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  1. #1
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    Default k3500 silverado vortec 454 possible fuel pressure regulator?

    I have a 97 silverado 3500 with the vortec 454 in it. It has 200k on it, and has a horrible low throttle input miss and a high idle at times. It is also way down on power and stumbles until you really give it some gas, but even then, you can tell its low on power. Unfortunately, this is how I aquired the vehicle with this condition. I changed the plugs, wires, fuel filter, and even the distributor for the common worn out gear, and man was it worn. Everything I changed was extremely worn out and each time, I though for sure I found the issue. but the issue is still there. In fact, it seems to hesitate even worse now. I do now have a p1345 code (crankshaft/camshaft correlation) since I changed the distributor, but have read that it can only be adjusted with scan tool. I do wonder though if the distributor was the issue and I have it one tooth off. I made sure to mark everything and put it all back. But I don't know 100 percent sure it was correct to start with.

    My main question now is: what is the fuel pressure suppose to be? With the fuel pump on, it registers around 50 psi. As soon as the fuel pump shuts off, it drops to 20 psi. But will stay there for hours. I have read that it should not drop at all and if it does, the FPR or injector could be the issue. I have read these engines need to run at least 60psi, but have also read lower psi.

    I guess I need to buy a service manual. But if anyone has had any experience with these engines and can point me in the right direction, I would greatly appreciate it.

    2005 CBR 1000RR..."mostly stock".
    1968 camaro... "in the works".


  2. #2
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    OK lets start with the basics. (1) Check your compression, the fastest way to see if they are all at least even with each other is to disable the ignition and roll it over with the starter. If it sounds like a nice even rhythm its probably ok. If it has a spot where it skips or sounds like it speeds up, pops out the exhaust or intake you got problems. (2) check your timing (if it's been doing this since you got it who knows what "they" did). the computer will have to be disabled to properly check it (usually it requires unplugging the input wire(s). (3) I don't know the exact fuel pressure, but if you call your local dealer/truck shop and ask real nice, they usually will help you out, it's not really the pressure thats the problem, but the volume...if it works at full throttle under load conditions (this is the most taxing on the fuel system) this is probably not the problem. If this truck is what I think it is, it has a "octopus" type injection system, making it virtually impossible to isolate any one injector at a time, they also take a sh-t quite often and are expensive to replace. Also, if you are thinking ignition, which is the next likely target, if it works at full throttle (again, the most taxing condition) then it probably has ENOUGH spark. All this being said (very long winded I know) if your compression and timing check out I would look towards fuel delivery system/ major air leaks between mass airflow sensor and throttle body, cam timing, worn cam lobes..... let me know how it goes question: does it have individual injectors (electronic) / TBI or octopus type injectors?

  3. #3
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    The vortec 454 does not have the same injectors as the small block vortec. It uses the same type injector LT1 and TPI engines. They are buried under the plenum.

    Do you have any signs of fuel in vacuum line to the regulator? Does the fuel pressure at idle seem steady?

    I seem to recall the pressure should around 60lbs as most GM stuff in those years were 4 bar. Do you have access to a scanner? What are the fuel trims telling you? I'm guessing you have a bad fuel pump.

  4. #4
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    Thanks for the replies.

    I think you may be right about the fuel pump EFI69. I have no idea if it has ever been changed, but from my experience with silverados thus far, if its original, its certainly due to fail. I was only think of the FPR since the pressure drops in less than a second once the pump is turned off. I have read a little on how to test the FPR, which I will do tonight when I get home from work. I haven't checked the vacuum line to the FPR yet as I can't even see it. I have to tear some stuff off to hopefully be able to at least remove the line. I've heard the intake has to come off in order to change it however. I really hope not, but I have to get this fixed before this weekend. If I don't, the camper won't be getting towed.

    alfatwin. thanks for the feedback. I will be checking up the things you suggested as well. I appreciate the feedback. It has individual injectors.

    I'll update once I get home and inspect things.

    thanks again.
    2005 CBR 1000RR..."mostly stock".
    1968 camaro... "in the works".

  5. #5
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    well, according a few things I've read. You can crimp the return line from the FPR and if it holds pressure, the FPR is bad. If it still doesn't hold pressure, then the Fuel pump is bleeding back into the tank. The more consistent information I am reading says 60+ psi with the pump on, and as soon as its off, it is suppose to hold within 10 percent of that amount for 20 minutes. Mine only runs 50 psi, then drops to 20 psi, but holds after that.

    I did the crimp test and it still drops immediately from 50 psi to 20psi. Im starting to lean towards the fuel pump. But I still can't verify if the operation of the pump is normal or not. I even stopped at the dealership to ask and they couldn't tell me. I was ready to buy their overly priced fuel pump too if it was in fact bad. But all they said was they didn't know. Their mechanics had gone home and they couldn't look it up anywhere. But did inform me that I could schedule an appointment,(a week out none the less) and get a diagnosis to the tune of 300-400 bucks. For that timeline and cost, I may be better off just replacing items and hope I get it right.

    so if anyone out there can tell me if the fuel pressure and bleed off I am getting is normal or not. I would greatly.....greatly appreciate it!!.

    I will more than likely just replace the pump as I really need this truck this weekend. I guess I will hope and pray that is the problem.

    I also verified the distributor was in fact in the correct location. I went one tooth back and one tooth forward just to make sure and it barely ran in those positions.
    2005 CBR 1000RR..."mostly stock".
    1968 camaro... "in the works".

  6. #6
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    I seem to recall that the pressure hold valve is on the outlet of the fuel pump. Its to keep the entire fuel system pressurized to speed startup. All the regulators I've ever seen are just a spring loaded diaphragm that bleeds fuel off into the return line when pressure on the diaphragm exceeds the spring pressure.

  7. #7
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    Yes, you are correct. I just talked with a friend of mine who is a master mechanic. He said he couldn't say for certain, but with his experience, the fuel pump fails just as you described and its very common on these vehicles for them to keep running, just loose pressure and have issues. The check valve fails and all of the gas rushes back into the tank. The fuel filter I changed was nearly plugged, and he said that more than likely contributed to the pump failing. He also said that 48 psi is barely enough to keep the truck running, that the vortecs need to be at the upper limit of their range, which I found out is 58-64 psi. And it is suppose to hold the pressure, not bleed off as fast as it does. he did say though its odd that it runs fine everywhere except light throttle inputs. But with pressure at the limit of not being enough, anything is possible.

    I will be tackling the fuel pump tomorrow.

    thanks for the help. I'll post back with the results.
    2005 CBR 1000RR..."mostly stock".
    1968 camaro... "in the works".

  8. #8
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    I'd like to know the outcome of this. I am having the exact same issues as you. I replaced wires, spark plugs, fuel filter and fuel pump. I am still having the same problems and I am almost certain at this point its the fuel pressure regulator that is wrong with my truck

  9. #9
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    good thread, I would like to know as well. I'm with your master mechanic, and it does seem to be possible that the pump will fix both problems, lack of fuel does some funny things...

  10. #10
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    Just an update. I have yet to do the fuel pump as my weekend was extremely busy. I do plan on getting to it this week sometime and will post back.

    makoshark
    I'd like to know the outcome of this.


    If I were you, I'd pull the distributor and look at the gear. Just make sure you mark everything really well so you get it back in the same spot. there is no way to time these, and you will need to drop the distributor back into the same spot in regards to the rotor, and the distributor housing as well. If they are both marked, you should be fine though. Although it didn't completely fix my issue, Im sure mine wasn't helping at all. The gear is very common to get worn on these engines, which I have found through research is one of the most likely causes of low throttle hesitation. I honestly don't know how it even ran with the gear as bad as it was. the teeth were paper thin, so the timing was jumping all over the place. I think I'm combating quite a few different issues though, and while Im gettting them sorted out, I still have a pretty major one in the fuel system. It definately has a lot more power than when I first started to sort these issues out, but the hesistaion is still very much there. Also, instead of the arc marks on the poles being lined up with the center, all of the marks were to the side of the poles on the cap. which meant the rotor was actually past the or before the pole instead of being inline. Maybe just pull the cap and look at the poles and see how the marks look.

    2005 CBR 1000RR..."mostly stock".
    1968 camaro... "in the works".

  11. #11
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    Mine is a LS motor. There's the difference, but the symptom will be the same. My truck while driving, if you mash the gas pedal on the floor, will pour black smoke out. It is running rich, which you can smell sitting at idle. I think its the fuel pressure regulator dumping too much fuel. My symptoms are exactly the same as yours though and the fuel pump didn't make any difference. Its been my experience with electric fuel pumps, they just go out without warning.

    On your motor, your running the HEI distributor, right? Have you checked the ignition module? They can cause a motor to run like yours if going bad. Usually the wires get frayed and split open due to the nature of it being bent over stressing the coating on the wire. I've dealt with that quite often back in the day, before the LS motors

  12. #12
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    ah, I thought you had the same engine. Mine does have hte distributor, but Im not sure its an HEI. I really don't know what to call it. Its got the funky LT-1 looking cap, and is computer controlled timing. The gear on mine was extremely worn down thought. I will definately take a look at what suggested. thanks for the info.

    It does sound like a FPR on yours though. Mine does not have a gas smell or black smoke. its kind of funny though. I did notice the exhaust sounds a little too muffled though. It also has a phht phht phht...sound to it. I almost wonder if the cat is plugged? Is anyway to check it without pulling it apart? The truck does smell like it runs hot. The actual temp is fine, but when you lift the hood, it really smells hot.

    I drove the truck this weekend. I noticed it does lack power basically everywhere above just off idle. It will smooth out once your into the gas as far as the hesitation is concerned, but it is definately not on par with where it should be. If I start out, it will have good power and sound normal for about a half of second, then you can feel the power drop right off and the engine just doesn't sound right. You have to give it a lot more gas to make up for it. Its hard to explain, but its being restricted somewhere. I am planning on the fuel pump. If that doesn't do it, Im not sure where to turn. Im fairly mechanically inclined, but this one is will have me baffled if its not the fuel pump.
    2005 CBR 1000RR..."mostly stock".
    1968 camaro... "in the works".

  13. #13
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    Just an update for those who may experience something down the road.

    It turns out, my cat was slightly plugged and the egr valve was weak. The extra backpressure was opening the egr valve and creating a lean condition. I actually found the issue a month ago and forgot about this post. I hate it when a post just ends, so I figured I would give it some closure.

    The truck now runs great and has really good power everywhere.
    2005 CBR 1000RR..."mostly stock".
    1968 camaro... "in the works".

  14. #14
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    Quote Originally Posted by justasquid View Post
    I hate it when a post just ends, so I figured I would give it some closure.

    The truck now runs great and has really good power everywhere.
    Thanks for the update.
    1970 RS/SS350 139K on the clock:
    89 TPI motor w/ 1pc rear seal coupled to a Viper T56 via Mcleod's modular bellhousing w/ hydraulic T/O bearing from the Viper, 12 bolt rear w/ 3.73 gearing, SC&C upper control arms, factory lowers with Delalums, C5 brakes at all four corners, Front Wheels 17x8's with Sumi 255/40/17 and Rear Wheels 17x9's with Sumi 275/40/17.
    Brief description of the work done so far can be found here: http://www.nastyz28.com/forum/showthread.php?t=112454




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