Big 2000 K1500 5.3L problem

[21sprint]

Need to get a little help. This truck has no codes stored but the problem started out like it was running out of fuel. Still has power but it's like the engine just goes to nothing when pulling to a stop sign but has never died. I check pressure and it's running at 55 lbs. I tried a new crank sensor, both upper OX sensors, fuel filter, another MAF sensor and a can of SEAFOAM. This problem just comes on some times, not all the time.
I tried putting truck into 2nd gear and running it hard, it never ran out of gas.
A good scanner was used and it shows miss fires on every cylinder, could plugs cause a truck to just lose power. That's my next move or changing fuel pump, which I hate to do with pressures right on..
I forgot to add the miss fires are come and go and must not be bad enough to turn on Engine Lite..

[j cAT]

random missfires p0300 would point to low fuel pressures or restricted exhaust.

remove the UPSTREAM O2 sensors and see if the engine runs better. leave the O2 holes open.

fuel pressure eng on need be above 53psi, key on engine off should be 60-62psi. the pressure should drop very slowly. rapid drop may be fuel pump/injector/regulator. remove vac line from the regulator you should see/smell no fuel.

I would replace the ECT . this sensor is now too old.

[21sprint]

Originally Posted by j cAT

random missfires p0300 would point to low fuel pressures or restricted exhaust.

remove the UPSTREAM O2 sensors and see if the engine runs better. leave the O2 holes open.

fuel pressure eng on need be above 53psi, key on engine off should be 60-62psi. the pressure should drop very slowly. rapid drop may be fuel pump/injector/regulator. remove vac line from the regulator you should see/smell no fuel.

I would replace the ECT . this sensor is now too old.

Thanks for responding. I got the truck to stop dying, changed fuel pump, it may have been a volume problem because pressure was fine. I also changed plugs to original A/C type, that got rid of missfires, none showing now at any time.
Now for the next problem, this truck when it gets out on hi-way and it gets into highest gear. You can hold it at any speed, but 40 or 45 you can feel this truck surge bigtime. It just feels like your taking foot slightly off throttle. I had computor on and with a another guy watching for any glitch none found but this surge is bad. I just knew fuel pump was it, but NO!.
I tried a known good MAF sensor, both upper OX sensors, crank sensor and looked for vacuum leaks, all sensors seem to be working right. Truck has power when you punch it, its just when you try and hold a speed, you feel engine pulling down then back up..

[j cAT]

the spark plug type in this engine is very picky. you must use the lasted recommended irridium ac plugs. I somehow got away with using bosch +2 plugs for about 50K mi. had no problems ,but many did have issues with non ac delco. I now use these ac irridiums and find over the cold/hot weather the engine cold start is better.

fuel filters need replacing every 30-40K MI. CUT OPEN AND SEE HOW BAD THEY LOOK .this will give you an idea of the quality of the fuel you purchase and when you need to do this.

sounds like you now have transmission problems. lockup is dropping out. have a tranmission shop check for the "GM" DRIVETRAIN CODES and check tranny pressures. do not use dexron III. the new fluid is now dexronVI. this fluid is now the GM approved fluid for this transmission.

[21sprint]

Originally Posted by j cAT

the spark plug type in this engine is very picky. you must use the lasted recommended irridium ac plugs. I somehow got away with using bosch +2 plugs for about 50K mi. had no problems ,but many did have issues with non ac delco. I now use these ac irridiums and find over the cold/hot weather the engine cold start is better.

fuel filters need replacing every 30-40K MI. CUT OPEN AND SEE HOW BAD THEY LOOK .this will give you an idea of the quality of the fuel you purchase and when you need to do this.

sounds like you now have transmission problems. lockup is dropping out. have a tranmission shop check for the "GM" DRIVETRAIN CODES and check tranny pressures. do not use dexron III. the new fluid is now dexronVI. this fluid is now the GM approved fluid for this transmission.

I was thinking Tranny problem to, but it sure feels like the engine, you can feel this surge and watching the tach you can see it sort of bounce just a little while you hold the speed at a set position. I will try to see a GM Tech buddy and let him check codes on trans.

[21sprint]

Had the Injectors flushed and surge is now about gone..

[j cAT]

Originally Posted by 21sprint

Had the Injectors flushed and surge is now about gone..

if the engine is droping power under a constant load, the torque converter will cut out. at speed above 40 MPH.

could be you have bad gas.

[maddogg45]

i don't mean to intrude, but i had the same problem in my jeep just after i bought it. was a used one with 40k miles on it. And around 40 to 50 when only slight on the gas would act the same way i changed the tranny fuild and the filter and so far knock on wood 10k miles later still no issues. which was funny because the dealer had just changed it i don't know if they used the wrong type or what but thankfully it took care of the problem.