spark knock or valve rattle
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Professional
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spark knock or valve rattle
i seem to have eather a spark knock or valve rattle a hwy speeds around 1500 rpms im leaning towards spark knock but insure
what are some ideas for fixing both
seafoam how to and what not
thanks nate
what are some ideas for fixing both
seafoam how to and what not
thanks nate
Champion
Joined: Dec 2003
Posts: 4,119
Likes: 5
From: Sycamore, Illinois (displaced to Arkansas)
RE: spark knock or valve rattle
I'll admit, I'm far from a "engine know-it-all." (Wire chasing, I can do that! 
)
I would suppose the first thing to ask is, what is the quality of the fuel? Is it old, is (for whatever reason) very low octane? (Yes, you can use regular, grade 87 I think it is, gas in these engines, unless you modify them). (I only ask this because I know that on performance motors, when you use less-than-specified octane fuels, it can cause a knock)
The next thing I would do is pull the plugs, one at a time, and check for proper gap (and, of course, condition). Doesn't matter if you had the 2.5, 3.9, or 5.2, the gap is 0.035 inch.
As far as running SeaFoam. I haven't run it (I will probably do so in a few weeks however, and I'll post a "how-to"). Basically, from what it says on the can, the website, and posts I've read about it, you disconnect the vacuum line from the power brake booster. You pour some SeaFoam down the vacuum tube. Than, after a couple seconds, you shut the truck off. Let the motor sit for some time, and start 'er up. You'll literally see the crap come out the exhaust (unless of course, your valve-train was all good 'n clean, than there's nothing to "shoot out").
You might want to try using some Marvel's Mystery Oil (the amount specified on the bottle) in place of (the amount specified on the bottle) oil. (I think you can substitue 1 quart). Many people have said it's helped with valve noise.
Other than that, I'm sure someone with a little more experiance will come along.
Post back with your findings.
)I would suppose the first thing to ask is, what is the quality of the fuel? Is it old, is (for whatever reason) very low octane? (Yes, you can use regular, grade 87 I think it is, gas in these engines, unless you modify them). (I only ask this because I know that on performance motors, when you use less-than-specified octane fuels, it can cause a knock)
The next thing I would do is pull the plugs, one at a time, and check for proper gap (and, of course, condition). Doesn't matter if you had the 2.5, 3.9, or 5.2, the gap is 0.035 inch.
As far as running SeaFoam. I haven't run it (I will probably do so in a few weeks however, and I'll post a "how-to"). Basically, from what it says on the can, the website, and posts I've read about it, you disconnect the vacuum line from the power brake booster. You pour some SeaFoam down the vacuum tube. Than, after a couple seconds, you shut the truck off. Let the motor sit for some time, and start 'er up. You'll literally see the crap come out the exhaust (unless of course, your valve-train was all good 'n clean, than there's nothing to "shoot out").
You might want to try using some Marvel's Mystery Oil (the amount specified on the bottle) in place of (the amount specified on the bottle) oil. (I think you can substitue 1 quart). Many people have said it's helped with valve noise.
Other than that, I'm sure someone with a little more experiance will come along.
Post back with your findings.
Professional
Joined: May 2006
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RE: spark knock or valve rattle
My 89 used to do about what your are describing here anytime I would run 87 octane fuel in it. I made a switch to 89 and it cleared up a bit.
Like dodgerules said though. Try giving it a tune up as well. Mainly check the plugs. Make sure they are gapped right and clear away any deposits that may have built up. I also had a cherokee once that would do something like this. I pulled the plugs and the electrodes were worn pretty bad. Burnt down inside the insulator. I was amazed it still ran. I made a change for the correct plugs and she ran like a top again.
Like dodgerules said though. Try giving it a tune up as well. Mainly check the plugs. Make sure they are gapped right and clear away any deposits that may have built up. I also had a cherokee once that would do something like this. I pulled the plugs and the electrodes were worn pretty bad. Burnt down inside the insulator. I was amazed it still ran. I made a change for the correct plugs and she ran like a top again.
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Joined: Feb 2006
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RE: spark knock or valve rattle
Several years back I noticed what I thought was a slight spark knock when towing on the highway. Didn’t think too much about it. Then it started showing up when I was not towing. It finally got worse.
It was not a spark knock at all, just an exhaust leak. One of the studs for the exhaust manifold had broken in the cylinder head and the rest of the nuts were slightly loose. I removed the manifold and drilled out the stud and replaced it. The leaking exhaust had “burnt†a very small place in the manifold. I used a high temp sealer on it and reassembled it. This took care of it and my “spark knock†went away.
This may not be your problem, just thought I would pass the info along.
95 3.9 V-6 – runs fine on 87 octane.
It was not a spark knock at all, just an exhaust leak. One of the studs for the exhaust manifold had broken in the cylinder head and the rest of the nuts were slightly loose. I removed the manifold and drilled out the stud and replaced it. The leaking exhaust had “burnt†a very small place in the manifold. I used a high temp sealer on it and reassembled it. This took care of it and my “spark knock†went away.
This may not be your problem, just thought I would pass the info along.
95 3.9 V-6 – runs fine on 87 octane.