Dealing with bogging for too long and need help because I've done just about everything!

[MalibuMike]

1997 Parker 2520 with a Volvo Penta 5.7 Gi-f 750 hours. Block is from 2007 so maybe the heads and manifold and other parts were transferred over after the 1997 engine was replaced.
Purchased the boat a few years ago and had a new VP fuel pump put in. I have never heard it whine. Bogging tends to take place above 3100 rpm's. There are no backfires or pops, just a gradual decrease in rpm and power. Today, I filled up 50 gallons of mid grade gas and drove 25 miles to the tuna grounds off the coast of California. At 3000 rpms I had no bogging issues. Fast trolled 13 kts for 3 hours with no bogging. As the tank got lower the bogging happened several times on the return home. When it happens, I pull the throttle back wait a few seconds and resume. Sometime I can quickly resume and push it all the way to 4200 rpms.

Here's what I've done recently. New cap and rotor, new plugs, new IAC. Rinda scan said ECT out of range but no other codes except for EGT since one of my risers doesn't have the port for it. I only see one coolant sensor near the thermostat. When I unplug it, the gauge at the helm stops woking. Removed the throttle body and cleaned it. The gasket is good and tight against intake manifold. PCV valve good. TPS showed 2% at close and increased percentage as throttle was opened.

What I've done in regards to fuel.

1. New filter along with Racor water separating filter (so I have two).
2. Remove gas cap to rule out a blocked breather.
3. Replaced fuel line from tank to filters in case there was internal collapse happening.
4. Blew in to pick up tube with top plugged to rule out cracks like when you have a crack in a straw and it won't "suck".
5. Cleaned fuel pressure regulator. No sign of debris.
6. Pulled all injectors and had them professionally cleaned.
7. Gasket on fuel cap seals.
8. Removed the screen from the pick up tube and removed the anti siphon valve. The logic was that maybe some large chunks of stuff were floating around getting caught in the screen or against the ball bearing and the big Racor could just grab it all. Problem existed before the Racor install so the additional filter did not contribute to restriction.
9. Sprayed starting fluid around parts of the manifold and didnt get an rpm increase.
10. After the bogging today I emptied both new filters. One small drop of water in the Racor and one small drop in the small spin on canister on the engine next to the fuel pump.
11. Removed brass 90 fuel barb on fuel pump to make sure it's not clogged.
12. Cleaned fuel rail before reinstalling injectors.
13. Checked both fuel pressure ports and they are within spec.
14. Made sure all fuel hoses are securely attached with tight hose clamps.
15. Made sure gaskets of fuel filters tight against sealing surface.

List of crazy ideas that run thru my brain at 3am thinking about this.
1) There is a paper towel or a piece of a rag or something large that gets sucked up against the tube. As the volume of gas drops, the chance of it hitting the the pick up tube increases. When I take the break, the decrease in fuel demand, and the action of the ocean, free it from the tube.
2) There is a leak in the intake manifold gasket that only breaks vacuum when the heat and rpm demands create a leak.
3) Maybe a heat related issue. Something gets hot and doesn't want to work. I will note that the right hand clip on the fuel pump is fairly warm compared to the other clip. Almost hot. But the coolant line feels cool and both high and low pressure pumps feel normal.
4) Fuel pump has junk inside the screens even though this a newer pump without paint chip problems. I have not looked.
5) The drops of water in the fuel are only what I see settling out after a few minutes and that there is a ton of water that is trying to pass thru that I cant really see. But if I had saturated fuel I would think that I'd get symptoms across all rpms.
6) ECM gets hot and cranky but recovery is so fast I don't think this is a hot computer needing to cool down.
7) Fuel pump is bad but I think I'd hear whining if it was failing.
8) I have a restriction or an air leak but need to figure out how to have a fuel pressure gauge attached at the moment it happens. Increase in vacuum would indicate a restriction and a decrease in vacuum would mean an air leak.

I'm complete lost on what to try next!

 

[Scott Danforth]

measure compression, post all numbers here

measure fuel pressure, post all numbers here.

what is your ECT. should be in the 170 range

 

[alldodge]

I think your loosing fuel pressure. Could prove it by connecting a gauge on the rail. The electric fuel pump doesn't suck very well and having 2 filters may be part of the problem if filter media is less then 10 micron

For testing, replace the antisiphon valve with a straight fitting.

Did find another parker with 2 filters and assume yours is similar

 

[Lou C]

Could water be getting into the fuel tank vent hose causing a temporary blockage as the boat moves with the waves?

 

[MalibuMike]

I think your loosing fuel pressure. Could prove it by connecting a gauge on the rail. The electric fuel pump doesn't suck very well and having 2 filters may be part of the problem if filter media is less then 10 micron

For testing, replace the antisiphon valve with a straight fitting.

Did find another parker with 2 filters and assume yours is similar
View attachment 389558

I replaced the anti siphons with a regular fuel barb. No bearing and spring. Problem exited before Racor installation.

 

[MalibuMike]

Could water be getting into the fuel tank vent hose causing a temporary blockage as the boat moves with the waves?

Bogging also happens with fuel cap off.

 

[Scott Danforth]

Bogging also happens with fuel cap off.

compression numbers?

fuel pressure?

 

[MalibuMike]

measure compression, post all numbers here

measure fuel pressure, post all numbers here.

what is your ECT. should be in the 170 range

I will do another compression test. Roughly one year ago, I did a compression test and the mechanic noted that there was just one cylinder just barely under the 10 percent threshold.
For my own mechanical knowledge, let’s say there was one cylinder that had really bad compression either due to bad rings, or a bad head, how could that be a factor in the bogging?
I have both raw water, cooled and freshwater cooled, and I run at 172 consistently at the gauge.

 

[kenny nunez]

Does your engine have a knock sensor that controls the ignition timing?
Also as AD and SD suggested have you tried monitoring the fuel pressure with the boat running as you normally use it?

 

[MalibuMike]

Does your engine have a knock sensor that controls the ignition timing?
Also as AD and SD suggested have you tried monitoring the fuel pressure with the boat running as you normally use it?

Is this the knock sensor?

 

[alldodge]

Yes, that's the knock sensor

 

[Lou C]

A defective knock sensor made our 98 Subaru run like it had no power; I changed that and the speed sensor twice in the time we owned it (18 years).
However these faults always set an easily read check engine code; not sure if marine engine management systems do the same thing.

 

[QBhoy]

Hi. Maybe not relevant and I’ve got it wrong all together…
But the mention of the original engine being 1997…then the new engine being perhaos block only…then somewhere in there, the mention of cleaning “all injectors”. The latter is suggesting that this new power plant must be an mpi engine with the mention of injectors in the plural sense. So if she’s indeed a multi point injected engjne with an injector for each cylinder into the intake manifold branching (and not a single or tbi throttle body injected system)…it would been to be more than just the block that was changed out. The whole top sides, manifolds, injection system, sensory items and ecu would need to also be changed out too. The original components from a 1997 unit (even if it was tbi), with particular reference to the ecu at least…just won’t work at all, should she indeed be multi point injection

 

[alldodge]

It's a VP Ford MPI

 

[QBhoy]

It's a VP Ford MPI

Maybe even worse then. Can see now, that the original engine is a ford there. But the one in it now…definitely ain’t a ford. That’s a gm. Surely means now that more than the block was simply changed out. Can’t imagine that much of anything would be interchangeable between the two.

 

[MalibuMike]

The current block is 100% GM. It is fuel injected with the Vortech style intake manifold. I do not know what the original block was in 1997 or what was on it. For whatever reason, the previous owner decided to put in the new block in 2007 and my assumption is that many of the old parts like heads , intake etc were brought over. I am also making this assumption because the crab style flat distributor cap is identical to what you would find on a 1997, 5.7 L GM 1500 pick up truck.

When I have time, I am going to perform another compression test and another fuel pressure test. I’ve been dealing with this ministry for over two years and the last time I did the fuel pressure test. It was in specs. A week later it was mysteriously bogging. Sometimes this fogging won’t happen for 60 minutes or two hours into a trip!

Is there any chance that the timing could be off where it runs well but gets grumpy above a certain rpm? There are times where I can easily push the boat to 4200 RPMs after the bogging rests for a minute or two, so I doubt it has to do with timing.

I did mention that one of the clips to one of the fuel pumps feels on usually warm while the other one feels cool. Maybe corrosion related or too much heat in the wires causing the fuel pump to shut down? But like I said, I can pull back the throttle and go right back to cruise speed.

 

[QBhoy]

Ok. Definitely two completely different engines there. One will be the old 5.8 ford fsi or whatever it’s called. The current, will be the mpi gm unit. Usually called a gxi or osi in vp form…given the flat cap. I think these were used in cars and trucks…long before they made it to boats.

 

[alldodge]

It's a VP Ford MPI

One of those Doh moments, don't know how I got mixed up. I even posted the pic of the GM 7.4

 

[Lou C]

Ok. Definitely two completely different engines there. One will be the old 5.8 ford fsi or whatever it’s called. The current, will be the mpi gm unit. Usually called a gxi or osi in vp form…given the flat cap. I think these were used in cars and trucks…long before they made it to boats.

I have heard many stories of this EFI system acting up & being difficult to repair. When our cars had carbs they didn’t run as well as EFI esp after a cold start but they were repair-able! With old boats & GM marine engines I prefer carbs, less failure points with respect to wiring and much less cost, and parts for carbs are more available than for 25 year old EFI systems.

PS that crab cap is a well known problem area they only last about a year or so. If you found a warm terminal I’d check that for sure might be the cause of intermittent fuel pressure drops.