Background: 97 GXE auto at 140,800 miles. Recently changed knock sensor, cleaned TB and MAF (with Throttle Body cleaner), stock intake w/K&N filter at 140,250 (with swiss cheesing for OSCAI-njmaxseltd). Before this tune-up, I was running Frankencar mid-pipe and Stillen Pop (no knocking noticed). Has Y-pipe and UDP (I don't think this is related, but I might be wrong). ECU checked at 140,800 and no codes detected. Always runs 90+ grade gasoline, 91 at recent fill-up, 93 is more usual (99% of the time).

The car is running fine but I decided to change the KS and starter since the starter was having intermittent problems. I went on with KS since the car still has its original KS and I believe 6 years of service would be a good reason to change it to a new one.

At first, the car pulls hard, harder than before and it's much smoother all around. However, I started to notice that the car is knocking at part throttle around 2000 rpm. When I pushed the throttle down, it will launch forward without hesitation, but the knocking always occurs at 2k rpm.

Read the manual and it says that knocking at part throttle is normal (to save up gas?). Did not believe the manual and decided to loosen the knock sensor and retorque it to 25 lb-ft (originally at 18 lb-ft). The knocking is still there. Went to Walmart and bought Prestone Octane Booster, and the knocking is still there.

Do you guys have any ideas what else to check?
I have a feeling that either my MAF is shot somehow (I cleaned it with TB cleaner), my new KS is bad (highly unlikely, car throw no codes) or my combustion chamber is full of carbon.

I am thinking to do an oil change with Auto-Rx (just arrived, so might as well) and run a B&G injector cleaner. This will burn the carbon from the TB cleaning which may decide to reside in the combustion chamber.

Other than this......hmm, perhaps retorque the KS to 30 ft-lbs?

And last resort.....try to "borrow" a new MAF from someone and if it's running fine.....then it would be the MAF.


What do you guys think? Any other ideas?

 

The knock sensor does NOT make a car knock..it only senses it.

Have you checked your egr system?

 

How do you check the EGR?
My thing with KS is......it should retard timing somewhat when it senses knocking......but it did not seem to retard the timing, hence the retorque.

How the EGR affecting this? When there is a lot of carbon inside it?

 

When I was cleaning the TB, there is a very small hole just ahead of the throttle plate. I remember that some of the TB cleaner went inside that hole.

Is this hole connected to EGR valve ....... in any way?

 

IIRC, it provides vacuum to a check valve for the evap canister system. But even if it does connect to the EGR valve, TB cleaner in there wouldn't have affected a thing, and by now it's evaporated.

 

How do you know its knocking? Do you hear it or just feel a loss of performance?

 

I hear it. There is no loss of perfomance, I think, but when my auto shifts from 2nd-3rd and 3rd-4th, it will knock right around 1.6k to 2.2k rpm.

I just changed the oil and put BG injector cleaner in there, together with Auto-Rx.

If BG does not help in reducing this knocking symptomps, my next bet would be the whole intake tubing from MAF to TB. I was watching my idle, and I could see the needle moving up and down very tiny, like going from 825 rpm to 800 rpm, and it keeps on doing this.

Consulted Haynes......... and vacuum leaks seems to be my gut feeling (although I am sure I tighten everything).

The knocks are independent of temperature. Southern WI had pretty low temperatures (up to freezing point) last week and high of 70s today. The engine still knocks regardless, and it's only doing it at 2k rpm.

Still open to other ideas.....

 

Take your intake tube off and start the car.
Get a can of Berryman Chemtool carb or intake cleaner and spray the whole thing in your intake while running the RPM's up by hand to keep the car from stalling. RPM's between 2k and 3k are the easiest.

I've done this for weird knocking problems and it works well.

Since you are also washing off ALL of the lubrication in your combustion system it is a good idea to use some Marvel Mystery oil in your intake as well.

At the very least you should let your car idle for a few minutes under normal operating coditions with all the parts back on before driving it.

Hope this helps.

 

Maximomo - u talking about spraying it directly into the throttle body? I think I need to try that.

Does anyone have any advice on checking teh EGR system. Thats about the only thing I havent done (done fuel filter, air filter, knock sensor, pcv valve, gas additives, throttle body cleaning, etc.).

That would be helpful.

 

Checking EGR valve is described in Haynes manual. It says you should see the stem moving around if you are going from 2-4k (open up to throttle) and let it to idle.

This "2k" thing is what interests me.

BTW, Maximomo, I will try your suggestion if all else fails. I am going to open up my intake tract now and redo all the connections.

Perhaps my KS should be retorque to 20 lb-ft.

Urrggghh.....

 

Yep, spray it right in the throttle body.


The EGR system usually gets clogged as it enters the back of the intake manifold. You have to take the manifold off to clean the port and the EGR tube.

I can't imagine the EGR system would cause your engine to knock unless it was causing a vacuum leak at 2k RPM.

 

Actually, it can. I'm not sure if this is exactly why, but the egr system lowers combustion chamber temperatures, and I think it only operates during partial throttle when the ecu is striving to maintain a stoichiometric afr. If the egr isn't working properly, then the combustion chamber temps rise and since the engine is right at the edge of running lean, it is possible to get light detonation. Since it's a partial throttle situation and therefore low power, only very minimal damage occurs. Not good in the long run, though.

 

Change to a differnt brand gas and see if that works

-matt

 

This whole EGR stuff is new to me. I am reading the Haynes manual as we speak, and let's see if we could find the solution. At least we have the spray thing if all else fails.

I believe our engine mapping is set to be on the edge at 2k rpm. The funny thing was, if I am driving in overdrive (shifts to overdrive at 34mph, 1200 rpm), it won't knock at 2k rpm. Just in 3rd and 4th gear it knocks like crazy.

I agree that the damage is very minimal, but I really don't like to see that my engine is knocking.

I did switch to different brand of gas, Philips 91 and Shell 93. In the past, I know that my car likes Exxon/Mobil/Chevron much better than anything else. I will drive my car around today and let's see what we got.

Thanks for your inputs guys, I really appreciate the suggestions.


Armand

 

Used to have a 99 Gxe ,Calif. I used 87 and the car was not happy with the cheap stuff right in the range where your trouble is . I switched to better gas (93 ) and the knock was gone. After some research, i found out that the knock caused by 87 got picked by the KS (that s why is called that way...), the computer in the car retarded the timing immediatley ,to prevent engine damage. The timing is retarded 20 to 30 degrees,fact that makes your car hesitate under heavy load (1800-2000 rpm). Now add to this situation a car that cries for a tune up (fuel filter,spark plugs,O2 sensors)...and that is the main reason for your car hesitation and bad gas mileage . Correct me if I m wrong

 

Astil,

I got your problem back when I was at 100k. Right around there, I changed one of the 02 sensor and it was done. You are correct, generally my Maxima does not like 89, and definitely not 87. I always filled up with 90+ grade almost 99% of the time.

For an update, I checked all connections and everything is tight. I tried to retorque my KS, but my tool snapped (got to get a new one), namely the 12mm flex.

I notice that now the knocks are a little bit harder to produce, but it has spread out to other rpm range as well. It's knocking even when the rpm needle goes down after the car changes from one gear to another (especially 2nd-3rd, 3rd-4th).

Seems to me that I need to get that TB cleaner, spray it like madman inside the tube.

If this does not fix it, although I don't want to come down to this, it might be my MAF sensor. Gotta research more about MAF failures at the .org though......

Oh, btw, my car's gas mileage is still good. I got around 450 or more per tank with 95% highway.

 

Hello guys,

Still wondering what my problem is. Could this be related to MAF?
I remember now that I might be spraying the TB cleaner too close to MAF wire element.

Knocks still occur at around 2k rpm (plus and minus 300 rpm) on 2nd, 3rd and 4th gear (not 1st and 5th).

 

Dude, you have to take the MAF off when you spray the intake.

The Max will run with it unplugged. I doubt you can hurt it spraying it.
But you can't get all of the throttle body area if you don't take it off.

That means you need to spry directly INTO the throttle body and around the throttle valve. This requires that all of the plastic and rubber tubing to your intake be removed.

If you are not doing this then your throttle body could still be the culprit.

Of course, for any of you who might be SCARED of a little external dirt, don't do this.

 

No you moron. If you take everything off the engine will turn off right away, retard. Do you have any idea what kind of dirt will get in the engine with no filter covering the TB? You leave everything on and just sllip the cleaner straw through a little opening between the throttle body and the acordion section, just peel it back a little so that it's enough to get the straw in there. I

 

Maximomo: Yes, when I was cleaning the TB I took everything off and clean the TB with rag and cleaner with engine off. This is the second one I did, so I know pretty much what to do. Plus, I was uninstalling my midpipe and Stillen intake, and installing a brand new starter, so yes, everything was off the car. I cleaned the MAF in my apartment (off the car). When I was cleaning the MAF, the wires inside it are dirty....perhaps due to K&N filter oil.

ivelweyz: I need to get the Amsoil power foam to spray it on with the engine running. I believe with MAF connections unplugged, the car will only go up to 2400 rpm (fail-safe) mode. I am planning to do it with your method, when it comes to it (put and hold that little straw between the TB and the resonator/accordeon section.

However, I was driving to Chicago last night and the car did not ping in the city. If this is true, then BG 44k is doing its job cleaning up the dirt inside the combustion chamber from the TB cleaning. I am planning to drive the car around today and let's see if the ping is still there.

 

Two things I'd recommend looking at.

1) EGR system - It may be working but the tubes that flow the exhaust gas back into the intake may be plugged. The ECU cannot detect that and without the EGR working correctly, you may very well get ping.

2) Along the same lines, consider having a complete intake and fuel injection cleaning service done. Nissan does provide this service, it's done on a machine and makes a huge difference in performance on higher mileage cars. It's a deep cleaning system that gets your entire intake system clean. Spraying the TB cleaner into the TB while the car is running also works good. But if you've got a lot of buildup in there, thats not going to clean it up properly. The intake cleaning systems injest cleaning solution into your TB while the car is running via a vacuum line. The process takes about 20 minutes, then a soaking period, then a foam flush that completely removes all the carbon and blow by oils from deep inside your intake path. The fuel injection service will clean up any carbon deposits on your intake valves and restore your injectors performance.

Marvel Mystery Oil is an excellent additive to help keep your injectors clean and lubricated. I use it every now and then on long trips. Always get upwards of 400 miles/tank on a trip when I put the Mystery in my tank. Also get in the habit of dumping a bottle of Techron in your gas with every oil change. That will keep your fuel system nice and clean.

 

After the TB is cleaned with the toothbrush and rag, you're supposed to empty the entire bottle into the TB with the method I told you. This will get rid of gunk deeper in the manifold. Don't empty the entire bottle at once, 3 or 4 times during this procedure you should slide the acordion over the TB and fire up the car...

 

The car no longer pings in the city, at 2k, 3k or in the highway at all. Better yet, acceleration in the 2k rpm has increased marginally.

I have finished about 12 gallon of gas mixed with BG 44k. I am also using the Auto Rx too, due for draining at around 1300 miles in the future.

Hi Tom!
......I never tried Marvel Mystery Oil....and it's kinda hard to find it in the local auto store in Wisconsin (perhaps it's a common thing in the east). I will be trying to order it online.

I checked the tube and the valve, everything is unplugged and working fine. I want to try the fuel injection cleaner service from Nissan when I am reaching 200k or so. At this point, using BG 44k and/or Chevron Techron every now and then seems to keep my system clean.

I believe you are right on about the EGR though, I spent my good 3 hours last night reading Nissan FSM and Haynes. They both point either to EGR system (MAF is the next thing after EGR).

Since my car is not pinging anymore now, I believe the BG 44K cleans out the carbon entered from TB cleaner.

ivelweyz:
Thank you for your post, but I was using my one can of TB cleaner twice, so nothing is left in the can this time. I cleaned my TB about 30k miles back when I was putting my midpipe, and now it back to stock snorkel.

I will research a bit about Amsoil Power Foam. It might be a better product to use than STP I used to clean the TB with engine off. This time though, I think the BG 44k saved my day.

On the spooky side, my flu is almost gone. It started when the car starts knocking, but now seems to me that both of us are recovering well.

 

I just finished my tank with BG44K and refill with Mobil 93. When I was driving around town last night, the car started rolling from a stop sign in 3rd gear, and there was one knock that I could hear.

Seems to me I either have to pour my last can of BG44k or bring the car to Nissan to get fuel injection and intake service.

 

Just for an update, my knocking problem is gone. I guess I really cleaned up the TB really good this time and it causes too much carbon build up in the combustion chamber.

I tried contacting a local Nissan dealer for fuel and injector service, but they apparently don't have it...... they only have the TB cleaner service which I already performed.

Following my first can of BG44k, I refill to full mixed with another can of BG 44K. Before refilling it though, my knocking is almost gone.... but it still knocks once or twice under heavy load. After the fuel gauge reached 3/4, I refill the engine oil with about 1/3 quart of Marvel Mystery Oil to my engine oil (was due for oil change in about 400 miles, due to Auto Rx) and the rest to my gas tank. Then I refill to full at 1/2 mark.

Since then, I hear no knockings.....even under heavy load. Perhaps some of you could say that our engine is knocking when it's hot out there, but mine knocks when it was 45 F outside (when I found out about it after the TB cleaning).

Conclusion: MMO and BG 44k works really well to clean up my combustion chamber, which apparently to be the culprit of my knocking problem.

 

The knocks decided to move up to 2800-ish with heavy part throttle at 3rd gear going 40-50mph (heavy acceleration from 30-40mph.

 

Are you burning any oil? I have the same sort of problem and my max was burning some oil. I think it was a bad pcv valve. But once I fix that my valve pinging went away.

 

I say you got a Bad Coil and Injector, Do a self diagnoses and see which cyl is missfiring.

I had the same prob with my 99 @ 45k, Turns out I had to replace an Injector and Ignition Coil for my cyl 1, Post up again

 

Guys,

First off, thank you for giving me suggestions and advices to diagnose this problem. This is a very long thread indeed.....and I thank you for replying here. This is a very long reply but I suppose I could supply you with more information about my car, so that those who are knowledgeable (or had this issue before) could diagnose this problem more precisely.

I searched around and found three excellent threads related to my knocking problem:

http://forums.maxima.org/showthread.php?t=257513
http://forums.maxima.org/showthread.php?t=256929
http://forums.maxima.org/showthread.php?t=252443

....and so far I got the following symptoms:

1. No CEL Light.
2. Knocking only occurs at part throttle (throttle is half pressed down), very pronounced at rolling speed (30mph-ish) to "get-go" speed (50-ish).
3. Knocking is siginificantly reduced when I am using additives....Marvel Mystery Oil (lower MPG significantly though), BG44k, or Tehcron.
4. MPS is normal, getting around 28 to 30mpg highway and 26-28 mixed.
5. KS is new and TB is clean.
6. Used to knock when the auto shifts from 2nd-3rd and 3rd-4th (when the rpm needle is going down).
7. Performance does not suffer.....in any range.
8. I have OSCAI (swiss cheesing intake - njmaxseltd) and car has 143000 now.

From what I read at the .org, I could suspect one of more of the following components go bad: MAF, EGR system, KS, coil(s) and/or injector(s), and PCV valve.

Looking at the symptoms, I could rule out the KS (it is brand new, and acceleration at 2k does not suffer), MAF (since knocking does not occur sporadically, not affected whether it's cold or hot outside, and mpg does not suffer), and EGR system (should be cleaned out with the two treatments of BG44K). PCV valve is due to be changed at 150k (last changed with fuel filter at 122k). The car is not using any oil, or if it does, pretty much undetectable (oil level is always consistent).

When I was reading the threads, one member stated that his knocking problems were significantly reduced when he is using fuel additives, but he later found out that it's one of his coil packs.

Now, my question to you guys, is it possible to have this knocking problems with no loss of performance (and it's stubbornly keeps on knocking - KS is new) and happens mostly at part throttle........ caused by coil pack/injector?

If it does, and no CEL, how do I know which coil pack/injector is the bad one?

I really appreciate your help guys..... and hopefully we could get this knocking problem goes away shortly.


Armand

 

Armand

I think it is one of the three, coil pack, EGR system or an injector. The pcv valve would not be the problem if you replaced it and are not burning oil.

With my car I am still going to check an injector that is looks damp maybe gasoline residue cause by a bad seal. This could be a part of my valve noise problem also. I still have to confirm wheither my oil level is still constant( last time I checked I didnot have to add any). I checked my coil packs and they checked out but when they are in operation they may perform differently. I do not know how to check for a coil that is starting to fail?(under load at 2000 rpm)

This weekend I will be checking the compression( tried it before but I did not have a proper guage) in my engine and also checking my injectors. I hope my cylinder Comp. is alright. If it is bad I will really know the reason for my valve noise. I like to check my check the egr components but I don't know if I will have the time. (girlfriend)

(I have to change engine and tranny oil to get ready for winter) Sorry for the long post. If I find Something I will let you know.

gerard

 

Gerard,

Thanks for your reply. I have the same hunch as yours. I really doubt the EGR system is the culprit, but then again....how come the car does not feel "weak" if one cylinder is misfiring?

I really want to take my car out tonight, find an empty road and make it trip that CEL (a deteriorating coil pack/injector will not trigger the CEL, only until that cylinder misfiring badly then...the CEL will light up).

I guess I just have to take it easy these days......


Thanks again for your reply,

Armand
ps: btw, valve chatter and engine knocks are two different noises though....are you sure you have the same knock that I have (pre-detonation)?

 

Yes I think its is valve chatter. I do not think it is engine knock. What does a Engine knock sound like?? (hammer on metal type of noise??). I know what valve noise sounds like though, by driving fords and dodges.

 

Keep in mind one other possibility, which is an intake leak between the maf and the engine. Possible leak points would be at the upper and lower manifold, throttle body, egr and iac gaskets.

I very recently had exactly the same sysmptoms as you after removing and cleaning the iac. I eventually found that the iac gasket had slipped down when I reassembled it creating an air leak.

Partial throttle pinging was also a chronic problem with early 90's Explorers, which were assembled with insufficient intake manifold bolt torque. The cure was simply to retorque the bolts to a higher value. Been there, done that.

The reason that an intake leak can cause partial throttle pinging is that partial throttle and low-medium engine load is when the ecu advances the timing the most, along with leaning out the afr to near stoichiometric. This is done for fuel economy and emissions control. Under those situations any extra air from a leak can easily cause the afr to go lean, which along with the agressive timing advance, causes light pinging.

 

Stephen Max

If I have a cylinder or two burning some oil (which will lower the octane level in that cylinder). Do the O2 sensors show the car is running rich and therefore create a leaner a/f mixture in the other cylinders inturn causing pinging

Do the o2 sensors have an effect over the a/f mixture? Is this train of thought correct?


Gerard
I heard about that manifold problem with explorer (4 l engine right)

 

I've never heard that, but I suppose it is possible.

The O2 sensors do have an effect on afr when the engine is in closed loop mode. The ecu should compensate for a lean mixture by adding fuel. Normally this would compensate for an air leak. In my case I would get pinging only when accelerating at partial throttle, so apparently the afr went lean faster than the ecu could compensate. Eventually the pinging would stop.



Yep.

 

Stephen Max:

Yup, I suspect the connections right after I put everything back together. I was looking for a leak, but everything was tight and good. I am planning to take apart and re-assemble everything back this weekend, just in case.

What interest me most is the fact that I don't hear any pinging if I put in BG44K or MMO in the tank.


maxger:

Pinging is not metal to metal sound....more like...hmm.......do you have any Pentel Tip-ex around? The one with the red bottle and has metal ***** inside it? It sounds very close to it if you shake the bottle (plastic-to-metal sound).

 

At about 143000 miles, I put in two bottle of Techron (one bottle for 12 gallon, hence two). I was thinking this is my last resort before tear apart the coils/connections.

Guess what, the car now is at 144,100 and the knocking is gone. I just got back from West Lafayette, IN and I opened up the car up to 90mph a couple of times, and I can not hear any knocking. Temp. was up to about low sixties today (Indiana), from around 40s here in Milwaukee.

Hopefully this condition will hold forever. I also did two fill ups since I put in the Techrons, and I used different gas station this time. So, the knocking might be due to bad gas or ignition/MAF/EGR. Seems to me it was the fomer.

Mpg is perfect, returning around 25 with combined cycle (city and highway), and today it was about 30 mpg (almost 31), 96% highway with some city driving. I reported no power loss when I started this thread, and none today.

I apologize if this thread and/or my last post seems inconclusive, but hopefully this *somewhat* helps other people out there who seems to have the same problem.

My next step would be filling up with 89 grade (uses 93 all the time) next time from my new fill up place and let's see what happens. I think the ECU should adjust timing accordingly......but maybe not.

 

does it make the sound of something like metal taping or hitting something ? my maxima has been making a knocking or more like pinging sound. i also have the egr system code on right now ?

 

You know, I can't really describe the sound of pinging/knocking. I know how it sounds, but it's not like a metal to metal sound. Plus, knocking is usually a series or knocks when it occurs...... like "knock-knock-knock-knock......" and it will subdue when the engine load decreases.

Another somewhat similar sound is valve chatter....but it's not like knocking. As far as I know, it usually happens at higher (5000 plus) rpm or when you just start the car (but not like timing chain noise). Quite frankly, I am not that familar with what may causes this.

Back to pinging, you could have it two ways. One, when you put more load to the engine, and second, when the your foot is off the gas pedal (engine load decreases, and supposedly no fuel is injected). If you have a code for EGR, it's more likely that you have knocking/pinging when the engine is under load (first case). You might want to check the EGR valve operation and make sure the hoses are not clogged. Haynes manual would help you on how to tackle this, and hopefully other member with extensive EGR system experience would reply to your post.

Good luck!