Thumping Noise

[hexgirl1013]

Hi all,
I've only had my new 2002 X-Terra for about two weeks and already I'm having a problem. I've started hearing a thumping noise coming from the truck once in a while. It's not a repetative thumping. It'll just thump once and not do it for another five minutes. It mainly occurs during acceleration but has happened twice sitting at red lights. I've got the V6 (non supercharged) engine. I'm wondering if it could be an occassional knock coming from the gas I'm using. The dealer said I should use premium gas in it, but the owner's manual recommended 87 octane (regular) so I figured I'd split the difference and put Exxon Silver (89 octane) and be right in the middle. Do you think it's the gas? Or is this occassional thumping noise common for the X-Terra? Or is it broke already? Help! Ease my worries, please.
Thanks so much!
Hex

[Stormy]

What did the dealer say?

[hexgirl1013]

It just started this late yesterday afternoon after I got off from work and the dealership was closed. I haven't had a chance to ask them yet. But, I was hoping this was something simple that maybe was common to these SUV's. I didn't really want them to make me out to be an idiot for taking it in for a thumping noise.
So, I thought I'd check with all of you first since you might know more about it than me. Is this a serious problem? I thought it might be the gas since I've only put one tank of gas in it and it was the night before it started making the noise. Maybe I got bad gas? Can water in the tank cause this kind of noise?

[OffroadX]

Originally posted by hexgirl1013
The dealer said I should use premium gas in it, but the owner's manual recommended 87 octane (regular)

If it's supercharged, use premium. If not, use regular (87).

I guess you're saying you believe this "thump" is engine related? I've never known an engine to make a thump sound, especially without it being repetitive.

The two "thump" type sounds that come to mind are either the gas sloshing in the tank, or perhaps a body mount needs an adjustment (though I think that was reported as more of a "pop" sound) but that's a shot in the dark.

Brent

[hexgirl1013]

It's not supercharged, so yeah...the book said 87, but the dealership said only premium which is weird to begin with.

Yeah, the sound is a definite thump or thunk. It's hard to tell where it's coming from. The first time I heard it was pulling out of a parking space barely moving and I was sure I had rolled over something. But I hadn't. You know how it sounds when you release the parking brake? Muffle that sound somewhat and it sounds like that. I was sure it was coming from the engine compartment on the right side of the engine. But, I had a passenger who rode with me and was sure it was coming from the rear. They swore it was probably suspension, but it's sorta impossible for it to be suspension if it makes the noise sitting still at a red light. Weird, eh?

[Stormy]

What about the wiring harness hitting the tranny thing? That was a problem for some people. Not sure specifically what it was...

Can you feel it under your feet or when you're holding the steering wheel?

[Schludwiller]

Sounds like you need to go see the dealer. One word of caution if your dealer tells you to put in higher octane to fix a problem when your truck is designed to run on regular, it might be an indication of how you'll be treated down the line. Sounds like he was hoping to get rid of you.

If it's a brand new truck, he should have said bring it on in Monday morning and we'll take a look.

If you keep having problems with them, then look for another Nissan dealer. It's important to have a good working relationship with your service department. Also, drive down to the dealership and tell your salesman about the problem. He should lead you right over to the service department and have an appointment set up right away. It's hard to turn people away when they're right in front of you, and the salesman "should" be ready to make you happy.

Oh, and here are my guesses. Really guesses cause I'm not sure what your problem is. Fuel pump problem, or the spare isn't tightened to the truck well, or the leaf spring has a problem and is popping to relieve some tension. Just guesses though.

[CheetaraX]

Can you feel the thump or just hear it?

[SarnX]

The dealer is wrong about the Octane. You should run what the owners manual says to run. In short any higher octane is wasted and any lower can be harmful to the engine.

Long description:

Octane is a measure of a fuels resistance to engine knocking. The scale refers to how the fuel relates to a mixture of Iso-Octane and N-Heptane. The scale is relative. Iso-Octane was arbitrarily set at 100 and N-Heptane was set at 0. Therefore a gasoline that has a rating of 87 octane behaves the same as a mixture of 87% Iso-Octane and 13% N-Heptane. On the pump it may say R+M/2 this refers to the testing of this resistance to knocking. There are two tests done to measure the octane rating of the fuel, the research method and the motor method and if you sum these up and divide by 2 the number must be 87. Both tests use engines to measure this resistance but use different conditions.

Today's modern engines with computer control and ignition were specifically designed to run on a particular resistance to knocking or octane. Therefore if you use a fuel with a lower number it is possible to damage the engine and if you use a fuel with a higher number you are likely just wasting your money. Some companies put in different additives etc. in there higher octane blends which can potentially keep your injectors etc. cleaner or keep your fuel system from freezing in the winter but most of the big brand names use the same additives in all of their grades.

SarnX. Chemical Engineer

PS - Hope this helps.

[coolerman]

My 2000 does this sometimes and has since I've owned it. I ignore it My best guess would be an exhaust component that's loose and hitting something occasionally. I hadn't thought about the spare though and will check it. Still, mine has never made the noise while sitting!

Engine knock is a constant repetitive noise that gets worse under load. If the engine is tuned correctly and still knocks then sometimes a higher-octane fuel will solve the problem. Your dealer should not have told you to burn high test! Save your money and run regular!

Good luck with your dealer...

[hexgirl1013]

I can't feel it under my foot or in the steering. I can only hear it. I've had the truck for 2 weeks and it just started this last night. That's why I thought maybe it was the gas, but I guess not. Hrmmm...lots of great advice to consider here. Thanks everyone. Anyone else with any advice or experiece with this problem? Your comments are greatly appreciated.
Thanks again!
Hex

[Xcanuk]

Is the thumping happening when you are at a stand still, moving, or both ?? I really don't notice it anymore, but I pretty sure there is a slight thump when taking off... for some reason I think it was passed off as the ABS check ?? Do you have a 4x2 or 4x4 ??

[hexgirl1013]

Nine times out of ten it happens when I'm accelerating from a stop or near stop (i.e., rounding a corner). That's also when it's the loudest. But even then it's not that loud although it varies in intensity. I've had it do it several times when I'm cruising along at like 35-40 miles an hour and I've got the gas pedal slightly depressed to keep it at an even speed. It's only happened twice while sitting still and then it was so faint I was not even sure that's what I heard. Oh, to answer your question I have a 4X2.
Thanks,
Hex

[Schludwiller]

Originally posted by hexgirl1013
Nine times out of ten it happens when I'm accelerating from a stop or near stop (i.e., rounding a corner). That's also when it's the loudest. But even then it's not that loud although it varies in intensity. I've had it do it several times when I'm cruising along at like 35-40 miles an hour and I've got the gas pedal slightly depressed to keep it at an even speed. It's only happened twice while sitting still and then it was so faint I was not even sure that's what I heard. Oh, to answer your question I have a 4X2.
Thanks,
Hex

Hmmmm..ChuckH had a sound like that when we put in the SLR shackles. There was too much space between the bushing and the shackle so the leaf would shift and contact the shackle on turns. Drove him nuts. I'm still stumped though. Make sure you post back here after the dealer finds out what it is.

[ozxterra]

Check your battery is locked in securely. When a new car comes to a dealership they often mess with the battery off the delivery truck - sometimes they install their own etc. (I dont know why). I have seen several brand new vehicles with loose batteries. There are two metal rods on either side that are secured by nuts. If the battery is loose at all it will bump at stopping and starting but not produce that "under the pedal feel." Also, get the dealer to make sure your shocks are tightly installed (Another issue I have run into). They will knock without creating any felt issue.

Good Luck!