NP 3.5L Noise whilst accelerating.

[CaptJack Junior Member Find all posts View Profile Close CaptJack]

G'day all,

Great site seems very informative and has been interesting reading.

I recently purchased a 03NP 3.5L 105,00klms on the clock. I have only had the vehicle for a couple of weeks but have noticed a distinct popping noise when accelerating. The "popping" only occurs whilst in gear and driving between approx 2000 and 3000rpm. I assume when the auto gearbox is changing between 1st to 2nd and onto 3rd.

Once at speed and I take my foot slightly off the accelerator the noise stops. I think the noise was there to begin with although for whatever reason it didnt seem as noticeable.

I have crawled around underneath and there is nothing so blantantly loose or rusted that I can see. Admittdley the grand canyon could be stashed under there and I wouldnt know better.

The car is going back to the dealer on Monday. I realise my query is as clear as mud but am hoping someone may have some advice as to the potential issue. Im sure if there is a problem they will say it isnt covered by the warranty and I would like to have somewhat of a clue.

On the flip side it could be a perfectly normal noise and I am completley paranoid and wrong. It wouldnt be the first time !. I thought better to be safe than sorry.

Completley Clueless.


Thanks

[psproule Valued Member Find all posts View Profile Close psproule]

Probably need a better description of the noise, but are you sure it isnt an exhaust leak from a cracked manifold (fairly common on them)?

Pat

[CaptJack Junior Member Find all posts View Profile Close CaptJack]

Yeah I thought that is where my post would fall down in not being able to describe a "noise" in words.

Although now I think about it an exhaust leak is exactly how I would better describe the noise.

If it is the manifold it should be fun chasing up the warranty. Thanks for your thoughts Pat even if they did make me feel sick somewhat. lol .



Car is going in tomorrow now (Thanks Pat) have spoke to the dealer. When I mentioned the noise perhaps sounded like an exhaust leak, he immediatley started down the line saying the noise was fairly common in that model and was due to the manifold being quite thin.

[psproule Valued Member Find all posts View Profile Close psproule]

It's not normal though if it sounds like a leaky muffler type of chuffing though. sound's like they are trying to fob you off. It will have a cracked manifold between the second and third ports on each side but you wont be able to see it as it will be underneath facing the head / block. A lot of people replace them with headers and reap a bit of a performance increase at the same time.

[kcandco Junior Member Find all posts View Profile Close kcandco]

Hi
Its amazing that you bring up the matter of cracked exhaust manifold as only 40 minutes ago I discovered passenger side manifold with crack like you said between 2nd and 3rd port. Do you know if these can be welded or am I in for a new manifold? Any comments welcome. i imagine headers would be quite expensive.

thanks Kc

[psproule Valued Member Find all posts View Profile Close psproule]

A couple of forumites mention having welded them. No harm in trying except all the fiddling to get them out. Headders seem to come in between $600 and $1200 fitted depending on make and exhaust shop extortion, which is aparantly comparable to new manifolds cost from Mitsu.

[icysyrup Valued Member Find all posts View Profile Close icysyrup]

The manifolds can be welded with an Arc Welder...just make sure to get Nickel Welding rod to weld the cast. Take the manifold off and then drill two little small holes with a drill at the end of each crack(so that the welding puddle wont get away from you) and weld a 1/8"-1/4" at a time and then let it cool and tap it with a regular size metal punch while it cools with just the weight of the punch....that helps it cool properly without cracking. I did mine for 10 bucks....the cost of 2 nickel welding rods.....pricey stuff but still cheaper than a new manifold and works just fine now.

[kcandco Junior Member Find all posts View Profile Close kcandco]

Thanks Guys

Headers sound expensive so I will try repair for a start. Nickel rods eh!! What size and amperage do you recommend? I imagine it would be very easy to blow holes in the manifold.

regards Kc

[icysyrup Valued Member Find all posts View Profile Close icysyrup]

I cant remember the amperage exactly...just start with less than you think and go up a little from there....you can look on the inside to see if it is getting your normal penetration that you need.....also....weld it on there good...meaning put a good couple beads on it...I did mine the first time with one bead trying to be aesthetically perfect with a nice uniform bead and it ended up cracking again in the same spot....so i went and took it off again and this time didnt care about the looks but put one over top of it where it cracked and then two down either side.....it didnt look purdy but its covered by the heat shield so who cares in my opinion anyways....

As for the size of rod...get the standard size....I dont think they come in very many sizes....hope this helps ya...any more questions post em up and i will try to answer them...

[kcandco Junior Member Find all posts View Profile Close kcandco]

Thanks Icysyrup Sounds like this will take a while to do but i am on the right track now.

regards Kc

[pajevo Junior Member Find all posts View Profile Close pajevo]

I get a popping noise from my exhaust when changing down gear at high revs sometimes, but i have determined that to be caused by not high enough octane fuel. I always fill up with 98, but 500ml of Nulon pro strength octane booster clears it right up. Unfortunately that costs an arm and a leg to do every tank but i suppose that comes with the territory when you purchase a racecar :P (evo pajero)