Josh29

Thank you for that video link. In those videos the old and new FSCM's were asking for a desired pressure of 43.5 Psi while it was running. It was doing exactly what mine is doing. I guess that's normal. Nobody at the dealership I had it programmed at could tell me that was normal. I feel much better now. The lack of power and hesitation must have just been from the plugged cats. Also I do have an exhaust leak now at the back of bank 2 exhaust manifold where it connects to the Y pipe. So I'm sure that could be causing that side to run a little richer trim. When the Y pipe was off we removed a few broken exhaust manifold bolts that were leaking a little. So technically I just moved the exhaust leak back 18" or so! Haha. I appreciate the help. Now I'm off to drop the tranny cross member and pull the Y pipe again. I despise exhaust leaks.

So I just took it out for a beat. Runs way better with the new cats. No more hesitation and pinging. My long term fuel trim is still wacky. Bank 1 is minus 1% and bank 2 is positive 8%. I don't see a deviation in air fuel mixture like that from one side of the engine to the other as a sign it's running right. And I just noticed on the scanner that the desired pressure the computer is asking for is 43.5psi. And it's maintaining that beautifully. For some reason the computer is just asking for a lower psi than what the specs call for on that engine. I can command the pressure up to 60psi and it does run stronger throughout the rpm range at full throttle than when I go full throttle at 43.5psi. I just can't think of any other reason besides bad or wrong programming in the FPCM.

Since I just got the new cats on after removing the plugged ones, I haven't got to check my fuel trims yet. Gonna do that in about an hour. The 02 sensors seem to be ok and I haven't checked anything to do with the MAF sensor. Even though the cats were pretty damn clogged I never got a code for them being clogged, overheated or out of parameter. Before removing the clogged cats, i had -6% LTFT bank 1 and +7% LTFT bank 2. Which I assumed it was trying to lean out bank 1 because that cat was more clogged than bank 2 cat. I'll report back new LTFT numbers later this afternoon. Thanks for replying and brainstorming with me. I needed somebody else's input after I exhausted the knowledge out of everyone I know. I had a really good mechanic at a private shop but he passed away a few years ago now.

Just checked and Eric at South Main Auto is about 2-2.5 hours from me. Not bad but I can't imagine I would be able to get there during business hours with my schedule. Can't believe how difficult the original fuel leak fix is turning out to be. CAN OF WORMS!!!

It's reading 43.5 psi on the scanner and the fuel rail. and it maintains that the whole time your driving within a psi or two. No matter what load or throttle position. When I first start it the scanner and the fuel rail mechanical test gauge reads the proper 62psi for 10-20 seconds then it drops to 43.5. The only reason I say it's being commanded down by the computer is because I can command it right back up with the scanner. It seems like they installed a program in the FPCM that is for a different vehicle or something. The old FPCM just rotted out and got water in it. And when I installed the new one it did fix the no start because after that I had power to the pump again. It just supplies a different pressure. I don't know enough about programming to know if it's possible to mess that up when programming the new FPCM.

If I didn't explain it well. This pressure drop is consistent and repeatable on both brand new ACDelco units I installed. And I purchased them online and installed myself. So two different regulators both brand new. I'll have to look up where he is located from me. Thanks. Never heard of that town.

Thanks for the response. Both new sending units I put in the tank contained everything. (Pump, regulator, level sensor, filter and tank pressure sensor). The tank was leaking from a rusted metal pressure line coming out of the top of the sending unit. And I agree, I normally would never have a dealership diagnose anything! But I always had good pressure 55psi+ before the new FPCM install and program. And I wanted them to replace their work for free if it was faulty. Which they agreed to. Then when I got the truck back and they told me about the cats I learned that they didn't test the FPCM at all. They are clueless at the dealership. If it was a pinched wire I would assume I wouldn't be able to command the pump on with the scanner and see full pressure.

Hello. New poster here. I have a 2008 Silverado extended cab 4x4 with a 5.3 j vin code. I replaced a leaking fuel sending unit a few weeks back. Truck ran ok for a few days then quit. Would turn over but not start. I had no power coming out of the fuel control module above the spare tire. So I replaced it with a GM oem control module and had a dealership program it. After that was programmed it felt real sluggish and slow. Started pinging bad under heavy loads. So I checked the fuel pressure. Should be between 55-62psi. With the key on engine off it jumps right to 62-65psi. Start the truck and it maintains that pressure for about 10-20seconds then drops straight down to 43psi. It's not a slow drop, it's immediate. So I assumed I had a faulty fuel regulator on the new sending unit, so I replaced the whole sending unit with another brand new one (ACDelco). Didn't change anything. So I replaced the inline pressure switch even though it read the same on my scanner that a mechanical gauge read on the fuel rail. No difference. I took it back to the dealer that programmed the new FPCM and asked them to diagnose the pressure drop. Meaning I wanted them to see if the new FPCM was faulty or possibly the program job. They charged me $220 for diagnostics and said I had clogged cats and said it could be causing the computer to force the pressure down. So I went home and replaced the Y pipe and cats which were clogged. Fuel pressure still drops. Anyone have any Idea how this can be happening? I can command the fuel pump on with my scanner and it will jump right back up to 62psi no problem. So why is the computer commanding the pressure down like this?