RobSquatch
Newbie
Hello! As stated: I have been lurking for some time, reading a gazillion posts and nothing is really lining up with my scenario, so here I am:
Background: New to me 1994 K2500 5.7, 4L60: stock TBI, only mod I can see are huge 10mm silicone sheathed race-style plug wires.
Symptoms: First the good: fires right up, idles beautifully except a light surge (fixed with sealing off a broken vacuum line). Free revs just fine: zooms to redline, and back down, no smoke, no rattles or weird noises. At light throttle just putting around town at 25-45 mph, it does fine...drives beautifully for a 29 year old truck. It's the light 3/4 ton...basically a heavy-half: 8 lug wheels and semi-float 12 bolt (I think it is?). RPO codes say it's 4.10 gears. The problem is when trying to get any performance out of it, anything more than a leisurely stroll it falls flat on its face with no power, smokes grey (tailpipe is thick black soot) it gets terrible mileage...worse than my old '95 C2500 with the 454...like 5 mpg bad, and it can't get out of its own way. The concerning thing is under load it knocks...doesn't sound like a rod knock...I've heard that several times over the years, but it's not normal pinging either. A side note is the oil pan gasket is gone...it hemorrhages oil scary bad, so that's the priority next.
What I've done: The plugs were worn out, mildly fouled, but nothing alarming. Everything else appears stock. New AC Delco plugs gapped at 35. Firing order is correct. Plug wires are tight...now...some were loose. Previous owner had synthetic oil in it. I'm running Delo 15W40 as its showing around 230K. That helped a lot, but the main issues remain. Oil pressure, even with the synthetic was a good 15-40 psi. The 40 weight didn't change much, just leaks out a little slower and not from as many places...the synthetic just ran out of the pores in the block it seemed lol.
EGR is seized and disconnected. I found the vacuum line was chewed off and leaking, so I hit it with a lighter and crimped it shut with pliers for now...not a permanent fix, just stopping the leak for now until I can replace the EGR, then I have to do a new line anyway. It sat for about a year before I bought it, so I've run the old gas out of it, added fresh fuel and B12 Chemtool, flushed the TBI with cleaner, checked for manifold leaks (none), tightened the valve covers and oil pan bolts...they were loose. The truck was purchased new and used as a shop truck by a local diesel shop for hauling a gooseneck service trailer. Guy I got it from bought it from them to tow a boat with and said he just wanted something newer so he bought a new truck and was just getting rid of this one. So its my problem now...apparently (from talking to the diesel shop via email) it was having problems for them too. Enough history
It starts right up beautifully..crank-crank-VROOM, just like expected. Very little grey smoke at cold idle, but smells of fuel and sooty exhaust pipe. No CEL, no codes when I checked today by trying to get the CEL to flash the codes by jumpering the OBD1 port. Done it before successfully on my old truck, but that doesn't mean I'm for sure doing it right this time...been a few years and I'm getting older Idle is smooth and steady at 700 rpm. Battery voltage is right on as is the alternator. Fuel pump is noisy at key-on, but seems fine. It doesn't feel like its starving, if anything, too rich.
My thoughts: priority #1 is that oil pan gasket, and check the rotating mass from underneath just for kicks while we're in there. Oil change had zero grit or shiny: just dirty and like any normal oil change. I dredged the old oil with a magnet and got nothing remarkable. EGR is shot for certain. Knock sensor harness looks suspect: thin, frail and cracked. MAP sensor looks OEM original, so it's on the list too. TBI been cleaned. IAC looks fine and it idles beautifully, so not worries there. The surge went away when I sealed the loose vacuum line. Couldn't find any other vacuum leaks. No over-heating: gets to 95 degrees, stat opens and coolant circulates. No leaks. No oil/water cross contamination. No back-pressure coming from the oil fill cap when the engine is running. In short it runs great until I want it to scoot. It really sprays the oil out when I give it the gas too...like showers out of the pan. It feels like the knocking sound is coming from underneath the truck; that's what has me so confused. I thought it was something loose, an exhaust leak or maybe a torque converter bolt at first, but short story: those don't add up when testing...unless I'm doing something wrong. The knock is not consistent either: Its worse when it's hot outside. Cold, rainy weather and it almost runs normally, just still low on power. Sometimes it's rhythmic with rpms, others it's like random..."whap-whap-whap-whap" vs "whap-whackathud whap whap whapwhapwhap whap whap". I do have a video with the sounds, just don't know if I am allowed to post that here yet.
If y'all still with me: I am disabled and don't have my tools anymore, so I personally can't do much more. I just need ideas to take to friends who are helping me do the work on it. I feel like I should just gut and replace all the ignition/emissions and fuel management sensors and components, but I can't afford to do that. I do think it is a stack effect of a lot of things a little bit out of whack; I just need to try to focus my troubleshooting instead of shotgunning wild at it. My preferred fix would be to pull the engine and replace it with a 383 long block and stand-alone aftermarket EFI, like Holley ProJection or Sniper system...but its only a 1500 buck thirty year old beater. The truck is just transportation for me, not a tow rig. It was just the best cheap garbage I could afford on disability after I lost my Jeep in a divorce~ Thanks all!!
Background: New to me 1994 K2500 5.7, 4L60: stock TBI, only mod I can see are huge 10mm silicone sheathed race-style plug wires.
Symptoms: First the good: fires right up, idles beautifully except a light surge (fixed with sealing off a broken vacuum line). Free revs just fine: zooms to redline, and back down, no smoke, no rattles or weird noises. At light throttle just putting around town at 25-45 mph, it does fine...drives beautifully for a 29 year old truck. It's the light 3/4 ton...basically a heavy-half: 8 lug wheels and semi-float 12 bolt (I think it is?). RPO codes say it's 4.10 gears. The problem is when trying to get any performance out of it, anything more than a leisurely stroll it falls flat on its face with no power, smokes grey (tailpipe is thick black soot) it gets terrible mileage...worse than my old '95 C2500 with the 454...like 5 mpg bad, and it can't get out of its own way. The concerning thing is under load it knocks...doesn't sound like a rod knock...I've heard that several times over the years, but it's not normal pinging either. A side note is the oil pan gasket is gone...it hemorrhages oil scary bad, so that's the priority next.
What I've done: The plugs were worn out, mildly fouled, but nothing alarming. Everything else appears stock. New AC Delco plugs gapped at 35. Firing order is correct. Plug wires are tight...now...some were loose. Previous owner had synthetic oil in it. I'm running Delo 15W40 as its showing around 230K. That helped a lot, but the main issues remain. Oil pressure, even with the synthetic was a good 15-40 psi. The 40 weight didn't change much, just leaks out a little slower and not from as many places...the synthetic just ran out of the pores in the block it seemed lol.
EGR is seized and disconnected. I found the vacuum line was chewed off and leaking, so I hit it with a lighter and crimped it shut with pliers for now...not a permanent fix, just stopping the leak for now until I can replace the EGR, then I have to do a new line anyway. It sat for about a year before I bought it, so I've run the old gas out of it, added fresh fuel and B12 Chemtool, flushed the TBI with cleaner, checked for manifold leaks (none), tightened the valve covers and oil pan bolts...they were loose. The truck was purchased new and used as a shop truck by a local diesel shop for hauling a gooseneck service trailer. Guy I got it from bought it from them to tow a boat with and said he just wanted something newer so he bought a new truck and was just getting rid of this one. So its my problem now...apparently (from talking to the diesel shop via email) it was having problems for them too. Enough history
It starts right up beautifully..crank-crank-VROOM, just like expected. Very little grey smoke at cold idle, but smells of fuel and sooty exhaust pipe. No CEL, no codes when I checked today by trying to get the CEL to flash the codes by jumpering the OBD1 port. Done it before successfully on my old truck, but that doesn't mean I'm for sure doing it right this time...been a few years and I'm getting older
Idle is smooth and steady at 700 rpm. Battery voltage is right on as is the alternator. Fuel pump is noisy at key-on, but seems fine. It doesn't feel like its starving, if anything, too rich. My thoughts: priority #1 is that oil pan gasket, and check the rotating mass from underneath just for kicks while we're in there. Oil change had zero grit or shiny: just dirty and like any normal oil change. I dredged the old oil with a magnet and got nothing remarkable. EGR is shot for certain. Knock sensor harness looks suspect: thin, frail and cracked. MAP sensor looks OEM original, so it's on the list too. TBI been cleaned. IAC looks fine and it idles beautifully, so not worries there. The surge went away when I sealed the loose vacuum line. Couldn't find any other vacuum leaks. No over-heating: gets to 95 degrees, stat opens and coolant circulates. No leaks. No oil/water cross contamination. No back-pressure coming from the oil fill cap when the engine is running. In short it runs great until I want it to scoot. It really sprays the oil out when I give it the gas too...like showers out of the pan. It feels like the knocking sound is coming from underneath the truck; that's what has me so confused. I thought it was something loose, an exhaust leak or maybe a torque converter bolt at first, but short story: those don't add up when testing...unless I'm doing something wrong. The knock is not consistent either: Its worse when it's hot outside. Cold, rainy weather and it almost runs normally, just still low on power. Sometimes it's rhythmic with rpms, others it's like random..."whap-whap-whap-whap" vs "whap-whackathud whap whap whapwhapwhap whap whap". I do have a video with the sounds, just don't know if I am allowed to post that here yet.
If y'all still with me: I am disabled and don't have my tools anymore, so I personally can't do much more. I just need ideas to take to friends who are helping me do the work on it. I feel like I should just gut and replace all the ignition/emissions and fuel management sensors and components, but I can't afford to do that. I do think it is a stack effect of a lot of things a little bit out of whack; I just need to try to focus my troubleshooting instead of shotgunning wild at it. My preferred fix would be to pull the engine and replace it with a 383 long block and stand-alone aftermarket EFI, like Holley ProJection or Sniper system...but its only a 1500 buck thirty year old beater. The truck is just transportation for me, not a tow rig. It was just the best cheap garbage I could afford on disability after I lost my Jeep in a divorce
~ Thanks all!!
