How to identify and repair a leaking fuel pressure regulator (GM CPI system) part 1

The CPI system began on the 4.3L engines in the early 90s and extended to the 5.0 and 5.7 engines around the same time with some slight variations. Around 1996 the CPI system became a SCPI which stands for Sequential Central Port Injection.
The CPI had one central electrical injector, while the SCPI had an individual electrical injector for each cylinder. On both types there where mechanical "poppet nozzles" that sprayed the fuel into the intake runners. These systems had unique problems due to the injector assembly locations and the mechanical injector poppet nozzles.
The vehicle being tested in this video is a 1995 Chevy S-10 Pick-up 4.3 L VIN W engine. The primary focus of this video is how to troubleshoot and repair a Central Port Injection system with an internal fuel leak.
Some other names for this system:
- central port injection (CPI)
- "spider injector assembly"
- vortec injection system
Engine Performance Diagnostics chapter 16 page 8
Symptoms:
- long crank time
- severe rich running condition (P0172, P0175)
- more gas mileage
- check engine light
- misfire trouble codes (P0300)
- rough idle
- stalling
Fix:
- replace fuel pressure regulator
Testing procedures shown:
- how to test fuel pressure
- how to manually energize a fuel pump on a GM
- how to determine if you have a fuel pressure bleed-down problem
- how to determine the cause of the bleed-down problem
- how to verify the the location of the leak that is causing the bleed down problem
- how to replace just the fuel pressure regulator on the injection assembly
- what to look for using an aftermarket part (you may break the housing!)
Tools used
- fuel pressure gauge
- jumper wire
- needle nose vice grips
- scan tool
Playlist
- (Chapters 14, 15,16) Fuel Delivery and Fuel Pressure Testing
• (Chapters 14, 15,16) F...
Related videos:
- How to identify a leaking fuel pressure regulator on a GM CPI system (part 2)
• How to identify and re...
- Fuel psi less than 50 psi = no start (GM CPI Vortec)
• Fuel psi less than 50 ...
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.

[@B81Mack]

This is a great example of someone who truly understands the "why", not just the "what". Excellent.

[@ricktarded5943]

A simple "Thank you" is waaay short of the gratitude I have for your excellent knowledge and teaching skills. You have just saved me tons of heartache and head scratching. These regulators have killed more trucks with spiders than we could ever know. Something else I must share is the oil pressure switch, located on the back of the block, can go bad causing rough idle, mysterious dieing, and no fuel pump voltage (improper voltage). They have a set if contact points inside and can either burn or internal spring failure. Its in a tough spot to service but a $21 pressure switch can save your truck.

[@ScannerDanner]

Thanks so much Michael. Just knowing these videos are still helping people is all that matters!

[@B81Mack]

Excellent presentation by a technician who truly understands the system at hand. Well done, sir. 👍

[@chucky10342008]

I purchased this truck in a garage sale here in Forida for $800.00 four years ago. seller thought engine was blown. I bought as is. water in oil. I tested every cylinder perfect compression. intake manifold gasket failed. I replaced total coolant system and gaskets. flushed the engine. extended cab 4wd truck. Its been my daily driver for the last 4 years. ac was shot, 1k to fix. no thank you. overall excellent truck.

[@randyfeguer1914]

Great video very well done. It's really nice to have someone that really knows what's going on and show how to do this stuff the RIGHT way. Thank you

[@judsonfrancis3659]

Instablaster

[@TrueBlueEG8]

This lad knows his onions, i love to see a proper diagnostician at work.

[@jamesrosado6472]

Thank You, Paul Great Detail. Love your work. Great Role model for us who really care about what we do. GB

[@SuperGmann10]

Great video. Back when I was green, the ex wife had a 93 S-10 blazer with this problem. I chased it for a week before consulting someone with more experience, who told me this was a common issue. This video sure would have helped!

[@jaberwocky6669]

Hi ScannerDanner. Because your videos over the years have been so helpful and because you've answered my questions in the comments sections of your videos, I have bought your ebook! Thanks!

[@ScannerDanner]

Thanks man! I really appreciate that. More than you know.

[@PineHollowAutoDiagnostics]

Hi Paul, thank you for these detailed diagnostic videos! Just made a quick buck with my scan tool and fuel pressure gauge for this exact internal leak issue on a 2001 Blazer. I am in the process of establishing my own shop here in central PA, specializing in automotive diagnostics. Keep up the awesome work, you are my inspiration to battle the parts changers!

[@ScannerDanner]

awesome man thank you!

[@damienbernier9378]

This was awesome. I’ve been going nuts trying to figure out where I was leaking fuel out of my 94 S10

[@chuckreed2677]

Great video, hoping to receive my copy of your book in the mail today. I was wondering why fuel pressure went up when you opened the throttle then a few minutes later you explained it, fantastic.

[@steveurso6435]

This helped me figure out what was going on with the fuel pressure drop in my 2000 4.3. Also now I know I have a SCPI system which has a similar FP regulator. The test on the fuel lines are very helpful to know. I'm a premium member and have the book yet still find your perfect vid I need hand fed to me by KZbins algorithm. Thanks for your years of compiling all this information. I love it!

[@ScannerDanner]

Thank you so much Steve!

[@sl5311]

You are one of the best teachers of anything on KZbin

[@clintsmith3408]

I know this is a 10 year old video, but it is exactly what i needed! About to tear into my 94 with the CPI. Looooong crank, running very rich. Thanks for this!

[@ScannerDanner]

Heck yeah, awesome. Thanks!

[@FuelTankerMan]

wow... just WOW... you're AMAZING. Thank you so much for sharing your expertise and I do mean EXPERTISE--this is fantastic info. And now, I'm gonna go fix my 1996 GMC K3500's problem. Every symptom you went over is what my truck is doing, including diagnostic codes (albeit it from my cheap little reader compared to yours). :) I can't thank you enough!

[@ScannerDanner]

that's great! thanks for the update. ill keep u posted on any new material. right now i am working on a page for page lecture of my book. it is about 50 hrs of material which i will most likely break up by sections. it would be in video format with my smartboard. in fact it will be like you are sitting in my class.

[@ScannerDanner]

@Drlovemachine Agree again, but we used what was available. But it is a good lesson on using aftermarket parts and the trouble you can run into

[@jackszumski7118]

Awesome video! You did a wonderful job explaining everything and you gave me all the information I need to tackle the same issue in my GMC Safari. I am very thankful for your efforts 🙏 bless you!

[@lovinawright128]

My son had me watch this video so I would know what he has to do to my Safari van. Same engine as this one. Very informative and it will help him get the job done. He is a good home mechanic. I am blessed by him and this video.

[@mr.sweetconcrete3108]

very informative and with a great attitude! THANK YOU

[@jeremys.4423]

EXTREMELY useful video! Helped me out a bunch. You seem to be a really knowledgeable guy

[@Vanbulance89]

This video was super helpful! Thanks so much.

[@spelunkerd]

That's a great point about maintaining pressure to prevent fuel boiling on the rail. No doubt that's a point made as a result of unfortunate experience. The lighting is great in this video.

[@MotorheadLars]

That was easily the most informative, well spoken and educational videos I’ve come across since I got my s10 blazer. Same exact condition on my truck so this helped me out a ton. Thanks!

[@ScannerDanner]

Glad it was helpful!

[@ScannerDanner]

Thanks friend, glad you liked it

[@barrytaircargo123]

Great training I have a 95 SS CPI S-10. This video helped me get her running better than ever thank you

[@stevenm3141]

You are a true professional this is the best video I've ever seen. I think you solved the problem for my 03 Blazer.

[@ScannerDanner]

Thank you so much! My newer videos 2016 and up you can really start to see the production side of these videos getting to be almost as good as the content.

[@ScannerDanner]

Yes! Great question

[@searnhardt8]

I want to "plus 1" all of the positive comments below. The troubleshooting steps were awesome and spot on for my 94 S-10. I saw a few folks ask about changing the Fuel Pressure Regulator while still in the car but as I've completed the job, I'm not going to search for the answer at this time. If it HASN'T been answered, I would LOVE to suggest that as an option if its possible. That part was all that was wrong ($50) but I broke the plastic tabs on one very difficult popette. So, $240 later, I now have an all new spider injector assembly. My suggestion would be to squeeze the clips with one hand and wiggle / pull the plastic (not the fuel line) with needle nose pliers. I think the ring of plastic near the tip of the popette is more solid than trying to wiggle the clips. Anyway, thanks for giving me the confidence to tackle the job.

[@ScannerDanner]

+searnhardt8 thanks man and nice job. Unfortunately those plastic tabs are brittle. I've done these with one broken clip and they hold, but not two. Sorry you had to change the whole thing.

[@anthonyskorner4511]

Paul, you are a walking, talking automotive repair manual. Wish I could retain half of what you do.

[@robbyddurham1624]

I'm 54, my life would have been different if I'd had the internet when I was 18 years old. Thanks for sharing you're knowledge Scanner Danner.

[@ScannerDanner]

Me too my friend, thanks!

[@ScannerDanner]

Awesome! thanks for the feedback

[@ultramediafx]

thanks for the invaluable info great video and skills!

[@ScannerDanner]

I would agree. As far as replacing the whole unit, I wouldn't do that. Your truck is a newer design and uses 6 separate electrical injectors as opposed to one. So it is called a Sequential Central Port Injection system. (SCPI) I believe the injectors are sold separately but I may be wrong, it's been a long time since I have been inside one of those. As for troubleshooting a leaking regulator. It would be the same steps I've shown in this video. Fuel pressure bleed-down test is the key.

[@sharmarule1]

Excellent explanation.

[@madisoncraig4761]

This is extremely helpful. Not much of a GM mechanic since I have only owned imports. My brother has a 92 Oldmobile Bravada that I have changed the Fuel Pump fuse and fuel filter, Cleaned the after market K&N cone filter. Ive put fuel treatment in it. Hasn't been able to start on its own, just long strung out cranks with foot to floor.

[@ScannerDanner]

Step 1 is to definitely check your fuel psi. There is a service port on the intake area and you can buy that particular psi gauge to fit specifically your application for like $30? Or rent one from the parts store? Less than 50 psi on these things and they will not start. Then also major flooding from the regulator rupturing, which again can be determined with that same psi gauge

[@thomassmith1183]

Very informative, excellent video. Thank you !

[@vankuikendavid8453]

had this problem on my 5.7 and updated to multi port injection while I was in there best thing I ever did for my truck !

[@CodyDoesIt]

Love the knowledge dropped on this video.

[@buzzedo1]

This is TOP video. Helped me a heap. Cheers!

[@CCROSS5882]

I've seen people use head mounted cameras, seems the amount of work you do on cars would be great for you freeing up your hands, always great videos anyway!

[@MrRestorations]

I'm not a mechanic but it helps to see what's involved.

[@62SHIVAS]

Tnx for this useful video now. I'm soon starting same trobleshooting on my Astro -95 4,3L ... :D

[@waynebolton4427]

Brother u got the best video I've seen about fixing something

[@jonsimmons3507]

Pinch pliers,not vise grips. Lol, had a guy that worked for me that used vise grips and cut 3 different lines until he bought some pinch tools. Great video and knowledge as usual.

[@ScannerDanner]

no problem and keep me posted on what you find. also I have some other videos on o2 sensor testing and short term and long term fuel trim if you need them

[@ScannerDanner]

Thank you and will do.

[@ruffdogg4g]

this video is the best i have seen yet, i have the same problem with a 1997 tahoe 5.7 when the weather breaks i am going to try this it is better than changing that spider.keep up the good work !

[@donmilleraaaa]

You are an excellent teacher!!

[@ScannerDanner]

Thank you Don!

[@Just1GuyMetalworks]

Very informative! Thanks! 👍😊👍

[@LTZ400Mark]

This is an awesome video man. I have at 95 ZR2 s10 with the same issues. Ive checked the fuel pressure and it hold, no leak down. So now im stuck, trying to figure out why its running rich and why it takes so long to start, with the gas pedal all the way down. The inside of the intake was all dirty, not clean like yours was in the vid. The person I bought the truck from has already replace a few parts. Map sensor, fuel pressure regulator, distributor cap and wires, plugs, And a few other parts. He couldn't get it to run right. Im thinking its the CPI or spider injectors, IT does have the new FPR on it though. But anyways... thanks for the amazing video man it must of took you some time. I appreciate it.

[@samcarrs]

Double check all your grounds there are many. Clean them with sand paper or wire brush and use electric grease

[@kx144cc]

Very nice i have been debating trying not to throw parts at my blazer. Has been a test for me since I bought it

[@georgemyers9559]

Brother I just watch this video of you doing this job I want to thank you very much for the inside on this I have a 99 S10 LS

[@ScannerDanner]

Thank you! Glad it helped

[@94vettelover2]

You r my fav. youtube channel.If your school ever makes a stink of you filming,you can say that if a student misses a day,he/she can watch what u filmed so that person does not get behind.I know that missing 1 day of Tech school,you miss ALOT.I look forward to your videos & hope to be as knowledgable as u someday.I will also click on all your ads to help u out everytime I watch your videosKeep up the awesome work.Thumbs up everytime too

[@dafuq2165]

Your video was the best ive seen so far i was looking for that valve to test fuel pressure thank you so much

[@ScannerDanner]

You are very welcome

[@streetslingersgrillcaterin9142]

excellent video, thank you for the information

[@mike-yp1uk]

Yes once again a video that explains every aspect. I like how you expained drill holes to let out gas and the regulator repair. If money was not a concern which pico scope would you recommend to the professionals

[@ScannerDanner]

The automotive 4 channel kit (4425 I believe). If you are interested in buying one, you can find it here www.scannerdanner.com/lab-scopes.html

[@jackfentress0281]

Great video.

[@ScannerDanner]

Yes, as the check valve is part of the pump itself.

[@jaymiller3759]

sounds like you know your stuff inside and out dude, bravo, more, these newer vehicles give this old man bad headaches, you make this look easy, which I am sure it is to you. Wanna be pals?

[@kevindendy6888]

what a great presentation and teacher!

[@JamesSmith-xs7sr]

Just fixed one. Rich bank 2 code. Dropped 30 lbs fuel pressure in 2 minutes, koeo. Pinched return line, still dropped. Removed intake, pass side manifold washed clean from fuel leaking from the pressure regulator.

[@victor35ma]

Good explanation... You Know Scannerdanner. I am right now purchasing your book. just to show you my sopport. thanks again

[@pabloarevalodelaguila8767]

Como quisiera estar en una de sus clases. Excelente.

[@valgeorgiev5739]

Thanx for the help man, just diagnosed I have a bad fuel pump check valve in my 96 chevy. I was just about to get the FPR valve changed but it holds pressure with the PSI line pinched

[@ScannerDanner]

Nice job man! Way to pay attention to detail. Even though everyone was probably telling you to put the injector assembly in it.

[@valgeorgiev5739]

ScannerDanner no kidding, it is a very similar symptom, but I'm getting a TPS code, and the gas mileage is normal, thanks again for your help

[@chrismeeks9808]

You are freaking amazing thank you

[@peterey2]

gotta love 'file to fit' parts! another great video tho. thanks

[@michaelsapp3182]

Really good video. Very informative. 👍😎👍

[@tommavrakos]

great,great video

[@OldSchoolNoe]

Very cool!, had a similar situation on a Safari Van with a similar system. Problem was all fuel lines are metal and couldn't pinch to verify.

[@ScannerDanner]

@MiniFun92 that's great! did you like our last video? it was fun shooting with Eric.

[@dannysmobilerepair1153]

Great video, specially the part about pinching off the lines. I'm troubleshooting one in which priming pressure rises to 30 psi and quickly goes to zero. I was thinking about pinch # 1; the pressure gauge (and fuel pressure) is in between the vise grips and the return side with the regulator still in the picture. To isolate the fuel pump/check valve, would it be a good idea to disconnect the fuel filter and connect the fuel pressure gauge there? Thks

[@Drlovemachine]

Safety glasses when disconecting the fuel lines don't forget,and would you need to stuff rags down the big open ports to avoid anything falling down them?,when dismantalling the injector assembly.Great video by the way.

[@ScannerDanner]

@TrueBlueEG8 Thank you so much :)

[@TheZenerDiode]

ty for this vid, im currently in the process of diagnosing my 01 blazer, it has nasty13mpg :-( and a slight maybe minor rough idle at times... no long crank though. debating just going for the multi port injector as its more efficient anyways, but i will definitely be following some of these tips to make sure!

[@michaelevans9516]

I've put hundreds of dollars n multiple mechanics n this is the 1st ive seen im sure this is the reason

[@ScannerDanner]

Good luck! Do your pressure bleed down tests I showed before pulling the intake off

[@ScannerDanner]

Nice. What you are describing is exactly the symptoms of a bad O2 (not a bad pump) on a Chrysler product. Watch this video "2003 Jeep Liberty O2 Bias Voltage Testing" and also "1997 Jeep Blown O2 Heater Fuse Case Study" which the 97 it had a blown fuse but a bad O2 itself will give you the same symptoms.

[@TheZenerDiode]

@ScannerDanner thanks for the info!

[@ScannerDanner]

@Drlovemachine Agree thank you

[@childofgod4575]

amazing!! I see why they call it the spider..

[@ScannerDanner]

Love your user name! A Father to the fatherless He is too!

[@jessiegoss3712]

Thats cool checks, Thanks

[@stuartmotorsports]

Hands down one of the most thorough and informative videos ever!!!!! I learned a lot, liked and subscribed! Thank you! If I block off EGR will that eliminate all the mess shown on the driver side of your intake (opposite the leaking FPR side which was not black)?

[@ScannerDanner]

don't worry about how black the inside of the intake is. Every car is like this and it is from PCV gases. it doesn't hurt engine performance at all. Thanks so much!

[@stuartmotorsports]

@@ScannerDanner I have a P1404 code and a P1416 cleared them then I got a P1415 and P1404 cleared them again but P1404 persists. What happens if I eliminate all smog, EGR, Secondary air pump etc , yet leave 3 OS sensors for closed course competition of course? Getting some misfiring especially around 1500 rpms, Also some high idle and occasional idle stumbling.

[@ScannerDanner]

@@stuartmotorsports The P1404 may need the battery disconnected to clear the memory of the closed EGR valve position kzbin.info/www/bejne/foWXgKGGabpjqtE

[@rubeclayton8233]

Great Video... But...If I had to replace the fuel pressure regulator on this engine... I would just upgrade it to MPI while I was in there....

[@jahrain1693]

please God bless u for ur good work.my question is do we have to pinch the pressure holes before or after the fuel pressure gauge

[@ScannerDanner]

both before (on the pressure line) and after (on the return line) to determine the cause of the bleed down problem. If it holds on the psi line, it is the pump check valve (needs a new pump). If it holds on the return line, it is a bad regulator. If it doesn't hold on either line, you have a leaking injector or regulator.

[@markbunn8576]

Excellent video! My truck is holding fuel pressure fine but i think i may not be getting fuel to the 4 & 6 cylinder. Is there any way to check for a clogged line or poppet valve? My temperature gun tells me those two cylinders aren't firing. Spark and compression are good. Any ideas??

[@jhartmac100]

IM about to do the same thing with my 1995 Blazer but I will replace the whole unit. The truck only has 60k original miles but, what many experience is the failure of the injectors and lines.....that is the lines themselves rotting. Excellent vid tho. thanks

[@jomansanarez3773]

Like it I learn something new

[@ScannerDanner]

@victor35ma Thank you very much!

[@rickdavis2104]

I enjoy all your videos and I am goin to subscribe to your online course. I tried to use the test wire for the fuel pump and the pump does not come on. Do I have to have the ignition on for it to work. Mine is a 97 S10 4.3 V6. Thank you!

[@ScannerDanner]

You do NOT need the ignition switch on for this test. It is a direct connection to the feed side of the pump. With it jumped, go underneath and verify you have a good power and ground to the pump. (Gray wire = pump feed, Black wire = pump ground)

[@SkilledEddie]

I have a 1997 tahoe with a 5.7 Vortec that has the same issue. I'm getting ready to replace the regulator. I was going to say why only the p0172 code for the one bank and not the p0175 for the other bank if the regulator is bad? but watching the video answered my question. On this truck the intake is divided in 2 halves unlike my truck where the intake isn't divided. My truck has p0172, p0175 and p0300 and has all the same symptoms.

[@monkeywrangler5200]

I like watching your vids Paul, and hey we even have the same accent. NE of the city here nearer to Millers Auto if you know them. Learn a lot watching your vids and want to subscribe with you as soon as I’m able to. You and Schroedinger’s Box are my favs.

[@ScannerDanner]

sweet! always great to here from another local

[@chrissherrick3412]

Hey Paul I want to thank you for putting out good info an making good learning process for us! I've learned so much for you that's helpes me dianoise vehicles! But I need your input on this one! 98 Chevy s10 zr2 4.3 liter truck! Truck is running very rich at idle like -30 when vacuum pressure is very high on a down rev an -20% just on a standing idle! Everything been changed in the spider injection new fuel regulator All sensor inputs are good o2 are functioning normal! No codes in memory! An at a idle my fuel pressure gauge is fluctuating from 45-55 psi rapidy hit the gas an it will go up to 60psi an smoothing out! So I thought myb it could be uneven cylinder firing an upsetting the vacuum pressure but vacuum is at 20 inches an it does creep around bout an inch up an down! I have a donor 4.3l blazer that I swapped over maf map sensor ignition module coil PCM an just bout everything! Now you think this is a case of a bad fuel pump cause I've never seen a fuel pump show this kinda activity before! Any input would be great! I'm ready to burn it to the ground days an days of diagnosing an nothing!

[@ScannerDanner]

Chris Sherrick I've had brand new regulators leak on these. How is your rest psi? Does it hold? Your fuel psi readings are not good either but they are low and would cause lean, not rich conditions.

[@koreystrauch6237]

need diagram of sensors

[@Micscience]

This was a good video. I'm dealing with fuel issues with a 96 blazer CSEFI system though. I was curious when you pinched both the rubber fuel lines pressure and return, if the check valve is bad how can you tell?

[@samcarrs]

Ac delco regulator is the factory GM Brand and has exact specs to fit.

[@ScannerDanner]

@TheZenerDiode Make sure your EGR valve isn't sticking open (it will set a code for this)

[@kilkill84]

I think I'm having this issue, occasional check engine light and poor gas mileage I even smell fuel near the intake plenum. Any ideas? I'm going to change the oil and get a code reader I'd hate for this to lead to a blown up engine or any real bad issues.

[@jasonsmith4243]

What if you don't have a bleed down problem but 0 psi when key on position I also notice smoke coming from my throttle body when removed after truck is warmed up

[@ScannerDanner]

@TheZenerDiode Your 2001 version is different as your design is a Sequential CPI system, meaning you have 6 electrical injectors as opposed to one in my video. Same regulator set up though and they have the same problem too.

[@ScannerDanner]

@MrJgonzalez2 OBD1 half breed, since it is a 95 I don't think it is fully OBD II compliant but I could be wrong

[@malisa696]

Hello mister Paul. I had a similar problem with one car with similar fuel system (Opel Astra). I wanted to test the fuel pump if the valve in pump is not holding the pressure so I connect my fuel gauges direct to the pump inlet (I remove inlet hose from the rail) and when I manually engage the pump pressure is coming but when I disengage the pressure it is coming down rapidly so I assume the pump inside is not holding the pressure. Fuel system have a pump and a rest pressure valve on the rail.