Noise

[deej]

I had a noise that came from the engine sometimes. It increased with RPM and sounded like there was something loose, almost like the rad fan was hitting light metal. I had my brother listen and he said detination, maybe bad gas. I upped the octane(87 to 89) and it seemed to go away. I still don't know if I fixed it or not. Has anyone else heard of this problem?

[88pathoffroad]

I've had my radiator fan shroud break and the fan hit it sometimes, but not all the time. It's since been replaced.

[deej]

Update:

I went on a 12 hour road trip this wknd and it showed up a couple of times. The noise is at the top of the RPM's (around 4000) and it's only when under load, when the clutch is in it disappears. It doesn't seem to matter if the engine is warm or not cuz it didn't show up till about an hour into the trip. Thanks for the info 88 but I don't think it's the shroud cuz of the "disappearing with the clutch in" thing. It'll keep my guessing.......I guess.

:confused:

[mikesmaximase]

throw out bearings

[sw]

if its only happening under load i would say detonation

 

check ignition timing, knock it back 5 degrees = no problems

[statikuz]

I'm kinda havin the same problem, but it only does it for a few seconds, and only at ignition and occasionally when driving... when the clutch is engaged the noise goes away too. Not sure.

[deej]

Stat,

Does it increase with RPM's while driving?

Mike,

What makes you think throw out bearings?

Steve,

If the timing was out, wouldn't I have this sound all the time on increased RPM?

Thanks for the input guys, I'm still not sure.

[sw]

no

 

the way detonation works is with the fuel spontaneous combusting before the spark from the spark plug

 

the spontaneous combustion is cause by excessive heat build up in a cylinder

the harder the engine is working the hotter it is - hence not all the time

this can be due to high carbon build up, high head pessure & too far 'advanced' timing.

 

what you are doing by 'retarding' the timing is not letting the engine get to this point of excessive heat. you loose fuel eco & power BUT you do save your engine from a very quick death

 

i retarded the timing on my path but i still slightly suffer 'pinging' if im not carefull but no where near as bad as before.

 

hope this makes sense

[ChromoTech]

Yah my truck does that once in a while when i start it too it sounds like metal on metal sound for like 2 or 3 seconds on cold starts.

anyone else have this problem???

[deej]

Thanks Steve,

That makes perfect sense. There's only one problem, my gas milage is pretty bad right now. I think I'll do what DJ Dank did and try a spark plug replacement first. 96 and up forum. Some of you should read it, the guys a genius with Nissan supplied tools(for changing tires, mind you, but good for that #6 plug)

[statikuz]

It doesn't really increase with RPMs, its mostly on starts, I don't notice it when I'm just driving around except for every now and again, but its so infrequent I couldn't tell you when that happens...

[sw]

Stat

the sheild on the cat is know for rattling

 

i heard Aaron mention it before, i think he just chucked his in the end, not sure tho

[statikuz]

I dunno if its that tho, it's not really random like that sort of rattling would be, more of a spinning sound for a few seconds at start...

[MatterHorn]

try checking for play in the mounting plates between the motor and the tranny ... you should be looking for the zinc (gold colored) plates that are mated between those two surfaces ... often times when the slicone between those gets worn out or compressed, there will be a rattle ... the rattle goes away when you depress the clutch peddle because there is no longer a force that is trying to push the tranny and motor apart, thus it tightens it's grip on the plates ...

[IowaPathfinder]

The cat rattling can be an issue at start. It will go away after the vehicle warms up. It will still happen occasionally while driving. I had mine cut off and never had the problem again. If you metal on metal sound is almost like a pinging when accelarating I would follow some of the other posts that said to look at the timing. That kind of With your rig being a 98 it does have that sheild and it is a very simple fix. My mech cut it off for free for me. I have an issue when it gets cold and I haven't changed out the oil from summer to winter viscosity I get some noise out of the valves. I know for me that it's not getting oil up in the heads right away. Hope it helps.