Part 2. GM no start no fuel troubleshooting "Oil pressure switch"

[@TSRay-jb9qh]

I realize this video was made over 10 years ago but I just wanted you to know that is still helping people today, so Thank you, Will. I have an 89 GMC Sierra SLE 5.7 TBI and have been struggling with a crank no start issue for a long time and no matter how many mechanics I have asked, unless you find one of the old school Shadetree mechanics that doesn't need to hook a vehicle to your computer do you know how to fix it, not one of them knew the answer because of the age of the truck. Your 2 videos on this topic, even though the truck is a newer year model, was the first that help me realized it could be the Fuel Pressure Oil Pressure Switch, which I have since learned differs from year models of GM trucks. ♦Please note for anyone dealing with the same problem please pay attention that it does matter what year model your truck is as to how many pins are in the fuel pressure oil pressure switch, 1988 - 90 will have only 2 pins in the switch, 92-95 may have 2 or 3 and 95 - 99 will have 3 Pins.♦Also, pay close attention that in other videos it may be referred to as a Fuel Pressure Sender which may be accurate in newer 3-Pin models, however in 1988 to 90 Fuel Sender is a separate component/part, in a different location, it is located on the Driver side lower engine block on year models 1988 to 90 and differs from year models 91 to 95 and 95 to 99 where the switch and sender maybe integrated. Video part two was extremely helpful in showing how to bench test a part to show how it works. 🔶Other than discovering this switch could be the issue for I no start, I have also discovered that is very important on your models 88 to 90 as well as 91 to 95 to inspect the braided body ground straps to the engine block. As well as the ground wires to the ECM and fuel pump relay which are black, black/white stripe together and a 2nd set that is a black wire & a tan with white stripe are ground wires that on 1988 to 92 models are typically grounded to the engine block on or near the thermostat housing(bolt)and can become loose over the years from vibration or corroded causing a faulty ground, which I stumble upon by learning from videos regarding testing for proper ground and voltage with a Non-Led test light. As it turns out when I tested where those grounds are mounted it showed a very weak or dim test light, so I jumped it to another ground on the engine block which had a very solid bright light, went to start the engine and was very shocked that it fired right up, all it was was a weak ground connection at the bolt where the ground wires were mounted to the thermostat housing. So if you're having this issue and have this year model of truck, hopefully I can save you a lot of time by checking this and all of your body ground wires to make sure they have clean, tight & proper connection.🔶 When you own one of these year models of trucks it can be very discouraging and frustrating to find out that many younger generation mechanics do not know how to work on them or even care to learn how, even though they are very plain and simple and more basic to work on the newer computerized versions where you just plug it into a computer and it tells you where to start putting parts in it to try to fix it, but don't give up keep searching & trying and you will find the answer.❗🙏I have much appreciation and gratitude to mechanics like Will and others who are old school or enthusiastic enough to learn in order to teach and post instructional videos on KZbin to help us out with our old classic GM trucks. Thank You All‼

[@robinsonsauto]

This is awesome to hear

[@williamsanchez3462]

you are the honest face that everyone wants to see in a car mechanic....your video is a lot of help ...thanks a lot

[@cliffordperry2499]

Man oh man, this dude is the bomb instructor!! All kidding aside, I really like how he fully explains each detail and even reviews and bench tested the old and new components in detail. This is the first time in my life I ever thought enough about anyone on here to consider giving a positive comment but Robinson you are deserving and the best instructor I have seen on youtube hands down!!! Thanks Bro and I will be telling everyone about "robinsonsauto"...

[@aaronthierath701]

Ok man I don't comment on vehicle repair videos , because I usually have to watch 50 to learn nothing , so I will comment on this one and say you have just taught me something that not one single other mechanic I have seen on you tube has ever mentioned anything about the oil pressure switch as a back up for the fuel pump ! And that my friend completes the puzzle of mine because Im getting a crank run speratic stall , I pull the fpr and it dies when now I know it should not , I have been leaking oil like crazy lately due to the front side of oil pan gasket , and I just kept up with it till I could get rid of the stall so you can see where my dilemma would be , and THANK GOD AFTER TWO WEEKS OF TRYING TO FIGURE THIS THING OUT I HAVE FOUND YOUR PERFECT VIDEI AND EXPLANATION ABOUT THE FUEL PUMP AND RELAY SYSTEM AND THE BACKUP SYSTEM AND HOW NOT ONLY DOES THE OIL PRESSURE SWITCH PLAY A ROLE IN THE ENERGIZING OF THE FURL PUMP IN A FPR FAIL BUT LOW OIL IN GENERAL WILL PLAY A ROLE AS WELL ! YOU ARE MY NEW GO TO MECHANIC YOU ARE THE ONLY ONE WHO HAS TAUGHT ME SOMETHING USEFUL I DID NOT KNOW ABOUT MY C3500 ! YOU GET THE MECHANIC OF THE DECADE AWARD IN MY BOOK MAN ! THANK YOU FOR BEING THROUGH !

[@markallred4520]

This 11 year old video helped me fix my truck after replacing the fuel pump and having intermittent issues. Thanks

[@robinsonsauto]

That’s great to hear

[@RueKake]

I don't mind even watching the ads because I actually want this guy to make money 😊

[@robinsonsauto]

Thank you for your support! It means a lot to me.

[@benkanobe7500]

If you ever think of retiring, you could be THE BEST automotive Teacher High School, College, Major Automotive company Senior Instructor,........ You absolutely know your stuff, are humble about it and you have that magic that allows you to make it so that others can understand and learn from you. Not using your shop tools and using what a typical home garage guy would have is beyond helpful! You are The Man! Thank you!

[@Freetheworldnow]

Probably the best video explaining the fuel pump relay no start related issue. Thanks for posting.

[@jimphillips8774]

Your video helped me repair my 1999 Yukon ,oil switch ,tapped it vehicle started ,pulled relay shut off .Sir you saved me from dropping gas tank and replacing fuel pump ,thank you

[@floydbrock7308]

I just wanted to share a special thank you for this two part video. I've had an ongoing issue with my 98 Silverado similar to the one in this video. My truck would fail to start on humid/rainy days. Following your videos, I found a cracked oil pressure switch, which was shutting off my fuel pump immediately after starting. The humidity was shorting the sensor. Thank you, thank you, thank you!

[@cr250rish]

If my fuel pump isn’t running at all this could be my issue?

[@fwblack]

Like others commenting here, excellent video. I'll add one other thing that can cause a no start issue when you have spark, and a good fuel pump, and good timing, and good everything else... a bad Throttle Position Sensor (TPS). The TBI engines will assume a flooded engine if the TPS giving a false signal that the throttle is wide open, and in that scenario it will not provide enough fuel for the engine to start. After spending hours and hours over days trying to locate the issue, I finally took a paperclip and read the diagnostic codes (plenty of videos to show you how) and it had a code for TPS. Replaced the sensor and it started right up.

[@CasselmanCanada]

After watching the two videos in this no-start series, you can work on my vehicle any time. Excellent explanation and logic.

[@BarbaraEClark110163]

Your 2 part video was great help for me to troubleshoot this problem. since I had already replaced fuel filter to no avail. due to circumstances similar to ones in your videos I'm almost positive this will fix my problems on my 2000 Tahoe. Thank you immensely...

[@wal18091]

Great video. Took my new to me 2005 coach with a 8.1 liter workhorse chassis. First trip broke down twice (not related to this issue). Got home and never was able to start again. Two weeks later, I have already dropped the fuel tank and the pulled the fuel pump. Tried to start and no go. I ran across your video and decided to pull the oil pressure sensor. I did your test to the pressure sensor and son of a beach!!!! That was it. Thanks bud.

[@jeffo881]

Other videos on GM fuel pump relays don't mention anything about the effect of the oil pressure switch on the fuel pump relay, thanks for helping me fix my problem. That little demo where you remove and re-install the fuel pump relay really helped.

[@yadavfamily6263]

Dear i have captiva when on key automatic not start fuel pump and wont start what i do

[@MegaBoosted]

Did your oil pressure gauge show oil pressure even though oil pressure switch was faulty?

[@ladder9110]

Thank you. I watched both videos. I am in the process of trouble shooting my 1989 Chevrolet Beretta no start. I replaced the fuel pump in the tank, and got the car running. Then I replaced the signal switch as the left side would not blink, and got the signals working. But then I could not get the car to start again. I have ordered a $30 fuel relay switch and hope that will get this 33 year old car running. It has been in the garden or garage since 2005, running it twice annually. We ordered it new in 1989.

[@anthonyrosa4388]

YOU ARE THE MAN!!!! please never stop making your video's you are helping so many people. THANK YOU!

[@robinsonsauto]

also wanted to add, I agree, if I were to leave it be with just replacing the relay chances are it would be fine for many years, however in that rare case the relay were to fail again, as long as there is oil pressure the "back up" pressure switch will keep you in operation. what you will experiences is longer cranking times with a failed relay and an operational pressure switch due to the fact pressure needs to be obtained to close the contacts... It’s simply just a backup, Hope that helps

[@DrgnRdr1231]

Had the very same problem, '96 Chevy C1500, instructions on both videos were spot on and understandable. Thank you very much.

[@imacrazy6872]

One of Americas top mechanics here, thank you for the great videos on how to properly troubleshoot!

[@jasmiinelee6633]

The two videos about the GM no fuel trouble shooting were spot on and very easy to understand.

[@larryhozak9565]

Excellent fuel pump relay diagnostic on GM . Basic common sense diagnostic video and commentary anyone can understand. Thank you Robinson auto for saving me time and money. Life is good !

[@camillabarnes6678]

A hero, so cool and confident. A good mechanic is like a musician, so talented.

[@deanstuder1775]

Thank you for an excellant tutorial. I want to add this feature to my son in laws car that he switched from mechanical to electric inline fuel pump. For safety shut off fuel when vehicle is upside down, perish the thought. And also to leave pump off when key on engine off. It's carburated so it will start ok then oil pressure will quickly bring the fuel pump on. I thought of a 3 wire oil pressure switch but didn't remember the details. You completely educated me on this switch. And can even do an electric oil pressure guage now.. Not wild about the oil tube type of gauge on it now. Leaks under dashboard potential and a leak under the hood spraying oil around "not cool" either.

[@dporrasxtremeLS3]

Will you are the best!!! You are so easy to follow and learn from. Thanks. I appreciate the comment from Dean Studer on fire safety and rollover protection. Now I have identified my no start. My 2001 S10 cranks, good spark, good prime, no start. Bad wire harness to the oil pressure switch. I found that after I replaced the intake gaskets, I had a no start. The 3 wire harness to the oil pressure switch broke because of age, heat, and movement on the gasket repair.

[@catalinasalazar755]

My 96 c1500 sat for 8 years. Gonna watch more of your videos to get an idea of why it isn't getting fuel. Thanks

[@weaslenut]

Thanks for the tip on oil pressure switch causing my fuel problems. Been a month trying to figure out why no power under load. Put the switch in and now feels like a new vehicle. Thanks!!

[@wherethefugarwe]

If already asked and answered, I apologize. My understanding is the oil pressure switch isn't for a backup. The relay in the box when powered works for 10 seconds allowing a start and oil pressure to build. Then the oil pressure switch takes over and the one in the box times out and stays off until the next time you turn the ignition on. Now, the reason I understand all of this is from watching your video and having the "a ha!" moment. Nice work.

[@D-train69]

Thank you O so much. I watched all sorts of other videos non clever come close to your most easily explained educational video, Thanks again

[@justsayw.y.n.n.towing1676]

Now this video is the best diagnostic of an Oil Pressure Switch that I've seen. I want to thank you for inspiring me to fix my friend 00 Pontiac Sunfire. It's easy to comprehend and I absolutely like the colored wiring diagram. I'm a new subscriber now and I highly recommend other folks do to!

[@Meatwad.Baggins]

These two videos are the first time I watched you and I had no choice but to subscribe. Well done sir. You are a good mechanic as well as a youtuber

[@PineHollowAutoDiagnostics]

Ironic that the back-up switch for the relay also went bad and left the truck stranded anyway haha. Way to go the extra mile and make sure all the components work as they should! Very clear explanation of the process as well. Right on par with ScannerDanner :)

[@coleorth2467]

Great job man, also in your honor I too am going to start calling it continudity. Keep up the good work

[@chucklinney630]

You noticed that too huh? Lol 👍

[@jasonlaughon2897]

Sir, you just saved me a pile of money on my 1994 Silverado. But a relay and he fired right up. So I unplugged after watching your video. It died right out. I’ll be swinging by the parts store in the morning or the oil pressure switch.

[@robinsonsauto]

thanks, i could of let it go with just replacing the relay it ran and started fine, however i just wanted to double check the system. glad i did

[@2cyclemix]

Great extra effort. That's taking pride in what you do and taking care of the customer. A lot of technicians would just replace the relay and then when/if the new relay goes bad the customer would be stranded, again.

[@jett-rampartflyer2852]

Excellent moving chart and description. You have so much potential and already so much knowledge. Thank you for this video. You made me $120 today. I really really needed it too. Thank you again!

[@johndishaw6600]

I just want to say thanks for the 2 videos here on this and walking through the troubleshooting process. I have a 1990 olds cutlass ciera that kept shutting off on me. I walked through it an verified all the components were fine. fuel pump, relay, and I had spark. Ended up being a fuseable link by the starter, go figure. Thanks a lot!! great walk through.

[@sirsweetness8332]

Awesome on first fix and to find the second helping the customer not to get stranded

[@dream_living96]

Nice educational video. Just bought my son a 305 throttle body firebird and it has a no start. Maybe not the same motor, but I learned something about testing the relay and oil pressure switch. Now I wish he had tested the fuel pump so I could have learned what to look for there. Maybe in the next video.

[@CardiacCat]

Great video set (part 1 & 2). I watched another one before yours and was lost. You speak in easy to understand terms, and it's obvious you are not trying to wow people with your brain power like that other one I watched. I completely understood every single thing you were doing and why you were doing it.

[@SUCONITNOW]

There is only one word to describe this presentation. " E X E C E L L E N T " !

[@deepspaceproductions6419]

Nice job buddy. Great explanation, good easy listen and you shoot it straight. New fan!

[@DvDjSpeedDemonVideoJunkies]

Excellent explanation, I'm about to install and external fuel pump on my 63 gasser and this is an excellent idea to shut off my fuel pump in case the motor shuts off, blows up, or if I roll over. Once the engine turns off and loses oil pressure... it'll definitely shut off my fuel pump.. Safety issue. Thank you 😊

[@earlhoney8533]

Very impressed with your knowledge, young man. I have an issue with my 93 Chevy Silverado K1500 ..long story short is that the truck runs normal but when it gets over 95° outside and I go for a 50 mile run with it when I shut it off, it will not restart until it cools down. Of many reasons ..replace the relay still happens. Saw this video and thinking maybe a fuel oil pressure switch functioning when it’s really hot. Your thoughts please. And yes, I’m very impressed with your videos and knowledge.

[@racebends]

Thank you for the visual on location of the pressure switch. I didn't know what it was under my distributor. Not even the manual shows the correct picture.

[@SteveRobReviews]

Well done !! What are the odds the relay and sender would be bad. Too bad GM stopped using the back up oil pressure system on its newer engines. I wonder how many shops would have just replaced the relay ?

[@creightongoodwin7535]

I don't normally respond to opportunities to state my opinion online, because I do not frequent the web and/or encounter situations in which you can honestly provide "positive feedback." Will Robinson is an exceptional mechanic and an equally impressive mentor. I am convinced of this fact because of the level of knowledge he exhibits and the manner in which he chooses to do so. Basically, I am discouraged by online mechanics who have a vast amount of equipment at their disposal that is not readily available to me. Further, these individuals are surrounded by a team of workers, when I generally have to complete my vehicle repair problems alone. I remember one occasion in which I sought information online, and this particular mechanic requested $35+ dollars to help me troubleshoot the problem. I am accustomed to the day in which you could go to the auto dealer, and briefly discuss your mechanic problem with one of the technicians. Now, people are trying to profit from their potentially bad advice. Will is a pleasant addition to the auto repair dilemma, and now many people won't be Lost In Space: There is no "danger Will Robinson" because you know what you are doing.

[@shimondan8779]

Flipping brilliant mate!!! Power On.

[@pedrorojascervantes3928]

I was under the impression that it was only OBD 2 that had this circuit. I had an occasional intermittent cold crank , no start on my 1991 305. I found the oil pressure gauge was not operating properly but once it does start it never fails to restart once hot. I replaced the oil pressure switch & the the cold no start problem returned. I'm in the process of checking all grounds & fusible links now.

[@daddytech]

very helpful! specially since my wife's suburban with the same set up is doing a random no start thing. her's is a little different issue but i think what you are doing here may have given me the answer i need to get hers going. haven't checked the oil in hers and she NEVER does so it may just be low on oil now that might be why hers will only start when it's warm out (assuming because the oil expands when it's warm giving her enough pressure to start) it won't start cold early in the morning

[@robinsonsauto]

Man im trying, took a little break this week. put allot of time and effort in the channel and website this past year... im surprised you don't get more hits man i been hooked spent a few hours last night checking out your vids, very impressed

[@miketiny6088]

Excellent video, you learn something every day thanks for taking your time, plus explaining with wire diagram and troubleshooting. I appreciate very much, will continue looking at other video's

[@cliffmarcie]

I know this is a pretty old video but I just want to let you know its really well done!

[@joekucera9519]

THANK YOU! YOU'VE EXPLAINED TECHNICAL, SO A NON... CAN UNDERSTAND!

[@robinsonsauto]

Thank you, you may be correct, one thing to remember, if the relay is good that will over ride the oil switch and the vehicle will start even with no oil pressure, so yes if you do have a bad relay it will be very long crank times and my not start depending

[@TOMAS-lh4er]

THE OIL SWITCH WAS FOR A BACK-UP FOR A BAD RELAY not for safty!

[@robinsonsauto]

just wanted to add i mentioned this further down the comments, some engines with excessive bearing clearances, worn oil pump, low bat. may not reach 3psi while cranking, i can say, it did helped some. had a couple in the past with long cranking times that just needed a relay. very rare though don't have the vehicle any longer, i will be more than happy to perform this test when i get it in for the next service,

[@tomhammer2346]

I want to know what wiring diagram you are using. Really helps me follow along.

[@vdubbeatz]

I wish I had a cool ass mechanic like you. Great work

[@JamesAnderberg]

Good stuff! Simple explanation with simple illustrations. Thanks from a grey beard.

[@charlesbrown9053]

My man that what I'm talking about I'm in school taking notes and very thang love this video

[@Skyrimnut]

Well my check engine light would come on after minutes of driving, I checked all I understood, THIS is likely why my 94 k1500 Sierra died! Thanks buddy, owe ya one.

[@anthonywilliams563]

Thank God for you taking the time for making this video this is a big help with the problem im having with my truck

[@matlineugene]

your video was very helpful, I liked you were easy to follow without any unnecessary wasted time as so many videos are. nice job.

[@zloben9000]

you know your stuff man ... no code diagnose is quite hard. but you are a Pro man

[@SkilledEddie]

Would a bad oil pressure switch cause engine misfires? I pulled my relay and the engine shuts off. 1997 Chevy Tahoe 5.7. I've been chasing a p0300 and specific cylinder misfire like p0308 but it's weird every time I take the upper plenum off and recheck everything when I put it back together the cylinder that misfires changes to a different cylinder. The most oddest thing I ever experienced. I replaced everything you can think of and cleaned up all the grounds wires. I notice the fuel pump relay doesn't energize sometimes when I test by turning the key on and off. I keep my hand on the relay and I turn the key on and I don't feel it click. Sometimes like 4 times in a row. I bought a new relay same thing. So would the oil pressure switch be causing this?

[@jeffreywasylucha8231]

Great troubleshooting. I am having similar problem with my 93 4.3. I will try this. thank you!

[@forabuck380]

You saved me!!!!!!.. this guy is the best

[@z26ta]

you can keep all the videos about 98 gm trucks coming please :)

[@bryans8193]

Thank you for the great videos! I have a 1993 gmc suburban 5.7 350. My fuel relay is on the passenger firewall. Can I use these same test methods on this vehicle such as starting the vehicle and disconnecting fuel relay to see if it stays running? One of the problems I'm having is the vehicle is stalling while I'm driving it. Any help would be greatly appreciated.

[@Rubensteezy]

Wow, I learned a ton from this video. Thanks man.

[@marklammers5119]

Great video with the exact info I needed. 1997 Blazer 4.3.

[@jaymillek1505]

Thank you...thank you...thank you!! been trying to pinpoint this problem for a long long time!! Very well made video. Perfectly explained

[@mazzmari]

Good video, I didn't realize that there were further problems in the first vid.

[@1947froggy]

I have 02 Suburban, starts & runs briefly then slowly dies. 15 psi fuel pressure with key on & dies off to zero. New fuel filter so I think it's the pump. Thanks for the video. :)

[@humidbeing]

Awesome video. Liked how you tested with air pressure and a regulator.

[@chriskeep9461]

on my 93' the pressure switch is not 1-1/8", its 30mm and you have to remove the distributer to get it off if its the original. Gm put these in tight and the tree is fragile and you will break it off if you don't support it with a 15 inch adjustable wrench while using a 30mm box on the sender. Have an extra distributor gasket. mark the position of the rotor and distributor base. Its quick and easy but adds a second possibility in diagnosing any problems if it doesn't run right. I try to restrict repairs to one thing so there arnt multiple possibilities to chase if a problem.

[@robinsonsauto]

Napa-permatex thread sealant w/Teflon i believe... i have a couple makes however i believe that's what i used

[@michaelneher5868]

Great video! Can't wait to try these tests! Thank you very much!

[@robinsonsauto]

thank you, that would make more logical sense, however GM was just using the pressure switch as a back up for the relay, so if relay failed as long as you had oil pressure the vehicle would still run. now if relay was bad, it would take real long cranking times to start if you could build pressure cranking to close the contacts that was their"theory" if the pressure switch were to fail or you lost oil pressure as long as the relay is good it will still turn on the fuel pump. hope that helps

[@PAMAROSHOUSE]

awesome video. is the oil switch located in the same spot for a 2000 2.2 gmc sonoma

[@dustinw5527]

Would a bad oil pressure switch cause the vehicle to crank no start also cause it to back fire? Any help would be greatly appreciated. Thanks for the great videos and your time.

[@tacoloco904]

Backfiring is usually an indication of distributor issues

[@z26ta]

first off great video I learn something new. so if I understand you correctly if my truck loses oil pressure that will shut off the fuel pump?

[@robinsonsauto]

My first response on how the system was setup was from Mitchell provided by GM. that was their theory any how. Will it do just that depends. In some cases it may not obtain enough pressure while cranking example, low battery, bearing clearances and so on. some engines with excessive bearing clearances, worn oil pump, low bat. may not reach 3psi while cranking, i can say, it did helped some. had a couple in the past with long cranking times that just needed a relay. very rare though

[@JayJay-de8vq]

Im curious about this. You had it running and pulled the relay and it kept d Running after you replaced the oil pressure switch. Now I wonder if you shut it off and try to restart with the relay still removed will it start and run??

[@shanehall5659]

awesome..am gonna try installing a new pressure switch tomorrow and will get back. thanks again.

[@spelunkerd]

Nice job, Will! Last year a watched a vid by Scannerdanner, and I was hoping he would do what you did today. You might send him this as a video response to his video. What puzzles me is, why did GM do this? What would happen if you had a bad oil pressure switch at that point? As far as I can tell, nothing, (grin)! An abrupt fuel relay failure would be very rare, and the worst that would happen is you would stall at speed, then coast to the side of the road.... What am I missing?

[@gntr93043]

That last check solved my problem,great video,Thanks"

[@robinsonsauto]

thank you, glad i got it out to you. hope you found it helpful. your more than welcome

[@chrisvill54]

My truck is a 98 k1500 5.7. Its the spider injected not the tbi like this truck on your video. Is the oil pressure switch still used on my truck for back-up for the fuel pump relay? I just replaced my pump and the truck is running fine no problem but when is disconnect the fuel pump relay the truck shuts off. Just wondering why you were able to get the truck started in the first place by just replacing the relay if the problem was the oil pressure switch? Does a bad oil pressure switch eventually cause the fuel pump relay to go bad. Thanks for all your valuable info!

[@robinsonsauto]

Control module keeps relay energized if engine is cranking or running(control module is receiving reference pulses from ignition module) if no reference pulses, module turns off pump within 2 seconds as a back up system to relay, the oil pressure switch also activates the pump, normally open until oil pressure reaches about 4psi. if relay fails, oil pressure switch will back up, only when with pressure, cranking time will be longer if fuel pump don’t receive current until pressure is achieved

[@robinsonsauto]

Good question, i should make a video response for this one. if i showed you first hand it will make more sense. say if the motor jumped time, Broken timing chain or belt depending or more extensive damage, you will hear a deference in the way the engine cranks, when in time you can hear the the starter working harder overcoming the compression from each cylinder... mechanical problem say a broken timing chain the starter would spin much faster less load, do to the cylinders without compression

[@truckandroll989]

Ive watched both videos and I only have one question. On my 95 GMC Sierra when I filmed what happened on my circuit which is supposed to receive 12V for 10 seconds with the key on it goes from null to battery voltage for a split second but then stays zero. Is that likely a pcm issue or an ignition switch. The other tests in the first video it passes but its not priming long enough

[@bluesriot2]

another great instructional video - hope you gave the customer a discount for using their truck lol

[@deanstuder1775]

The intention of this wiring configuration is for fire protection, for when the vehicle has rolled over and is up side down. In that event it is important to stop the fuel delivery. The way it works is that the oil pump will not have any oil in the sump to pump, thus no pressure. And those contacts, in the oil pressure switch, will open to cut off the fuel pump. Rather than putting full fuel pump motor current though the light duty contacts in the oil pressure switch, a relay is used. Otherwise, a much larger, more heavy duty oil pressure switch would be required. And this is all bypassed , during "start", before oil pressure has been developed. The same as old cars with ballast resistors and points worked.. Been wrenching on cars for 50 years. At first there was no fire protection because fuel pumps were mechanical and cars had carburetors with float bowls that shut off the car if rolled. Then electric fuel pumps got popular and fuel injection and fires occurred after crashes that required to be dealt with. That is when and why wire oil pressure switches came in to play. Today, inertia switches are used instead of oil pressure switches. It is not for in case of relay failure or any other convenience.

[@janj0n]

How then did the engine run with a good relay and bad pressure switch?

[@themechanic6117]

Dean Studer so you could have a bad relay and never know it due to the pressure switch?

[@baddriversofnorthtexas6850]

lol this debate has been going on forever. Who cares what the intention was, whether because of wrecks and rollovers, or to save a motor from seizing up because the owner didnt notice the engine didnt have any oil in it. Either way the OBS trucks left too many people stranded in parking lots because of bad sensors, having to use a paper clip to get home. Finally they scrapped the idea. Who knows, maybe because OBD2 and later PCMs were able to log enough data to show GM to prove to the customer "no we wont warranty your blown engine, you didnt put oil in it, your own fault".

[@TOMAS-lh4er]

@@janj0n BECAUSE THE SWITCH IS NOT FOR SAFTY!! ITS IN CASE THE CHEAP GM RELY FAILS THE GAS WILL STILL GET TO THE ENGINE!!

[@slvrserfr]

Thank you!!! I've had a similar problem with mine, cold starts fine but once it warms up, I get symptoms of low oil pressure and the car stalls unless I keep my foot on the gas. The starts get harder as the car gets warmer and there's oil leaking from the oil pressure switch. Been researching this for awhile but this helps alot in knowing how to test the fuel pump relay which I recently replaced to narrow the symptom. Car has 150,000+ miles on it - accelerates fine, just stalls at idle when warm after the oil thins and warms in the engine.

[@dude5576]

Hey will wouldn’t the oil switch have bad oil pressure

[@robinsonsauto]

Yes I do believe if you lost oil pressure it would shut it down. Same as if the switch would fail

[@dude5576]

@@robinsonsauto ok thanks

[@Bart12349]

Great video Robinsons auto. I know a Robinsons excavation. Do you perform excavation and landscape work too?

[@buddybuchanan1767]

Good video, I work with my own stuff all the time but would not have thought about the oil pressure switch. I'm working with my GTA, fuel pump wont run after sitting for a year, ran fine when parked. I would start it on occasion, but now no start. I have power at the relay and 2 sec. on prime. Is the fuel pump known to just seize from sitting? I need to run direct power to the pump at the connector above the axle next, mist likely power there and need to drop tank and change out the pump.

[@charlesstewart5165]

Another excellent video. Thanks very much. Hopefully will enable me to make some decisions following logical troubleshooting.

[@xxxreaklingisking2xxx975]

Thanks! Best teaching video and GOOD info I've had the pleasure to watch!!!!! GREAT