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So I recently purchased a 2003 Silverado 2500 with an lq4 6.0 in it and all I was told was that it was sitting for 3 years and ran when parked. Got it home and put new gas in it, started it up and it runs but only on a few cylinders. Replaced spark plugs and wires and checked to make sure all coils were sparking and they were. Pulled the injectors and one was leaking so I replaced it with one that I had laying around that did not leak. Drove the truck down the street after putting coolant in it and it blew a massive plume of white smoke for about a half a mile and then the smoke subsided. When I first started the truck it had a P0106 code, replaced the map sensor, no change. Today after running it for a little while it has P0101, P0300, and P0336. Any advice would be appreciated, thank you.
Having sat for 3 years, the first thing I would do is clean the injectors and fuel system. Ethanol in our modern fuels is corrosive and when fuel sits for a long period, it can become “gunky” or produce solids. Dumping fresh gas in on top of the mess in there won’t help this. This could explain all of the codes except the 336. That’s a crank sensor code. Be patient and tackle each thing independently to see what has made a difference here. Good luck.
Having sat for 3 years, the first thing I would do is clean the injectors and fuel system. Ethanol in our modern fuels is corrosive and when fuel sits for a long period, it can become “gunky” or produce solids. Dumping fresh gas in on top of the mess in there won’t help this. This could explain all of the codes except the 336. That’s a crank sensor code. Be patient and tackle each thing independently to see what has made a difference here. Good luck.
Another thing I didn't mention is that I've completely bypassed the fuel lines and hooked am external fuel pump directly up to the rails and I swapped the entire passenger side fuel rail with a known working one as that is the side that seems to be running worse. I'm going to 0
Put a fuel filter in it tomorrow but how would you recommend cleaning the injectors? Not trying to dump a fortune into this thing and get all new I hector's but if that's what I have to do in the end I will.
Another thing I didn't mention is that I've completely bypassed the fuel lines and hooked am external fuel pump directly up to the rails and I swapped the entire passenger side fuel rail with a known working one as that is the side that seems to be running worse. I'm going to 0
Put a fuel filter in it tomorrow but how would you recommend cleaning the injectors? Not trying to dump a fortune into this thing and get all new I hector's but if that's what I have to do in the end I will.
What's the fuel pressure since you did that? Does that year of truck have a return style fuel style system with the regulator in the factory rail?
If not..I can tell you exactly what your problem is.
What's the fuel pressure since you did that? Does that year of truck have a return style fuel style system with the regulator in the factory rail?
If not..I can tell you exactly what your problem is.
Not entirely sure of the fuel pressure but it ran the same off the external pump and the in tank pump. I have a fuel pressure gauge at work that I'll put on it tomorrow, but I doubt that's the issue. Ordered cheap Amazon injectors and they'll be here Tuesday so we'll see if they work any better.
So today I installed a fuel pressure gauge on the rail. After priming the pump a few times the gauge would go no higher than 20 psi. I bought a new fuel pump for it and after taking out the old one it was completely destroyed. After installing the new fuel pump the fuel pressure gauge read around 60 PSI which is where it should be but now the truck will not start. It cranks and will sputter a little bit but will not run under its own power. I verified the truck has spark by hooking a spark plug up to the wire and cranking. The truck is obviously getting fuel as the fuel pressure gauge reads fine. I thought it may have something to do with the crankshaft position sensor so I replaced that to no avail. What should my next steps be? Thank you
So today I installed a fuel pressure gauge on the rail. After priming the pump a few times the gauge would go no higher than 20 psi. I bought a new fuel pump for it and after taking out the old one it was completely destroyed. After installing the new fuel pump the fuel pressure gauge read around 60 PSI which is where it should be but now the truck will not start. It cranks and will sputter a little bit but will not run under its own power. I verified the truck has spark by hooking a spark plug up to the wire and cranking. The truck is obviously getting fuel as the fuel pressure gauge reads fine. I thought it may have something to do with the crankshaft position sensor so I replaced that to no avail. What should my next steps be? Thank you
Are the new injectors in yet? More fuel pressure will exaggerate the gunky crap getting into the injectors because now everything is moving more. Pull the fuel rail up off the intake, plug injectors in…make sure clips are in the top of them all…and try and start it. All 8 should blow fuel spray. Be careful here as gasoline is flammable and point the assembly away from folks. This step will ensure your injectors are firing and/or clogged up. Seeing fuel pressure doesn’t mean injectors are firing if they are clogged up. You want to make sure your fuel tank and lines are clean and clear before installing new injectors, or your just blowing crud into new injectors. Does that thing have a fuel filter? Some vehicles don’t have a filter these days. If so, buy a couple new ones and change it out after you’ve ran a tank of fuel through the vehicle.
Are the new injectors in yet? More fuel pressure will exaggerate the gunky crap getting into the injectors because now everything is moving more. Pull the fuel rail up off the intake, plug injectors in…make sure clips are in the top of them all…and try and start it. All 8 should blow fuel spray. Be careful here as gasoline is flammable and point the assembly away from folks. This step will ensure your injectors are firing and/or clogged up. Seeing fuel pressure doesn’t mean injectors are firing if they are clogged up. You want to make sure your fuel tank and lines are clean and clear before installing new injectors, or your just blowing crud into new injectors. Does that thing have a fuel filter? Some vehicles don’t have a filter these days. If so, buy a couple new ones and change it out after you’ve ran a tank of fuel through the vehicle.
New injectors should be here tomorrow, will try to put them in during lunch time and see if she starts. Also have a new fuel filter to put in.
Put the new injectors and the fuel filter in today. Truck still cranks but will not start. Cranked while injectors were out and fuel is spraying. Had a buddy check plugs on both sides and it's still got spark. Only code it's throwing now is P0336 for the crank position sensor. It's just weird to me that I was able to drive the truck about 5 miles to the shop, granted it barely made it here, and then once I put a fuel pump in it it will not start. Whenever I go to crank it, it sounds like it wants to start and fires off one or two cylinders but won't actually run on its own. I'll upload a video shortly of what it sounds like.
When you pull it out, make sure there isn't a bunch of rust scaling on the block. If it's enough, it can keep the sensor from getting close enough to read the reluctor wheel correctly.
Maybe it's flooded? Were the plugs fouled or had wet gas?
BTW, where are you guys finding cheap injectors? I've got some mis-matched L59 engine with a LM7 tune, and getting a lean(?) code on both banks. I'm pretty sure it's a difference in injector flow rate. I don't know enough HP Tuners stuff other than VATS and rear ratio calibration.
Seems easier to swap injectors, but I've looked at RockAuto but a set of 8 injectors is a good $350+ with core?
Put the new injectors and the fuel filter in today. Truck still cranks but will not start. Cranked while injectors were out and fuel is spraying. Had a buddy check plugs on both sides and it's still got spark. Only code it's throwing now is P0336 for the crank position sensor. It's just weird to me that I was able to drive the truck about 5 miles to the shop, granted it barely made it here, and then once I put a fuel pump in it it will not start. Whenever I go to crank it, it sounds like it wants to start and fires off one or two cylinders but won't actually run on its own. I'll upload a video shortly of what it sounds like.
Couple things here…did you buy a replacement injector for the exact original? If not, a tune is in order here before it ever runs. How do spark plugs look, wet and dark, or tan and dry?
This entire issue could very well be a CKP problem. You said you changed it out. Could be a wiring harness deal, especially since this thing sat for a few years. Mice will chew the wiring out of any vehicle…maybe start doing some tracing on the harness to see if you have issues like that. The 336 code isn’t a fluke.
So last night I left the battery unhooked all night and plugged it back in this morning. After cranking it for about 10 seconds it finally started. Still wasn't running right so I started pulling plug wires to check spark. Turns out cylinders two and three are not sparking at all. Swapped coils over and even tried coils off a different truck the problem stays with two and three. I pulled up the diagram of the coil pack wiring connector and checked each lead with a multimeter. 12v is good, both grounds are good on both and I checked for continuity between the PCM and the coil for the signal wire and it everything checks out. Should I try in different PCM next? I'd rather try anything else before that but I do you have another PCM for this year ls. The only issue is it's for a 5-3 so I'd have to reprogram it. Any help would be appreciated. Thank you
So after hours of diagnostics I think I finally figured it out. A guy I work with suggested that I pull the crank sensor and stick a mirror in the hole and see what it looks like. I crank the engine while he looked in the hole and he noticed that the crank reluctor wheel was bent. Tomorrow I'm going to pull the oil pan off and try to bend it back if that does not work I'm not sure what my best approach would be. I bought the truck to sell it so I'm not trying to put a bunch of money into it so if bending it back does not work then I may look into replacing the reluctor wheel but if that's too much work then I'll just sell the truck as is. A video of the reluctor wheel will be attached. I'll keep you guys updated but any suggestions or advice would be appreciated. Thank you
Well folks unfortunately this will probably be my last update on this thread. I pulled the pan off to try and bend the reluctor wheel today, and things are not looking too good for this motor. The first thing I noticed was chunks of metal in the oil pan. Once I looked at the windage tray I saw very large holes that looked like bullet exit holes. Reluctantly I pulled the windage tray off to find the cylinder number 2 connecting rod had decided to leave the chat. It was obvious that this had happened a very long time ago as the cylinder wall has some pretty serious pitting. I guess this would explain how the reluctor wheel got bent. Interestingly enough after bending the reluctor wheel wheel as much as I could, the engine actually ran quite a bit better, obviously not firing on cylinder number two, but a lot better. Unfortunately it looks like it's time to start looking for junkyard engines or to sell the truck. If anyone's interested in the DMV area let me know. I'll include pictures of the Carnage. I appreciate everybody's help in trying to figure this out, and hopefully it goes a little better next time.
11-27-2022, 12:03 PM
LQ4 barely running after sitting for years 
