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Discussion Starter · #1 ·
Hi,

I’ve been following all of your great suggestions for months. I’ve researched my issues and tried the most probable solution. But I’m still experiencing the same issue.

So this problem has been going on for at least a few months. Possibly since last year. I’m pretty sure it’s fuel related. It’s an all stock 2003 3.3 NA automatic.

What it does is once the car is warmed up, driving about 20-30mins, if you’re heavy on the gas or stop and go then the car will sputter and go no where when stepping on the gas. Once the sputtering, and bucking starts, if you give it gas it makes it worse or it just does not go. The Rpms will drop and even bounce around. If I keep giving it gas it will even stall out while driving.

It happens more frequently when I run the AC for the first 20-30mins and if I use the cruise control a lot. If I’m light on the pedal and don’t use the ac or have a lot of stop and go, I can drive it a real long time without acting up. But as soon as I apply moderate throttle, have to stop and pick up speed a lot, or start running the ac then it’ll start bucking and fluttering.

NOW one way around this is if I quickly put it in Neutral, shut the key off, turn the key on for a second, and start the car. Put it in drive and off it goes no problem for another 5-20mins before it starts up. When I do this trick I can floor it and pick up speed with no worries about stalling out.

Even during the first 20-30mins, if I go WOT it’ll start to miss as it climbs. Eventually it tops out and you feel a drop in the pull. It’ll pull, drop, pull, drop, pull, drop. It just can’t go any further. If I tried this when it’s warmed up, it’ll just bog down and buck and die.

The problem gets much more frequent and worse when the gas goes to a 1/4 tank. As time went on it got worse at 1/2 tank. Then at 3/4 tank. So I always keep it full until 3/4. But it will still happen at full once warm.


Things I’ve replaced:

Fuel pump x2

Fuel filter

Fuel sending unit

Distributor

Knock sensor

MAF sensor


Things I suspect it may be-

Fuel pressure regulator

Fuel sending unit- my dad replaced this along with the pump last year. When I went to put another new pump in it, I noticed that the pump wasn’t mounted to the sending unit. It was just connected by the hose and dangled into the tank and sitting on the bottom. Can anyone tell me if the sending unit is supposed to hold the pump with a bracket in a particular spot?

Also can a faulty unit cause flow issues?

Fuel pressure before rail is right in spec. No way to check at the rail.

I’m going to pull the upper plenum to check the FPR, replace the VC gasket, and maybe check the injectors if anyone thinks that’s a good idea.

That’s the best I can explain it. Sorry for the long post. I’m taking any suggestions. Throw em at me.

Thanks a lot.
 

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Discussion Starter · #2 ·
No CEL I have a real time reader. Been driving for about 800miles this way.
I could do fuel trim report but I don’t know what it means.
 

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Did you buy a distributor from nissan or a knock-off?
 

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man you have hit just about everything as TBass stated what brand dizzy did you buy? also what brand MAF? and were these new or rebuilts? that fuel sending unit sounds worrisome. i would check the dizzy and maf again to be sure they are good, maybe get known good ones from a junkyard or see if the place you purchased would be willing to warranty them so you can see. OEM for many parts is best any sensors tahta re magnetic such as the crank pos sensor knock, etc are best to be oem, same with the dizzy and maf (oem brands being Hitachi for most, which you can usually find this brand on sites like rock auto) one other thing would be to check the functionality of the crank sensor, this will usually cause hard/no start condition with little change in drive-ability but can cause drive-ability issues.
 

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Not having any codes is odd with what you are describing. If one of the new sensors is bad I would expect a code to be thrown but maybe not. Are all of the grounds clean? Did you adjust timing when installing the new distributor? If not, I would get a timing light and just do that anyway. What is the condition of the plugs and wires? I would also suspect the fuel injectors and maybe one is going bad although that would seem like it would be more of a constant issue and not intermittent. I would also expect that a code would be thrown if a cylinder is dropping out. I am wondering if the MAF or camshaft position sensor is not sending the right signals to the ECM and the adjustments while driving aren't being made correctly. The signals could be within "tolerance" for what they should be putting out so a code isn't being thrown but maybe the signal being sent to the ECM isn't right.

Some things I am seeing in the service manual for the VG33E engine include:
  1. Even a slight leak in the air intake system can cause serious incidents.
  2. The amount of fuel injected from the fuel injector is determined by the ECM. The ECM controls the length of
    time the valve remains open (injection pulse duration). The amount of fuel injected is a program value in the
    ECM memory. The program value is preset by engine operating conditions. These conditions are determined
    by input signals (for engine speed and intake air) from both the camshaft position sensor and the mass air flow sensor.
VARIOUS FUEL INJECTION INCREASE/DECREASE COMPENSATION
In addition, the amount of fuel injected is compensated to improve engine performance under various operating
conditions as listed below.
<Fuel increase>
  • During warm-up
  • When starting the engine
  • During acceleration
  • Hot-engine operation
  • When selector lever is changed from “N” to “D”
  • High-load, high-speed operation
<Fuel decrease>
  • During deceleration
  • During high engine speed operation
4. The ignition timing is controlled by the ECM to maintain the best air/fuel ratio for every running condition of the engine. The ignition timing data is stored in the ECM. This data forms the map shown. The ECM receives information such as the injection pulse width and camshaft position sensor signal. Computing this information, ignition signals are transmitted to the power transistor.
e.g., N: 1,800 rpm, Tp: 1.50 msec
A °BTDC
During the following conditions, the ignition timing is revised by the ECM according to the other data stored in the ECM.
  • At starting
  • During warm-up
  • At idle
  • At low battery voltage
  • During acceleration
The knock sensor retard system is designed only for emergencies. The basic ignition timing is programmed
within the anti-knocking zone, if recommended fuel is used under dry conditions. The retard system does not
operate under normal driving conditions. If engine knocking occurs, the knock sensor monitors the condition.
The signal is transmitted to the ECM. The ECM retards the ignition timing to eliminate the knocking condition.

5. Idle Speed/Ignition Timing/Idle Mixture Ratio Adjustment UBS007UZ
PREPARATION
1. Make sure that the following parts are in good order.
– Battery
– Ignition system
– Engine oil and coolant levels
– Fuses
– ECM harness connector
– Vacuum hoses
– Air intake system
(Oil filler cap, oil level gauge, etc.)
– Fuel pressure
– Engine compression
– Throttle valve
– Evaporative emission system
2. On air conditioner equipped models, checks should be carried out while the air conditioner is OFF.
3. On automatic transmission equipped models, when checking idle rpm, ignition timing and mixture ratio,
checks should be carried out while shift lever is in “N” position.
4. When measuring “CO” percentage, insert probe more than 40 cm (15.7 in) into tail pipe.
5. Turn off headlamps, heater blower, rear defogger.
6. Keep front wheels pointed straight ahead.
7. Make the check after the cooling fan has stopped.
 

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one other thing would be to check the functionality of the crank sensor, this will usually cause hard/no start condition with little change in drive-ability but can cause drive-ability issues.
FYI, crank position sensor per the factory manual "This sensor is not used to control the engine system. It is used only for the on board diagnosis"

However, the crank angle sensor aka the camshaft position sensor inside the dizzy will cause no starts and stalling when heated if bad as will the coil. I test every circuit and sensor. You can also just unplug sensors like the MAF, MAP, Throttle position etc which puts the ecm in default mode. If the car still runs the same after unplugging a sensor, the sensor is probably good.
 

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FYI, crank position sensor per the factory manual "This sensor is not used to control the engine system. It is used only for the on board diagnosis"

However, the crank angle sensor aka the camshaft position sensor inside the dizzy will cause no starts and stalling when heated if bad as will the coil. I test every circuit and sensor. You can also just unplug sensors like the MAF, MAP, Throttle position etc which puts the ecm in default mode. If the car still runs the same after unplugging a sensor, the sensor is probably good.
but do NOT unplug the MAF while the vehicle is running this can fry the ecu, and maybe thats the case on the 1st gen crank sensors but the 2nd gens will not start most of the time or have a very difficult time in doing so if one has failed and this can, but usually does not cause issues while running. I have seen tons of them (vq nissan equipped vehicles so think 2nd gen xterra, 05+ frontier, 02+ pathfinder, 350/370z, 03+ maxima, 03+ v6 altima, g35/37 etc) working at a parts store in college where the owners have weird issues with bucking, loss of power and acceleration and odd idle issues and/or hard or no start conditions off and on and try many different things get frustrated and then finally ask for help and had they simply changed the crank pos sensor then that $50 part would have saved them time and hundreds of dollars on wasted parts they did not need.
 

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but do NOT unplug the MAF while the vehicle is running this can fry the ecu, and maybe thats the case on the 1st gen crank sensors but the 2nd gens will not start most of the time or have a very difficult time in doing so if one has failed
True, when I test unplugging sensors, the car is not running, sensor is unplugged, car is started. Should have clarified that. My bad dizzy was telling me my driver 02 sensor bank was bad. Unplugged all four 02 sensors, still had the identical stumbling, stalling. So that pretty much ruled out the 02 sensors but how many people see 02 code and immediately buy a new one, a lot...

And yes, all of those models you mentioned use the crank sensor. Just the 1st gen relies totally on the cam sensor in the dizzy.
 

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True, when I test unplugging sensors, the car is not running, sensor is unplugged, car is started. Should have clarified that. My bad dizzy was telling me my driver 02 sensor bank was bad. Unplugged all four 02 sensors, still had the identical stumbling, stalling. So that pretty much ruled out the 02 sensors but how many people see 02 code and immediately buy a new one, a lot...

And yes, all of those models you mentioned use the crank sensor. Just the 1st gen relies totally on the cam sensor in the dizzy.
yep, they have cam sensors too but they use them more in the opposite fashion the the vg33 in the 1st gens its more of a check and verify sensor. most of the time 02 sensors even completely bad will not cauuse any major issues other than a slight fuel mixture imbalance lower mpg and maybe some lost power because the engine uses the maf for air volume and temp and then simply uses the 02 sensors to verify the mixture is as close a as possible to 14.7:1 and adjusts the fuel flow rate as needed (in the vg33 since it does not have variable timing, intake or cam phasing to help with this) on more modern engines such as the vq40de in the 2nd gens the computer has alot more resources when an imbalance is detected, it can adjust the timing in an almost infinite range to correct knock or raw fuel dumping to correct the ratio, maintain balance and power etc. thats kinda what makes this puzzling and makes me wonder if he got a bad or simply not working well enough off brand component such as the maf or dizzy that is still causing the issues. if either were rebuilt i would rreturn, if possible and buy a new (not rebuilt) at minimum and preferably the oem brand
 

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makes me wonder if he got a bad or simply not working well enough off brand component such as the maf or dizzy that is still causing the issues. if either were rebuilt i would rreturn, if possible and buy a new (not rebuilt) at minimum and preferably the oem brand
Bingo, I'm guessing he didn't splurge 375 at a dealer for a real dizzy after tax. This is what I got for 5 dollars last junk yard run. BTW, I have a spare sensors/relays/fuses for everything, whole box in fact. That rusty coil on the right still is in spec and was actually submerged in a flood hence the rust, still works, I have 2 spare coils. Spare TPS and MAP on the right and fuses. The left sheet of paper is the new distributor guts I stripped and put in my original dizzy.
IMG_20181003_130122927.jpg
 

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Discussion Starter · #11 ·
Thanks for the replies.

I bought a quality aftermarket Distributor but not OEM. Not cheapo but not Nissan. The bearing in original looked perfect. The guts looked good too in the old one. There was absolutely no change immediately after swapping. I used a test light and set the timing according to spec.

I bought a refurbished Hitachi MAF and also an aftermarket one just in case. I did a volt/ohms check as it was running and all checked out well, even on my original. No change immediately after changing.

I bought a Nissan KS and did relocation technique.

I forgot to mention I replaced all the plugs while I was at it. Not the wires though. They look to be in good condition but I know that doesn’t always mean they are internally. So I’ll do that soon. I just dumped a bunch of money into getting my ford on the road because I’m sick of dealing with this problem.


The CEL hasn’t been on in a few hundred miles since the misfire code and KS code. Which was mainly because I was really holding the gas when it was sputtering which was making the rpms drop and bounce as it would try to keep up with accelerating. It started to misfire and threw a KS and misfire code. When I let off the gas it will level out and idle. When I go to accelerate it will have trouble pulling and start to bog down and buck and miss. Then I’ll put it in Neutral and shut it off while I’m rolling, once I restart it, it runs good and pulls strong for a bit. As long as I’m light on the pedal I can usually drive on flat ground for a while.

After it cools down completely, it’s less likely to do it right away.


It feels fuel related. What should I do when testing injectors? Ohms and spray pattern test?

Could a bad FPR cause fuel drop out when warm?

Could a broken plug wire internally get warmed up and cause issues? But as soon as I restart the car, it drives strong for a few minutes up to 10min or more. Then it acts up and I restart it while I’m rolling down the road.


I did get an insufficient CAT bank one a few hundred miles ago could bad CAT do this?

It’s the craziest thing and I can’t believe it’s taken me this long to figure it out.

I appreciate all the suggestions
 

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Definitely check the FPR. When the car starts acting up, pull over and pop the vacuum line for the FPR off the back of the intake manifold. If it's got a punctured diaphragm you will get gas coming out of the vacuum hose. When you rev the engine or turn the ac on the RPM bumps up and the vacuum in the intake manifold will increase. With a punctured diaphragm this will pull more un-metered gas directly into the intake manifold and cause a rich condition. Given enough un-metered gas and you would get stumbling etc. A leaky FPR may not show up on a pressure test.

A leaky FPR will cause a random misfire. It will often show a misfire in cyl 6 first because that is the cylinder closest to the vacuum line for the FPR so it gets the most unregulated fuel.

What is it idling at when first started and then when warmed up?

If you have a OBDII scanner, check what your O2 readings are when it is warmed up and idling. Then check what they are when you try to rev it (not in gear) and maybe when it is in gear, but get someone to read it for you while you drive. If you can get a good 10 seconds of reading and it shows consistently high or low voltage on O2 sensore 1 on either or both banks 1 and 2 it will go a long way towards diagnosing the problem.

Normally the voltage swings up and down between 0.1 and o.9 volts, but centers around .4 or .5 volts. If the sensor is consistently reading high then you have a rich condition and if it is consistently low, you have a lean condition. If you OBD reader has a graphing function it will give you a more accurate idea than just a number readout, because you can see the actual peaks and valleys as it fluctuates.

Also, keep an eye on your temperatures. An excessively lean or rich mixture can cause overheating, which will also cause stumbling and stalling as the engine tries to protect itself.

I use a little OBD Link that connects to my phone via blue tooth. It allows to me to keep track of all the OBD info in real time on my phone. MPH, RPM, Temps (the real temp), O2 sensors, Fuel trims, fuel consumption, and basically any other piece of info the OBD computer has to offer. The OBD Link starts at around $50, but there are plenty of chinese knock offs etc on ebay for around $20. It's an invaluable tool.
 

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Oh, and an extreme rich condition caused by a leaky FPR could cause your cats to read as ineffecient as the excess unburned fuel overwhelms them. It will also kill your cats if left.
 

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Discussion Starter · #14 ·
I’ll see if I can check the FPR line. I thought it was unecessable unless the intake was removed.
I have an OBD scanner for my phone and can check those values later today.
When it first starts it idles at around 1200 but immediately drops to 7-800 And is stable there.
Is there anything to learn from fuel trim? Idk what it means or what they’re supposed to be.
I’ll report back later today with O2 values and temperature.
 

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At the back of the intake manifold there are two small vacuum lines. They're about 1/4" thick. One of those is for the FPR. Just check them both. The FPR itself is burried under the intake manifold , hanging off the back of the fuel rail. If you do replace the FPR make sure you get a new ORing.

The fuel trims can be used in conjunction with the O2 readings to diagnose rich or lean conditions depending. Fuel trims should bounce back and forth to plus and minus levels, but should be relatively low numbers. Mine tend to bounce around between +/- 4. It's a direct result of the O2 readings as the computer adjusts the injector open duration to get the ideal fuel/air ratio.

Also, comparing you pre and post cat O2 levels may help in diagnosing your cat health. The post cat numbers should stay relatively level at a low voltage. They will bounce a little, but they shouldn't mimic the pre cat levels in levels and side of fluctuation.

If they are, it may be a cat issue. You may also want to use an infrared thermeter to check the temps pre and post cat. Post cat temps should be about 100 degrees higher. My point is that if you have one or more plugged cats it is possible that a partial clog allows enough flow to handle idle and low rpm, butw when you stomp on the gas there isn't enough flow for the increased exhaust volume, so it bogs down. When you turn it off for a minute the built up back pressure has time to escape, which makes run ok for a bit again until the pressure builds back up

Of course if your cat's are clogged it would be indicative of a deeper issue such as a rich condition from a bad FPR etc.
 

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Discussion Starter · #16 ·
Can i check vacuum with a vac pump on the FPR And see if the diaphragm is good?

I’m addressing an issue with the ford right now but afterward I’ll hop in the X And take it for a 20-30min ride to graph all the values of fuel and o2.
Thanks a bunch satito.
 

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It's easiest to just pop the vacuum line off while it's running. If the diaphragm is bad the pressure from the fuel system will push gas out the line. This allows you to check it without going through the hassle of removing the intake manifold and only takes about 30 seconds to complete.

If the diaphragm is bad and you use your vac pump with the FPR in place, you may get a pump full of gas. It probably won't do the seals in the vac pump any favors. Also, since the fuel system is sealed (more or less) you probably won't notice a rapid loss in vacuum with the vac pump unless you remove the FPR from the fuel rail first.
 

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Discussion Starter · #18 ·
Okay. So here’s what I’ve come up with. I took it for a pretty hard ride to gather data and get it warmed up to start stuttering.

I have a bunch of fuel trim values and the O2 values were low around .3-.7.

But I’m the middle of driving I got a CEL for P0456. An Evap system Very small leak.

When I got home I went to check the FPR and pull the lines to see if they were leaking fuel, but instead I find that the upper line has a hose that goes up to a big diaphragm or something, BUT the lower port isn’t connected to any hose at all.

Does this connect to the evap system?

Where does the lower hose go to? I’ve have some hose that I can install but I don’t see where it would go.
There is a steel line right by the egr pipe that’s not connected to anything. What’s that go to? Right by the oil dipstick.

I can give you trim values but they were pretty wild depending on throttle. Not +-4 like you said.

More like +-15 or even +20 on short side, which is usually the negative side.

I’ll keep looking for a vacuum diagram and try to put a hose on this.
 

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Discussion Starter · #19 ·
Oh, wait. I’m realizing that those are not for the FPR. It’s two steel lines under the EGRC-BPT Valve that’s mounted to the intake on driver side. The steel lines come right about the valve cover.

Can anyone identify these missing hose locations?
 
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