# Rod knock or Vavle issue?



## Twin_Turbo_300zx (Apr 19, 2010)

I just replaced my Head gasket and fuel injectors, before I had done that I didn't drive the car for 4 months or so due to leaking injectors. When I would start the car every few weeks the valves would tick pretty loud but go away after running the car for 5-10 minutes.

After I completed the job I started the car up. Tweaked a few things and while doing so I heard a Knocking sound at random. It seemed to be like a rod knock/Spun bearing. I shut the car off looked over a few things started it up again the car is running ok as far as idle goes but now the knocking/Very loud ticking is constant and gets a lot faster even with a very low rpm increase. The car seems like it is miss firing or something when it is revved up.

I read somewhere that the way to tell the difference between a valve problem and a rod knock/spun bearing is the speed change as the rpms increase.

If I do have to replace the bearings can I do it by just dropping the oil pan? Would I be able to pull the crank without pulling the engine?

Tutorials would be awesome if you guys know of any!

Thanks for the help!
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## Twin_Turbo_300zx (Apr 19, 2010)

I just noticed it shows no oil pressure so I shut it off right away and started to look for the cause I noticed the plug that connects right near the oil filter seems to be missing a wire, I cannot for the life of me find the wire. I assume that is just for the gauge though right?


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## Shadao (Aug 14, 2007)

sounds to me like rod knock, which could be caused by bad gas... you did say it sat for 4months over winter... perhaps empty the gas out put new stuff in as well as check your possible oil issue..

as for doing a in car rebuild... there isnt enough room in the engine bay to change plugs without removing half the engine let alone replace bearings and such... so if you do have to do a rebuild you're gonna have to pull it...

pulling it will be easier anyways and it gives you a chance to upgrade other things as well...

when you did your head gasket did you get new bolts or did you reuse the ones you had? cause as far as i know you should never reuse your head bolts... even if they are ARP


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## Twin_Turbo_300zx (Apr 19, 2010)

I replaced them. You're saying bad gas can cause knock as in pre-ignition right? That is different from rod knock from a spun bearing. Right?


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## rogoman (Dec 16, 2004)

Bad gas will not cause a rod knock but can cause pre-ignition which will result in a pinging sound. Rod knocks are caused by bearing failure because of lack of lubrication, excessive bearing wear or a spun bearing.


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## NissanPartsDept (Mar 31, 2010)

Are you certain that nothing fell into any of the combustion chambers or intake manifold. I would pull the spark plugs and check to see if any of their tips appear to have been hit by something.


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## Twin_Turbo_300zx (Apr 19, 2010)

It turns out it was just an extremely loud lifter! Thank god I just ran the car trying to see where it was coming from and it slowly dissipated and as soon as I drove the car a few feet it went away completely. 

Anyone with a knocking sound it may be a loud lifter, it was loud enough to be a rod knock so check it out before pulling the motor.

Now the car is running amazing, except after driving the idle surges between 500-1000 rpms every few seconds about 5 or 6 times before leveling out at about 900 rpms, I found a few boost leaks and it seemed to help some but it still surges does anyone know what would cause this?

I still have 1 or 2 very small boost leaks no more than before the new injectors and head gasket though.


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## Twin_Turbo_300zx (Apr 19, 2010)

Could this be related to bad O2 sensors, I had a DSM and I could not stop the idle surge for the life of me took it to 3 different shops and no one knew what to do. I replace the O2 sensor and bam bye bye idle surge.

This morning I started the car let it run for 2 minutes and tried to drive away it felt like I was towing a 5th wheel trailer. I had a similar problem on a cooler day it went away after driving around the block. It seems like this could have something to do with an O2 sensor as well....?


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## Twin_Turbo_300zx (Apr 19, 2010)

I am still having weird power issues when the car isn't at running temp. It feels like when I had a leaking injector. I get boost but the car bogs.

I also noticed that when it is colder outside I don't have any idle surge problems.


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## rogoman (Dec 16, 2004)

Twin_Turbo_300zx said:


> I found a few boost leaks and it seemed to help some but it still surges does anyone know what would cause this?
> 
> I still have 1 or 2 very small boost leaks no more than before the new injectors and head gasket though.


You need to eliminate all boost leaks. The best way to do this is to disconnect the hot pipe at both ends and cap the ends. One of the caps has to have a pressure gauge and a provision for pressurizing the hot pipe. After pressurizing, the reading should hold steady.


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