Fuel pump

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#31
With my 65 Buick that I put 330K miles on, could repair the fuel pump for a buck, how this has changed. Sure have crap today, if you run an electric fuel pump on the bench with a load on it, will burn it up in about five minutes. Needs to be soaked in gas for cooling. Most vehicles don't even have an access plate, have to drop the tank. And when they go bad, this is after you just filled the tank.

The ride from the battery to the pump is a very long ride, any connectivity problems reduce the voltage to the pump, if below the fuel regulator setpoint, current skyrockets to burn that little POS up. Fuel regulator has a return line to the tank, but with his new crap, got away from this. Not only the pump, but the fuel filter, regulator, and the fuel sender is all part of the assembly and mounted inside of the tank. This saves that long return line, more money for the stockholders.

Permanent magnet motor, commutators, most have brushes about 3/4" long. Since air is far less dense than gas, those feed lines can have a small leak someplace, clear from the engine way back to the tanks. Use to have one fuel line to replace, now have three on many vehicles, really a problem in road salt areas, do paint them first, last a little longer.

Fuel evaporator systems are another problem, use to mount the canister and purge valve high up on the firewall, now at the rear of the tank where that carbon canister is exposed to road salt slush. Gets wet and sucks in moisture and also freezes up the purge valve. Ha, know I am an old guy, but sure making crap today.

Used to have only one brake line, with ABS, have four now, four times the work to replace, the list goes on.
 

kev2

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#32
we will post the line up "ticks " Will need to know a 2dr or a 4dr, I will add later.

As for that PSI drop KOEO nick is right to not ignore that 17 PSI drop it is too much.
Its often either pump check, or a leaking component ie injector or FPR - easy checks.

NLDP a mopar acronym for something like "Natural Leak Detection Pump" think EVAP system.
 

nickb2

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#33
thx kev for the correction on the acronym, the "N" threw me off.

Even so, a LDP would not cause this sort of pressure drop, that only tests the evap system.
 

nickb2

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#34
we will post the line up "ticks " Will need to know a 2dr or a 4dr,
2dr or 4dr have same for alignment ticks, as kev asked but one is 7 o'clock, the other is 4 o'clock.. Here is a snapshot, so check it out. I have done literally hundreds or more of these, but a picture is worth a thousand words.;)
Screenshot (64).png
 
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hidden1

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#38
I'll get the readings again .i do recall the STFT reading to go up an down evenly at -3 to 8 --mine uses %...even with low fuel.at idle.Im going to retest it as im stopping slow at light . I'll send pic.
NLDP is a emmisions sensor- Natural leak detection pump.

Thanks for the great info on it ..
 
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billr

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#39
Is it really that easy and inexpensive to replace the pump, that you don't want to bother checking pressure while the problem happens? You already have a gauge, correct?
 

nickb2

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#40
Is it really that easy and inexpensive to replace the pump, that you don't want to bother checking pressure while the problem happens? You already have a gauge, correct?
I agree, and since I hate beating a dead dog, but I am always game, fuel trims would not be be what you wrote. 3 to 0,8%. They should be 20% or more with a 17psi drop.

But hey, here is some good reading material, not my writing, source taken from here. http://www.autoserviceprofessional....-works-and-how-to-make-it-work-for-you?Page=2


Auto Service Professional
Tech Stuff
Fuel trim: How it works and how to make it work for you
Posted on February 11, 2015 by Jacques Gordon
42


Figure 2. Notice how equivalence ratio and short-term fuel trim mirror each other.

What’s normal, what isn’t?

When looking at fuel trim on a scan tool, it should be checked for at least 30 seconds at three different engine speeds: idle, 1,500 rpm and 2,500 rpm. If you make a scan tool recording while driving the vehicle, you can see how fuel trims change under changing loads.

When everything is stable and working correctly, fuel trim numbers should be no greater than 10%, and total fuel trim should be no more than 10% when the numbers are added together. For example, if LTFT is 4% and STFT is 4%, the total is 8%: that’s acceptable.

If LTFT is 12% and STFT is negative 6%, total fuel trim is 6%. This shows that the PCM has enough control to keep the catalyst working correctly, but the high LTFT number shows it’s compensating for something. On an older engine, LTFT is typically a bit higher as the PCM compensates for normal wear.

If fuel trim is significantly greater than 10% positive or negative, the PCM is compensating for more than just normal wear-and-tear. Whether it’s an older engine with a simple oxygen sensor or a newer model with a wide-band air/fuel ratio sensor, LTFT will continue to shift as needed to keep the STFT swings in the correct range.

LTFT can shift surprisingly far, but when it reaches plus or minus 25%, the MIL will be illuminated and a code will be set. Fault codes specific to fuel trim are:

  • P0170: fuel trim bank 1
  • P0171: system too lean (bank 1)
  • P0172: system too rich (bank 1)
  • P0173: fuel trim bank 2
  • P0174: system too lean (bank 2)
  • P0175: system too rich (bank 2)
By the time LTFT gets to 25%, there will be other codes, too.

But if LTFT is below that limit with or without other codes, you can still gain a lot of information from the scan tool before connecting additional test equipment to confirm your diagnosis.

Why are the fuel trim numbers high?

If LTFT or total fuel trim is greater than plus 10%, the PCM thinks the air/fuel ratio is too lean and it’s adding fuel to bring STFT control to the correct range. This presents three possibilities:

  • Unmeasured air is reaching the combustion chambers.
  • Less than the commanded amount of fuel is reaching the combustion chambers.
  • One or more sensors is reporting incorrectly.
When thinking about what would cause each of these conditions, the first thing to consider is how the PCM determines airflow. If the engine uses a mass airflow sensor (MAF), high fuel trims at idle are a classic symptom of a vacuum leak, especially if LTFT decreases at higher engine speeds.

Since the amount of air flowing through the vacuum leak doesn’t increase, the leak has less affect on air/fuel ratio at higher speeds and loads, so LTFT will come down as engine speed goes up. When you look for vacuum leaks, don’t forget the various “calibrated vacuum leaks” like crankcase ventilation, the evaporative emissions (EVAP) purge valve and, if equipped, air-shrouded injectors.

A dirty or faulty MAF sensor can also cause positive fuel trim numbers because it “under-reports” airflow, driving the base air/fuel calculation lean.

On engines that use a manifold absolute pressure (MAP) sensor to determine airflow, a vacuum leak does not affect fuel trim because the extra air (pressure) in the manifold is still measured by the MAP sensor.

Low fuel delivery will cause an increase in LTFT as the PCM tries to compensate for extra oxygen in the exhaust stream. Remember, the PCM doesn’t measure fuel flow; it only knows injector pulse width and assumes fuel delivery is correct as commanded. Is equivalence ratio changing, too? If you add propane and see LTFT and equivalence ratio numbers come down, there probably is a fuel delivery problem. If there’s no change, an oxygen sensor may be faulty or shorted to ground. Don’t forget to check this at different speeds and loads, because fuel flow problems often don’t show up at idle.

If the engine has two cylinder banks (even some four-cylinder engines are split into two banks), compare the readings to see if the problem affects both banks.

The PCM consults all oxygen sensors in the system when calculating fuel trim. Normally the rear (post catalyst) sensor voltage will be fairly stable near the middle of its range, but LTFT will likely increase if that sensor reading is low (remember, low is lean).

A catalyst code will influence both short- and long-term fuel trims. An exhaust leak after the catalyst will probably only affect the rear oxygen sensor.

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Tags: Fuel trim Jacques Gordon Long-term fuel trim LTFT Short-term fuel trim STFT
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Comments (29)
cx-7 mazda 2.3L with Turbo
- Posted 16 days ago
Ok, all the explanation is nice and good but what about low LTFT readings ??!!

Clint
- Posted 19 days ago
@Josh if you are still fighting your GS, check the fuel pump. I work at a Lexus dealership service department and we had your exact model of GS have the same symptoms and issues. Fuel pump was weak above idle. Usually fuel pumps (at least Lexus/Toyota pumps) either work or they don't so we were first looking for a restriction. But rare as it may be, it was a failed/failing pump and that fixed it.

Jack and Jones
- Posted one month ago
Hello, appreciate for the info. I have a 1600 cc Mazda 3 which runs on LPG. The question is; Ltft is always 14.8 never more sometimes even less, while the stft is average +-1. Any ideas? Regards.

Finn
- Posted 4 months ago
KenC, check evap purge valve if stuck open and PCV valve.

Finn
- Posted 4 months ago
ahmed, perhaps catalytic converter clogged.

Finn
- Posted 4 months ago
Mathematically greater than 1.0 is the command for a lean air/fuel ratio (less fuel) and less than 1.0 is a command for a rich mixture.

Finn
- Posted 4 months ago
Mathematically

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64) Equivalence ratio: This is the desired air/fuel ratio, a command issued by the PCM. Greater than 1.0 is the command for a rich air/fuel ratio, and less than 1.0 is a command for a lean mixture. Mathematically

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64) Equivalence ratio: This is the desired air/fuel ratio, a command issued by the PCM. Greater than 1.0 is the command for a rich air/fuel ratio, and less than 1.0 is a command for a lean mixture. Mathematically

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64), Equivalence ratio:

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64)

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64)

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64)

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64)

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64)

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64)

Finn
- Posted 4 months ago
Fuel mass = Air mass x (short-term fuel trim x long-term fuel trim) divided by (equivalence ratio x 14.64)

KenC
- Posted 5 months ago
My STFT on both bank at idle just staying at 1.15-1.20(15-20%) positive range since my LTFT have been turn off by my tuner.(base tune for idle datalog for pulley mod). Have check all the vac leak by smoke machine on intake and even on exhaust and all are good. Replace the front o2 sensors, IAC, MAF, EGR valve,new fuel filter, doing flow test and ultrasonic clean the all injectors. The STFT still at the positive....What else can cause the lean short term?! cylinder head gasket have a little leak as I know so far, but I don't think that will cause this.(vehicle: 2004 Ford F-150 SVT Lightning)

Josh
- Posted 6 months ago
And I have no codes at all

Josh
- Posted 6 months ago
I have a 01 lexus gs300 2jz the ltftb2 is fine but ltftb1 is normal at idle but while driving it's anywhere from 10.5 to 14.1 and engine bogs down checked for vacuum don't see any I'm stumped any idea.

ahmed
- Posted 7 months ago
I have a problem in my car Lifan X60 2014 model, its start and move normally but sometimes when I try to pass another car my I feel the car chocked and the rpm falls slowly until I change the transmission leaver to neutral position and wait for 5 seconds then every thing back normally and the engine response and accelerate the vehicle. This problem happing specially when the vehicle moves over bump or turn to one side ( not all times ) . the reading of fuel pressure is 55 psi , I replaced all the injectors and fuel filter with new one, below the reading

Bakack
- Posted 7 months ago
@Robert looks like a vacuum leak....SMH

Paul
- Posted 7 months ago
I have b1s2 and b2s2 both pinned at 99.2% but everything else is fluctuating within spec? Getting p0420 & p0430 ?

William
- Posted 7 months ago
My ltft a are at -20.31 and getting p0172 and175 I changes maf,map sensors and plugs and wire still having issues.

Robert dixon
- Posted 10 months ago
What kind of issues would it be if on one bank the LTFT is like 18 percent but the STFT seem fine
The Trims tend to even out when under throttle
Also the rear 02 for that side fluctuates rapidly but stays low around .06 to .3v

Robert
- Posted 10 months ago
Great article. I read the article but have a few questions.
What would it be if I have around 18 percent positive long term fuel trim on one bank. But the short term trims seem within reason. The Trims to tend to even when under throttle
Also the rear 02 on that side with the LTFT that is high fluctuates rapidly but stays low like .06 to .3v

Abel Sanchez M
- Posted one year ago
Hola, felicitaciones estés el mejor, mas amplio y explicito documental de los fuel trim jamás visto agradesco ampliamente a los técnicos, ingenieros y demás personal que gracias a su experiencia hacen de este tema difícil de explicar algo fácil de entender.
Si ay algo que pueda acer desde México en agradecimiento por tan buen aporte, mas allá de recomendarlos ampliamente por favor dejenmelo saber

Quedando a su dispocision
Muy agradecido.

From Galaxy fuel injectio
In Puerto Vallarta jal
Abel Sanches M

Mamery
- Posted one year ago
Great article on fuel trim to print

Stewart
- Posted 2 years ago
Now we teach them how to get their on their scanners?


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nickb2

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#41
So to break this down, easy, check my highlighted portion here, and then read back to my other previous post, This vehicle is running fine.

For example, if LTFT is 4% and STFT is 4%, the total is 8%: that’s acceptable.

you wrote,
i do recall the STFT reading to go up an down evenly at -3 to .8 even with low fuel
That is impossible in my opinion.

So now, I have a bbq chicken to deal with, and I will let the op take time to read and comprehend how fuel trims are the best tool now for him.

Peace out, my hands are tired of typing and cutting veggies for the bbq.
 

nickb2

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#42
something is eluding this poster/op.

But we are here to help, but you must take time to post proper readings with proper tools.

Bye for now, I think my chicken is done.
;)
 

hidden1

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#44
I have 10 snap shots an videos of recording of the lt an st fuel trims..
Not sure how to load them to page but it IS staying in recommended range..im using APP program that shows ranges on chart live in percent ranges .fluctuation is in normal range 20170601_105528.jpg 20170601_111255.jpg
 

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hidden1

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#45
MiI have 10 snap shots an videos of recording of the lt an st fuel trims..
Not sure how to load them to page but it IS staying in recommended range..im using APP program that shows ranges on chart live in percent ranges .fluctuation is in normal range View attachment 9590 View attachment 9591
 

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