on, it would build pressure at the rail, but then it would quickly loose pressure. I replaced fuel filter first, but no change
- I changed upper intake manifold gasket, knock sensors, knock sensor harness, valve cover gaskets, and water channel seals. I turn the truck on and backed it out of the garage and around the house and turned it off. I tried turning it back on but it would only crank. I tried turning it on and let it crank for 15-20 seconds until it finally sputtered and groggily turned over. I had to give more fuel in order for it to start running smoothly. Truck ran but it had a knock sensor code.
- I warrantied the Delphi knock sensors and replaced them with AC Delcos. I pulled intake manifold and replaced it.
- I replaced the fuel pump couple days later to address the initial start-up issue in No. 1 point of this list. It fixed the startup issue.
- Now, the truck runs but has misfire in No. 6 cylinders.
- I checked plugs. Couple plugs have oil on threads. Gaps are good. I moved spark plugs from No. 6 to No. 4. Code did not follow plugs.
- I checked coils. Swapped plugs back and then swapped coils from No. 6 to No. 4. Code did not follow coils.
- I checked injectors. Swapped coils back and then swapped injectors from No. 6 to No. 2. Code did not follow injectors.
- I sprayed around intake and vacuum hoses with cleaner but there is no reaction from engine.
- Additional information: Truck has around 240k miles. Truck has had a P0420 code for Catalyst System Efficiency Below Threshold Bank 1 for a year or so. I do not know if this is a clogged cat as there hasn’t been a misfire until messing with intake and fuel pump.
