GM Fuel Pump Relay Testing
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- Опубликовано: 1 окт 2024
- The vehicle being tested is a 1999 Chevy Suburban with no fuel pressure. This truck had a new fuel pump installed and still did not have fuel pressure. In this video I will show you how to troubleshoot this entire fuel pump electrical system, including the fuel pump relay, wiring and computer.
Engine Performance Diagnostics chapter 3 page 26
Symptoms
- no start with good spark
- no fuel pressure
- no trouble codes
Fix
- repair wiring to the fuel (new pump was wired backwards
Tests shown
- how to test a fuel pump relay in a power distribution box.
- power side switched circuit design description and operation.
- Fuel pump power and ground testing.
- how to manually jump a fuel pump from the fuse box
- how to test a fuel pump relay
- relay pins (what each one does and how to test them)
- how to verify computer control of the fuel pump relay
- bias voltage (what is it, how to use it, how it can cause misdiagnosis when using a voltmeter)
- wiring diagram review of a fuel pump relay circuit in my classroom (a ScannerDanner premium segment)
- how to measure fuel pump current
- what sets a fuel pump relay control trouble code
Tools used
- ATD Tools 5519 Auto Ranging Digital Multimeter
www.jbtoolsale...
- incandescent test light www.jbtoolsale...
- backprobing pins AES' Electronics Accupuncture Probes www.aeswave.com...
Playlist
- (Chapters 14, 15,16) Fuel Delivery and Fuel Pressure Testing
• (Chapters 14, 15,16) F...
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- Fuel Pump Electrical Circuits Description and Operation
• Fuel Pump Electrical C...
- Fuel Pump Relay Problem
• Fuel Pump Relay Problem
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• How to test and fix a ...
- How to test an electric fuel pump (1997 4.3L Chevy Blazer CPI)
• Fuel psi less than 50 ...
- Fuel pump electrical circuit diagnosis (no fuel pressure testing) GM
• Fuel pump electrical c...
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.
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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.
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You answered my question before I could ask and yes I'm subscribed to SD prienun . Learning your insight and methods I was instantly going to say, would it light a 2 ohm bulb if you found 12v on an unkugged sensor. No it would not. Anyone watching Paul's free vids, do yourself a favor and subscribe. He's just teasing you with the free ones and giving you insight. The forum is amazing, the new video player is awesome and Paul does respond to any questions . Best money I spend every month even though I've completed the course. Always something new and always there for a refresher. Oh and keep his book In your toolbox!
Thank you so much for this comment my friend and for your long time support
The Oil pressure sensor is also a source of power for the fuel pump, while the engine is running. This is done to keep you going in case of a fuel pump relay failure, once you turn the engine off, no oil pressure, no power to the fuel pump from that source!
If theres an issue with the fuel pump like maybe a short is there the possibility of the oil pressure gauge reading near max? Ive heard that extra “symptom “ with a fuel pump problem
Curious at this point if that union would shut off the fuel pump if the ecm read no oil pressure coming from the oil pressure sensor. Thinking im gonna test that theory. Pull the oil pressure sensor and ground on engine and plug the hole. See if vehicle runs
@@pitchforkpeasant6219how did it go? I’m having the same issue
How do I trigger fuel pump
Of course you know I am going to say yes. But I think you will find that after you have it you will want to buy a scope simply because of how accurate you can be with one. I do teach other methods of testing (DMM, test lights, Scanner etc.) IT is not all scope stuff and you certainly don't need a Verus to do what I am doing. I think you will agree though that alot of the stuff I am doing you couldn't do without a scope.
After starting your course I figured save up for a picoscipe which I would love. You explain a scope in so much detail that I went with a Hantek and uscope. I figure use the things while I save and I'm glad I did . The experience is the most important part!
At 12.40 you say pin 86. I think you mean pin 85. I am working on this same fuse box. Pin 30 melted, so someone wired in an external relay. I have no voltage at pin 85. I do have signal when cranking. The pump is always running when relay is plugged in. That says 30 and 87 are wired so the relay leaves this thing running.
sinking or open collector transistor. Used widely in industrial control, jumped the fence at GM and invaded our cars when computers became standard. Coil load tells the computer there is a load there. When the transistor is told to turn on by the computer it SINKS to ground and loads up passing voltage! The test light acts as he said just as the relay coil would. 42 years of electrical and the last 16 in training others one of the best descriptions of sinking and open collector I ever saw. Awesome!
+John Goodman thanks for the comment! Feel free to keep going! I've never heard the terms "sinking or open collector". I only know this from a mechanic standpoint. If I could clone myself, I would go back to school for electronic engineering. Love hearing from guys like you
GREAT VIDEO.....THANK YOU FOR THE VERY COMPREHENTIONAL BREAKDOWN OF INSTRUCTIONS AS WELL AS THE BREAKDOWN IN PHASES IN TROUBLESHOOTING.....MOST OF ALL ...THANK YOUY SO MUCH FOR NOT PAUSING IN THE MIDDLE OF EVERY SENTENCE TO GO.."uh, uh?"...LIKE MOST OF THESE WANNA BE AUTOMOTIVE VIDEO GURUS USUALLY DO,,,,CAUSE ITS ACTUALLY MAKES THE VIDEO TWICE AS LONG......YOU GOT DOWN TO IT AND GOT RIGHT THROUGH IT!....IMPRESSIVE! ONCE AGAIN...THANX.
I've gotten better since 2012 in filming and editing but thank you so much!
In the beginning was the Word, and the Word was with God, and the Word was God - All the Glory to JESUS CHRIST. May God save you !
Exactly who needs to be saved and what do they need to be saved from ?
I'm having trouble with my fuel pump on my 2002 chevy Silverado 2500HD the fuse is good the relay is good im not going any power going to the fuel pump itself...test light was used on the lines going to the pump but not lighting up...please help me
Hey I know this is a super old post you have but did you ever get it figured out cuz I'm having the exact same problem
Poor guy had no business rewiring the pump. We have a saying in the Electrical trade that comes to mind. It goes like this: "1 wire hook up, 2 wire f*** up, 3 wire drag up!" Awesome job Scanner Danner.
I'm not sure you can bypass this type of system without some type of add-on electronic unit. They use a resistor that is built into a hall-effect switch that is part of the lock cylinder. The re-learn on these was to simply leave the key on for 10 minutes (until the security light stops flashing) and possibly repeat the procedure.
I'm hoping that will fix my problem on my 1999 Chevy Suburban. Everything worked fine until I pulled the trouble codes with my scanner and cleared them. Now the fuel pump won't kick in and I followed your video to the T. This is exactly what is happening. I'm hoping the 10 minute relearn will work. Thank you for the great video.
Great job on describing the bias voltage! You took something that could be extremely confusing and made it fairly simple.
Thank you!
Mr Danner.. Thank You . Working on my first fuel injected GM product. How about a video why the engineers .?.They must be Suffering from a mental health issue to not put in there design a metal panel that can be removed topside to remove an repace the fuel pump.Instead of dropping fuel tanks.
Paul, I've immersed myself in *your videos cam/crank sensors, Hall effect pull up/dn testing, mostly in troubleshooting an 01 I30 no start for weeks and you've impressed me to no end. But **this lesson here has inspired me so much so that I *had to write to commend you on your style, brilliance, tenacity and skill! Even more thank you for your technique in imparting knowledge to the layman now so rarely found I'm sure. I'm an FAA Certificated Airframe & Powerplant Mechanic since 16 years old (63 now,) Commercial Pilot and Instructor since 1974 and tow truck driver shade tree automotive wrench too, admittedly **not even close to your realm - Learjets vs. Maserati = two different beasts. But where does one start explaining your passion? Brilliant teaching technique? Abundant resource of the mind? Vast stores of vital bits of info that just... I mean... and you produce smooth relevant attractive media seeming to come from out of nowhere like this: Pwd Side Circ Bias Vltg and backprobing IR drop right **there in the trenches with simple test light and VOM!!!??? And for free???!! I mean you are so cool - meticulous white board drawings, manuals books, well I just wanted to say thank you for being so kind to us out here. Your students I hope will be touching my vehicles out here and you've restored my confidence raising my opinion of auto wrenches in general. I hope they appreciate your stern yet friendly demeanor, temperance, ethical mentorship and carry your legacy paying it forward and so on for quite some time. There will never be another sage like you, and at such a young age. Amazing. Thank you! Paul The Pilot, San Diego
The effort you put in to this video and your teaching skills are amazing. Thank you very much for doing this.
You know bud there can be to top lefts etc. Who's view? Where you standing? A fukd mess off the git.
thank you so much! what a great comment. this bias voltage is cool when you know how to use it. it is a major time saver for troubleshooting wiring problems for sure. nice to know that you appreciate the material
I have a LED test light and it lights up for the 2 second prime but it stays kind of lit when the prime is done. is that an issue or is it because it is an LED?
It is because of the LED light and the low voltage bias line making it glow. An incandescent light would not do that
I Couldn't Believe It When I Saw The Wiring... I FELL ON THE FLOOR LAUGHING!!! 🤣🤣🤣🤣🤣😂😂😂😂🤣🤣🤣😂😂😂😂🤣🤣🤣🤣😂😂😂😂😂😂😂😂 WTF!!!! 🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣😆😆😆😆😅😅😅😅😅😂😂😂😂😂😂😂😂😂😂😂😂😂😂
@Bonfield2002 Did the bias voltage part make sense? Was it clear enough? It was certainly difficult to explain.
This is what real troubleshooting looks like! Great job!
you need to find out what you are missing when it doesn't restart. spark or fuel
Hi Scanner Danner, great video! I learned a lot, thank you. I have a 1997 C2500 5.7, (bought new, cared for, now has 229,000 miles and looks a drives like new) and I'm curious about amperage. I'm drawing between 9 and 10 amps. I used my Fluke 337 clamp on amp meter on the wire to pin 30. The reason for all of this is the 30 pin got so hot it cooked the surrounding plastic. I repaired everything and now for the first time, I'm checking for heat and finding some after a 10 minute drive. 30 and 87 are hot to the touch. Is this normal, or could this be a sign my pump is going out? I'm on my third pump. First one died of low pressure. Second one didn't work after a six hour drive. I appreciate your help.
I have seen a jump start do the trick. I have another video on this system where I show the tests you need to do. Search "fuel pressure" or GM cpi
Your lucky you didn't smoke the computer. As you know, be super cautious with this kind of test.
@contagiousFX The pump circuit was wired backwards so this just causes the electric motor to spin in reverse. This caused a low amperage no psi condition. The other two wires were computer sensor wires that do not carry any measurable amount of current and would just cause full to be empty and empty to be full on the gauge. Funny thing is half tank would have been accurate.
Great example of why when diagnosing an electrical issue a test light and a meter should be used when trouble shooting.
Thanks for the video,very informative!
thank you very much! I never liked the corny music that was played in training videos. If I ever start doing that...shoot me. :-)
Who is this guy!? Great instructor and definitely a passionate person. Thanks Scanner Dan, you saved me some money on my diagnostic and I learned something really cool.
Thanks so much! My name is Paul Danner and I am an instructor at Rosedale Technical College in Pittsburgh PA
ScannerDanner help please
I cut one relay open and made it into a manual push button to 86 and 85 with a micro switch for testing
So what happens when I have no bias power on this circuit, crank no start, no fuel pump?
can you define very weak? test light or voltmeter?
If you jump the load side contacts of the relay will the truck run? (jump 30 and 87 and DON'T jump 85 and 86)
HEY PAUL, YESTERDAY I HAD A CHEVY TRUCK WITH NO FUEL PRESSURE, THE CUSTOMER HAD REPLACED THE PUMP HIMSELF 3 TIMES AND DECIDED TO BRING IT TO THE SHOP, THE PUMP PRIME AND RAN BUT NO PRESSURE, AFTER DOING ALL MY CHECKS,,,,, IT WAS A PUMP MADE IN CHINA , I NOTICED THE PUMP MOTOR HAD REVERSE POLARITY NOTHING THE CUSTOMER DID, THIS IS THE SECOND TIME I SEEN PARTS FROM CHINA WITH REVERSE POLARITY, BE AWARE OF PUMPS MADE IN CHINA!!!!!
2004 GMC Savana 3500 cutaway, with a 15' box. No start, no pressure. Was able to jump the correct pins (you explained very well) and send constant power to the pump to investigate further. Found out to be a bad connection w/ the connector at the pump. Would have never stumbled across it without your information. Was sending it to the shop tomorrow....Great work and fantastic information!
great video I have messed that up a bunch of times test light is only way to check them I finally bought tge Lesley relay extentions do all my testing with them very handy
Connect your light to pin 85, turn the key off and wait 5 seconds or so, then turn the key back on (don't crank it). Let me know if the light, lights up for a second or two.
I very much appreciate this video! Although it wasn't the issue I was experiencing at the time (fuel pump working intermittently), it did get my brain gears in motion. I had removed the bed to change rear cab corners, and had just loosely placed the ground bolt back in place, that just happened to ground the bed lights AND the fuel pump. After finding no continuity between the pump lead ground and the frame, the a-ha moment smacked me like a freight train. A very good feeling freight train :) Subbed, and thanks for the content!
awesome and great find by you, good job and thanks for the sub!
I also was thinking I should check for voltage when the car is off as well
See of it starts when you spray carb clean in the intake, if it does then it could be the pump.if it doesn't then check it for spark next.
hello ok so when you spray starter fluid in intake and test start ive seen you need to remove relay first! is this so??
For sure, but I was getting third hand info. on this one. I never talked to the owner, just the owners friend who dropped it off at the school. Not sure what that guys was thinking:)
Thanks for the detailed video. I have a more serious problem that maybe you could help with? When testing for power at the fuse box as you did, I have zero power/volts. Where does my problem lye? Is my ECU Shot?
check the power and ground at the pump while cranking and give me your voltage readings.
Having similar issues, but when I did the bridge I have fuel pressure, but when the relay is plugged in "brand new" it doesn't give the system the prime it needs to start, any answers?
with the key on, tell me what your voltage is on your TPS or MAP sensor, one of them should be reading 5v and if it is not, we then have some direction
Scanner Danner is awesome!
+Michael Hart thanks Michael, I'm really not, I just enjoy what I do.
I have a 99 Ford contour I'm trying to see if fuel pump bad the car stalls every now and again won't start right away the first like 3 tries but eventually it does it starts right up .now when heats on I'm smelling burnt rubber coming through the vent .lately the car has stalled it has like pushed a little like pulling me .is this My fuel pump and how much do u think it will cost to replace opinions please???!!!
@@ScannerDanner help got the same problem 4 mecanic and no luck do you have a shop in Texas
It is called a smartboard.
If you want to learn more about what I am doing you should get me eBook. Go to my channel page for the website listing, or it is embedded in all of my videos. (Auto Computers Troubleshooting)
yes, this is exactly why I do not like LED test lights.
bypassing the fuel pump relay with a old wire I accidentally shorted the wrong pin and the 20 amp (ECM B) fuse blew, I replaced the fuse but now it turns over but no spark ??
year, make, model and engine please
@@ScannerDanner 1997 Chevy K 1500 regular cab, 5.7L 4X4
Looks similar to my 96 Silverado K2500. How did they not notice the wrong colors on those wires were connected together? Why didn't they just tell you that somebody attempted to replace the fuel pump beforehand? Those wires should have been shrink tubed and soldered.
+Rod Palm I think one of his enemies snuk in his driveway in the middle of the night for some rewiring fun?
LOL yeah that's what happened T Bear!
Hey Danner I have the 97 chevy express I replaced the pump hooked wires up correctly pump wasn't coming on so I got under the vehicle with a tester light hooked it up to a ground and the grey wire and pump ran I turned the van off let it sit and cranked it again now it comes on with no problems any ideas whats causing this
do you have a voltmeter? I can help if you do and can follow some directions
Great video. I like the comment on the lean pop through the intake at snap throttle. I have been using these videos to troubleshoot electric fuel pumps measuring current and the armature waveforms. These videos have been very useful. Thanks.
Awesome!!!!! I have been in the automotive repair industry since 1983 as a tech and as an instructor, you did a very good explanation of the bias voltage.
Thank you John!
ScannerDanner
ScannerDanner
Thabk you Idaho
I h axes ve been working with this shocks since 2008 or 9
@roro560v8 Cool man thanks!
On the wiring, I'm not sure what that guy was thinking.
you should have two power feeds during cranking and one power feed with the key on.
tell me what you have.
If it is a GM there should be an orange wire which is the key on power (load side of the relay)and a green/white wire which is the cranking/running power (control side of the relay)
What if I have only have constant power and no second power when cranking on the relay. Fuel pump is working but computer is not sending signal to the injectors. Brand new tank, pump, injectors and filter. Started and ran with tank hanging. Bolted tank up in and now won't start.
I have fuel up to the throttle body but to not thru injectors
@@matthewgettman8766 need more info than this to help. Year, make, model, engine, when the problem started, and if you have spark or not, also what trouble codes if any?
its not a shop. i teach at a technical school for auto mechanics. Rosedale Technical Institute
Many of the GM's had a red wire (usually located in the proximity of the fuel line quick connectors) that connects to the normally closed contact of the fuel pump relay that can be used to power the fuel pump directly, with key off engine not running. Known as the fuel pump priming connector. Handy for pumping skankey fuel out of the tank, testing the fuel pump itself, etc.
Fantastic troubleshooting! I’m pretty sure It’s going to fix my problem where the previous owner bypassed the relay to make a pump run continuously Instead of diagnosing
Do some voltage tests at the tank wiring and report back your findings
@5am8011 I don't work on to many of the German cars although I have had my share. For some reason the Germans like to hide their information from us aftermarket guys. If I had to pick my least favorite cars to work on (due to lack of good information) it would be the German market. I suppose if I had a factory scan tool and factory information it would be a different story.
Your a good teacher,you get off teaching,if one would listen to your video 10 times it would just click just like that little piece of plastic your working on when you turn on the key a flow of electric current reaches
Transistor and it clicks, sending that current in a controlled flo To open the pump which pumps
Fuel to whatever system
You have.
The one who changed the pump pretty sure was a hell of a mechanic 😂😂😂😂😂😂
I am sorry you feel this way. There is one thing I need to clarify and I should have but didn't in the video. We placed our t-pins between the terminal and the plastic housing NOT in the female part of the terminal. As for the wires that were damaged under the vehicle, they were like that when we got it. I understand you not liking piercing a wire to do a test but sometimes it is necessary. Hopefully you will give me another chance to see that I am not a hack. Either way, Have a great day.
this may be your problem. remember the relay can work (click) but still not provide power to the pump if there is a problem with the load side switch contact or relay pin contact problem. The burned pin in the PD box suggests poor contact with the relay pins. This would be unwanted resistance in an unwanted location which equals HEAT. This will cause loss of power to the pump.
The gray wire is the pump feed wire and you will not have power on this wire unless the relay is energized. Is the control side of the relay functional? Do you hear it click?
The control side of this relay is power side switched my the PCM. Do you have two power feeds during a crank to this relay?
No! Absolutely do not do that. Just a simple fuel.psi test would be next step to be sure. You can buy a gauge for your truck for less than $20
Yes, the next thing would be to check for spark and injector pulse and tell me what you are missing.
The PCM needs an RPM input to power this circuit cranking but that doesn't answer our no power during the key on cycle. You know this power will only be there for 1-2 seconds right? So if no power for sure then we need to go toward the PCM powers and grounds next.
With the key on see if you have a 5v ref. on one of the TPS wires. This can answer a lot of questions for me.
Thanks Danner for sharing your expertize. I've been looking very hard for clear instructions on by-passing the security fuel shut off on 2000 Chevy Blazer Passlock. This year doesn't have the resistor on the key like most youtube videos on the subject. You're the ideal person to do such youtube demo if possible. I Changed the body control module and needs re-learn and programming. Would a by-pass still work without a relearn or the vehicle has to be in running condition? Dan's the Man!
you saved my butt showing bias voltage . I was making check on my 1998 5.7 vortec and showed 12.24 v. this was messing with my head and i was thing something else was wrong.... I had watch someone else on this relay and they said no voltage on that pin with key off.....thanks so much.
Nice! So many people have no clue it is even there.
My bet is the distributor cap is crossfiring inside. common problem on this truck.
Fuel psi should be over 60 psi cranking and around 54-55 at idle.
57 at idle is fine, 57 at WOT or cranking is not. So when was it 57?
Yes, your fuel psi is to low during cranking. This system needs to be higher than 50 psi to start. Spec is at least 60 during a crank. When the fuel pump gets weak on this design system, this is the exact symptom. The weak pump with only 10-11 volts (system voltage during a crank) cannot produce enough psi, but with 14 volts (running voltage) it can.
Thank you! Be sure to keep an eye on your spam folder after your purchase.
I took 3 years of automotive classes in high school. I now sit in front of a monitor 10 hours a
day for a living but never lost my love in fixing cars. This one of the best or the best instructional
video on one topic. It's direct and no nonsense instructions and disruptive background music.
Excellent continuing education program.
for sure and the heat you felt was from a resistance problem. a melted connector would be next if you didn't correct the issue.
Because the amperage was very low (around 2 amps), a plugged filter causing no fuel pressure at all would have caused very high amps. Also from my experience if you have a fuel filter that is plugged so bad as to cause a 0 fuel pressure reading, that filter has already ruined the fuel pump. So you put a pump and filter in it. Of course you could always replace the filter and re-test if you desire.
Great Vid. Any suggestions on what to do when the computer control side on the relay Pin 87 isn't sending power?
@5am8011 85 was a switched feed for the coil, 86 was coil ground (constant). I agree about pin 87 and 30 being mixed up, but it was clearly marked 87 on the relay and it was hot all the time (load side feed). Maybe the relay was marked wrong because the diagram shows pin 30 being hot all the time and pin 87 being the N.O. contact and 87a being the N.C. contact. Either way I have seen 4 pin relays wired like that, but the 5 pin shouldn't be, so I think the relay was marked wrong.
This is why I have Scanner Danner premium on his website. Even if he never makes another video, how can u thank him for the humongous library chocked full of instructional material. I have watched this video several times. But now I have an 01 GMC 4.8 in the shop. And that bias voltage will help me identify control pins. GM relays will plug in both ways and that throws me off. Thank u Paul!!
Bill Rimmer
Even if they plug in both ways it's still the same in the box. ...
So it wasn't starting because someone was colorblind
😂 pretty much
when you jump the relay the 30 has current going to it and the 87 is being grounded?
If there is a return line, pinch it off and check pump max psi next. (should be near 100) Then if it stays at 50, check your power and ground.
Most likely it is from a weak pump. Watch my other videos on GM CPI systems. I describe in more detail why this happens on your system with the mechanical poppet nozzels.
ScannerDanner, thanks for a GREAT video! I appreciate the detailed explanations and diagrams. I work in the medical device field as an Electronic Tech and I've been doing my own auto electrical for 3+ decades, but I still learn new things from your videos that have puzzled me. Looking forward to getting your book.
Thanks so much!
LOL! agreed
I've always checked for voltage and ground closest to the fuel pump with out removing the tank, amp gauge or probe. Then work towards relay and ecm. jmo.
i did this test im getting three grounds one hot why
yes, do what you said you haven't done yet. Check your power and ground at the pump with the relay jumped.
@5am8011 Hey Sam, I have seen some cars have no prime with the key on and only run when the PCM is receiving a crank signal. I think older Chrysler TBIs were like that but I'm not sure. I know older Toyota with the 7-pin Vane Airflow Meter did not have a prime with key on. FP on those only ran during a crank or with VAF air door open.
I like that idea. they also sell relay testing adapters that come in a kit that I have my eye on
I have 5 volts on both TBI and Map sensor.
Danner, You just made my day with that biased voltage explanation. Awhile ago i was working on a relay circuit and my voltmeter "found" this and it threw me for hours. Nobody
I talked to ever had an answer. Like a Christmas present LOL Thanks. Hope Santa brings you one of those Lisle relay test jumper kits. The dink that stabbed, cut and miss wired that pump should get coal.
When it doesn't start you need to check your fuel psi. It is possible to have an intermittent problem with the fuel pump motor itself. That is most likely your problem based on your symptoms.
Wow. How the hell did they mix it up?!
Great video Paul!
In the premium channels you mentioned that it's safer to energize the relay with a test light instead of jumping the pump power. How is it done?
you can't easily when the relay is mounted in a fuse box
I have a 1997 Buick Lesabre & my car started and cut right back off after a few seconds & i also rolled down my back windows. When i tried to crank it back up it wouldnt. My car windows wouldnt roll back up & my fuel pump would not cut back when i turned the key. I checked all the fuses & they are good. Checked the relays with the hand test & they seem to be ok. I cant figure out what the problem is. This is the 3rd time that this has happened. Usually after i let the car sit for a while & try to crank it, it cranks right up, but now it wont. PLEASE HELP
Post your question to my forum please.
www.scannerdanner.com/forum#/
Thanks!
@foxholewilly haha I know right? What was this guys thinking? I like the touchdown off of someone elses fumble analogy. That is just completely dead on accurate.
High praise for this video! Danner is thorough and provides all the necessary background to understand what's going on. Great diagnostic technique. Very professional! Thanks.
My 1999 Chevy Tahoe won't start. When I test the fuel pressure it's only putting out about 55 PSI and sometimes it jumps down to 40 PSI. I've heard that these trucks need at least 60 PSI for the fuel to open the poppit vales. Is this true. Will they not run with pressure under 60 PSI?
Should be 60 during a crank and less than 50 it will not start.
I am directing all help requests to my forum. Sign up (it's free) and create a new post. Be sure to add a name under "alias" as this is the name that will appear in the post.
Here is the link to the forum.
www.scannerdanner.com/ForumRetrieve.aspx?ForumID=3226
thanks very much, and pin 87(top right) is the melted one ,more info as i get it
I found this video In hopes of learning what all the pins of the relay are for. I already jumped the relay and got the pump going, but the truck stopped running after a few moments, so I figured the other pins on the relays diagram were pertinent… with just a few minutes in, your voice reminded me of some douche bag that does these videos, and they are super long winded, I think just so the guy can hear himself talk… I thought you were that guy and I was aJUST ABOUT to go elsewhere when suddenly you started speaking on EXACTLY the info I was looking for. I watched every minute of this video, and learned so very much from you… Thank you so much!!! I am a well seasoned backyard mechanic, but there’s things us guys will never know until REAL mechanics like you spread knowledge of “bias voltages”. Luckily, I have an electronic engineering degree, and have plenty of understanding when it comes to bias voltage, but never knew it would be presented and misleading as it is in this real world situation. With or without knowledge of bias voltage, without the discussion you gave and the two different methods of testing the control side voltage, it would have kicked my lily white ass!!! Thanks again! Great video, I subscribed, and bro… you sound just like Bradley from sublime!! Lol… 🤙🏼
Best comment I've read in a long time. Thank you! When you need it, you need it right? My man. Did you fix it? Sorry if I missed that. Still smiling from the comment
That engineering degree made that happen for you. I'm sure you could teach me a thing or two on that front
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Great skills, I wonder if this is my issue I'm having with my 98 blazer, it has no power going to the pump with key on.even the same thing happens with the relay, no click.
The person who was working on the pump prior to you looking at it should stay away from auto repairs. Seems everybody has a buddy that can work for cheap and as you noticed no training equals cheap work. Great vid and I never knew about the bias voltage on the control side , thanks !!
Probably someone who was Color blind wired and installed the new fuel pump....
So what happens when its wired backwards? Will the fuel pump fail? Or ?