Backpressure
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- Oct 30, 2014
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Hey everyone,
Been lurking here for about 6 months and decided to join so I can ask this question. I did search the forums and came up with nothing that matches my issue. 1996 4.3L Vortec C1500 140k miles.
About 2 weeks ago, I replaced my cap and rotor, plugs, and wires to fix a miss. Everything was fine until about 5 days ago when the truck developed a new (and much worse) miss. The thing is, the miss only occurs in gear (any of the forward or reverse gears) and when I am sitting still (i.e. at stop lights, in traffic, any time I am still for more than 15-20 seconds) or when going up a fairly steep hill. If in park, the truck will run perfectly until the sun burns out. The longer I sit, the worse the miss gets. It starts out about once every 10 seconds and progresses to almost constant if I sit long enough. When the time comes to take off, the truck will hesitate and miss a time or two, then be perfectly fine until I stop again or go uphill. I checked all of the wires, none are crossed; all the plugs are gapped correctly and none are fouled. The only real clue I have is a fairly loud click every time the engine misses. I took a video of it both in the engine bay and inside the cab to show you what I mean. The cap and rotor still look clean and nice inside; no severe fouling or copper buildup in the terminals from bad plug wires.
I am simply at a complete loss. I can't imagine it being a fuel injector/pump issue because it's perfectly fine under none, low, moderate, and heavy loads unless going uphill. I figure if it was a timing issue, it would occur at different times throughout the drive and while in park. The plugs are OEM Delcos gapped to 0.60", plug wires are Bosch (can't find Delcos locally), cap/rotor are Duralast Gold (again, all I can find locally) I've had the truck for 7 years and have never had any issues save the cap/rotor needing replaced annually. Oil is fresh, air filter is clean, fuel filter is less than a year old, fuel pump primes flawlessly, has the normal whine, and was replaced about 3 years ago. I had a 97 K1500 5.7 do the same thing and it turned out to be a throttle position sensor that was bad; I replaced the TPS on my current truck - no change in the miss.
One final note: I do have a "bad" cat. It is bad simply in the fact that the asbestos coating has broken free. There isn't any clogging inside of it and no vaccuum from the exhaust. There is a code for the cat because exhaust is flowing around the broken coating instead of being filtered, so the O2 sensor is throwing a fit. I can't imagine that causing this type of miss/stumble. It's been broken for a year with no issues until now.
Also, the oil pressure jerks pretty badly when the miss occurs. Don't know if that's relevant,
Thanks in advance.
video:
As best I can tell, the click is coming from the passenger side. This video shows what I mean by "the miss gets almost constant if i sit long enough". It sounds like one cylinder is misfiring every time its turn comes up.
https://www.youtube.com/watch?v=J0Qc3IGcBMg
In the second video, there is a miss early on and four in quick succession toward the end. I took this one to show how the oil pressure gauge jumps.
https://www.youtube.com/watch?v=FclFKsRGJ_4
Been lurking here for about 6 months and decided to join so I can ask this question. I did search the forums and came up with nothing that matches my issue. 1996 4.3L Vortec C1500 140k miles.
About 2 weeks ago, I replaced my cap and rotor, plugs, and wires to fix a miss. Everything was fine until about 5 days ago when the truck developed a new (and much worse) miss. The thing is, the miss only occurs in gear (any of the forward or reverse gears) and when I am sitting still (i.e. at stop lights, in traffic, any time I am still for more than 15-20 seconds) or when going up a fairly steep hill. If in park, the truck will run perfectly until the sun burns out. The longer I sit, the worse the miss gets. It starts out about once every 10 seconds and progresses to almost constant if I sit long enough. When the time comes to take off, the truck will hesitate and miss a time or two, then be perfectly fine until I stop again or go uphill. I checked all of the wires, none are crossed; all the plugs are gapped correctly and none are fouled. The only real clue I have is a fairly loud click every time the engine misses. I took a video of it both in the engine bay and inside the cab to show you what I mean. The cap and rotor still look clean and nice inside; no severe fouling or copper buildup in the terminals from bad plug wires.
I am simply at a complete loss. I can't imagine it being a fuel injector/pump issue because it's perfectly fine under none, low, moderate, and heavy loads unless going uphill. I figure if it was a timing issue, it would occur at different times throughout the drive and while in park. The plugs are OEM Delcos gapped to 0.60", plug wires are Bosch (can't find Delcos locally), cap/rotor are Duralast Gold (again, all I can find locally) I've had the truck for 7 years and have never had any issues save the cap/rotor needing replaced annually. Oil is fresh, air filter is clean, fuel filter is less than a year old, fuel pump primes flawlessly, has the normal whine, and was replaced about 3 years ago. I had a 97 K1500 5.7 do the same thing and it turned out to be a throttle position sensor that was bad; I replaced the TPS on my current truck - no change in the miss.
One final note: I do have a "bad" cat. It is bad simply in the fact that the asbestos coating has broken free. There isn't any clogging inside of it and no vaccuum from the exhaust. There is a code for the cat because exhaust is flowing around the broken coating instead of being filtered, so the O2 sensor is throwing a fit. I can't imagine that causing this type of miss/stumble. It's been broken for a year with no issues until now.
Also, the oil pressure jerks pretty badly when the miss occurs. Don't know if that's relevant,
Thanks in advance.
video:
As best I can tell, the click is coming from the passenger side. This video shows what I mean by "the miss gets almost constant if i sit long enough". It sounds like one cylinder is misfiring every time its turn comes up.
https://www.youtube.com/watch?v=J0Qc3IGcBMg
In the second video, there is a miss early on and four in quick succession toward the end. I took this one to show how the oil pressure gauge jumps.
https://www.youtube.com/watch?v=FclFKsRGJ_4
Last edited:
