How to Diagnose a Failing Fuel Pump with Fuel Trim data / Pro OBD2 Diagnostic Scanner NOT Required

I cover how to diagnose a failing fuel pump with fuel trim data without using a PRO-level OBD2 diagnostic scanner. If you are wondering how to diagnose weak fuel pump with fuel trim data, or maybe you're not sure what fuel trim data means, you will find this video helpful. It will help with how to tell if your fuel pump is going out using just fuel trim data which very basic OBDII scanners have via live data. It also covers how to diagnose a vacuum leak with fuel trim data. Shor term fuel trim (STFT) and Long term fuel trim (LTFT) are defined and interpreted in relation to fuel delivery and vacuum leaks.
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Timestamps:
0:00 - Intro
0:19 - What are fuel trims (STFT & LTFT)?
1:06 - Diagnosing fuel pump issues with fuel trims
2:26 - How to differentiate fuel pump from vacuum leak issues
4:02 - Wrap
#fuelpump #fueltrim #STFT #LTFT #DIYAutoworksNG #weakfuelpump
Credits:
Image at 1:26 - "Diagram showing the operation of a 4-stroke SI engine" (en.wikipedia.org/wiki/Interna...) By Zephyris (commons.wikimedia.org/wiki/Us.... CC BY-SA 3.0 (creativecommons.org/licenses/...)

[@8power0]

THAT VIDEO WAS VERY CLEAR AND EASY TO HEAR WITH A UNDERSTANDABLY GOOD EXPLANATION OF A VERY COMPLEX SYSTEM . THANK YOU FOR YOUR TIME AND WE HOPE TO SEE MUCH MORE FROM YOU !!!!!!

[@DIYAutoworksNG]

Thanks.

[@CerealKiller187]

I appreciate you taking the time to put this together. I know a lot of people don't get credit where credit is due, but thank you. This has helped me in tracking down my own suspected fuel delivery issue(s).

[@DIYAutoworksNG]

Many thanks for your comment. It means a lot.

[@crystrezerex2life]

Very well explained and in a timely manner!! Good job from tech to tech!! 👍😎

[@DIYAutoworksNG]

Salute to a fellow Tech! 🤝🏼

[@emekaudolive]

Finally found you bro!! Thank you for so many great videos. My notifications are turned on for your posts!!! 👍👍👍

[@DIYAutoworksNG]

You're welcome! Thanks for following. Happy to have you!

[@abdul-kabiralegbe5660]

You fix people and cars (doctor & mech). Imagine a patient comes in for treatment and you fix him/her AND their vehicle, LOL! The quality of your videos is world class. Like for real. Great to see that some people in Nigeria know what they're doing and talking about. Respect!

[@DIYAutoworksNG]

😂🤣 Thanks, boss!

[@egbuonyelambert.chiedu7753]

@@DIYAutoworksNG Good morning sir, I have been going through your videos and they are interesting.

[@egbuonyelambert.chiedu7753]

@@DIYAutoworksNG please do you offer trainings? i mean to someone who wants to learn from the scratch?

[@egbuonyelambert.chiedu7753]

Sir please Can i call you, if yes. Let me have your number Thanks

[@DIYAutoworksNG]

Glad you find them interesting! Many thanks!

[@freefreesetmefree2234]

Thank you. After few years I changed fuel filter and was very dirty on input side from tank to filter and this was creating Fuel Trim issues. After 362000 km i will change fuel pump anyway. Thanks.

[@azzamhaq9556]

Thank you very much for the video. very useful .

[@DIYAutoworksNG]

Glad you found it useful! 🙏🏼

[@mohdibrahim1350]

Rhanks sir. Good info I myself would start with the last method which is testing before adding stuff.

[@DIYAutoworksNG]

Cool plan

[@mtm-hi5nm]

You are a true master !!!!

[@charlesleake930]

very helpful ! thanks : )

[@DIYAutoworksNG]

Glad it was helpful!

[@egbuonyelambert.chiedu7753]

This is very interesting ❤️

[@egbuonyelambert.chiedu7753]

Please do you organise training on OBD2 repairs and programming?, if yes, let me call you

[@DIYAutoworksNG]

Not really. Nevertheless, we can chat on IG or you send me an email [e-mail]

[@okparasamson7984]

Nice video bro

[@DIYAutoworksNG]

Thanks!

[@anonymoususer5794]

Thanks so much. I haven't tried the test yet, but you made it easy to understand the concept. I'm having high idle issues after a TB cleaning, seems my 99 civic is getting enough air to idle just above spec..with the idle air screw, screwed all the way in. It's either in need of a proper idle relearn (I tried manually, with no improvement) it's a bad IACV that I swapped out, I have a vacuum leak at the IACV itself, or I'm ruling out inadequate fuel pressure with this test, even though I have no other symptoms of inadequate fuel delivery. Closed off idle screw, and thumb over IACV port kills the engine immediately, so I can pretty much rule out any major vacuum leaks downstream of the throttle plate, though I checked hoses, and sprayed a bit of brake cleaner to be sure. Gonna spray the IACV tm, get it scanned with a proper scanner to make sure it's zeroed out, reset, or calibrated, then change out the original IACV that I mistakenly swapped because I DID have a vac leak that was throwing a P0505. I tried setting the idle screw back to spec, then doing the idle relearn manually..no luck. They say you must pay for your education.

[@DIYAutoworksNG]

Thanks for the compliment. Was the car otherwise fine before the TB cleaning?

[@anonymoususer5794]

@@DIYAutoworksNG Ehhh, idle was a little high, but pretty sure that was from an under torqued egr valve vac leak. I also found a bunch of gunk on the intake manifold from the throttle screw port when I cleaned it, so I had a vac leak, and clogged idle screw port..lol I've ruled out vac leaks now, as well. The tech drenched the throttle body and surrounding area with brake cleaner. I'm not running lean either. Just idling high. Otherwise looks healthy on OBD scan. The IACV was at 0 for a few ticks, he actually said, "that IACV is dead," then went to 9, and stepped down to 8, at least,(The guy at the shop was scanning it for free) but I feel like it's not working correctly. The valve itself, out of the car, and at rest is in a different position than the OEM. OEM is probably 15-25% open, while the Walker model, and a cheap Chinese Amazon model are both almost completely shut. I'm convinced now, it's probably a faulty aftermarket IACV. I'm changing the IACV back to my cleaned up Denso. Voltage and resistance tested. It was definitely better before the cleaning. If that fails, I'm going to have to take it to the Honda dealership. They could do in an hour, and about $150 what it would take me weeks to troubleshoot. I did get weird TPS values. To get 9.8% (.49v) and 89.8% (4.49v) on my basic scanner, I was at .54v closed, and 4.6-ish WOT at the harness. I assumed, on a 5 volt scale, .5v is 10%, 4.5v 90%. This is how the Honda service manual basically describes it. 10%-90%=.5v-4.5v..because math.

[@anonymoususer5794]

Background. I was getting an EGR code, cleaned the valve, no luck. Changed the valve, no luck. Aha..cleaned the passages and chamber. Bingo! No more EGR code. It was replaced fairly shortly with an IACV code. Cleaned the valve, and throttle body. Still coding. Changed valve. Still coding. Decided to re-torque my work and check all my mating surface. Little to no improvement. Still coding. Embarrassingly, I think I caused the P0505, fixed the original cause, but replaced with a bad IACV in the process. At least I hope so. After I swap the original IACV back, I'm pretty much out of ideas. I've literally used the Honda service manual troubleshooting flow chart, and "Replace IACV" is where I ended up.

[@fredguerra4917]

Excellent video. The best I have seen on the subject. I purchased the xtool computer but truly I did not know how to read the data. I will go back again and check for clues on my fuel or vacuum problem? I was wondering if you have any input as to the reason why the pressure tester readings are so low when testing my 350z nissan. They are about 20 psi. I have not able to find the proper male adapter to connect to the line going to the engine. Presently the pressure tester has one end securely plug. I welcome any help!

[@DIYAutoworksNG]

Thanks mate! The right adapter is the place to start! Do you mean 20psi on the scan tool? That sounds quite low. Do you know the spec for your Nissan? I'd say you look into restrictions in the fuel line, clogging of the filter or a defective fuel pressure regulator/pump. Let me know how it goes. All the best.

[@fredguerra4917]

@@DIYAutoworksNG I used a generic pressure tester from my local auto parts rentals. It read 20psi. My 350z Nissan normal operating pressure is 51psi. The current factory "return less" fuel systemin my car does has the regulator inside the pump. I will check both today! Thanks for getting back.

[@mark.r8900]

Great tutorial. My 2007 audi a4 b7 quattro 2.0l turbo at idle has stft at 18% and ltft 0%. Raising the rpm to 2500 and 3500 did not affect the fuel trims much. During normal driving the stft fluctuates between 18% and 23% while the ltft stays at 0%. The car intermittently loses all power. Stepping on the gas pedal only see rpm slowly rising and car barely moves. Can this be a bad fuel pump? Any help would be greatly appreciated. Thank you.

[@DIYAutoworksNG]

Any codes?

[@kmp5480]

I have a 2000 mustang gt I keep getting p0300 my stft and ltft are usually under +/-10 at idle but with an increase of rpm my ltft increases to 25% or more but my stft still look good being under +/-10

[@DIYAutoworksNG]

This is the V8 correct? It will be good if you split the STFT & LTFT by bank as per the values STFT1 & STFT2 and so on. Share values at idle, 1500 and 2500 rpms.

[@kmp5480]

@DIYAutoworksNG And yes it is a V8

[@axjr6393]

It says my vehicle is going 17mph on the scanner when I'm parked ,why would it say that ? My speedometer revs when trying to drive it sometimes won't change gears and my cruise control doesn't work ,I've already changed the vss and my truck is lean with multiple misfire code

[@DIYAutoworksNG]

A car revving itself has multiple causes, one of which is misfires from spark plugs or ignition coils. I suggest dropping cylinders in a bid to isolate the problematic cylinders. Also, what codes you have specifically have? Vehicle indicating 17mph while stopped, plus inability to engage cruise control, as well as transmission issues may be pointing to the VSS. Did you replace with new OEM? Or its used? .

[@dyardsale5475]

It took too long for me to understand, I watched it 10 times, finally I formed a plan

[@DIYAutoworksNG]

Glad you got there in the end. Mastering fuel trim data interpretation takes time and is key to troubleshooting emission problems.

[@dyardsale5475]

@@DIYAutoworksNG I have a fuel problem. I don't know why it is so hard to read fuel pressure from an analog gauge while driving and experiencing hesitation. I am trying to go around fuel pressure gauge and use fuel trim.

[@ericstern1754]

Stft B1 stays the same at 25. Ltdt stays the same at 8. Is that lean?

[@markwalker652]

I have a Peugeot 207 1.4 petrol 16v done about 125,000 miles, the car starts perfectly every time, but when the engine is cold I have to sit there for at least 5 mins until the engine warms up, then I can drive off. If I don’t let the engine warm up, I drive off and the engine is sluggish, pedal to floor and no movement, then it will all of a sudden kick in, if I stop at junction the engine will cut out. When at Idle also sounds rough until it has warmed up. I have changed the following: Spark plugs Coil pack MAP sensor Camshaft sensor Variable valve oil solenoid sensor I have no engine management light on and no error codes when scanned. I run the test in this video and from a cold engine my short term fuel trims run between 0 and -10, surely from a cold engine they should be positive? Do you think I have a fuel problem?

[@DIYAutoworksNG]

It should be in the negative (which is rich) from cold start. What is the LTFT at? A failing coolant temperature switch can cause what you describe. Try this... First thing in the morning use live data to check the temperature reading from the coolant temperature switch(or equivalent) it should read practically the same with the ambient air temperature switch. If either is off, the switch with a reading different from the weather temperature is the bad one.

[@markwalker652]

@@DIYAutoworksNG the LTFT is showing a constant +10, can I send you a screenshot of the live data?

[@DIYAutoworksNG]

A single snapshot of livedata may not do much. If the the car warms up, where the STFT hover around? Also, with the car warm, and you hold RPM at 2500 how does the STFT react? If the LTFT changes too let me know.

[@markwalker652]

@@DIYAutoworksNG so with engine cold STFT are about -10 then as engine warms up they go between 0 and -5. LTFT stay the same cold and warm during idle at about +10 When I rev the engine STFT read between +2 and +10, LTFT read -5 during revs After I stop revving STFT read between -5 to +5 and the LTFT read a constant +13 I will run another test adding the coolant temperature to the live data like you said. Thanks for your help so far. 👍🏻

[@markwalker652]

So coolant temperature, ambient temperature and actual temperature all read the same degree

[@octysa]

what scanner brand is good for this?

[@DIYAutoworksNG]

Depends. I guess there'll be other things you need in a scanner? Those should also guide your decision. If its just this test a really basic scanner with good livedata activity should be fine.

[@octysa]

@@DIYAutoworksNG Most of the problems in the Vw 2.0tsi always come from the gasoline pumps. In my country, very few people have the equipment to read this information. I'm looking for something that simplifies that work

[@DIYAutoworksNG]

Is it just for you, or you fix people's cars and have a shop?

[@octysa]

@@DIYAutoworksNG for me and some friends

[@user-nw3vm1op5l]

I'm working on mercedez w204 with m272 2.5 litres engine. All 3 spark plugs on bank 1 is black colour while all 3 spark plugs on the other bank is white. Upstream oksigen sensor on bank 1 show 2.2 mA and LTFT is +26%. Upstram oksigen sensor on bank 2 show 0.1 mA and LTFT -0.1% When I push acc pedal to 2500 rpm and keep there for about 5 sec and suddenly rev up to 4000 rpm and quickly realese the acc pedal, upstream o2 sensor current on bank 1 drop to nearly 0 and soon back to 2.2 mA. Sometimes when all 3 spark plugs is very dirty black i got CEL light on and the dtc show Multicylinder missfire. Is this upstream o2 sensor on bank 1 need to replace? I was try to cleaned all the oksigen sensor, maf sensor, injectors and all spark plug but the results is the same, only 3 days after all 3 spark plugs on bank 1 got black colour. Btw, bank 1 catalytic shows higher temp compare to bank 2 catalytic temp. Do I need to reset LTFT after cleaning all the o2 sensor, maf, injector and catalytic ? How to reset LTFT? Any help would be highly appreciate...

[@DIYAutoworksNG]

Hey. What codes do you have on the car apart from the multiple cyl misfire? Bank 1 appears to be running lean with the +26LTFT, but wasn't expecting them to turn black which indicates rich running. When last did you change these spark plugs?

[@user-nw3vm1op5l]

@@DIYAutoworksNG if i remember correctly it is p0300, p0301, p0303, p0305. I don't know when this car last change the Sparks plug but i did try to switch the Sparks between Banks. Result is Sparks from bank 1 which installed on bank 2 is white colour and Sparks from bank 2 which i installed on bank 1 became carbonized black colour.

[@user-nw3vm1op5l]

@@DIYAutoworksNG also, i did switch the all 3 coils between bank and the result is the same. Bank 1 Sparks plug still black carbon.

[@DIYAutoworksNG]

The engine has a primary O2 sensor per bank, right? If it's easy, maybe swap that, let's see.

[@thedogpack]

Hi, I have a 2007 ford expedition. My bank 1 ltft is +25 and my bank 1 is -23. How do I approach this? Thanks.

[@DIYAutoworksNG]

I believe you mean bank 1 and 2. This will need significant troubleshooting. What codes do you have?

[@thedogpack]

@@DIYAutoworksNG hi, thanks for quick answer, the car has a p0340, p0344, p0307, p0303, and other cylinder misfires at random times,

[@DIYAutoworksNG]

Appears you have camshaft related issues which is messing up engine timing. I recommend you troubleshoot the P0340/P0344 first. Loose connection/poor contact/actual damage of the camshaft sensors are potential culprits.

[@thedogpack]

@@DIYAutoworksNG i have done that and had the sensor replaced which did not help. I have had those codes since I have owned the vehicle which is over 2 years. I believe the next step is to open the engine up. It may need timing equipment. I do not have the 2k to 3k that people want to do that. The car runs well after I get it to about 35-40. It is only running slightly rough at start up or at idle.

[@DIYAutoworksNG]

Maybe before opening the engine, do you want to check for exhaust restriction on the bank that is rich? Seems to be an issue reported on Ford's. See www.ford-trucks.com/forums/1549350-5-4-running-very-lean-on-bank-1-and-rich-on-bank-2-a.html

[@shaijugm]

Hi bro my car idel around 850 rpm long ft B1S1 shows. - 3.906 and short ft b1s1 0% and my car has around 2000 rpm while driving tomuch pinging sound, let me know what is ur option

[@DIYAutoworksNG]

Fuel trims look good at idle. Any codes?

[@shaijugm]

@@DIYAutoworksNG no code buy car always tomuch pinging around 2000 rpm

[@DIYAutoworksNG]

Use a good fuel system cleaner and see.

[@shaijugm]

@@DIYAutoworksNG thanks

[@shaijugm]

Bro sorry, can check my reading 2159 rpm, intake air, 48 degree Celsius knock learn values 15.156 long FtB1S1 11.719 % maf 37.7 O2FTB1S1 4.688, O2B1S1. 720v short FTB1S1 2.344%

[@mujtabapolani3229]

Hello dear i change my fuel pump and strainer but my ltft is still on 2.34 positive not changing

[@DIYAutoworksNG]

2.34 is good.

[@mujtabapolani3229]

@@DIYAutoworksNG but when i accelerate it does not change

[@DIYAutoworksNG]

@mujtabapolani3229 LTFT doesn't change as fast. It's STFT that changes quickly.

[@mujtabapolani3229]

But as you said if LTFT remain lean so it would be fuel pump issue , is i need to change fuel pump

[@smalanning9693]

👌👍

[@DIYAutoworksNG]

🙏🏼

[@skeltonantonio]

I did this test my stft b2 went to positive 14 at 3000 rpm

[@DIYAutoworksNG]

If fuel trim was normal at idle, you likely have a restriction in the fuel line, clogged filter, pump that is going weak etc. Bank 1 data was good?

[@skeltonantonio]

@@DIYAutoworksNG yes trims normal at idle, rough idle, rpms goes up then down sometimes it stalls on me. B1 good

[@skeltonantonio]

Yes B1 data good

[@michaelmartinez4515]

​@@skeltonantonio yo dude you ever figure out the problem, my 4.6 explorer is running the same STFT normal at idle but LTFTB1 AND B2 ARE +18 AND +12.5 when driving, idles up and down and i can smell the exhaust a lot more.

[@mlowen9424]

❤️❤️❤️❤️❤️❤️❤️ 💪😘

[@skeltonantonio]

What if you raise the rpms and stft b2 reads +14

[@DIYAutoworksNG]

Think of restriction in the fuel supply on Bank 2.

[@skeltonantonio]

What may cause this

[@DIYAutoworksNG]

Dirty/clogged fuel filter, failing fuel pump. This assumes that the car has separate filters/pumps... Do you know what your fuel pump assembly setup is like?

[@skeltonantonio]

2006 Mercury mountaineer filter is separate pump inside tank

[@DIYAutoworksNG]

I've also seen a dirty MAF sensor can cause this, as well as injectors on Bank 2. Maybe try to clean the MAF, get a good fuel system cleaner in the tank and see if it helps. If it doesn't, try reading fuel pressure on Bank 2.

[@JCGible]

Now I know I have a vacuum leak SOMEWHERE 😊

[@DIYAutoworksNG]

Now, time to smoke it out🤓

[@JCGible]

@@DIYAutoworksNG I did a smoke test and. Nothing... thanks for your video.

[@DIYAutoworksNG]

Thanks mate. Also reduced/restricted fuel supply will also lean out the mixture.

[@JCGible]

@DIYAutoworksNG Yeah, I changed the fuel pump and attached a fuel pressure gauge. The preasure is good. My LTFT slowly creaps up to 20% as it idles until it misfires. I just opened up the exhaust flange to see if that would help, but it didn't. Tomorrow, im going to look harder for a vacuum leek. Maybe the dipstick pipe.

[@DIYAutoworksNG]

When you do the test in the video (holding RPM at higher RPM), what happens to LTFT?

[@Dmonieluv]

Excellent and precise simple explanation. I'm currently getting these codes and here are my trims: kzbin.info8JQoFlVakio?si=9mbJ-7X930AvtScE So according to the test I have a vacuum leak. But after running a smoke test the only one I found was at the EGR valve, which I replaced along with the MAF, PCV, fuel filter, and I'm still getting a lean condition P0171, P0174. What else should I try Rhanks sir?

[@DIYAutoworksNG]

Yea, those fuel trims are consistent with a vacuum leak. Did you also check for cracks and hose clamps on vacuum lines are tight? I'd say you double check. Also remember checking the EVAP for leaks too. A worn intake manifold gasket is another culprit, did you do any work in that area before this started? What car is it?