k3500 silverado vortec 454 possible fuel pressure regulator?

[justasquid]

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.

[alfatwin]

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?

[EFI69Cam]

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.

[justasquid]

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.

[justasquid]

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.

[EFI69Cam]

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.

[justasquid]

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.

[Walter s]

I have same problem but if I change fuel grade it stops what can that b