Need help diagnosing a 97 Q45 engine stumble

[Toadmck]

I've got a '97 Q45t in the off-white color. I convinced my girlfriend (now wife) to buy this car off a 2 year lease in '99 with about 45K miles because I had read great things about the car/engine and Infiniti had done such a poor job of marketing that you could buy them at deep discounts to Lexus, Beemers, etc.

BTW, I live in the San Fernando Valley area of LA and use the car to commute about 10 miles roundtrip to work - a mix of street and freeway driving. Today it will be 106 degrees.

The car currently has 104k miles on it and has been an awesome car with a few minor exceptions. I've religously changed the oil every 3k-4k miles, but have not done much else in the way of general maintenance. At 65k, I had a new set of plugs put in. At around 90k, the alternator went bad and I had it and a couple of drive belts replaced.

At around 95k, I got a check engine light. As I had just moved and didn't have a local shop, I gritted my teeth and took it over to the dealer - Miller Infiniti. They diagnosed a faulty valve timing sensor and replaced it. A day later the "check engine" light came back on, so I took it back. Turned out they hadn't done a good job of hooking up the connectors. So much for inspiring confidence, but eventually it got fixed.

Prior to my dealership experience, I began to notice a slight "stumble" in the engine. Basically, when sitting at a stoplight and idling (600 rpm), the engine would act like it was "missing" on a cylinder for a turn. The car would have a slight shudder and then it was fine. When I asked the service manager at the dealership to check it out, their "diagnosis" was that every spark plug has its own coil and that evidently one of the coils was going bad. But, since it only did it every once in a while, they had no way of telling which coil. Their recommendation was to REPLACE EVERY SPARK PLUG, COIL AND WIRE IN THE IGNITION SYSTEM, for which they would only charge me $2400. Admittedly, the service manager wasn't even a big proponent of this method. I declined to that, figuring that if it really was an individual coil problem, I would drive it until failure, at which point I'd know for sure which one it was. Not having a service/repair manual, I wasn't sure I bought that whole theory anyways.

Since then, I've put another 10k miles on it, but the stumble seems to be getting more frequent. Basically, it seems more pronounced if the engine has a slight load on it. For example, if you're sitting at idle, it will occur every 15 seconds or so, especially if you have the A/C on. Also, if you're driving at 40-50 mph in high gear, turning about 1500-1700 rpms, it's pretty pronounced. Usually, if you get over 2000 rpms, it doesn't occur.

Maybe there's been a slight falloff in power, but I may be somewhat numb to it and accustomed to its current performance. Gas mileage is running at about 17 mpg.

I'm now fed up with it and want to get that old surging engine performance back. I started searching the net, ostensibly for an independent shop in our area (got any recommendations?) when I ran across this forum. I shut the door to my office and spent the whole day trolling the online mechanic forum where I found a few topics that seemed relevant (MAF related) and what seems like alot of other good advice. I especially appreciate the enthusiasm for the Q ship, as I really like this car and would like to drive it for another zillion miles. I'm handy with tools, but haven't done much of my own work on this car as it seems pretty buttoned up under the hood. I'd appreciate any help you could give in diagnosing and fixing this problem. (Consider me chagrined for not finding this site earlier and attacking this problem sooner!)

[maxnix]

Well, welcome in, stranger no more!

Have you read all the posts about the intake path cleaning?

Assume you are religous about filters and the like? A little maintenance history, please?

[Toadmck]

Well, when I say "religously", you could qualify that a bit. I've cleaned and replaced the air filters periodically. I can't stand the "upsell" methods at the local EZLube, so I do that myself. From now on, I'll be ordering in parts from the everything infiniti guys as their OEM prices are better than you can get at the PepBoys or Autozone on aftermarket stuff.

I'd appreciate any comments or instructions on what I should do first on things like:MAF cleaning (I read the procedure on Q45.org. My 97 looks a little different.)Other intake cleaningFuel filterBG44k treatmentetc.

Also your transmission filter/service frequencyCoolant flushetc.

I recognize that I need to put some $ into the deferred maintenance.

[maxnix]

Gosh, Keep reading. All filters every 12K miles. Might seem overly agressive, but when you monitor them, you sill see this is about right. Includes cabin filters too! Fuel filter is a not conveniently located item.

MAF should be OK, unless you have let the engine air filters turn into the La Brea tarpits. All the gunk on the throttle body should be on the back side of the plate and the intake manifold plenum. Plugs?

BG44K before oil the oil change.

Brake fluid every 12K - 18K, depending on climate and use. DOT4 for the few pennies more.

I use Royal Purple 75W - 140 in my differential for TX summer heat. Any within OEM specification synthetic should be fine.

ATF mechnically exchanged every 12K - 25K, depending on your driving. ATF cooler a must on these cars. How does your fluid look (White paper towel test!)? How about PS fluid? Pan drop and filter replacement when exchanging.

Use only distilled water and Water Wetter with appropriate coolant.

Keep reading!

Oh, and get the FSM and TSB from http://www.nissan-techinfo.com/infiniti/

[elwesso]

alright lets try and get down to actually diagnosing the problem here...

So to recap in my own words, youll be sitting at a stoplight or something, and it will start shuddering and then it recovers. Has it ever stalled??

My suspect is the MAF. Y33 owners have experienced this.... Im not certain if the Y33 Q uses the same MAF as the G50, but that is certainly my first inclination. Unfortunately, even with a service manual theres really no way to tell it will fix the problem unless you install a known good one. Generally its nice to find someone who has a Q and then you can swap them....

Im sure theres someone in your neck of the woods that wouldnt mind lending you their Y33 MAF for a little bit to see if it fixes it....

THere have been a few other posts by "FarFetched" and "Q_ship" about similar problems. I dont follow Y33 things as much, so i dont recall what their problems/fixes were but if I recall it was very similar to yours, and they also were very generous in posting fixes! Knock sensors shouldnt be ruled out, but they would have thrown a code....

As far as what brian posted, im pretty much down with that. I dont drive a lot, so my maintenance schedule is usually "whenever I remember" and thats generally within 15k on anything... These certianly are important things to consider but its easy to get sidetracked and overwhelmed....!

BTW, send an email to [email protected] and I'll set you up with a Y33 service manaul....

[Toadmck]

Thanks, Wes. It's never stalled. Just feels like an infrequent "miss" on the firing sequence. You can feel it missing as you're accelerating up through the 1500-1700 rpm range, then it seems to settle down a bit.

Any truth to the dealer service reps description of this model having a separate coil for each plug? They were telling me that the replacement cost was $240 each X 8.

[elwesso]

Yes they have individual coils, but those dont tend to fail... VERY rare and I think they used the same ones on the G50 as they did the Y33.... There have been SOME failures but not many. MAF seems more likely cause, as a coil, IMHO, wouldnt cause an intermittant sort of symptom... I think it would seem more like an injector failed...

Since its intermittant I doubt its a coil, but rather something else like the MAF....

[maxnix]

The coilpacks are different between the VH45DE and VH41DE.

The dealer sounds lazy, or incompetnent, or both. Be sure anytime you go to the dealer you ask for the senior Infiniti technician to work on your car. He should have been an Infiniti technician since 1996 when they were trained on the FY33.

I think Farfetched has a thread on this behavior. Don't know if he cured it.

I wouldn't try without verifying the intake path cleanliness first.

[Toadmck]

Just wanted to provide an update on my efforts to get rid of the dreaded rough idle/stumble.

1) I've started the "Techron" treatment regime recommended by GreenQ45. Based on the commute home, that seemed to help a bit. I suspect that my gas supply here in CA is a contributor and dread the 91 octane fill-ups at $2.75+ per gallon, but it seems like it's necessary.

2) On Saturday, in the midst of the heat wave, I did the MAF/intake cleaning regime. It took me about an hour and half, since I'd never done it before and was a little nervous about tracking all the nuts, bolts and connectors. I removed all of the intake path parts up to the throttle body and did a fairly thorough cleaning, including the MAF. I tried to clean as far into the TB as I could reach. I reassembled everything and started her back up. It idled high for a few minutes and then settled back down to about 800 rpms.

3) I replaced the air filter with an OEM from everythinginfiniti.com. I also had them send some BG44K and plan to follow up on the Techron if I detect any further issues.

I took the Q out on the road for a test. Amazing difference. It's like I got my old car back. No idle problems and great power all through the band. I'm a bit PO'd that I didn't think to look for this forum earlier.

Next up is a service appointment where I get all of the fluids replaced.

[elwesso]

EXCELLENT news!! glad to hear you got it taken care of!

[99q45t_vl]

I've had the same issue with my 99Q. I addition to the steps explained above - which helped it somewhat - I have replaced the PCV valves - THAT helped it.

[elwesso]

PCV valve is osmething thats commonly overlooked but should be replaced anytime your "in the area"....

[FarFetched]

Let me help as the one who's been through that ordeal!First use ONLY GOOD QUALITY GAS, not cheap "SHIZER" you will see the difference. Treat the engine fuel system with 2-3 BG44K. Than replace KS (some say harness too). Clean TB and IAC. I've had the same "symptoms", now my OldLady has a clean bill of health Doo all that and see what happens. Dealeship advisors(service writers) dim-witted money sucking bastards whos interest is to get you in their claws and "kill". Listen to NICO fellas - we'll can only help (others will harm you) Cheers!

[SardarQ]

Had the same problem - it isnt fixed. What you guys did, although helpful to the performance of the car is not the fix for that shudder.

After intense looking, reading and trying to get to the bottom... here is what I have concluded:

1. Its not the coils.... 2. Not the MAF (was my first guess).3. Not the spark plugs...4. Not the IAC 5. Not the TB.....

Are you guys ready.....

Its the alternator!!!

Anyone who has this problem .... under a full load (all lights, heated seats, etc in the ON mode).. check the voltage... if its close to or under 13.... bingo!!!!

I am certain the alternator is responsible for this..,.. although I read in a post that someone recently changed their alternator.... I'm willing to bet its not an OEM or is not performing as it should. Everyone go check your alternator reading... and post.

My car is reading 12.98 V under full load.... getting close and the shudder is getting worse.

[DAEDALUS]

Unless the battery measures over 12.98V after you shut the car down, the alt is supplying more than enough energy to power everything. Not saying 12.98V is good (usually around 14), just that nothing on the car is lacking. What do you suspect is not performing well because of the voltage?

[SardarQ]

The mean voltage is what we are measuring at any given time. When the alternator starts to go its often with sharp voltage drops. This occurs very rapidly and is almost spontaneous. This sudden downward spike in current is what causes the "misfire" like symptoms. Or at least that is what I have been told. This makes much sense becuase I have ruled out the MAF and all other possible culprits listed above EXCEPT for the alternator which I know is getting close to replacement.

[DAEDALUS]

The ignition system as designed needs to perform flawlessly at startup, where the voltage can reasonably fall to 10V. Current draw is higher at startup than at idle. If the amplitude of the voltage spikes is that much of a concern then investigate the battery. A good battery is a great voltage damper.

[SardarQ]

So do you think this is battery related? You guys are the GURUS of the Q, you would know much more than I. I have just posted from my experience and knowledge gathered from mechanics. I keep my MAF clean as possible as well as the filter. A dirty MAF and filter = very low MPG - no good in todays gas market.

[DAEDALUS]

Not saying the battery is good, just that I don't think it's causing what you're seeing. I don't think the voltage spikes off the alternator are really that great in amplitude. 12.98V is sufficient.How old are the plugs, and how did you verify the problem isn't in the coils?

[SardarQ]

I changed the plugs about 10k miles ago. I did not check the coils. From experience with other nissans (maxima) and an old 94 Q45, the coils have never been a problem. Possible however. I wonder if anyone has had these symptoms with a new OEM alternator. That would rule out this possibility.

[DAEDALUS]

I've had 2 coils go bad. Made a post about it a while back but apparently it was "lost" at some point, as the search function cannot find it. Plugs looked like crap. They were actually corroded and had carbon traces on them.

[DAEDALUS]

Ah, found it.

zerothread?id=21142

[infiniti tech]

If you eliminated all other possibilities the next thing to do is do a 3m Injector clean. It is made with techron. It is the only factory recommended fuel injector/intake carbon cleaner. Whats happening is the fuel sprayes on the back of the intake valves and soon turns to varnesh/carbon. The carbon soaks up the fuel and causes at times individual cylinders to misfire or lean misfire. Also this happens to the top of the pistons with the carbon buildup. You can do a top engine clean but it is expensive and time consuming. You use GM top engine cleaner poured down the spark plug holes and let sit overnight. The next day turn the engine over without the spark plugs to remove the liquid. Start engine and watch it smoke for 30 minutes and then change the oil. Its a nasty job but is effective. Techron is some good sh-t, I had a injector sticking on my 01 suburban so I put a full can in the fuel and 5 months later has not re-occured

[crimsone96Q45]

hi el question ... will the knock senors make the car buck and lose power as well ? i went to autozone and they said that i have a bad knock sensor, when the car gets hot while i am driving it the problem gets worse, today it shut off. just replaced the fuel pump and before the proble starts it runs ok, but i need to replace the spark plugs. the guy from autozone said that the sensor problem was intermittent ? 96 q45

thank you for any info

Earl

[Q45tech]

"commute about 10 miles roundtrip to work - a mix of street and freeway driving. Today it will be 106 degrees."

How many minutes from crank until shut off at work....10, 15, or 20?

Classical conditions for valve back and stem, injector, pistion top, plug fouling.

Without a weekly blow the crap out session [few minutes above 4000 rpm oscillating to 6,000 rpm] even BG44K won't keep engine clean for more than a few weeks of such commuting.

As to coils the lower the supply voltage the lower the output voltage,

A 1 volt input drop will reduce output voltage by 2500 volts.

Coil weakness is common with age [after warranty] on the 97 and later Q, usually not a problem if plugs and engine is clean as brand new!

[audiovisiony33]

I'm going through the same problem and after use of BG44k eliminated the problem 95%. Once a while restart when engine cools down it does it again. I didn't clean the MAF or the TB yet but is your problem solved for good? also do I need to remove TB to clean them and if I do do I need to replace with new TB gasket after cleaning? What do you recomend to clean TB with?

[Vmo]

Audiovisionny - Just get some Gumout TB cleaner in the spray can at any parts store - take off the intake tract and push open the butterfly valves and spray liberally - I might recommend parking the car on an incline with the driver's side lower so it'll drain out easier....

I've had the stumble off and on since I bought my 99 t 1.5 years and about 10,000mi ago. I replaced plugs, cleaned MAF, TB, replaced all filters, ATF, Diff fluid and regular BG44K. maintenance has been performed via the Severe Use schedule.

Yesterday it finally threw a #2 Cylinder misfire code. I wasn't able to determine whether it was single or second trip.

Typically, the car will do it from the time it is started to the time it is shut down at idle and light acceleration loads, but is smooth during normal driving 99% of the time. About half the time the car drives normal with no apparent hesitation -

like stated before, the stumbling comes and goes on a trip-by-trip basis, and I haven't really noticed an increase (or decrease) in frequency of occurence over the time I've owned the car. I also didn't notice much difference after performing the aforementioned maintenance with the exception of adding BG44K. It helps, but only temporarily.

My question to the knowledgeable people here is.. what next? I figured maybe a FI cleaning or a new coil pack on the #2 cylinder, but after reading this post it sounds more like something's gummed up than not firing.....The car runs about 50mi round trip Completely highway per day, takes about 35 mins each way. I always fill with either Shell or BP 93 octane.

Thanks for all the time you guys put into helping others on this site - it is definitely appreciated and it's been fun to learn so much as well!Billy

[maxnix]

Switch your coilpack with cylinder #4, monitor codes (after they are cleared) and report back.

If you haven't done your plenum and EGR tube in the plenum, might not help. There are two TB in tandem, so without taking them off the plenum, you only clean the TCS one and not the nasty on the backside primary one.

[Vmo]

True about the TB - I should have the time on Sat. to break it down. Thanks for the reply and I'll let you know how it goes!Billy