Hey guys, I'm totally new to the TL world. I have loved the 3rd gens for ever. I finally got a 2007 TL base white diamond pearl last week. It's got 76K miles and is in excellent shape. Although, I've started to hear a quick knock right before the engine starts. The engine actually starts really quickly like nothing is wrong but just before it starts I hear a quick knock(just one knock) immediately before the engine fires up. And then everything is fine. Any ideas on what it could be?
Thanks in advance!

 

Like a mechanical knock (misfire) or a structural knock (clunk)?

 

I would not say it was a misfire...so I guess a structural knock? It's immediately before it starts. It's so quick and not that loud either.

 

I'd check engine mounts. Is it during cranking?

 

Yes, it was during cranking. It's so quick to start though...but ya, it's during cranking.

 

starter/flywheel?

Pull the fuel pump/FI fuse and try cranking it. Having a second person to either crank or put their head into the engine compartment would be helpful.

 

Ok, I'll try that in a day of two as I don't have anyone around for a day or so. Thanks so much!

 

LaJay007, any progress troubleshooting this problem since your original post? I have the exact issue with my 07 Type S! I get it during 50% of the startups. I would describe it as a structural clunk; it feels like the entire engine moves, however, it doesn't seem like it is hitting anything. Rather the noise seems a result of the abrupt twist of the engine itself during the crank.

I suspected an engine mount earlier, although there is no other indication of a problem.

I will change the spark plugs next weekend and see if that helps. My thinking is, if it only happens sometimes, it might be related to piston position during the initial crank and if the spark doesn't arrive as expected it might cause the harsher engine movement.

I will update!