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I got an IR gun finally so that means I need to mess with everything naturally. 7 cylinders are reading 510-520. Cylinder is running between 590-600. Tomorrow morning I’ll pull the plug to see what it looks like. That big of a variation warrants looking into right? Or am I over thinking?
If plug is ashy looking, then I’m guessing injector is clogged or something. Black would be too much fuel so either spark or injector stuck open. If plug looks fine, then I need to do compression test to see if valve isn’t closing all the way?
Any other thoughts??
Readings were taken around 3” from header flange on each tube.
Last edited by 90project5.0; Jun 10, 2026 at 04:15 PM.
decided to pull plug real quick. Lighter color is #3, other is #2 cylinder. Not a major difference, but there is one. If it makes a difference at all, I do run a 6A box.
decided to pull plug real quick. Lighter color is #3, other is #2 cylinder. Not a major difference, but there is one. If it makes a difference at all, I do run a 6A box.
Don't do like me. I changed the plugs, wires ect. Passanger side pipe and cat glowing like a stove burner on hi. Got the schenatic and rewired all the plugs. Does much better now. I'll be 68 in a few days, so after over 50 years now and I still make a boo-boo every once in a while.
I recently exchanged 2 or 3 serpentine belts thinking they sold me the wrong size. I was routing it wrong! Using the diagram.. I understand boo boos! Wire routing is correct and I even have separators on them to avoid cross fire! Thank you!
I would probably just run it and monitor it for a while before tearing into it.
About 10k miles ago (3yrs), heads were pulled and R&r’d, ported and 17.2 roller rockers. New cam was installed as well. New 19lb injectors were added (originals were 14).
I wouldn't expect too much from a bottle of cleaner but it won't hurt to try.
Doesn't seem like much mileage in 3 years. When was the last time it went for a good long drive?
Last month. 2 hrs each way. 99% of my driving is stop and go inner city pulling a landscaping trailer. Once a week if not more, I do take her down a straight away and launch throw the rpm’s to help clean the cylinders some.
Those plug gaps don't look right to me. The gaps look too large and the tip looks to be rounded off the edges. Not so much that they are bad, but if I had them out, I would not put them back in. The larger the gap, the harder it is for the spark to jump that gap. Since the spark is lazy, it will find the easiest way to ground. A sure fire way to burn out the weak links in the ignition system.
Those plug gaps don't look right to me. The gaps look too large and the tip looks to be rounded off the edges. Not so much that they are bad, but if I had them out, I would not put them back in. The larger the gap, the harder it is for the spark to jump that gap. Since the spark is lazy, it will find the easiest way to ground. A sure fire way to burn out the weak links in the ignition system.
The gap is set to .050 and I verified that when I pulled those two that they were still there. MSD said to run them at .055, truck says .44, so I split the middle. I did notice the tip as well, but they all looked that way when I put them in. Figured it was “manufacturing difference” with Autolites.
Seeing that I just found a damn yellow jacket nest the wrong way, I’m done working for the day! I’ll go get a set of Motorcrafts and toss them in.
I would always recommend to follow specs but when it comes to facts, it is harder for the spark to jump a larger gap.
Just because your ignition system can jump a huge gap, does not mean it's a good idea to open the gap that much. Obviously, having a gap too small is not good either. Somewhere there is a number that works and this number is different with every manufacturer. I have seen so many problems where the plug gaps are so large that the spark finds it's way to ground through spark plug wires, caps, rotors, etc. Sometimes it just does not fire at all. Plugs do wear out and the gaps will increase due to wear. I tend to eyeball the new spark plug gap and shove them in.
It's just my opinion that the grounding electrode should be about a 90° angle. When I see angles above/below that angle, I see a problem. It's just me and like most people here, we are set in our ways. You're 68 and I'm 65 and I am past that age where it's harder to change my mind. I'm not trying to say I am right or others are wrong. It's just what I do and that seems to work for me.
I would always recommend to follow specs but when it comes to facts, it is harder for the spark to jump a larger gap.
Just because your ignition system can jump a huge gap, does not mean it's a good idea to open the gap that much. Obviously, having a gap too small is not good either. Somewhere there is a number that works and this number is different with every manufacturer. I have seen so many problems where the plug gaps are so large that the spark finds it's way to ground through spark plug wires, caps, rotors, etc. Sometimes it just does not fire at all. Plugs do wear out and the gaps will increase due to wear. I tend to eyeball the new spark plug gap and shove them in.
It's just my opinion that the grounding electrode should be about a 90° angle. When I see angles above/below that angle, I see a problem. It's just me and like most people here, we are set in our ways. You're 68 and I'm 65 and I am past that age where it's harder to change my mind. I'm not trying to say I am right or others are wrong. It's just what I do and that seems to work for me.
When my step son bought his truck, used, the plugs were soo worn out that no joke, the gap was around .120. I couldn’t believe it ran like it did… I struggled and did some research on where to put the gap. There was soo many arguments both ways between .44 and .54 especially with the msd. Maybe I’ll run this new set at .45 and see how she acts.
It's only an argument when you say the other person is wrong. The world is too binary. As a professional mechanic, I know I am 100% right all the time. It's your problem if you don't agree with me.
There are just a bunch of different opinions. When it comes to a simple plug gap, there is no reason for anyone to get their panties in a bunch.
I remember when I was a kid, some of the GM products had some really large gaps. All for the improvement of something. I just know, that with that large gaps, it certainly caused problems with the other 'marginal' components. I swear most of the plugs I install on a customers car come pre gapped. I just eyeball them and they go in. I tend to look at the old gaps to determine how long ago the plugs were replaced. I don't usually notice a before/after difference when I am replacing spark plugs. I tend not to notice a 5 horse power difference too. I would notice a 2-3 MPG difference and I really can't believe a gap change would do that.
Just remember, the larger the gap, the more difficult the spark has to jump. The more difficult it has to jump, the more important the secondary ignition system has to be perfect.
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