I've posted in the "strange hesisitation porblem" thread and everyone seems to have different kinds of hesititation that posts there. Mine starts up fine, idles fine in P/N, but every so often you put it in D and it will sortof stumble as you are trying to drive it, but only lasts for about 15seconds of RPM bouncing before it comes back to full life (somtimes scary if you tried to use a lot of gas pedal to compensate for the sputtering, then you are suddenly at WOT when it kicks back in). Doesn't always matter how hot the engine is but I usually park on a slight uphill grade both at work, at home, and at my grandparents' house.

So my question is, based on the fact that I have that retarded fuel leak upon filling my tank up (somwhere on the rubber section of the filler neck hose i believe, or the smaller overflow hose), or for any other reason, is it possible for air bubbles to get into the fuel line at any point leading up to the fuel rail? That would explain a lot, why it waits a sec to sputter (gotta wait for that much fuel to move the bubbles to the fuel rail), why the RPM bounces (high when fuel is present, low during a bubble), and why it then comes back to life (bubbles are no longer present at all). So if that's what is happening, maybe there's a small leak somewhere, or maybe something allowing fuel to leave the system and backflow into the fuel tank (check valve perhaps?) or whatever. Though I can offer no explaination as to why it'd happen sometimes but not others.

Any thoughts?

 

With air pressure around 1Bar, fuel pump pressure around 2 Bar and the pump's construction and location such that it sucks only liquid from the very bottom of the tank? ............... well - no.

Given the design of the fuel system, it would be basically impossible unless you are, at the same time, also complaining of huge puddles of fuel appearing under your car (fuel lines allowing fuel out and possibly air in).

Apart from that - when the motor is running, the fuel pump is going full tilt and the fuel pressure regulating valve on the fuel rails is looking at pressure and regulates fuel flow to ensure a constant supply of fuel at a fixed pressure to the injectors (pressure depending on engine vacuum) - any "extra" fuel not required to maintain pressure in the rails gets returned to the tank.If it idles fine in "P" and "N", and you switch to "D" with your foot on the brake - without touching the throttle, will it always idle stably and consistently at the 700-800rpm mark as it should even though you may expect it to stumble if you should decide to drive off?

 

I was more wondering about air entering the system when the car was off, and then the air being pushed to the rails by the fuel behind it, and then just the air pushing thru the injectors. But if air can't enter, then air can't enter. I only experience gushing puddle of fuel under the car when I fill up, but it takes about 4 miles of driving to burn enough gas to stop dripping. Either way there is some opening in the fuel system, just maybe not in an incredibly critical location.

It idles fine in P/N, and even in D, but as soon as I start the car in gas-pedal-assisted motion it will drive a short distance then stumble or stumble right off the bat (keep in mind sometimes it doesn't stumble at all; sometimes it works just fine from startup to motion to trip's end). And by stumble, I mean the car's about to shut off, but somehow doesn't, and then all the sudden it comes back to life as if I've stabbed at the gas pedal, but in fact I have kept the same pressure on the gas pedal the whole time. I have also seen it sputter some while still in P, or while in D but with the brake applied, if I sat still long enough for it to do so. But usually I've started moving by the time it starts stumbling... which is why I notice it most then. I think the AAC fights the stumbling really hard, to prevent it from actually shutting off.

 

My first guess would be a funky fuel pump (if you have a decent and clean fuel filter) - get a fuel pressure guage (an oil pressure guage works just as well) and plumb it into the fuel line just after the filter, then monitor the fuel pressure while you are "stumbling" ................ should be constant at around 40psi or 2Bar. (Assuming you have checked all connection on the TPS, IACV and MAF and they are all in good condition?)

 

Fuel filter was replaced in December as an attempt to fix this problem. And I was thinking to get a fuel pressure gauge. Haven't checked the aforementioned connections but I have the next 2 days off. Where's the IACV is the big thing due-Driver-side of the TB, correct? ANd for the TPS do I just make sure the wire is snug or should I open the little casing and make sure it's not dirty on the contacts and blow it off w/ canned air or something?

 

It also may be a bad fuel pump relay. I think this car has a fuel cutout relay also. One of those may be bad. Mine tested out good and the only way I knew it was bad was to replace it and the problem went away.

 

Sure - but monitoring fuel pressure will tell you all about that too.

Look at this too

The TPS is a semi-sealed thing - if you cannot figure how to open this its probably best to leave it alone (I had mine open after 277000km and it looked like new) - just check and clean the connector - there are a few people in threads around that have reported bad connectors in there causing hassles similar to yours.

 

I tested the fuel pressure with the engine off and it running and it looked fine. Just running under certain circumstances the relay would cut out for a few seconds.

 

If you didn't have the fp guage in the cabin and happen to be monitoring it at the time of the relay going faulty you would not have picked it up using that method - if that relay refused to work for "seconds" you will most definitely come to a grinding halt and fuel pressure would be zero to indicate the situation

For the record only - switching on the ignition without actually starting the motor will get the fuel pump running for a short time after which it stops again till you actually start the motor and a "engine rotating" signal gets sent to the fuel pump relay to modulate the 20Hz pump driver signal

 

I have looked at that post some. Mine doesn't stumble for about the first 30 seconds of warmup, or on-ness actually. It's done it fully warm too, just after I turned the car off and got back to it minutes later.

http://forums.maxima.org/showpost.ph...4&postcount=67

Tonight was more extreme than that one.. sadly, camera was at home though. I'll get a better video as soon as I can.

 

Yeah - that clip actually confirms the near distortion-less operation of your sound system only.

When you do the video again try and eliminate as many extra variables as possible - check and clean all the connections to all the engine bay sensors and make sure they are all ok - perhaps in doing that alone you may never have to video the issue again.

Also - from your latest description the rotor and distributor cap (if yours is a VG motor) could also play a role (pull-off from idle uses max timing advance and a set of bad contacts inside the distributor could kill the spark till such a time as revs and engine load reached a point where the spark happens at the time when the rotor is properly centered on a cylinder tip inside the distributor iso possibly right on the edge of the connector) .......................

and another thing:

Your MAF has a little sensor (resistor) sitting in the air flow - I would clean that first too (threads detailing removal + spraying with some carb cleaner are around) ...................... theory being that the EFI gets confused by inaccurate low air-flow rate MAF measurements caused by slow responding/dirty sensor, causing super poor mixture.

 

Cadaver...how old are the plugs/wires/dis.cap/????

 

The book calls for testing the fuel pump pressure when the engine is idling with the pressure regulator connected, then again when the regulator had a vacuum applied to it.

Did both tests and it didn't find the problem. Trying to rig up the fuel pressure gauge to be used while I drove the car, especially to diagnose a problem that occurred very sporadically ( maybe once a day) was not practical for me. I threw in the test with the engine off to make sure it was pressurizing during startup.

 

Bad idea unless you like killing MAF's. Get the CRC MAF cleaner. It works great.

~Alex

 

plugs are two days old. I bought Bosch plugs last november, they sucked, so I went back and bought NGK and put them in saturday evening.
the 2 on the left are my just-pulled-after-4000-miles Bosch Platinums. The one on the right is one of the NGK plugs that the car had when I bought it.
All 6 contacts looked like this.
Wasted...

the wires, cap, and rotor are all 5 months old, to the day. fuel filter and PCV were replaced the week before Christmas. Currently i'm running 89.5 octane and 18degree-BTDC timing (Aaron92SE himself used his timing light to check it.. so you know 18 is right.) the filter+valve were deliberately to try and fix this problem.

 

I still think its the fuel pump. I could pull one from the junkyard if you want.

~Alex

 

.. there's junkyards here too. I want to look into it further before I get something like that. I will get a fuel pressure gauge first to make sure i have proper pressure. And i'm going to check my codes and TPS/MAF/IACV connectors

LvR - the car did it before and after all tuneup tasks. on the video you can still watch the tach, and note that when it hits 1500 and holds there, I'm giving it the EXACT SAME amount of gas as i am when it finally kicks in and goes to 2500. I then stopped lifted and stopped... to keep from running a stop sign and driving into someone's yard...

 

I had a similar problem with "stumble" a while back. Thought it was fuel related so changed fuel filter, ran 93 octane and injector cleaner, replaced plugs, cap and rotor, cleaned MAF, etc. Finally I stood on the passenger side and watched the engine wires as I "hand" reved it over 2000rpm. It became clear that cyl #3 plug wire was arcing in the cylinder head/valve cover. I had checked the resistance earlier and it was fine, but may have created a problem when removing and reinstalling the spark plugs multiple times. I would highly recommend checking, or replacing your ignition wire set. Your "stumble" may be an electrical problem, especially if you have no ECU error codes.

Just my two cents, maybe you have a similar problem. Good luck.

 

see post #15, which I just edited for clarity
i have changed plugs twice, and my wires are only 5 months used. I always make sure it's nice and snug down on the plug tip. i grabbed some codes, i'll post that stuff in a sec

 

http://s164.photobucket.com/albums/u...sis/?start=all

i labelled all the pictures, and they're all 1600x1200. [I tried not to mess up my TB gasket when I took it off but I'm getting the spacer prototypes in like, a month anyhow, but I can get some RTV or another gasket if you really think i need to.]

I screwed up with the codes so i'm going to take another video. I didn't understand that what I saw was how to enter a mode so i'll repost that video, done properly.

 

OK here's the ECM code

I didn't start or drive the car, so this code is from memory. I cleared it after I shot the video, so I'll drive it around a little bit tomorrow and take the code again, to see if it's the same.

Anyhow, I got a Code 33 - Heated Exhaust Sensor Circuit is Shorted or Open
is that the same thing as saying my mixture is off, or is that a separate issue? i'm going to recheck tomorrow, in modes 1, 2, and 3. That way i'll see my mixture ratio too, which I am thinking is rich...

 

Hellllllooooo?

Bad o2 sensor....Replace it...

 

and it is in fact true that a fudgy o2 sensor will cause the problems i described? I had the option of getting one when I did my tuneup but I was like "no... it costs too much." because autozone wanted to charge me $120 for a freaking 02 sensor. so i was totally not feeling that just for something I didn't think was broken.

 

Yep.

Here in South Africa we dont have those beasties on our VGs - the ECU has obviously been modified for local conditions - lucky us!

 

and it will cause blackness on the plugs and poor fuel economy, if the o2 sensor is being ghey?

 

From what I have seen reported on the 3rd gen forum yes. Personally I have no experience with them because I am in SA, but in general mixture quality is controlled by the EFI while its looking at all the sensors it was programmed to ............... since the O2 is part of YOUR setup it certainly could

 

Bad o2 sensor = ecu freaks out and dumps too much fuel in the engine. THATS why your plugs smell like gas...and your mpg sucks. Replace it. Check advance and brians website...

~Alex

 

!! I went and spent like, $120 getting all the stuff I already did to it, and go figure the biggest problem was the one part I chose not to change. Or do I have 2 of them? Either way, that's wetawwded.

Who's brian?

 

Internetautomart = brain.

I did the same when I started driving the max, I did a full tuneup minus the o2 and hoped it worked. I just got 28mpg highway so Im assuming it does...

~Alex

 

assuming what does what? assuming that the tuneup minus 02 was a good idea?

 

Just saying that mine worked, but its probably getting replaced after I start working.

~Alex

 

 

I was wondering if you'd catch that :P I knew you would since they pay you to patrol the 3rd gen forum.

~Alex

 

They pay me with doughnuts...

 

Agreed that Code 33 means replace the O2 sensor or check the wiring/connectors. You can get a new Bosch Premium Oxygen Sensor (PN 13387) from Pep Boys for $86.99. Other Auto parts stores I checked were a bit higher. Good luck with the change out and let us know if it cleaned up your problem.

 

it should help with the engine-drinking-gas-like-Koolaid a little but I don't think that's gonna solve my occasional stumble. That's because the o2 sensor is only regarded during closed loop (post-warmup) situations, and the stumble often happens when the engine is cold. Therefore the car isn't going to look at the o2 sensor when the engine is cold whether the sensor works or not. I'm going to clean throttle body, and several other items to hopefully help with the engine.

right now the idle has a mind of its own. this was after a couple of trips different places and the engine was plenty warm and stuff. the biggest drop near the end may have been the radiator fans coming on but it shouldn't be jumpy like that. i know it's only like 200rpm total variation but that's still not as good as it should be.

 

Dude,thats a pretty good idle...A little bobble once there,but otherwise steady..

 

oh... it had been smoother before. it used to be stuck on 750 like glue. but it sounds a little worse than it looks. who knows. i'll let aaron sit in it next time i visit.

 

Clean TB, IACV, bleed the cooling system, replace the TPS and see where you stand. I still think its a fuel pump but doing that will get your car driving alot better.

~Alex

 

Start from TPS if it is possible at all. It is expensive new but can be got from a junkyard. I sort of self inflicted the similar problem to my 93 SE - after last time I was messing around TPS I didn't noticed that one pin on its socket slightly missed its hole and was pushed out when I put it in. So, one wire was just touching the TPS contact and the car was almost stalling in very unpredictable way. I could drive for days without problems and then out of blue it started to act like it was going to die any moment. Then, it would come back to normal like nothing happened. I did find the problem and it behaves fine since then. I have more unstable idle then you do and this didn't seem to change a bit through the whole ordeal - it idles the same shaky way. Still working on it .