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Discussion Starter · #1 ·
I have a 1990 k2500 5.7 and I have what looks like its a hole that could almost fit a spark plug on the header and I know it's not a spot for a plug I just don't know what it could be I can cover it up with my hand and it makes it run quite but I've looked all over the internet and can't find an answer would have a picture but I can't figure out how to upload one thanks for any help you might have
 

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Could be a bung for a O2 sensor. It may or may not be threaded. Some headers require welding a fitting on that if not threaded.
 

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Discussion Starter · #3 ·
It is threaded and it's only on one header it's on the passenger side. You think I should just try to fit and o2 sensor in there and if it fits just leave it alone or will the damage somthing
 

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I would just put a pipe plug in it and call it done since it would have to have 2 holes (one on each side for sensors). Sounds like this truck was modified and someone eliminated the O2's.
 

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Discussion Starter · #5 ·
Ok thanks that's what I'm gonna do its a beater truck anyway just trying to do cheap fixes it's got 350k on it so I don't expect perfect
 

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Is the hole down at the collector or is it on the #2 tube? Normally there is only 1 O2 sensor on the driver's side down by the collector/exhaust pipe flange. If your truck is an "emissions" truck with the AIR (Air Injection Reaction AKA Smog) pump there should be a fitting on both side by #s 1 & 2 exhaust valves. "Federal" trucks don't have the smog pump. My 88 is a CA "emissions" truck so, even in AZ I have to have the AIR system on it, see pics

upload_2019-5-22_18-39-55.png


upload_2019-5-22_18-41-57.png
 

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Play with TBI is correct. In either scenario it appears that either the O2 sensor was removed or the AIR system was removed. This vehicle wouldn't pass emissions with these parts missing so I have to assume you are not in an emissions compliant area or its a farm truck not driven on the roads etc.
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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If it’s the size of spark plug, an 18mm drain plug will fit perfectly.
 

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Discussion Starter · #9 ·
Thanks for all the info I got the truck for free so I just was looking at it today and noticed some things on it so I thought I'd ask for help on this one. This is the hole I was talking about if the picture is clear
 

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Thanks for all the info I got the truck for free so I just was looking at it today and noticed some things on it so I thought I'd ask for help on this one. This is the hole I was talking about if the picture is clear
On my 99 k1500 5.7 vortec l31 thats a coolant intake hose port i only know because mine is currently leaking
 

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On my 99 k1500 5.7 vortec l31 thats a coolant intake hose port i only know because mine is currently leaking
We're talking about a 1990 TBI engine. That port is in the exhaust manifold. IIRC it's an 18 X 1.5 reverse taper fitting. The only O2 sensor is on the rear of the driver's side exhaust manifold.
 
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