marianm

I'm back for more help from the board...
This morning, I was in a bit of a rush to get to work, so I was accelerating hard up some hills.
First there was a slight hesitation of the engine (dropped to about 3-400 rpm) as I stopped at a traffic light. Then just as I descended another long hill, it stalled as I stopped at a traffic light. I cranked it, and started back again and proceeded for a while, then, when going up another hill (I must say the steeper hills were behind me at this point), it started to hesitate (like when you're running out of gas) going 40 mph in OD (~1400 rpm). Once it got level the hesitation stopped. I figured I must be having low gas (I was at the 1/4 fuel mark, which was fine before) so I stopped and added 6 more gallons which pushed well above the half tank mark. A number of miles of relatively flat roads ensued, and then after 2 more hills it stalled at the traffic light again, car oriented front uphill. I started it and proceeded up another hill experiencing hesitation again (40 mph, ~1400 rpm). I timed the next traffic light so I wouldn't stop, then as I entered the parking lot at work (short slight uphill) it stalled again, and then 3 more times by the time I parked it.

At lunch I checked for CEL (used the code reader - no codes) and decided to test around the parking lot, and I didn't notice any issues.

Here are some possibly related issues with the car:

- 3 weeks ago, I ran out of gas on the freeway, traffic did a trick on me, first time ever for me. It started at first try once I put a gallon of gas in. Ended up filling with a total of 17.3 gallons - I thought we had 18.5 gallon tanks?

- 2-3 month ago I had white smoke comming from the AC - alternator area with a burning rubber/plastic smell. It did 2-3 times and hasn't happened since. I had the same thing happen last year in autumn, high heat but it happened whe starting AC not on. The alternator and AC pulleys spin freely. After the 2-3 months ago events I noticed a whine coming from possibly the center of the dash that varied with rpm and electrical load.

- 5 months ago the car would not even click when I went to start it. It turns out battery acid completely ate the center of the copper positive battery clamp. I mended it of sorts, then it was all fine.

- for about 1 year or more, I've been noticing a gas smell from the rear of the car after parking, made worse after finishing a drive at a higher elevation (lower atmospheric pressure)

Relevant maintenance 2 years ago: fuel filter, spark plugs, TB clean, IACV (may have botched this one by going too far with the disassembly, those screws are not turned the same amount), air filter, pcv valve, replaced 2 failed vacuum hoses.

I hate intermittent problems.
Thanks for reading!

JvG

Possible issue with fuel pressure?

marianm

Thanks for the reply JvG.

I drove the car back home after work taking it easy, first on a 5 mile descent, then 17 miles on the freeway without issue... until I had to exit the freeway. Leaving the traffic light at the off-ramp the engine pulled funny, then at the next traffic light it wanted to stall - I quickly changed neutral and it went back to idle. Driving away from the traffic light the engine sputtered dropping from 1700 to 1300 rpm in 2nd gear. Same story repeated itself for the next 2 miles ... (tapping the gas pedal in neutral, sputtering in gear). It finally stalled but started back after 1-2 seconds of cranking.

At this point, I tend to believe the issue is related to the engine being hot. Today was a 100F day, which I'm sure didn't help. If it is related to the fuel pressure, why is it only doing it while the engine is hot?

JvG

For most of us, it's fall and cooler temperatures.
I wasn't expecting that kind of temperature.

This new information might help others provide a solution. I can't think of one right now.

M in KC

Do you have access to a known good MAF.? If so, swap those out and see what your symptoms are then. Also check your Intake Air Temperature Sensor's resistance when hot. I don't have the ohms values at hand but they are in the FSM.

marianm

Thanks for the reply. I have no access to another MAF.
For the IATS - measure when the engine is hot?

I took it for a short drive today under 2 miles, obviously the engine didn't get hot, I didn't have any issues (I did some harder acceleration).

To sumarize, the simptoms are (only when engine is hot):
1. stalling when coming to a stop in drive, when the engine would go from almost no gas to having to keep idle - some (sudden) load on the engine
2. sputtering around 1500 rpm with more than a light load on the engine.

marianm

I tested the TPS and I get 0.6 kOhm at idle (I have elevated the idle a bit - to 700 rpm), then just as I start moving the throttle I get a spike to between 1 and 15 kOhm, then drops down to bellow 1 and continues gradually until 3.85 KOhm at full trottle. Does anyone else get that spike at the beginning of throttle?

I am unsure on how to measure the MAF, IMO the manual is ambiguous when it comes to connector orientation. Am I supposed to measure the voltage from the pin towards the power steering pump or the one towards the airbox?

And to update, it has now stalled in park (not only in drive) after warming up for only 2-3 miles.

Evening edit: I checked the MAF voltage from the pin towards the power steering pump. With a warmed up engine I got:
Ignition on, engine off: 0.35V
Idle: 1.25V
2500 rpm: 1.9V
4000 rpm: 2.3V

marianm

So last night I finally get a change to work on the car and drive it on the streets for around 1 hour in 55F temperatures. I had no issues whatsoever, idle was great. After I park, I check the resistance on the TPS and the spike was minimal, staying under 1 KOhm. Even though it was past midnight, I can't let go so I decide to drive it some more. I start it and then it dies right away. I start it again and struggle driving it for about two block with sputtering, then I pull over, engine stalled; I disconnect the TPS. I smell the gas pipe and it smelled rich (like it smells in the morning). I start the engine and the rpm go straight to 2000 rpm for a little bit then go down to about 900 rpm. Based on this and the smell, I'm thinking there a condition of running rich, when the sputtering occurs?
I drive around with the TPS disconnected and the check engine light on for a while, everything seemed consistent: idle rpm to about 900, including in drive, car always surging forward and transmission shifting very abrupt and late, but no hesitation, sputtering or stalling. I get tired of this kind of shifting, and reconnect the TPS and drive it around a bit more with no issues.
What do you say?

Icemule

Did you get this fixed? If so what was the problem so others can be helped in the future. I had something similar, turned out I knocked a vacuum hoses loose when I took the intake off to get a stuck boot off of a spark plug. car ran fine in cool weather at night but would bog down around 1300-1500 rpms but I got a code for map/baro, something like that but it was a hose that connected to the throttle body area, don't remember exactly. You might want to want to check ALL vacuum lines as it's free to do that.

Truthfully it sounds like a fuel issue, just wanted to bump your thread and find out what happened to help others.

marianm

Thanks for the reply. I was planning on updating this once I knew the problem was solved, but I am not sure that is the case.
With further driving I observed that the issue only happened in hot weather. As of last week, weather is pleasant in SoCal, so I can't say wether I fixed it or not.
I can say that it wasn't the TPS, as I replaced the OEM faulty one with a new Beck&Arnley part, and the problem stayed.
I have cleaned the TB and the MAF and that did not help either.
I had noticed the exhaust pipe getting black soot on it.
I bought a OBDLink SX and started recording, unfortunately the Maxima's OBD2 port is slow, and I would only get a reading every 4s. I suspect I was getting negative longterm fuel trim readings when the problem manifested itself, but with the weather cooling down, I didn't get enough recordings, and I have to look more at the data.
By this time (11/16), the used OEM MAF I bought from ebay arrived, so I installed it. I haven't had any of the sputtering/stalling yet with the used MAF, but the weather has been cooler.
I wiped the exhaust pipe clean, and it hasn't blackened yet. The LongTerm FuelTrims have no dips in the negative, but they are mostly positive. With the original MAF the average was 1 and 2 for banks 1 and 2 respectively, and they are now 2 and 6 with the used MAF. I interpret this as the ECU thinking the engine is running lean. The voltage measurements are a bit lower with the (new) used MAF, but still within spec.
The prevailing theory right now is that the original MAF had some sort of contact failure when it's hot due to aging solder (just like the clock display not working in hot weather). When the continuity was broken no airflow would be registered so the ecu would think it's running rich and cut off the fuel supply, causing the stuttering... Well that's my theory. I have to wait for hot weather.

DBear

Re the MAF contacts, did you find this thread? https://maxima.org/forums/4th-genera...ml#post7963527

marianm

Yes I did find it, DBear. It reminded me of the clock fix. I will open up the original MAF when it gets hot again.

SneakyBastard

I was just going to suggest the same thing. My car was doing the same thing a while back and after several weeks of trying to figure it out, it turned out that one of the contacts came loose from its solder point in the MAF.
The male connector on the MAF can be unscrewed, however, there is NO room to re-solder the connections. I ended up just bending the connection leads down at the tip with a pair of needle nosed pliers until I could get another.
They are around $140 here in California from Autozone. But the bending trick worked for quite a while... so long even that I forgot I needed to replace it!

marianm

Almost a year after replacing the MAF has passed, and the problem hasn't resurfaced; it's safe to say it was the MAF.

marianm

Of course I had to jinx it. Hot October is back, and I've been having the same driveability problems yesterday and today (with highs at 106F).

JvG

First things I would do are checking the fuel pressure, and re-visiting the maf.

I have not experienced maf issues myself, so I only know what others have said on this forum.

Otherwise, if a car has power issues when going up hill or on a freeway on ramp, the cause is insufficient fuel flow or pressere.

I would say replace the fuel filter, but you have done that already.

DBear

I'm inclined to agree with JvG, that it's a fuel pressure issue. If this was the Olden Days, I'd suggest vapor lock, but that hasn't really been a thing for years. There isn't any strange routing of the fuel line near a hot exhaust point, is there?

Barring that, have you tried replacing the fuel pressure regulator?

And is there excess pressure when you take off the gas cap? I've never really had problems in this area, but if the heat is causing the gas vapor in the tank to expand and it isn't being properly vented, maybe that is interrupting the fuel flow somehow. Just thinking out loud here...

JvG

DBear might be right.

Fuel Pressure regulator.

Thinking out loud is a good discription of forum car repair. Educated guesswork .

The injectors act like squirt guns. How much they squirt is determined in part by the fuel pressure regulator.

If fuel pressure is too low, it is most often noticed during periods of high fuel demand. Since you are also having issues at idle, one can suppose that there is not enough squirting action happening.

Start with removing the vaccuum hose from the fpr. If you see or smell gasoline in that hose, the regulator is definitely bad. If there is no smell, it could still be bad. A fuel pressure test should be done.

marianm

Thanks, I'll have to learn more about the fuel system in the Maxima.
I have taken the old MAF apart, the 6 commonly referred to solder joints all seem fine, no moving, no high resistance.
This whole issue is intermittent and brought on by heat... In August I took a roadtrip to Idaho, 2300 miles at 70-95 mph, including hills, high 80s temperatures at times, even driven halfway up mountains on steep, bad dirtroads. The Maxima didn't skip a beat.

To further elaborate on the current symptoms so far:
Monday, after a freeway drive I noticed the a stumble and short drop in rpm at a traffic light, then as I got to where I needed to get, it wanted to stall in the parking lot. I haven't noticed stumbles at higher rpms later that day.
Tuesday, after a 20 mi freeway drive (freaking 95F at 6am) with no incident, the car sat for about 2 hours. Then as I started and was setting up the laptop to record some OBD2 data, it stalled. I started it right back up then it died again. Same story one more time, then it seemed to run for another 10 miles to get me to work. In the afternoon, I drove it for about 22 miles with no issues that I could feel, until I got to the third traffic light. After idling for a while at the red light, I started giving it gas on green, but it just didn't go for about 3 seconds, then rpm shot up and I got going. It felt slugish for the rest of the 2 miles home.

With the old MAF, I had stumbles even at high rpms, I remember one time the engine stumbling at about 3000 rpm, doing 60 mph. Bear in mind, I haven't ruled out high rpm stumbles with the used ebay MAF currently on the car, they just haven't happened yet.

marianm

Thanks, the fueling system is stock.
I did check gas pressure in the tank yesterday after the drive back home; I took the gas cap off, and just a little (normal) vapor came out, so a little positive pressure, not unlike other times /other cars.

marianm

Should removing the vacuum hose form the FPR be done with the engine running, turned off, cold ... ?

JvG

Thanks for clarification regarding when your problems occur. I can't relate the problem to the driving conditions though.

The fuel pressure regulator in these cars is installed in the fuel rail on the engine. Fuel pressure is created by the fuel pump. The fpr returns unused fuel back to the gas tank. It acts as a restrictor valve, to keep the fuel pressurized while driving, and also when the car is parked for a while.

If the fpr is defective, it often requires lon cranking times to develop enough fuel pressure to run the engine properly.

The fpr has a diaphagm inside it. If these rupture, some of the fuel is sucked into the vaccuum line, then inside the cylinders. If there is a leak, you should be able to smell or see gas inside the vaccuum line. Do this when the car is cold, for safety reasons. Start the car, then shut it off immediately.