zachlovesxj

greetings to day my 98 sport developed knocking sound,the engine started idling rough at the same time.when idling the motor never moved now it is visibly shaking not a lot but some it did not do that be for.this leads me to beleive i also have a miss fire.although check engine light is not on i have read about loose flex plate bolts but because of the rough idling i am thinking it could be some thing else.any help or advise would be appreciated this is a high mileage motor over 300,000 miles i am afraid to start it oil pressure is normal and engine did not over heat when this happen engine had only been running for a few minutes i was pulling a small bush out in 4 low if it matters

thank you for the help

zachlovesxj

for got to mention,plugs cap and wires have less than 30,000 miles on them.would any of these cause a knock?

Radi

Loud metallic knock? Dull thud type knock?
Might pull the plug wires one by one and see if the noise disappears or changes. Also look for one that does not change the idle when disconnected.

zachlovesxj

thank you for the reply it is a Dull thud what are you thinking worst case could be?Broken rod?am i batter off trying to figure this out with out starting the motor by turning it over by hand or at this point is the damage all ready done dose not really matter the sound is not un godley loud


and thank you again

Radi

Ack. I don't like dull thuds, that tends to indicate internal trouble...piston skirt, rod, bearing.. pulling the pan and taking a look might be the only accurate way to find out.

ETA: I'd borrow a cooling system pressure tester and see if you have a head gasket leak before I dug further in... that might cause a misfire and light knock. I don't think it will hurt to run it long enough to pull each wire and see if it changes.

zachlovesxj

well thank you ill update this thread as i find the problem is there ever a situation where a non firing plug would create that that knock

Radi

This is one of those "you really have to be there" sort of things. A noise that is loud to you might be minor to me, and vice-versa. (it's always louder and more ominous when it's my wallet that's involved)
Certainly a misfiring engine can make noise, trying to judge what you have without seeing/hearing it is basically just guessing. A recording would be very helpful.
Meanwhile, I'd pull each wire and see what happens. If the noise lessens or goes away when you pull a certain plug wire, I'd look for piston-related trouble.
That should also tell you which cylinder is misfiring...when you disconnect the misfiring cylinder the idle won't change. Fix the misfire and see if the noise goes away.
If the plugs are all firing and you still have a misfire, next thing I'd do is a cylinder leak-down test to check the head gasket, valves, etc. If you can't do that a cooling system pressure test might root out a leaking head gasket.
If the noise goes away after the misfire is fixed, I wouldn't worry any further.
If the noise remains, pull the pan and take a look.

zachlovesxj

ill find a youtube vid and post the link later

zachlovesxj

flex bolts were lose thanks for your help radi

Radi

Awesome! I was way off in the wrong direction, lol. Always good to find a cheap fix. What was causing the misfire?