Fuel psi less than 50 psi = no start (GM CPI Vortec)

This video covers the basics of fuel pump pressure, current, power and ground testing that can be applied to ANY electric fuel pump. We also go into some unique properties of the GM CPI “poppet” style injection system, and where it differs from typical fuel injection systems.
Lower than normal fuel pressure is often misdiagnosed on the central port injection system. For example: Fuel psi at 49 psi during cranking will be a no start! Just about every other fuel injection system will start and run fine with this kind of pressure. But the GM CPI needs a minimum of 50 psi to open the mechanical injector poppet nozzles.
This design was used on the 4.3, 5.0 and 5.7 engines throughout the 90s.
Engine Performance Diagnostics chapter 16 pages 2 - 6, 9 - 16
Symptoms
- intermittent no start condition
- starts when a fuel source is used (carb. Clean, starting fluid etc) and may continue to run normally after it starts
- possible hesitation/bog on acceleration once running depending on how weak the pump is
- fuel system lean trouble codes (P0171, P0174)
Fix
- fuel pump replacement
Tests shown
- how to check fuel pressure on a GM CPI system
- how to use a GM fuel pump test connector and fused jumper wire to energize a fuel pump
- using a low amp probe and scope to check an electric fuel pump
- how to check an electric fuel pump power and ground
- understanding the impact of a plugged fuel filter on fuel pump current
Tools used
- fuel pressure gauge
- low amp probe
- fused jumper wire
- lab scope
Playlist
- (Chapters 14, 15,16) Fuel Delivery and Fuel Pressure Testing
• (Chapters 14, 15,16) F...
Related videos
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• GM Fuel Pump Relay Tes...
- Low Fuel Pressure from a bad fuel pump ground (Ford Ranger)
• Low Fuel Pressure from...
- How to identify and repair a leaking fuel pressure regulator (GM CPI system) part 1
• How to identify and re...
- How to identify and repair a leaking fuel pressure regulator (GM CPI system) part 2
• How to identify and re...
- Fuel Pump Electrical Circuits Description and Operation
• Fuel Pump Electrical C...
- Symptoms and Causes of Low Fuel Pressure (Part 1)
• Symptoms and Causes of...
For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium www.scannerdanner.com/join-sc... There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!
Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC.

[@mph5896]

Spot on sir. I had 45psi cold crank and no fire on one of these. New fuel pump and it starts perfectly.

[@ScannerDanner]

It is really cool that 21 years later, I get to teach along side my mentor. I love to see when my students respond like I did so many years ago. It feels like watching that car leave the shop, purring like a kitten that no-one could fix and you did. When I see that light in my students faces, it feels just like that. What a rewarding career this has been.

[@CharlieAtkins]

Nice Video! The 95-up 4.3L (VIN code "W") (RPO L-35) motor needs 60 PSI minimum to start cold ,and the pump should "Dead Head" @ 72+ PSI

[@JoelAutomotiveInaction]

a lot of people is questioning and not absorbing good info and tkz for effort, come on you are getting this for free I have been in automotive school and believe me you are paying a lot of money and getting poor info and not enough hand on vehicles . thank you Paul

[@spelunkerd]

This is a great demo, thank you. Checking any pump by measuring pressures is an imperfect gauge of how well the pump works. Just like a voltage drop test, the best way to decide if a pump is bad is to see what volume it can put out (analogous to current rather than voltage). It would be nice to have a volume output test to help decide if any pump (water, or fuel, etc) is up to spec.... Older methods would have you put the fuel line in a safe bucket and measure output over 10 seconds, ha ha.

[@ScannerDanner]

Wow thank you! Most of my formal training came from the school I now teach at, Rosedale Tech. My instructor (who is still with us) was Dan Svitko. To this day I am still thankful for what he did for me and the knowledge he shared. For taking this long haired over partied teenager with no direction in life under his wing and showing me how to make a life for myself. Of course I absolutely loved electrical and electronic systems from the get go. I am still fascinated by it!

[@nickeagle2580]

Very good, nice and detailed description of the fuel system.

[@keithyount3518]

Thank you for solving my problem because everything you showed was what I was doing.

[@Carlitosway211]

Then what was the problem?

[@michaelszczys8316]

Just posted on similar situation on other video. It brought me here. Going through this as I write, going for ground tests next as pump is brand new.

[@ScannerDanner]

yes, as well as with the timer tool. I have found it to be very accurate. I'll have to do a video on the transducer in the rail.

[@martinsmartinsautobodyandr6740]

thank you for your help brother . i checked fuel pressure and only had 30 cranking so i put the pump in and its good to go. thank you for your help brother

[@ScannerDanner]

Joel thanks for the comment. I don't mind the questioning though. I think it is a good way to expand on the topic. As long as we all stay polite and be respectful to each other, I say the more the questioning the better the learning

[@dalix1951]

Paul, thank you. Best fuel pump testing video I've seen so far.

[@darrellhodges1050]

I have a 97 GMC K1500 and you duplicated my exact issue. Swapped out the fuel pump, put on a new fuel filter and it fixed the problem. Thanks for posting these helpful videos.

[@ScannerDanner]

awesome! Thanks for watching!

[@redfury111]

Depending on the vehicle, it might be more work to cut a hole in the floor than to drop the tank anyway. It all depends on the tools you have available, such as a tall transmission jack and a helper. A full tank of gas is usually the only thing that makes it difficult short of stubborn tank straps.

[@Georg1979]

Great video, as always. Thank you Paul! And Happy New Year!

[@bp22307]

A neat tip I learned was to use fingernail polish to cover up the holes in wire insulation caused by direct piercing the wire. Some RTV's emit ammonia when curing. Thanks for the cool videos.

[@BBS_Robski]

well as a rule of thumb a fuel pump will have an in-rush current of around 12-17A to get it spinning from static, so if you got yourself a little library of current captures from static you would get a quick idea of the in-rush current of a good working circuit & spot quickly one that has a volt drop.

[@clintronicsrva]

my 2000 chevy s10 that I seldom drive, does the same thing, I thought it had a bad fuel pump but after putting it on the battery charger over night it started right up. This vid explains why perfectly.

[@clintronicsrva]

@@Junk_fishing101 just boost it 1 or 2 volts

[@jasonhull5712]

Man I love dan... so much knowledge, so humble.. great guy. True gear head.. 👨‍🔧

[@richardaragon9142]

Nothing wrong with a man loving another man especially a mechanic

[@jeremyshanks6937]

Great video Danner. Very good detail.

[@MrMattuwon]

Thank you my 01 blazer has a fuel issue cranks and after a bit it kicks like it will start then dies. This was very helpful.

[@redclift30]

Paul is just so inspiring it's sick. I am really thinking of moving to Pittsburgh to attend his school.

[@jamesdriver2985]

Sure wished I'd found your video earlier. My 350 is doing everything you are showing. I just purchased a fuel pressure guage and I'm getting same readings as you.

[@ScannerDanner]

Pinch the return line and check max psi. It is stays at 50, it's the pump, but check power and ground before dropping the tank. Also be sure to change the in-line fuel filter too!

[@rogermerritt6470]

Very informative video! I've got a cranky Suburban that has rough running after warmup. Had to replace the fuel pump and the fuel pressure regulator last year. Was supecting maybe timing issues since when i'm in driving and RPMs are between 1000 and 2000 I get an occasional motor shake. Will tak another look at the fuel pressure readings. Have been seeing 50 lbs of pressure. 5.7L Vortec 1999 Suburban.

[@dreamer2355]

Love your video! One of the best channels on KZbin period

[@Amopower]

That makes sense, it probably would be unlikely that all injectors are clogged at once (unless it's been 20+ years and none were ever cleaned), and so the clogged/faulty ones would show up on that transducer test.

[@ScannerDanner]

thanks man, you don't know how much grief I get over doing that. the alternative here would be to replace the pump and cross your fingers that you don't have a wiring problem. and that is on acceptable in my eyes.

[@henryrobinson9837]

yes indeed, i've seen a 1lb pressure below the min cause a no start on the old 4.3 with poppet valves,but they redesigned the replacements

[@ScannerDanner]

Last comment for the rest of you guys. If you have low or no fuel psi and you bypass a relay (like i did in this video) and now have good fuel pressure, you have a relay circuit problem. If your fuel psi is the same as when cranking or running then feel free to finish your power and ground tests with the relay bypassed. This will save your battery and starter motor in the case of a no start. Plus your friend doesn't need to crank the engine over & get pissed cause ur taking too long:-)

[@martinsmartinsautobodyandr6740]

ok cool , ill check it again tomorrow or friday and go from ther and get a fuel pump. thanks for all the help. i owe you for your help.

[@JoelAutomotiveInaction]

wow , what a quick response Thank you I was measuring on the fuse and on wiring diagram shows only one leg is share from same fuse to vcm only

[@ScannerDanner]

It is and in that case would be worth replacing the filter and retesting psi. Thanks for the compliment!

[@vron2891]

thank you so much i have the exact same symptoms on a car at work

[@TRcustomengineering]

Thanks again for another great video, I appreciate it a lot.

[@ScannerDanner]

If all the injectors are clogged, you are going to have some major running issues and severe lean misfiring which is easily identified using a scope and watching the secondary ignition waveforms. other than that, the timer tool is very reliable. you could also use a transducer in the fuel rail to ID

[@martinsmartinsautobodyandr6740]

i checked the video out. very helpful. if i am correct my fuel pressure is different but i am sure they all varry but i will recheck it tomorrow or friday and get back to you. but yea it starts on starting fluid and does the exact same thing as the 4.3 in your video. ill keep you updated on my progress. i remember saying when i was younger ill never mess with the newer cars and all that computer and diagnostic stuff but after working in repair shops i still find so many things that i learn every day . thanks for your help

[@ScannerDannerPremium]

Same system bro. I'm sure of it. It's only different in the injector designs. Same exact pressure specs

[@martinsmartinsautobodyandr6740]

OK thanks brother. I owe you for your help. What it is, I bought a 98 express 3500 work van for 400.00 last week and I am good at finding deals like that but I get the headache of figuring out the problem. Same with my 90 f150 and 2000 Durango. 500.00 each 2 years ago that I fixed and run strong today thank you

[@martinsmartinsautobodyandr6740]

OK thanks brother. I owe you for your help. What it is, I bought a 98 express 3500 work van for 400.00 last week and I am good at finding deals like that but I get the headache of figuring out the problem. Same with my 90 f150 and 2000 Durango. 500.00 each 2 years ago that I fixed and run strong today thank you

[@MrJgonzalez2]

The jumper wire is hooked to bat.neg and ran all the way to the back as close to the tank. It provides a known good ground for the multimeter to the two voltage tests, power and ground (while cranking).

[@abewiebe7356]

Thanks for the video was helpful

[@SteveRobReviews]

Fantastic Paul.Thanks!!

[@alekstolstoi]

I keep in mind, thanks scanner danner...

[@lutherbolton5338]

on s10 1994 v6 vortex got it fixed with what u showed me but it's kinda tuning little rich gonna put plugs wires on it going to take fuel pressure before I do that

[@ScannerDanner]

ahh, I see. That is a great tip! Thank you very much. I will add it to my "tool box"

[@JoelAutomotiveInaction]

to places where I am wondering fuel pump, but I will check it close to the pump as well I will do voltage drop thaks for your advise , other is i do not like ignition pattern firing line on snap other cylinders about 20kv firing line and spark line less than 3kv , misfiring cylinder firing line 40kv and firing line at 12kv with normal burn time in your experience will this mean rich i am thinking as the injector poppet does not close and keep spraying, Thank you for your knowledge and your tim

[@DeMacChannel]

dang i was bout to go do what i said n then i c this video. and thats what bn doing to get to work last few days until i do everything you bn helping me with. you say its unusual but thankfully so lol i carry the quick start carburetor or air intakes starter thing and it lasts was doing the three seconds spray as to before it would just turn off in the middle of somewhere like a red light anyways I'm still going to do all that today since I have the day off and I worked at night anyway. I'll let you know thank you

[@uriel0002]

Very professional.

[@GRUSSNewton]

Great video Paul! Would you recommend using a scope for ground to ground voltage drop measurements rather than a DMM or graphing meter? I've just picked up a snap on vantage pro . Great for quick tests and jobs rather than setting the pico all up...

[@stevensapyak7971]

Paul where did you get your training in electrical theory ? I was trained as a industrial elect/instrumentation tech so I have a deep understanding on power and electronics . You are in the upper one tenth of one percent of techs! You are a natural instructor!!! Best videos on the tube!

[@ScannerDanner]

thanks man. i was feeling a little crappy until now :-)

[@cpon777]

This is cool. Very intresting

[@lutherbolton5338]

best videos ever show how to 1video

[@ScannerDanner]

That is exactly correct my friend.

[@hddm3]

i wish all tech teachers were this smart an had the pasion he has. i would be a tech vs hvacr tech.

[@juanjolivares3291]

How often do you do a volume test for a fuel pump? Would u consider it a most when checking the fuel pressure because I know pressure may be good but volume might show otherwise. Thanks love your videos

[@MrJgonzalez2]

I'm not questioning your methods, neither that the relay was at fault. When you activate the fuel pump and read battery voltage at the pump that only tells u that that wire is intact.Leaves out the rest of the relay circuit at question.I understand what u did, you saved yourself time with that test, I personally would have cranked it.

[@gvvq-pi5ml]

Hi Paul, never seen this before, great video, i have had a Bosch K Jetonic car that done simlar, but they have virtually no electrics on the fuel system, the injectors or purely opened by fuel pressure, i think they run around 50 or 70 pounds psi, i cant remember quite what it was but lot higher than electronic type...from Fred in England.

[@joellevine940]

TKS FOR YOU HELP

[@haddenvladamiriii7137]

Hi ....I purchased a used 1999 Chevrolet Astro van 4.3L V6 Vortex Motor I replaced the fuel pump fuel filter all relays coil distributor cap and rotor but my issue remains crank no start ....I'll be replacing all spark plugs wires pick up coil soon....as well as ignition module....but was wondering if you can suggest something I am over looking because I'm not getting any spark to the pump in order to get pressure....55psi.....also had an issue with passive key needed to do a key reprogram 10 minute intervals total of 3 = 30 minutes including 5 second off intervals total of 3 = 15 second intervals it cranked and ran for a solid 4 minutes then shut off ....keep having a weak battery issue....

[@MrJgonzalez2]

The ground scenario was only a suggestion, by the way what is the "low side and high voltage side"? I believe it is called "control" and "load" side of a relay.

[@zappa916]

does this car have an initial fuel priming circuit and while not the underlying cause of the no start, could have contributed to identifying the bad fuel pump? i had the exact same symptoms on my car and found out as soon as the fuel pump control module thats responsible for the priming packed in i had the no start condition. If left overnight and the fuel rail emptied back into the tank, then a no start. Throughout the day it was fine. Turned out to be a bad pump and FPCM in the end.

[@jonathanmclaury8480]

How much current should the fuel pump be pulling? I heard 7.5-10amps for the Vortec engines/pumps. Mine is pulling only 4.5amps while running. Only getting 41-50psi. Drives, but has a periodic studder while driving at constant speed and seems like it is running lean at the upper RPMs. Maybe the system has a bad ground? Things replaced so far, Cap/Rotor, Wires, Plugs, Fuel Pump, Fuel Filter, Spider Injection+Regulator, Fuel Pump Relay.

[@ScannerDanner]

i guess i would but i need some type of baseline. what should i look for? how accurate would it be and what are the variables? thanks!

[@prospexican]

Great thank a lot. Im a auto tech but wasn’t sure if 45 psi was enough.

[@JoelAutomotiveInaction]

thank you,I was reading your book under common secondary failures o and watching your video for pattern to see if injector is stock closed lean, any way I sent you to your e-mail a shop stream capture from verus if you have a time to see that I will appreciate your answer to get direction what could cause that burn line to be too high

[@Symbol84]

CSFI system used in that 4.3L 96+ Vortec

[@BSMOODHA]

Good idea adding an external battery charger to keep the cranking VDC up...

[@BBS_Robski]

that's right, but if the in-rush currents good you know the circuits good & it's more likely the pump, it can be a good preliminary observation point.

[@sanjuan780]

As usual your videos are unmatched down to the minute details, which is everything. As you know what might be obvious to one person may be a complete mystery to another, thanks for recognizing that. One question though, what size fuse do you suggest for jumping the fuel pump?

[@ScannerDanner]

a 20 amp fuse will be fine my friend. Thank you!

[@hajrudinkavazovic2231]

4.3 l on this engine is from low to high 55psi /60/to 62 in perfect start up and running conditions thanks Mr.DS

[@BBS_Robski]

Paul, do you use the 'in-rush' current at all in diagnosis of pumps/motors ? It can give an idea of volt drop or not ..............

[@JoelAutomotiveInaction]

part 2 @ mr Danner, how ever the humps are there normal and pump speed is about 6,500 rpm and fuel pressure at idle stable 52 psi and wot snap 62 all the time, my question how can be amps so low and pressure be ok, CPI system, I already replace cap, rotor,wires and plugs oem, I checked current ramp on injectors and are ok, when doing secundary ignition test I see some weird activity on cylinder 5 the spark line goes higher and the burn line start at 1 kv while on other cyl at 2.8kv thk any

[@ginoc2576]

question about RTV after a pierce. wouldn't it absorb moisture? I know it prob wouldn't affect where you live but whats your take on RTV after a pierce? thanks

[@retroguitarmaster]

Hi Paul, I have a 89 toyota mr2 non supercharged and someone poured dish soap in the fuel tank, I took out all the contaminated gas and put new one in but it seems like the pump is not working right and it stalls under load (when in gear) and sometimes on idle. I checked amperage through the diagnostic port with a Vantage MT2400 (jumped two wires) with KOEO and only has 3.44 amps running through, is this a bad pump? Should I get an amp clamp and try KOER?

[@hddm3]

dannner is awsome if i had more money i would fly in an go to danner school. guy is great man if i was a teen again

[@brakedd]

was the 50psi to open the poppets the same across the board with the other vortec motors? 4.8, 5.3, etc etc basically anything that uses spider injectors, correct?

[@JoelAutomotiveInaction]

Mr danner in my area we have no good trainers teachers so, diagnostic techniques I have learn are from your book, video lecture and your you tube videos. how ever I have 00 chevy express 5.7 8 cyl, misfire cylinder 5 only under load ,I did fuel pressure test and current to pump dual channel on verus and pressure tranducer, but I am confused on all current to fp I have checked before I have seen amperage above 8 amps but on this while priming is about 7 amps ,cranking about 4 and running 0amp

[@williamanton295]

great teacher

[@ScannerDanner]

you got it my friend

[@AutoTechHector]

Mr Danner,i think i have a stupid question...to what ports did you hook up your leads when doing the amperage test?

[@Amopower]

Do you have any videos of testing to see whether the injectors need cleaned? I wasnt sure if there was a test for that, and if you covered it already. I know you have the one where you use the fuel pump pulse tool but that is just a relative test, so if all your injectors are equally clogged that test wouldnt catch it.

[@chalinoahuesoduro5566]

Im having the same issue on a 99 tahoe 5.7 csi. Exact same situation. Only thing is that in the last 3 years this woukd be the 3rd pump being replaced counting the initial pump replaced. Replaced filters both times. Replaced connector once. Pressure holds for atleast 20 minutes at 50 n it will start with fluid after that it will start all day till next morning relay doesn't show signs of overheating burning. My question is what could cause pump to keep going out so frquently? Its a common issue as ive seen on the net. Customer was initially advised to not let tank go below 1/4. But still

[@user-qz6tc2co2g]

These have a vacuum fuel regulator that raises psi when vacuum decreases. Maybe that's why it stayed running also?

[@ScannerDanner]

Thanks man.

[@MrDeterministicchaos]

So if I have a new fuel pump and bad fuel line somewhere maybe cavitating will this same thing happen

[@rudimaier3679]

Hi! Why you never check the amps in line with a multimeter what mostly go up to 10 amps?

[@EzRepairs]

hi danner, my 01 4.3l blazers fuel reads 30psi cold and 40-45 psi after a good warm up. car iss running lean, i will use another fuel gauge to recheck pressure and check power and ground like you did on the video, any comments on why running with such low pressure. i will post the results. thanks.

[@cujo1975]

does a 1998 olds bravada have a wire to check the fuel pump, if it does where would it be. my truck just cranks but if i put starter fluid in it turns over then shuts down. spark is good and the fuse n relay r good. shows no pressure when i put the gauge on it. also no fuel comes out the schrader valve. n i don't hear the pump activate when i turn the key

[@erikturner5073]

I've had problems where the fuel pressure regulator inside the intake bleeding off pressure and produce the same symptoms.

[@ScannerDanner]

You're allowed to question me, I make mistakes too. And you would not have been wrong in your approach. I chose this method because it allowed me to measure pump current from under the hood. If pump current measured good with low psi I would have skipped the power and ground test. That was the main point. Also when checking power and ground here in the rust belt by the time you ID the correct wires to test and find a good ground you overheated the starter and killed the battery

[@jacklight7628]

I've got a 94 s10 4.3 vortec with the same problem it getting gas I checked the injecter to makes sure and it's getting fire in all 6. Ive replaced the fuel pump 7 months ago it shouldn't be out yet but I guess weirder things have happened?

[@adamdynasty6525]

Do you connect the meter in series or in parallel?

[@ScannerDanner]

How are you going to use that jumper wire in this case? You cannot get to the pump connector without lowering the gas tank?

[@ScannerDanner]

it is not necessary my friend. whatever your preference. i like a graphing multimeter myself

[@serchmarc]

yes im waiting too. why are you gonna dislike this one?

[@JoelAutomotiveInaction]

where did you get the adapters for the propane?

[@martinsmartinsautobodyandr6740]

hey brother , i didnt forget to get back to you we just had rain here so today was clear so i checked the fuel pressure and was only 30 cranking but i ordered a fuel pump and i put it in today and im good to go and thank you for your help i have another car that bugs me so ill explain in my next comment

[@xxl_mccoy5440]

Oo is my by

[@PAMAROSHOUSE]

I a d issues with my 2000 Sonoma no start. issues.testd fuel relay was good, checked my ecm fuses all good, checked all fuses just for giggle all good, checked hot wire to pump , good, but the ground was shot, regrounded pump and started right away.

[@danpettis1675]

nice video. but started to glaze over when you broke out the fancy scan tool hahahaha

[@ScannerDanner]

sorry man. I'm a professional mechanic and instructor for the past 17 years. Don't get scared off by the fancy tools. A lot of what I do can be done using less expensive equipment.

[@hankyhates]

When I turn to Key to the on position with the tester hooked up it will jump to 60 and the drop pretty quickly. The truck has been taking a long time to start would this cause this ? Is it normal for it to drop like that.

[@rupertoecruz]

Is high current draw from a fuel pump ,when you have low pressure at the rail,a good sign of a restricted fuel filter . P.S . Paul I just have to say I have learned more from your videos than I did in the school I attended.Not that the school was bad ,just overcrowded.This delivery method you use to teach (video) gives us the ability to absorb the information much more efficiently.

[@floydmurphyable]

My fuel pump is making a loud rumbling noise...car been sitting for 7 years...and now it won't keep running....could my fuel pump be bad?