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Mysterious Knock

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Old 01-09-2018, 09:51 AM   #1  
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Mysterious Knock

I've got a 1993 Maxima SE, bought new, and maintained carefully for just shy of 25 years now. Needless to say, I love this car, and in most ways it runs very well.

For the last month or so, it's been a bit hard to start when the engine is cold. I had to depress the accelerator a bit, which I normally don't have to do, and once it caught it would run rough and smell like gasoline.

My mechanic, who specializes in Zs and has been servicing the car for 20 years, decided it was an injector and replaced it. In the course of diagnosing the problem, something happened that isn't clear to me and the car developed a knock. At one point, they turned the engine over with the spark plug out of that cylinder (#1) and a lot of gas spurted out.

They replaced the injector (#1) and the starting problem & smells-of-gas problem were solved. And the knock is significantly quieter. But it's still there. You can't hear it when you're moving at say 30 mph or more, but with the car stopped, you can hear it at all rpms. It sounds like it's coming from #1, but it's awfully hard to be sure.

My mechanic thinks that something happened when that gas shot out of the cylinder that maybe damaged a lifter or a valve. A friend thought maybe the connecting rod is very slightly bent. Either one sounds BAD.

Does anybody have any suggestions or thoughts about this? What it might be and what I can do?

Many thanks --
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Old 01-10-2018, 10:38 PM   #2  
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search VTC clack on VE30DE engines, common issue if that is the noise. pricey to replace the VTC but you can bypass it by grounding them

to damage a lifter or valve with the engine in time the cylinder has to either have ALOT of fuel in it, really bad pre-det or out of time enough for the piston to contact a valve. same thing to bend a con rod, either has to be alot of fuel or liquid in the combustion chamber to create the pressure to bend it or bad pre/post det to bend it. sounds like it was a injector sticking open, id search VTC noise first then go from there.
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Old 01-11-2018, 08:45 AM   #3  
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That's a great suggestion. Thanks. I didn't know what the VTC was. Now I do. And I've seen/heard a video and it does sort of sound like that.

My mechanic was stumped by this thing. He's heard of hydrolock damaging a valve or a lifter, but in 30+ years of work on Nissans, he's never personally seen it. And how much gas there was in that cylinder is hard to know, but maybe not as much as would be needed to break something. I have to guess that he's considered the VTC, but I will ask.

Thanks again --
Steve
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