Why do the TBI trucks have so much valve rattle?

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redfishsc

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So I've owned 2 1990 half tons (4.3 and 5.7) and a 93 S10.

The S10 was only 4 years old when I got it with 25k miles. The 1990 4.3 was 8 years old with about 90k, and the 1990 5.7 was a solid 25 years old well over 200k.

They all had valve rattle when accelerating "lightly to moderately". No rattle noticeable at WOT or cruising.

Rattle disappeared if I ran 92 octane.

I assume this was spark knock/detonation.

Should I have been running colder spark plugs? I can't remember what plugs I was using, that was too many years ago. I was using whatever Pep Boys sold me.

I've owned 2 Vortec 5.7s and I drive a 2004 half ton with the 4.3 for work, never once hear valve rattle, I suppose because of the knock sensor doing it's thing.
 

L31MaxExpress

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I would say something mechanical is wrong. I have owned several TBIs, driven dozens more and the only time they ever pinged enough to hear was during the ECMs forced knock test. The ECM cranks the timing up a couple of times while you are driving when the engine is warming up to test the knock sensor and ESC module.
 

Schurkey

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valve rattle when accelerating "lightly to moderately". No rattle noticeable at WOT or cruising.

Rattle disappeared if I ran 92 octane.

I assume this was spark knock/detonation.
Detonation/spark knock/ping has nothing at all to do with the valves.

Calling it "valve rattle" gives the wrong impression.

Should I have been running colder spark plugs? I can't remember what plugs I was using, that was too many years ago. I was using whatever Pep Boys sold me.

I've owned 2 Vortec 5.7s and I drive a 2004 half ton with the 4.3 for work, never once hear valve rattle, I suppose because of the knock sensor doing it's thing.
If the knock sensor system and EGR was working on your vehicles, you wouldn't have heard it on them, either.

SOMETHING is wrong.

Verify fuel pressure and initial ignition timing. Connect a scan tool to verify the computer system including the knock sensors/EST. Assure that the EGR is fully functional as intended. Make sure the heated air intake system regulates air temp properly--not fully-hot all the time.
 
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