Spark Knock Issues

Hi all,

I have a detonation issue in the #3 cylinder on my 1998 4.0L.

Usually occurs when under load and low RPM (like when the TC locks in OD), but can also occur under high RPM and load (like going up a steep hill at 2500 RPM).

So I ran some 93 to confirm...and it stopped. Now being that I fill my tank 4 times a week, I cannot afford to run 93 all the time.

So I seafoamed it 4 times (twice through TB and twice through booster vaccuum line).

Smoked up a storm, ran better, but no change in pinging on 87.

I then did a full tune up (plugs/wires/cap/rotor) with high quality parts.

This was when I saw that the number 3 plug was toasted -- obviously the pre-ignition issues are mainly in that cylinder. The other plugs looked perfect.

And the result? The damn thing still pings under load. 89 helps but does not resolve the issue 100%. What should I try next?

Do you have the "heat shield" on your intake manifold? There was a recall for one to be put on due to the fuel in Injector #3 being too hot and vaporizing before it got through the injector....

JNickel101 said:

Do you have the "heat shield" on your intake manifold? There was a recall for one to be put on due to the fuel in Injector #3 being too hot and vaporizing before it got through the injector....

Click to expand...

No idea on that one....I'll take a look but I don't recall seeing anything like that the last time I was under there.

Think I could make one if it does not?

Probably, but since there was a recall on it, the dealership should install one for free...I'll look and see if I can find more detailed info on it....

I found it....I think.

Looks like it only applies to the newer style intake (99+)?

Yeah, but the way they wrote it up seems funny..."debris accumulates around the #3 injector..." so they install a heat shield to keep it from catching on fire?
Ok...so next idea....

you ran a bunch of sea foam through there - I've heard that stuff can jack up your O2 sensor - if your sensor is jacked, that could cause your air/fuel mixture to be off....ya? Maybe? Anyone? Bueller?

I had the exact same knock. When I replaced my cylinder head it went away. The old head was pretty sludged up. Don't know what fixed it. Maybe a sticking valve?

Engine has recently been auto-rx'd and looks totally clean and shiny inside the valve cover (from the little that I can see).