grinding noise in my 1990 pathfinder

[SWAY]

Hi,

I just bought a 1990 nissan pathfinder SE automatic and I notice whenever I press the gas pedal I hear a noise that sounds like metal rattling. This happens in drive and reverse but not when I press the pedal in park or neutral, and the noise goes away once I take my foot off the gas. It doesnt happen when I first start moving but around 15 mph it starts. Acceleration is good and the suspension seems good too. I could'nt see anything loose under the hood but I have'nt checked the underbody. Any Ideas would be of help and greatly appreciated. Thanks in advance.

Sway

Modified by SWAY at 2:03 PM 11/9/2004

Modified by SWAY at 2:08 PM 11/9/2004
Modified by SWAY at 3:15 PM 11/9/2004

[s13sr20chris]

two things...1) are you familiar with spark knock?2) are you familiar with broken exhaust manifolds?

if so, does it sound like either of theese two things? both are common on your vehicle.

[SWAY]

I'm not familiar with spark knock or the exhaust manifold but Meineke just replaced the muffler and tailpipe. What should I look or listen for.

[s13sr20chris]

ok, spark knock sounds like a bunch of bb's rattling in a tin can. it happens under load. most common would be going up a hill or something. it happens more often in underpowered vehicles like(no offense) pathfinders. my old honda accord i used to have did it really bad. it usually does not happen at full throttle as the ecm backs off the timing. number one cause(especially on pathfinders) is advanced ign timing. other possible causes are bad plugs(like bosch platinums yuck), bad wires(any aftermarket), bad cap and rotor(aftermarket), and carbon in the combustion chamber.

solution #1 for you to try in this case. go to nissan dealer and buy oem spark plugs, wires, cap, and rotor. do not get aftermarket! i have had too many probs with aftermarket ign components! install parts. when installing the plugs spray some carburuetor cleaner down the plug holes. start car up. while it is running pull of a vac hose(one with actual vacuum sucking at it) and spray carb cleaner or better yet seafoam(fancy cleaner stuff). do this for a while. if it stalls just start it back up. when you feel like you are done kill the motor(needs to be really hot by this time) and unplug the tps. start back up and check ign timing. the spec for ign timing is under the hood or in the fsm/haynes manual. once done, plug up tps again, shut off, start up, and install fuel system cleaner to gas tank.

approved fuel sys cleaners: seafoam, bg 44k(my personal favorite), chevron techron. there are some others but i would stay on the safe side by using one of those with a full tank of gas.

leaking exhaust manifold will be a ticking noise mostly when engine is cold. you should hear it from under the hood and it may be louder on one side of the engine. you can verify this by running a little bit of atf through the vacuum hoses(like the brake booster hose or something). the atf will not burn but will come out the tail pipe and any exhaust leak as well. if you need a manifold then i suggest going to a dealer as the studs usually break off in the head as well. this requires specialized tools and some skill.