Just bought a used 1998 Mustang GT (4.6L / manual trans): after purchase, started to notice rattling sounds from underneath the car when I start it (for a second) and when underload during acceleration. My original thoughts were that it's a vibration problem coming from something when underload (exhaust rattle?). Also, had occasion detonation and did have engine ping sounds (most gone since tune-up).

For tune-up, I put new plugs (all of old tips were burned to below insulators), New wires, cleaned K&N air filter, oil change/filter, and finally added fuel injector cleaner and put in half tank of 93 octane (half full with 87 octane).
However, this morning, started to hear a new noise, irregular but under load from passenger side (appears top side of engine / rocker arms?) when RPMs above 2k (not steady but intermittent). I stopped driving car (immediately)at this point as now I'm more convinced of engine problems / not rattles from an exhaust.

Gauges indicate good oil pressure and even seems to run cool (gauge has indicated below "Normal" with 70degree outside temp and highway driving).

Where do I start with problems?

 

our motors are OHC not OHV... id start with a TOB if it does it in neutral.. under slight load and a rattling.. id check for loose bolts or damaged suspension parts.. what is this "irregular" noise explain it

 

Compared to a loose rocker/tappet sound that I've heard in past experience (Chevy 350 - shattered rocker arm) which is a ticking/tapping sound tied to RPM but not consistently there. I basically heard it while driving and sound came through glove box of car. Strange though as it isn't constant and definitely seems to happen only under load. Don't believe I heard it while reving the engine in neutral but will investigate further?

I'm only suspecting to be passenger side near firewall. My concern there is that when I changed those back two plugs (this weekend), I thought they might have been wet but I'm not sure if they were. I'm not a mechanic but I always thought that wet plugs would show water/liquid in the oil and major corrosion of plug (for major problems)...etc. Where like a flooded lawn mower or weed eater when you remove the plug (wet from gas). Therefore, since the anode tips were worn below insulators, I figured it was gas and they were not firing properly?

 

the ticking .. if you can hear it in your compartment.. is most likely an exhaust leak. id check the passenger side exhaust manifold.. have you noticed any leaks underneath the car?? could be a bad injector?

 

I will do some investigating of the exhaust condition. Also, I going to try to reproduce the sounds in neutral (which I do not believe I've heard before) so I can listen to it run from under the hood...

Thanks!

 

if its an exhaust leak.. it usually can be heard when the vehicle is idling maybe its not that bad of a leak.. i dunno keep us updated good luck!

 

im having similar probs...... does it hesitate when u give it gas. like kinda bump a little bit? if so ive been having same prob for weeks now. i cant figure out. my first thought was exhaust leak but it ive been told it wasnt. does it get worse in higher rpms and worse in 3rd and 4th?

 

Okay, the top noise sound disappeared??? Just as it was making a ticking / tapping sound yesterday morning, it went away when I looked at car last night. I imagine if its a real problem, it will come back but I drove the car to work this morning. I wonder if it was related to the work I'm doing to the engine (oil change / fuel injector flush with 93 octane) that might possibly loosened up somecarbon in the cylinder chamber or ?

As for the sounds heard bottom side of car, I tried reving in neutral and could hear these sounds then as well.Sounds like shaking up pennies or small metal objects in a coffee can (ireggular / not ina harmonious sync with the engine rpms). I still thinkits either a rattle of lose hardware or in the exhaust itself.Will keep looking as I found one exhaust hanger disconnected and reconnected (near axle) but noise did not go away. I also found a loose bracket on the intake manifold and retightened it.

As for performance, I don't have any hesitation during acceleration / shifting. What I still get on occasion is some detonation when upshifting (sounds like popping up close to or at engine) at higher RPMs (2.5-4k range). Even that almost seems to be improving as I drive the car more. The title of the car shows that it has not been driven more then 700 miles in the last 1.5 yrs. So maybe the cars been sitting for some time (????)

I'll keep looking into things - Thanks for the help...As for Epinephrine186 I'm new to this but your problems sound different then mine...

 

what kind of spark plugs are you using? what brand and what size have you gapped them to? as for the pennies rattling, maybe loose suspension part? id get under the car (when its not hot) and start feeling around to see if anything is loose. usually a rattling can be accompanied with a loose oil filter ive heard, give it a twist to make sure its tight.

 

Spark plugs are Motorcraft platinum series gapped at .052.

I put in 93 octane but I'm wondering if that can be an issue? I've read other postings saying that the car octane level should be same as what it is tuned to (I guess meant by timing and computer???).

I'm really not sure what octane level I should use? mid-grade?