2000 gmt400 3500hd 7.4 vortex low power

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Carlaisle

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Your fuel pressure is too low. You had better fuel pressure with the old regulator after your initial work. This indicates the pump is (or at least was, very recently) capable of delivering the required pressure. Based on what you have shared here, the original fuel pressure regulator does not appear to be malfunctioning. The newly installed fuel pressure regulator appears incorrect for the application or faulty. There are multiple options that will physically fit, but not all have the same pressure. If this was my problem to solve, I would reinstall the original FPR and check pressures KOEO and running. If good (58-62psi), the next thing I would check is the stock injectors. Does this vehicle have a hot start issue? I.e. after running up to operating temperature, shut it off and leave it for 15 minutes and then try to restart. Does it require an extended cranking time to start? If yes, your injectors are leaking, for which the stockers are notorious. If that truck sat for a few years the fuel in that rear tank is likely bad. and is being dumped into your front tank by the onboard tank balance controller. That may be the root cause of your low power problem.
 

jtbarnes67

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On the small block, you would put a valve in place of the filter, prime the pump, close the valve and check for a pressure bleed down. If it held, it’s the pump. If it drops, it’s an injector, external leak or leak back through the return.

You’d then open the supply, prime system and block the return - there’s a union on the return line adjacent to the filter for installation of a valve. If it holds, then it’s leaking back into the return. If it drops, then it’s an external leak or an injector.

Your injectors are external, right? You pulled each injector with system pressurized?
The injectors are under the plenum . With the top half of the plentum off Energizing/pressurizing system you can see if the injectors are leaking or not. They did not appear to be .
 

jtbarnes67

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Your fuel pressure is too low. You had better fuel pressure with the old regulator after your initial work. This indicates the pump is (or at least was, very recently) capable of delivering the required pressure. Based on what you have shared here, the original fuel pressure regulator does not appear to be malfunctioning. The newly installed fuel pressure regulator appears incorrect for the application or faulty. There are multiple options that will physically fit, but not all have the same pressure. If this was my problem to solve, I would reinstall the original FPR and check pressures KOEO and running. If good (58-62psi), the next thing I would check is the stock injectors. Does this vehicle have a hot start issue? I.e. after running up to operating temperature, shut it off and leave it for 15 minutes and then try to restart. Does it require an extended cranking time to start? If yes, your injectors are leaking, for which the stockers are notorious. If that truck sat for a few years the fuel in that rear tank is likely bad. and is being dumped into your front tank by the onboard tank balance controller. That may be the root cause of your low power problem.
No hot start. It always starts up easily. I'm fairly certain the rear talk is empty. I totally agree that the new FPR seemingly is too low. 48 lbs is what it's running at idle witch is what my 5.3 LS engine runs. It came from AutoZone, the numbers on the box is at least correct but they could have gotten wrong boxed somehow. I wish I had of recorded numbers on part itself before installing.
 

jtbarnes67

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So I didn't get to spend as much time with truck as I hoped but. I have got some new interesting info.

Borrowed a different scan tool with more functionality. Bank one sensor one o2 sensors is not switching. Staying around .140 v if I remember rt. I will double check and edit if needed. Swapped bank 1 sensor to bank 2 etc and issue stayed at one.

The scam tool keeps flashing egr and o2 sensor . So Did a thorough test procedure on egr the only thing that was out of spec maybe was the resistance in the solenoid was 19 ohms and at room temp was supposed to be around 9. Couldn't find anywhere if this was too out of spec so rigged a piece of wood between the EGR and manifold and it made no change.

I fixed an exhaust leak where you take exhaust apart that has a cat on either side of it. And while doing so noticed that there was pieces of cat in the muffler. Didn't seem like a lot wes there but if you shake muffler around you definitely can hear it in there. I took muffler tsil pipe down from the hangers and spend hours trying to get it out from under truck to clean cat debris from muffler and it would not come out. So I bolted it all back and will address at a later date. I drove the truck for years with it in their I'm pretty sure there's not enough to cause a problem or is causing this problem at least.


So I've saved the best for last this scan tool has a manufacture specific area for dtcs toll is saying there is 40 codes. Specific to this truck. Not sure how that's even possible and it still running and still no check engine light. I waited to address the o2 sensors until I got some input. It would be my understanding with that many codes the ecm is bad. That's the only thing that could cause all 40 codes. There is a possibility the ecm was swapped out while truck was sitting or it most likely is is just bad if that turns out to be the case. The large tag is missing from ecm but the small one is still there. See attachment what next please. And thanks guys fir staying with me
 

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stutaeng

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You can squirt some carb cleaner into the intake and monitor O2 waveform to see if O2 is reading correctly or responding, but looks like you have confirmed it's not the O2 by swapping O2 sensor from the other bank.

Most likely your cats are damaged by wrong air/fuel ratio being burned by extended period of time running.

Not sure about all of those codes. I normally try not to clear out codes, but you may actually want to do that and see what comes back on, and go from there.
 
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jtbarnes67

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You can squirt some carb cleaner into the intake and monitor O2 waveform to see if O2 is reading correctly or responding, but looks like you have confirmed it's not the O2 by swapping O2 sensor from the other bank.

Most likely your cats are damaged by wrong air/fuel ratio being burned by extended period of time running.

Not sure about all of those codes. I normally try not to clear out codes, but you may actually want to do that and see what comes back on, and go from there.
Cats are gutted already. As far as the o2 sensors not sure swapping them out absolutely says they are fine with problem staying on bank 1. If I understand what I've read there can be another issue that could effect the o2 voltage. If someone could confirm that for me thanks
 

yevgenievich

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I would still suspect injectors. Even if they don't actively leak, can still have poor delivery
 

ralmo94

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Cats are gutted already. As far as the o2 sensors not sure swapping them out absolutely says they are fine with problem staying on bank 1. If I understand what I've read there can be another issue that could effect the o2 voltage. If someone could confirm that for me thanks
It could be an issue with wiring harness and and or ground. You can check an O2 sensor with a torch off of the vehicle, and a multimeter. There are lots of videos on YouTube about it.
Also how do the spark plugs look on that bank? What does the scan tool say O2 voltage is with them disconnected?
Should be right about 450mv or so. What is the code for the O2, is it the heater, or a lean code?
There is a signal wire and a ground wire for the O2. The computer reads the difference between the two, the other two wire are the heater circuit and polarity doesn't matter on them.
If you moved a functional sensor to the nonfunctional bank, and got the same results on the sam bank, it's not the sensor but the circuit. If it was the sensor the problem would move with the sensor.
Does the exhaust get hot, with a plugged up muffler it could be some of your low power, it might have seemed to work fine, then got plugged more? 454 likes to breathe.

I wouldn't worry about the egr yet, unless it's stuck open. If it's closed I would leave it attached and unplugged until fueling is diagnosed.

That's a lot, but all I can think of now.
I generally like to prove what's wrong with something before I just throw parts at it.

Low fuel pressure would make you run lean, but it should still be able to trim it out.
Egr malfunctioning wont cause too much problems exept it could mess with your timing, as long as it's not stuck open.
O2 circuit seems to be in question.
Exhaust is probably restricted

I would treat these as four different problems and start with confirming fueling problem. If the pressure is hight enough it should be able to run open loop just fine. Have you checked fuel pressure with a second tester?
 
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