lost 800 rpms at wot

[stu man do]

If I had a bad high pressure side fuel pump, would it still allow me to over trim and get higher RPMS? One engine does 4400-4600 trimmed down, other will only do 3800 rpms. Problem engine does nothing when last 1/4 of throttle is applied.
4.3 volvo Penta TBI

 

[Bondo]

Re: lost 800 rpms at wot

If I had a bad high pressure side fuel pump, would it still allow me to over trim and get higher RPMS?

Ayuh,... Over trimming, Unloads the motor, so of course it'll rev higher...

 

[stu man do]

Re: lost 800 rpms at wot

Will a bad oil pressure switch affect WOT. Just fishing here, trying to figure out what to check next from reading other posts.

 

[stu man do]

Re: lost 800 rpms at wot

Below is my original post.
At my wits end, having issues with one engine not reaching wot. Best it will do is 3800 rpms under load, trimmed down. The other engine will do 4400 rpms. I have done a turn up(cap, rotor, plugs), had codes read by marina mechanic, only code was low oil switch. Would this cause an rpm loss? They got the code to clear by wiggling the wire to sensor/switch.

I have added sea foam, injector cleaner, cleaned air filter, replaced gas filter. It is like I do not have the last 1/4 throttle on the one side. The engine scan proved spark advance is right, so anything I am missing?

I checked the TBI and the butterfly is wide open, measured the throttle linkage and same as other engine.

Went through Don's list, no prop changes, clean hull, etc.
I plan to have the fuel pump pressure tested this week.
The engine idles fine, and sounds perfect.

If there was an exhaust blockage (this engine does not have the flapper) where would it be, outdrive? I am asking because I did have an impeller go bad, never overheated, just lost a few fins. I have found most of them in the thermostat housing.
2000 VP PEFS TBI SX-M Drive 2660 Regal
Thanks

 

[stu man do]

Re: lost 800 rpms at wot- update

Re: lost 800 rpms at wot- update

I had mechanic out to take a look and the only thing he could see is that the engine had a lot of moisture built up (white cream) in the valve covers, cap, and he suspects the underside of the manifold too. The oil on the dipstick is as clean as if it just came out of the bottle. This engine had the undercooling issue for 3 months last year so that is why the moisture has built up. The engine never warmed up enough to burn of the moisture. Any suggestions on how to clean the moisture out ? Will a can of Engine flush work followed by oil and filter change? I did seafoam it (PCV valve, MAP hose to carb base, and in valve covers) and ran it for a couple of hours yesterday. It seemed like the first time up on plane the engine ran stronger, but after that it was back to no torque and 3800 rpms trimmed down wot.

Would a bad map sensor cause a loss of power? Does this MAP sensor measure pressure in the intake manifold(TBI), or the pressure inside the engine (valve cover under manifold?)

 

[Bondo]

Re: lost 800 rpms at wot- update

Re: lost 800 rpms at wot- update

Any suggestions on how to clean the moisture out ?

Ayuh,... Run it up to temp,+ it'll evaporate off...

and 3800 rpms trimmed down wot.

So trim it up...

 

[stu man do]

Re: MAP Sensor cause loss of rpms?

Re: MAP Sensor cause loss of rpms?

Would a bad map sensor cause a loss of wot and limit boat to 3800 rpms?
What are the syptoms of a bad map sensor? Boat seems to idle fine, just not reach wot.

 

[blrnar]

Re: lost 800 rpms at wot

I have the exact same problem reaching wot on twin 2000 4.3 Volvos carbed, one engine reaches 4400 and the other only 3800. Please post if you figure out the problem.


Thanks,

Brian

 

[stu man do]

Re: lost 800 rpms at wot

Will post if I can figure out problem. Was out on lake the other day and another Regal owner has the same problem to. The only difference on the motors is that the port engine with the problem is connected to the water heater. Going to bypass it today and see if any difference. Sounds stupid, but now there is at least three of us with the same issue and all with 4.3 volvo..... Have you done anything to figure out your problem? Going to switch the MAP sensors and temp. sensors in the manifold today. Hate swapping parts but do not have much choice. Trying to eliminate everything possible. Next is a compression test.

 

[blrnar]

Re: lost 800 rpms at wot

Yes I have done a comp. test, replaced plugs, wires, distributor cap, rotor, rebuilt carb, checked timing. This is the starboard engine (connected to the water heater) on a 2000 Regal 2660. I am going to check the complete fuel system today.

Thanks,

Brian

 

[stu man do]

Re: lost 800 rpms at wot

Same boat, 2001 2660 Regal, 4.3 TBI. My motors are actually 2000 model year. The only difference on the two engines is the water heater...taking a mechanic, computer, and fuel pressure gauge out for a ride on Friday to see what the engine is doing under load.

 

[blrnar]

Re: lost 800 rpms at wot

I took the boat out on Sunday after I had swiched out fuel pumps and the only noticeable difference was on the problem engine it would surge to aprox. 4500 to 4600 rpms and then drop back to 4000. Surging only occurred after 3000 rpms and it was infrequent. I am now checking the antisiphon valve.

Thanks

Brian

 

[stu man do]

Re: lost 600 rpms at wot

Re: lost 600 rpms at wot

went for a ride with mechanic, computer on starboard engine. Nothing showed up. Confirmed only getting 4087 rpms. Went back to dock and checked fuel pressure, low side would go to 6 lbs, and drop to 0 almost immediately, high side read 31 lbs holding while running. Got the mechanic stumped too. Just to make sure everything on fuel pressure was ok, tested other engine with exactly same results.
Still have a lot of the moisture in top of engine, (oil is still clear and tan like new), seams like less than before so it is evaporating, Going to flush the engine using an oil additive to see if I can get the rest of the moisture out.
Whats left? Compression test, moisture may of caused valve rust or valve seating rust deposits? Hoping engine flush cleans that.....
Rebuild TBI and fuel regulator? (if fuel regulator was bad, don't think I would hold pressure at 31 lbs.)
checked plugs, little black carboned up, but not bad.
Running out of ideas.

 

[blrnar]

Re: lost 800 rpms at wot

This question is kind of unrelated, however what do you have the timing set at?

 

[chaparall villain 2]

Re: lost 800 rpms at wot

mine lost about that much when i had a plug not firing all the time replaced plugs and wires and it went away but i know you say plugs look ok right

 

[whitney]

Re: lost 800 rpms at wot

If you're looking for crazy ideas I have one. Keep in mind I have been wrenching all my adult life on cars and motorcycles, and boats are new to me

Start swapping stuff from one motor to the other and test. I'm not sure which of these apply but here are some thoughts:

- Swap entire distributors and all plug wires
- Swap ECUs (is there an ecu on a TBI volvo?)
- Swap all the injectors and fuel rails
- Swap fuel pumps (2 fuel pumps?)
- Swap all of the spark plugs
- Swap throttle bodies and/or intake manifolds

The nice thing about a swap test is that if there is no change to your running problem, it absolutely absolves that component as possibly being the problem. If you

Problem is, this takes a lot of time. If you're mechanically inclined this is cheap in dollar amounts, but if your mechanic is doing the work you might want to take a different approach.

One other random thought -- check manifold vacuum on both motors while running... Look for a difference, which could implicate throttle plate, valves, or vacuum leaks (not likely).

Good luck!!

 

[stu man do]

Re: lost 800 rpms at wot

Thanks for the reply chaparall villain 2, I am going to replace spark plugs and wires on Friday. If I do the simple math, 4800 rpms divided by 6 cylinders, equals 800 rpms a cylinder. It would make sense that one is not firing and producing hp. (loss of 800 rpms at wot) I did have a very hard time on the one side getting the plugs in due to the hot water heater only being 2 inches away from exhaust manifold, maybe I screwed up the gap on the back plug. I did start switching stuff, from one engine, just sensors, but your suggestion for major components is a good one.

Bryan- I do not know, mechanic set timing with computer.

 

[stu man do]

Re: lost 800 rpms at wot

new plugs and wires.... no difference. Thinking of rebuilding throttle body injection.

 

[blrnar]

Re: lost 800 rpms at wot

Stu man do,

Why rebuild the throttle body injection? If you suspect it just swap it out. I just finished swapping out distributors and the starboard engine(the problem one) runs much smoother however the baffling thing is that the port engine seems to have no change. I will find out when I water test it on Monday and I will post results.




Brian

 

[stu man do]

Re: lost 800 rpms at wot

Brian,
please let me know the results. After plugs and wires it did seam to run smoother at idle, I mean less vibration. The reason I am thinking rebuild TBI is that I took it out for a test run and with my buddy driving, got to view both engines. Throttles advancing the same but port engine really has a big power jump, while the starboard engine just plugs along with a bogging sound. I will have to get new gaskets and O rings to swap the TBI's, so I might as well clean it up a bit. My fuel pumps are a little different than yours I think, I might try switching those. If your ignition swap does the trick (they are the same on the GL/GI), then you may have something here.
We are running out of summer here soon...
Was it hard to switch the whole distributor, and tricks to it? worried about messing up timing...