Plug reading 101
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Plug reading 101 Only have about 1.5K on these plugs, engine has 90K on it. Junkyard 2003 LM4 stock, just slid it into my '39. Have not done a compression test yet. all plugs look like the one on the right and #8 (left) is very different. Any ideas what is going on with #8 cylinder? Other test I can run to find the problem?
Thanks
Thanks
TECH Addict
Joined: Oct 2016
Posts: 2,513
Likes: 480
From: PDX-OR-USA
The reddish tan color on both is the fuel package additives and dies, but the left plug is getting some extra fuel it kinda looks like, got a weak /dripping injector on that hole maybe?
I always start simple/easy and work up to hard/expensive..
I always start simple/easy and work up to hard/expensive..
Swap that injector with the cylinder in front of it and see if your discoloration moves with the injector to the new plug. I'm not convinced that it's too much fuel, though...but that would be a free test you can do. Do you have the diagnostic port wired up on your harness? If so, look at fuel trims on that bank with a scan tool.
Also,
It kinda looks like that plug has been running hotter than the others and maybe even leaking some compression. Was it good and tight? Be sure to install new plugs dry (no anti-seize) and tighten them with a torque wrench.
Also,
It kinda looks like that plug has been running hotter than the others and maybe even leaking some compression. Was it good and tight? Be sure to install new plugs dry (no anti-seize) and tighten them with a torque wrench.
Last edited by socal57chevy; Mar 8, 2017 at 05:09 PM.
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Thanks guys, fuel trims look good/equal from bank to bank. I do have one noisy lifter that I thought was #8 and this confirms something is going on. Next is to do a compression test and see how it measures to the rest then put it back together , run it again and see if the header is the same temp as the rest. I guess pulling the valve cover to see if something is wrong with the valve train on that cylinder would be in order too.
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
Thanks Fierofly, that may solve several problems. I have a whistling noise that climbs as RPMs go up, then drop after each shift. Couldn't figure it out...until you pointed out the seat. I looked at the head and there is nothing to indicate a seating problem and the plug seemed tight when I took it out. Also discovered I have the wrong plugs. Have AC Delco 41-110 but should have 41-962. Will still do a compression test tomorrow after some honeydos.
Thread Starter
Joined: Mar 2014
Posts: 699
Likes: 59
From: Alamogordo, NM
One of the post mentioned not to use any anti-seize on the threads. I've heard pros and cons on this subject from gall to heat transfer. What is the proper thing to do?
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Torque specifications are always a dry torque number unless explicitly noted otherwise. Antiseize changes your final torque value as well as adding resistance to the ground side of the spark plug. It can also decrease heat transfer to the cylinder head, which is how the spark plug cools itself off. I use a thread chaser (not a tap) to clean the spark plug threads, then install the plug dry and torque it with a quality torque wrench.
Last edited by socal57chevy; Mar 9, 2017 at 10:11 AM.
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