I’m trying to trace an engine noise and it’s driving me nuts trying to find the source. I’ve had this same phenomenon on two 3-liter VQ engines and on the 4.0 VQ in my Frontier.Specifically, I’m getting a ~rattling~ noise coming from the engine bay when the engine is cold and while under load, such as when pulling out into traffic even under light/normal acceleration.It doesn’t do it when idling and it doesn’t do it as the engine warms.The noise sounds almost like pre-ignition ping, but it’s not.This is much louder/more pronounced.It doesn’t appear to be a heat shield or anything loose/vibrating.Again, it sounds similar to pre-ignition, but it isn’t.No codes, etc.Any ideas? Talkinghorse1 (formerly Talkinghorse)

 

May be your timing chain guide. They make no or less noise when warm.

 

Belt tensioner ...

 

Chain tensioner.. Which year model do you have? Search on user CS_AR with the word tensioner in the keyword argument. You'll see the before and after videos.

 

It's either gonna be a belt pulley or timing chain tensioner. I've had both but only occasional rattling/ticking on cold starts but crashed the car soon after it started.

For checking bad pulleys you can watch them as the car is running and look for wobbling or take the belt off and see if one of them wiggles a good amount

They also have cheap $3 mechanics stethoscopes to find where noises are coming from

 

TH - Here's the thread to the tensioner information with before and after videos. Need to know your year model to size the effort.

 

My chain makes a bit of a racket when it's cold. If I let it warm up for a minute or two it gets a lot better and then goes away pretty much completely when the engine is at temp. I even had the tensioner out at one point... argh.

 

Same here. I have a 96. I took the tensioner apart. I stretched the spring a bit. I thought that might increase tension. This happened while I was replacing the water pump.

I let the engine run a few seconds to develop some oil pressure. Then I blip the gas to maybe 2k rpm
for an instant. Doing that gives increased.oil pressure. The rattle goes away faster if I do that.

 

Thanks for the inputs...I experienced it on my '98 Maxima, '00 I-30, both with the 3.0 VQ engine and currently on my '06 Frontier with the 4.0 VQ. When the engine is cold and let's say I pull out into traffic from where it's sat all day at work, the engine will rattle like hell on acceleration...acceleration doesn't have to be heavy...light/medium acceleration will bring it on. When idling, even when cold, there's no abnormal noise. The noise goes away after the engine begins to warm up, maybe 1/4 mile down the road. All 3 of the cars began to do this when they had over 100k on them.

 

 

Serpentine belt tensioner or timing ~chain~ tensioner?

 

 

Definitely worth a try and will give it a shot before moving on to the timing chain tensioner . The engine/truck has 200k on it and the belt tensioner is original.
Thanks to all for your inputs

 

I replace the belt tensioner along with the belts whenever I buy a 4th gen. If you have a Nissan 4.0, there is a whole different set of issues with timing chain noise compared to a VQ 3.0.

Changing the chain tensioner on a (97-99) VQ 3.0 is not a bad job. For a 95-96 model, it is considerably more work.

 

When you are coming off a stop or a slow gradually accelerating up in speeds, it would sound like a metal rattling knocking noise coming from the engine area. I have heard plenty of 3.5ls and my quest are doing this, it's most likely the lifters or rocker arms that are making this noise, it's more noticeable when you are low on oil or around the time to change your oil. I would start checking with the oil levels and if it's low fill it up and check again. I can hear my quest do this and i fill it up alittle over the fill the noise goes away and it gets quiet.

 

Yes, the noise is as you say, but only when the engine is warming up, operating (not idling) under load. For example, I live on top of a little hill and to get out of my subdivision, I have to go down the hill and then back up another at very low speed as it's thru a neighborhood with speed bumps. The noise starts when I start going up the hill to exit the subdivision...there's a speed bump on the hill going up, and it rattles after I slow to roll over the speed bump, then accelerate gently to resume up the hill when the engine is under greater load. Same thing after it sits all day at work...I pull out of the parking lot on to the street and it rattles like hell on acceleration. Once the engine begins to warm and I'm on my way, the noise doesn't present itself. Being low on oil isn't it as none of the engines use/used a drop of oil. I fill the 4.0 with 5.5 qts and it stays on Full for the full duration of the oil change. Engines have always been well maintained...had to change valve cover gaskets on the Frontier last year and this is what the head looked like with 180k on it. No sludge/varnish or obvious wear. Think I'm going to try replacing the belt tensioner for kicks and see if it makes any difference. Thx

 

I get a similar rattling/metallic noise when accelerating harder. I only notice it when warmed up, as I take it easy when the engine is cold. 87 or 91 gas makes no difference.
It could be motor mounts.

 

I realize this thread is OLD... but there was no resolution at the time. But...

Having just recently picked up a '97 i30 (107k miles) in near mint condition AND experiencing this exact same issue, I can say with near certainty that the noise is coming from the IACV. How or why this is happening exactly is still a mystery. I had removed the lower windshield cowling to clean things out, so there was less "seal" between the engine bay and hood, which really accentuated the sound right in my face (the IACV being directly in front of the driver). Very loud and hard clicking in step with the engine speed, not at idle but under light/normal acceleration when cold. Goes away within a mile of driving. Initially, it sounded like some horrific oil starvation issue, but it's just not. The next evening, I was able to put a "listening device" directly on the IACV while revving under the same cold conditions, and the sound was definitely coming from the IACV assembly. I have to wonder if there's something going on with the pintles banging around during dynamic air pressure changes. Perhaps the springs are also changing as they get hot? It really is bizarre. I also have a '96 i30 with 300K and an identical IACV which only very faintly produces the problem, so it could just be more characteristic in certain IACVs as they age? It's worth noting that the IACV in question is working perfectly. Stepper motor controls the idle speed perfectly. Power steering and AC solenoids work as expected. Other than sounding horrible, I don't think it's a problem that HAS to be fixed. However, I did pick up a junkyard IACV, so I could play around with making some mods and find the root of the problem, hopefully. Sounds like a common issue at least.

 

Ok, I think mystery solved on this one. For this issue of LOUD clatter under mild acceleration, getting worse a cold temps, the Back Pressure Transducer (BPT) valve is the culprit, at least for the noise as described by Talkinghorse1. I had originally thought that it was coming from the IACV, so much so that I bought a cheap OEM IACV off ebay and stiffened the solenoid springs. Those solenoids for the AC and power steering make a loud "clack" when closing, and I had thought that the pintles were chattering? Nope. Swapped the original IACV for the modified, and it was no better, maybe even a bit worse. Re-installed the original IACV and wandered off, defeated, scratching head, until...

I finally had a good opportunity with freezing temps this morning to really check it out. Immediately after starting I went under the hood with my listening "device" and pretty much just touched everything I could while gently revving the engine. It's such an "in your face" sound, yet very hard to pinpoint. However, as soon as I touched the "stethoscope" to the BPT valve, it was painfully obvious that this was the source of the chatter. It sits pretty much right below the IACV and throws the sound everywhere.

The good news is that this sound comes from the BPT working properly. The bad news... well, same thing. Nothing to fix. This device, by nature, has a diaphragm that moves up and down with the pulsating back-pressure from the exhaust, which is what we're hearing. This diaphragm is alternately sealing and venting a small vacuum signal to the EGR valve under acceleration, exactly as it's supposed to, but for some reason it's just freakishly LOUD when it does this at cold. It goes away quickly since it's directly connected to the exhaust and heats up fast. I've visually verified that the EGR valve is also moving as it should, and I have no flow warning codes (cleaned EGR tube, etc.). I can also run the bench test on the BPT and see that it functions normally, so at the end of the day, the crazy thing is just noisy. My '96 5sp with 200K more miles on it only "hints" at the same sound, so it may be that some of these BPTs are just more prone to being noisy than others? The red arrow notation below shows the part of the BPT that moves up and down with exhaust pressure, alternately venting to atmosphere and causing the clatter.