Hi everyone. I’m new to the forum and was hoping to find help in resolving an issue that I’m having with my Silverado (I also own a 2004 Tahoe with the same engine). If you have time to read this post and have any suggestions, I'd greatly appreciate your help.
I’ve got a 2002 Silverado with a 5.3L Vin-T that I purchased new. The truck’s been well maintained, despite the deterioration resulting from the NE Ohio salty roads. It has 350k miles on it and still runs smooth and strong. It starts right up every time, idles smooth, drives and shifts like new. Two years ago it abruptly lost power and acceleration on the freeway and I opened the catalytic converters, emptied the contents and re-welded them shut. I also installed O2 sensor extensions on the post cat bungs to ward off any unsuspecting emission DTC’s. In the end (after I purchased an OBDII scanner), it actually turned out to be the knock sensors, so I replaced them and the harness with genuine GM parts. The intake received new Fel-Pro gaskets. Ever since, no CEL’s and things have been great for the last 35k+ miles. It has an AC Delco fuel pump that I installed about 100K miles ago.
Problem: While driving the other day, I began to feel a single-cylinder miss while stopped at a red light. Continuing on, it began to lose power and shutter whenever I would push the accelerator beyond 2k RPM. That’s when the CEL began to flash intermittently and would then go away. But the acceleration issue remained. I limped home on backroads at 45 mph top speed, since I couldn’t get the rpm’s up enough to accelerate to highway speeds. The OBDII scanner showed a P0300 (Random Misfire) code. The voltage of the post-cat O2 sensors fluctuate uniformly as if they’re working properly. I’ve since cleared the P0300 code, and during my test runs it has yet to reappear.
Since then, the miss at idle has resolved itself (sea foam & injector cleaner added to fuel) and it runs perfectly smooth as before. I checked all of my AC Delco Iridium plugs and all eight were tan-colored, dry and still gapped at 0.040”. I pulled each plug wire and all eight coils showed good spark. Out of curiosity, I swapped the MAF sensor from my other truck and nothing changed. I hooked-up a fuel gauge to the rail and it showed 50 psi with the key on and 48 psi at idle. To experiment, I ran the fuel gauge up through my hood so that I could observe the gauge through my windshield while driving. That’s when things became fishy. The gauge stayed at 50 psi while cruising at around 1,500 RPM, would drop to 45 psi under gentle acceleration to just over 2k RPM and then recover right back to 50 psi. However, once the accelerator is pushed down to a certain position (~ 2,500 RPM) the engine begins to shudder, RPM’s drop, it pops through the intake occasionally and then the fuel pressure drops suddenly from 50 psi down to 5-10 psi. If I floor it, the same thing happens (fuel pressure drops to 5-10 psi). But what’s odd, is that if I let up on the accelerator slowly, there’s a particular position in the accelerator’s travel where the engine immediately smooths out and the fuel pressure shoots right back up to 50 psi. I don’t know if the immediate pressure drop is something that occurs electronically as part of a “limp mode” process or something. It doesn’t seem that a dirty fuel filter or partially plugged fuel pump pick-up screen, or even a faulty fuel pump would cause such a drastic and immediate change in pressure like this. I did change the vacuum operated fuel pressure regulator on the fuel rail, but this had no effect.
I’ve been reading forums and watching Youtube videos for the last three days, hoping to find someone who experienced something similar with respect to the fuel pressure drop relative to the throttle position in their 5.3 with the P0300 DTC. I’ve heard of people performing a crankshaft position re-learn procedure. However, I’m not sure if this would help, since the problem had an immediate onset and wasn’t something that started off mild and progressed over time.
I don’t mean to beat this topic to death. But if anyone has any experience with the conditions described and then found a resolution, I’d sure appreciate your input. I’d sure like to get this old horse through one more winter without dumping a whole lot of money into it.
I’ve got a 2002 Silverado with a 5.3L Vin-T that I purchased new. The truck’s been well maintained, despite the deterioration resulting from the NE Ohio salty roads. It has 350k miles on it and still runs smooth and strong. It starts right up every time, idles smooth, drives and shifts like new. Two years ago it abruptly lost power and acceleration on the freeway and I opened the catalytic converters, emptied the contents and re-welded them shut. I also installed O2 sensor extensions on the post cat bungs to ward off any unsuspecting emission DTC’s. In the end (after I purchased an OBDII scanner), it actually turned out to be the knock sensors, so I replaced them and the harness with genuine GM parts. The intake received new Fel-Pro gaskets. Ever since, no CEL’s and things have been great for the last 35k+ miles. It has an AC Delco fuel pump that I installed about 100K miles ago.
Problem: While driving the other day, I began to feel a single-cylinder miss while stopped at a red light. Continuing on, it began to lose power and shutter whenever I would push the accelerator beyond 2k RPM. That’s when the CEL began to flash intermittently and would then go away. But the acceleration issue remained. I limped home on backroads at 45 mph top speed, since I couldn’t get the rpm’s up enough to accelerate to highway speeds. The OBDII scanner showed a P0300 (Random Misfire) code. The voltage of the post-cat O2 sensors fluctuate uniformly as if they’re working properly. I’ve since cleared the P0300 code, and during my test runs it has yet to reappear.
Since then, the miss at idle has resolved itself (sea foam & injector cleaner added to fuel) and it runs perfectly smooth as before. I checked all of my AC Delco Iridium plugs and all eight were tan-colored, dry and still gapped at 0.040”. I pulled each plug wire and all eight coils showed good spark. Out of curiosity, I swapped the MAF sensor from my other truck and nothing changed. I hooked-up a fuel gauge to the rail and it showed 50 psi with the key on and 48 psi at idle. To experiment, I ran the fuel gauge up through my hood so that I could observe the gauge through my windshield while driving. That’s when things became fishy. The gauge stayed at 50 psi while cruising at around 1,500 RPM, would drop to 45 psi under gentle acceleration to just over 2k RPM and then recover right back to 50 psi. However, once the accelerator is pushed down to a certain position (~ 2,500 RPM) the engine begins to shudder, RPM’s drop, it pops through the intake occasionally and then the fuel pressure drops suddenly from 50 psi down to 5-10 psi. If I floor it, the same thing happens (fuel pressure drops to 5-10 psi). But what’s odd, is that if I let up on the accelerator slowly, there’s a particular position in the accelerator’s travel where the engine immediately smooths out and the fuel pressure shoots right back up to 50 psi. I don’t know if the immediate pressure drop is something that occurs electronically as part of a “limp mode” process or something. It doesn’t seem that a dirty fuel filter or partially plugged fuel pump pick-up screen, or even a faulty fuel pump would cause such a drastic and immediate change in pressure like this. I did change the vacuum operated fuel pressure regulator on the fuel rail, but this had no effect.
I’ve been reading forums and watching Youtube videos for the last three days, hoping to find someone who experienced something similar with respect to the fuel pressure drop relative to the throttle position in their 5.3 with the P0300 DTC. I’ve heard of people performing a crankshaft position re-learn procedure. However, I’m not sure if this would help, since the problem had an immediate onset and wasn’t something that started off mild and progressed over time.
I don’t mean to beat this topic to death. But if anyone has any experience with the conditions described and then found a resolution, I’d sure appreciate your input. I’d sure like to get this old horse through one more winter without dumping a whole lot of money into it.
