Totally lost noob with silly question, but I've been reading everything I can find with no avail...
- Thread starter RobSquatch
- Start date
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A couple of things jump out at me, check to see if the coolant temp sensor wiring/connector are compromised maybe under torque the wiring is moving and causing an open circuit which would make the the E.C.M. think it was very cold thus enriching the A/F NOTE this is a very unlikely scenario yet it would be worth looking at, next thing that jumps out at me is like many others have stated is check the fuel pressure, is the regulator working properly? last thing that you may want to look at is an exhaust leak especially close to the o2 sensor if exhaust is leaking it can draw ambient air into the exhaust stream making a false lean condition, if you can get a scan tool it would really help. Good luck.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 olderIdle 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
RobSquatch
Newbie
UPDATE!
Been slow, just because...life things, but have made some progress! I am still kind of stumped:
New oil pan and valve cover gaskets
New oil pan and valve cover gaskets stopped the oil hemorrhaging. New EGR and 02 sensor. A new power steering cap fixed a mystery leak! I was getting fluid I didn't recognize all over the front of the engine, but the pump looked fine. Then I noticed the cap had no gasket! New cap, no more leak.
Coolant leak at the radiator was a loose expansion tank hose clamp and a bad radiator cap. New cap and clamp and the heater hose started gushing! New cap let the pressure actually build and the quick connect fitting failed. For the cost of the removal tool and a new fitting, then I saw the cost of the hose assembly!!! so I replaced the quick connect and pipe with a pipe nipple and hose. A bit difficult to get a screwdriver in the tiny space between the distributor and EGR (new EGR too) but thats fixed too!
In this process I found several vacuum leaks and fixed them. It runs SO MUCH better now!
Still a gutless poop-pile, but it is a mid 90's TBI...those were gutless new. Replaced the PCV hose with a chunk of bulk hose because the parts store couldn't figure it out. It was collapsed and rotting, so the new hose is an upgrade (it is emissions hose, not a heater hose, so it shouldn't rot out too fast). The drivers side bank PCV hose is shot, that's the next replacement.
After all of this, the weird knock is mostly gone! Got a HORRID exhaust leak where the mechanic who did the oil pan gasket broke the cross over donut gasket. Thats supposedly on order. Its getting better and actually fun to drive now!
Been slow, just because...life things, but have made some progress! I am still kind of stumped:
New oil pan and valve cover gaskets
New oil pan and valve cover gaskets stopped the oil hemorrhaging. New EGR and 02 sensor. A new power steering cap fixed a mystery leak! I was getting fluid I didn't recognize all over the front of the engine, but the pump looked fine. Then I noticed the cap had no gasket! New cap, no more leak.
Coolant leak at the radiator was a loose expansion tank hose clamp and a bad radiator cap. New cap and clamp and the heater hose started gushing! New cap let the pressure actually build and the quick connect fitting failed. For the cost of the removal tool and a new fitting, then I saw the cost of the hose assembly!!! so I replaced the quick connect and pipe with a pipe nipple and hose. A bit difficult to get a screwdriver in the tiny space between the distributor and EGR (new EGR too) but thats fixed too!
In this process I found several vacuum leaks and fixed them. It runs SO MUCH better now!
Still a gutless poop-pile, but it is a mid 90's TBI...those were gutless new. Replaced the PCV hose with a chunk of bulk hose because the parts store couldn't figure it out. It was collapsed and rotting, so the new hose is an upgrade (it is emissions hose, not a heater hose, so it shouldn't rot out too fast). The drivers side bank PCV hose is shot, that's the next replacement.
After all of this, the weird knock is mostly gone! Got a HORRID exhaust leak where the mechanic who did the oil pan gasket broke the cross over donut gasket. Thats supposedly on order. Its getting better and actually fun to drive now!
That's a 3/4. 9.5 14 bolt so and 8 bolt wheels. Bbc got the full float 14 bolt. Should be a 4l80e though
someotherguy
Truly Awesome
Yep I think we were addressing this from go, but didn't get a specific answer. You are 100% correct that the 8 lug truck will have the 4L80E, which will help if/when he needs to lookup stuff for it like filter and pan gasket kit.
Richard
Really old thread, not sure why you quoted me.
Sorry didn't realize it was old until after I did that
That’s ok, I guess I was really just asking what your post meant.
RobSquatch
Newbie
@Moofus02 Thank you!! That is excellent to know! I am not familiar with this chassis. I was hoping it was an 4L80. The trans shifts and works great.
As I fix more little things, and the stuff that pops up from those, it is getting better. I really like the truck, and it's actually drivable now. Need to fix the IAC as it stalls after warming up if I have to turn the wheel (like when parking) at idle. It's fine when cold. Warm the idle drops to about 500 rpm indicated. Still surges at idle too. I'm wondering if I should replace the injectors. The maintenance doesn't look like it's been kept up with recently. I have only put about 200 miles on it since I got it, all around town. Planning to get it out on a back highway trip in a few days just to see how it does and let it breathe.
As I fix more little things, and the stuff that pops up from those, it is getting better. I really like the truck, and it's actually drivable now. Need to fix the IAC as it stalls after warming up if I have to turn the wheel (like when parking) at idle. It's fine when cold. Warm the idle drops to about 500 rpm indicated. Still surges at idle too. I'm wondering if I should replace the injectors. The maintenance doesn't look like it's been kept up with recently. I have only put about 200 miles on it since I got it, all around town. Planning to get it out on a back highway trip in a few days just to see how it does and let it breathe.
RobSquatch
Newbie
Update: It was running good, getting a lot better, but smoking intermittently usually when warm at idle. Then a couple days ago...poof. Head gasket failed. Truck is DOA. Bummer, I really liked it. Can't afford to fix it, so it's heading off down the line.
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