Rod Knock! OR is IT?

[Rob1]

My 89 supra was in my garage for a compression test. results were not great, 140,100, 135, 110, 130, 140. So with head in hands i put the coil packs and intake piping and what not back on and fired it up to check a few things.

Here is where it gets interesting, It ran fine for about 1 min, then i headr a knocking noise. Started slow maybe one loud KNOCK every fifteen seconds or so the progressed to a steady, very loud, knocking.

Well i let it idle for about 3 min a week later and it was knocking up a storm. Then like magic is just STOPED! there was still a faint metalic sound but not a knock maybe valve chatter.

So near silence for about ten seconds. then there was one loud KNOCK, after this knock the engine speed fell down to almost stalling, and when the idle came back up the steady knock had returned.

I have repeted this proccess twice now and it follows nearly the same pattern each time.

Any ideas about what it could be? cuz rods dont normaly just stop knocking. any advice would be greatly appreciated thanks

[Travis89Turbo]

Have ya checked your oil?

[cre]

Yes, a knock can be intermittent.... and thus a royal pain to diagnose.

Was the engine warm when you did that compression test? The only way to do a compression test with a cold engine is wet and that's note really the best indicator either. Did you do a wet and a dry test?

If you run the engine and the knock remains long enough pull the spark plug wires one at a time. When the knock goes away or fades significantly you'll know which cylinder is the problem, then you just have to diagnose the one.

[Rob1]

i did it cold and dry and i did that to see if i blew my head gasket then this started.

[cre]

Originally Posted by Rob1

i did it cold and dry and i did that to see if i blew my head gasket then this started.

The reason for doing it warm is so that the rings will expand and valves will have a more true seating... that way compression escaping past the rings isn't mistaken for bad rings. The wet test (done with the right amount of oil) will only ensure that even less air escapes past the rings; The two (wet and dry) are used to determine the health of the rings. Also, keep in mind that if the air can escape past the rings too easily it'll never get pressed past a small leak in a HG... no good for diagnosis at all in that case.

[Rob1]

Ok i might re run it. the knock is VERY loud which i thought it was weird for it to be that loud then just vanish ta know.