Help Identifying Cause of Low Fuel Pressure |
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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I could use some help with a fuel issue I'm having in my 2001 SAN (Here is the background on the boat). I took it out for the first time and the boat struggled to get over 1800 RPM and can't get on plane. It sounds decent in idle and revs up out of gear. It just doesn't have hardly any power under load, runs rough, etc. I immediately replaced the rotor / cap / wires / plugs as this hadn't been done in a while. Before taking it back out to the lake to test to see if the ignition tune-up resolved the issue, I put a fuel pressure gauge on the fuel rail and ran the boat off a hose. To my surprise, I'm getting 10 PSI off the schrader valve on the fuel rail and the HP pump. I talked with the prior owner and he has a video of 40 PSI when running the engine out of the boat. He also just replaced the LP and HP pumps, filter, injectors, etc. I have absolutely no reason not to trust him, he's been very helpful giving me more ideas to try and even offered to send me a new pump. Here's what I've done so far (w/ references to Service
Manual):
Based on the above, it seems like the logical next steps would be to:
What else should I try?? (Note: I cross posted this on PN -- hope that is OK. Let me know if that is a party foul and which site is a better place for these sort of questions!) |
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MrMcD ![]() Grand Poobah ![]() ![]() Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3734 |
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First, how old is the fuel in the gas tank? I worked on one last year that had sat a few years, when they tried to launch it the fuel plugged up 5 of 8 injectors right away.
The low pressure pump feeds the High pressure pump, if the LP is working you should have a steady 8+ PSI if the HP is working it will bump up to 40 or so, I don't know the exact for your engine. You said a 2001, would that be a 351W engine, GT40 Pro Boss. The fact that the previous owner had the pump apart points to them also having the issue you are fighting now. Mark
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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Thanks Mark! Really appreciate your help. I've got the GT40 Pro Boss. The fuel is pretty new. The previous owner pulled the tank and replaced the fuel, he put in enough to run the engine himself before handing it off to me. So max a couple months old. Still I picked up a bottle of Seafoam and will definitely run it through the system.
Sounds like from your post that the issue centers around the HP pump then given I'm not getting anything over 10 PSI. Do you know if the fuel regulator could have an impact on the HP pump? Said another way, is it possible that a faulty regulator is incorrectly providing feedback to the HP pump that shuts it down? I'm just debating whether it is logical to replace the fuel regulator, or if I can eliminate that as a potential issue. |
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Gary S ![]() Grand Poobah ![]() ![]() Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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I believe if you disconnect the vacuum hose from the fuel pressure regulator and then plug it,it is supposed to max the fuel pressure,or if you can carefully clamp off that hose that will work too.
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KENO ![]() Grand Poobah ![]() Joined: June-06-2004 Location: United States Status: Offline Points: 11018 |
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Your next logical steps sound pretty logical to me ![]() You can test the regulator per the manual to make sure it responds and controls pressure. Section 3H-15 is a good starting place More than one person has screwed up that little discharge hose inside the FCC when reassembling it so that it's twisted and kinked and not allowing much flow at all. PS .......your background link doesn't work
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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Thanks!! Will give those ideas a shot.
FYI here is the link to the history on my boat, not sure how to fix it above: https://www.planetnautique.com/vb5/forum/classified-group-buy-section/boats-for-sale-by-owner/633506-2001-san-project-for-sale-or-part-out |
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Gary S ![]() Grand Poobah ![]() ![]() Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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FYI section 3H-15 is on page 3H-7 in the GT40 manual
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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Fuel regulator was in stock at my local o'Reilly's for $27 so I went ahead and replaced it...no change. Time for the FCC...fingers crossed!
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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Woohoo, the tube inside the FCC was totally shot. Not sure how that happened but the outer coating essentially disintegrated. Plenty of cracks and holes. Definitely the cause.
Do I need to order the tube or is it something generic I could buy locally? |
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KENO ![]() Grand Poobah ![]() Joined: June-06-2004 Location: United States Status: Offline Points: 11018 |
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Here's a link to the SkiDim hose You can pretty easily see SAE 30R10 on the hose. It's fuel injection rated hose available and most likely in stock at any auto parts store anywhere ![]() You'll have it fixed by sometime tomorrow
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Mpost ![]() Senior Member ![]() ![]() Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329 |
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Sure sems like if the PO had just replaced the HP fuel pump he would have notice the condition of that hose, based on your picture on PN????
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84 SN Sold 98 SN Lund Pro V 1975 Alumacraft
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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He said that hose was brand new in Feb. I think he must have used hose that was fuel rated for the inner portion but not exterior-- and it just deteriorated. That's my best guess.
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KENO ![]() Grand Poobah ![]() Joined: June-06-2004 Location: United States Status: Offline Points: 11018 |
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The inside doesn't exactly look too good either
![]() Plenty of deterioration there, if the inside was good, it wouldn't have leaked and killed your pump output pressure.
The SAE 30R10 hose is submersible
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MrMcD ![]() Grand Poobah ![]() ![]() Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3734 |
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Standard fuel hose is only good for 15psi or so, as Ken instructed buy a quality fuel injection hose rated for 50 psi and you will be fine. The local parts stores should all carry it. Measure your connection so you know what size to ask for, 1/4, 5/16 or 3/8” are popular and available locally. If the hose is rated for more pressure that is fine but it can’t be rated for less.
Glad you found the issue.
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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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! |
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KENO ![]() Grand Poobah ![]() Joined: June-06-2004 Location: United States Status: Offline Points: 11018 |
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Strictly a guess here, but could you have accidentally unplugged the TPS while working on the engine?
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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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.
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Gary S ![]() Grand Poobah ![]() ![]() Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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I’m curious of why after getting a code telling you that your tps was out of range you took an entirely different path of pulling your injectors. With that hose degradation I understand but you can’t be jumping around. Investigate that code, if you have ? Google them- many of these ? have come up before on 5.0 Mustang forums . Some of those guys are sharp fixing them - they have been modifying and working on them for a longer period of time than any boat guys.
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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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.
Edit: Just ordered new 24 lb injectors here: https://lmr.com/item/M9593LU24A-K/Mustang-Ford-Racing-24lb-Fuel-Injector-Kit-w-Adapters-86-04
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KENO ![]() Grand Poobah ![]() Joined: June-06-2004 Location: United States Status: Offline Points: 11018 |
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Sounds to me like you're on the right track here Dave
Injectors pulsed open the same amount of time by the computer equals a buttload more fuel being injected ![]() Maybe the cylinder with the one decent looking plug had a plugged/restricted/screwed up injector
I wonder if you'll have any more "surprises" in store for you |
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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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. |
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KENO ![]() Grand Poobah ![]() Joined: June-06-2004 Location: United States Status: Offline Points: 11018 |
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Can't help but notice that you got one reply to your post on PN...................from yourself ![]() They're better for some things and not for others NautiqueJeff shows up on CCF at times with questions on older stuff.
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KENO ![]() Grand Poobah ![]() Joined: June-06-2004 Location: United States Status: Offline Points: 11018 |
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The seller sounds like an OK guy
![]() BTW He goes by Lucky McElroy here on CCF
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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Just for the sake of documentation, the TPS seems to check out.....0.95V at idle, 4.65V at WOT.
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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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! |
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KENO ![]() Grand Poobah ![]() Joined: June-06-2004 Location: United States Status: Offline Points: 11018 |
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I think it's normal.
After a couple of seconds with the key ON and no PIP signal from the distributor to say that the engine is running the computer shuts things down Somrtimes I think wrong, but I think in this case it's normal
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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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!! |
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bwinn ![]() Senior Member ![]() Joined: July-13-2009 Location: ct Status: Offline Points: 396 |
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David, did you confirm no plug wires got switched when you replaced the wires at the distributor yet? I also would check the gap on the plugs.
Burton |
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JayG80 ![]() Senior Member ![]() Joined: January-07-2007 Location: United States Status: Offline Points: 170 |
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It could be a bad baffle in centek muffler causing back pressure and loss of top end power. My story linked below.
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2007 Ski
2002 Ski |
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dshack ![]() Groupie ![]() Joined: June-11-2021 Location: Utah Status: Offline Points: 47 |
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Thanks for the suggestions. I've double checked the spark wiring but will definitely take a look again. I'd love it to be something that simple!!
@Jay: Sounds like a fun repair you had to do. Should I just pull the muffler to check? Or is there a way to test the baffle? Thanks! |
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