M45 knocking sounds

[tigerclaws1318]

Earlier on my way home I noticed a knocking/detonation sound coming from the engine. It happens when the car goes into second gear at around 1800rpm. Dont know what it could be. I always use 93 octane fuel.

[ken in az]

I wish I had 93

[tigerclaws1318]

I wish I had 93

You guys dont have 93?

[M45Runner]

Some places only have gas up to 91 octane, so you are lucky, so do I.

But, for the knocking sound, it could be bad gas - maybe there are water in the gas or the octane level is not what they stated - This could happen when using non-brand name gas, AKA 2nd or 3rd tier gas.

[szh]

The most likely scenario is bad gas or water in the gas. Much less likely is some carbon buildup (happens to the VK engines).

Try a bottle of ISOHEET (not plain HEET - that is not isopropyl alcohol) in the gas tank, and also fill up at another station and see if the problem persists.

If ISOHEET and another tankful of good gas does not fix it, a session with BG44K is what I would try next - instructions are simple, please do a search for previous posts of mine on the topic.

California does not have anything higher than 91, by the way.

Z

[tigerclaws1318]

Probably was bad gas but I've used shell 93 all the time. The only reason why I use shell is cause of their nitrogen enriched fuel. Now that I switched over to BP 93 it seems to be gone for now.

[Shoebox]

Its not bad gas its your exhaust manifold gone bad. I just had the dealer replace mine under warranty, dealer said it was about $1200 to replace without warranty. It does sound like bad gas knocking but a lot louder. Exhaust manifolds collect engine exhaust from multiple cylinders and deliver it to the exhaust pipe. Are there after market headers for these engines?