Help Identifying Cause of Low Fuel Pressure

It's probably worth mentioning that the breaker supplies the fuel pump relay too along with the fuel pumps if you're looking for possible "culprits".

For a replacement, Spectra FD-14 has been  a good CCF choice over the years.

Seems lately that the most common fix to GT40 running problems is the PIP sensor. I have had the crank shaft position sensor,which is basically the same thing go out on every Jeep I have owned...... 

JayG80 wrote: Removing the muffler would be down on my list after “exhausting” all options and shooting my dog.

My buddy is a pretty fair mechanic, he brought his boat over to find out why it is so rich at idle and had no power above 2,800 RPM.   His is a Chevy 350 but he had two wire switched in the fire order.   He paid a shop to look at it and they claimed his coil wire was loose and they tightened that and told him it was fixed.   His Chevy fire order is 18436572, he had wires 3 and 6 switched.  The two were close enough that it ran but ran badly one of his plugs was fouled black but the other actually looked pretty good after running wired wrong.

It could be a bad baffle in centek muffler causing back pressure and loss of top end power.  My story linked below.

I took the boat out today and the power under load was significantly better, but it's still not running great. Whereas before I couldn't even plane, now I'm topping out around 32 mph / 2800 RPMs. It also hesitates when accelerating and just generally runs rough / surges. The idle is also still rough but that isn't as big of a deal to me right now.

I gotta admit I'm getting frustrated and could use some help with where to look next as it feels like I'm running short on options. Maybe replace the coil? Maybe the full distributor? I'm also gonna open up the main wiring harness and start tracing all the wiring to make sure everything is correct.

A few more details:
-It sounds a bit like a misfire at WOT, but I can't say for sure. I also think I hear a tinny clicking noise too
-About the last 3-4" of travel on the throttle doesn't increase RPM.
-I disabled the oil pressure switch / water temp switch to bypass limp
-I don't think it's a fuel issue (fuel pressure was 39 at WOT, all new injectors, new fcc tube, new filter, checked anti siphon, new fuel pressure regulator)
-I couldn't find any vacuum leaks
-New MAP sensor
-New rotor, cap, wires, plugs
-All the wires are making a spark

Now the other direction I do have to consider is more serious mechanical issues. I did another compression test with the engine warm (but dry) and got 100-115-115-115-110-95-100-110. Not great numbers, but if you adjust for my elevation they would be about 15-20 higher at sea level so more like 120-145 range. Is that a huge red flag? Think its worth a leak down test on the 95 cylinder?

Thanks for helping me stay sane!!

Update: Installed the correct injectors today. Engine fires right up and sounds much better, but I still have a rolling idle. Pulled the IAC valve and cleaned it, but it didn't look too dirty. Just to verify though, the solenoid fired when I turned the key on / engine off to open the valve, and then it closed a couple seconds later. Is that what should have happened, or should the valve have stayed open with KOEO?

I'm planning to check the vacuum hoses for a leak in the morning. Then I hope to do a lake test in the afternoon to see how the engine does under load. Fingers crossed the injectors / FCC tube solved my top end power issues!

The seller sounds like an OK guy

Thanks! I'm sure I am going to have plenty more surprises at this rate haha.

To the sellers credit, he has been super responsive and without any prompting sent me a generous refund on a portion of the purchase price.

Yeah I just was running short on time last night, going to check the TPS this morning. I may have just had a breakthrough though, I looked up the injectors and they are 42 lb, looks like they should be 24 lb. They were replaced recently by the prior owner. My theory is 42 lb injector + 10 psi fuel pressure was a workable combo. But now 42 lb injector + 40 psi fuel pressure is running incredibly rich.

Hmm, I know for sure I didnt unplug it, but the prior owner definitely could have. I forgot to mention that after getting code 53, I did clear the codes and run the boat for about 15 minutes on the water and retested them afterwards...no codes. Not sure if I gave it enough time for the code 53 to come back or if as you suspect that was an old irrelevant code.

Making progress, but still having issues and I could use some help with where to go from here.

I replaced the tube in the FCC and immediately got 38 psi fuel pressure (had 10 before). But, the engine is now hard to start when cold. I have to put throttle at almost WOT while turning key to get it to start, whereas before fixing the FCC tube it fired right up without needing any throttle. It also wants to die when I return to idle until its warm..

I then took it out for a lake test and I'm also still unable to get over about 1600ish RPMs. The engine does sound better. It accelerates smoothly to about 1400ish RPMs, then it levels off at 1600. Pushing the throttle past this point makes it almost sound worse. I did run a quick key on engine off test and got code 53 which is TPS out of range.

After the disappointing lake test, I came home and pulled the fuel rails and injectors. They were all in good shape, couldn't find any debris. Flushed with lots of carb cleaner. I manually ran the injectors off a battery with an air compressor and the spray pattern looked good. Tested resistance and they were all about 15 ohms. I haven't tested it on a hose yet, but I don't have much hope that this cleaning did anything.

Also, I was curious and pulled all my almost new spark plugs to inspect them. 7 of the 8 plugs were covered in heavy carbon deposits, suggesting to me they are running rich maybe? Not sure why 1 was clean though? Could my formerly lean engine that now has great fuel pressure be overcompensating?

Next steps:
-I'm thinking the TPS could potentially be malfunctioning? I'll try to test that tomorrow.
-Inspect IAC / spark arrestor
-???

Thanks again for the help!

The inside doesn't exactly look too good either