Lost Top End - VP 4.3GL

[simpsondb]

I have a 1999 Volvo Penta 4.3GL/PWTR (s/n 4110173554) that recently lost acceleration after 1/2 throttle. The engine has 300 hours/one owner and has been serviced every year at the marina we use.

It starts like a champ, accelerates to plane up to about 30MPH / 3,000 rpm at 1/2 throttle. From 1/2 to full throttle, it only gets to ~38 MPH and 3,800 rpm.

In the past eight years, the boat at WOT would always zip up to ~50 MPH at 4,600 rpm. Gas consumption is now poor also. It doesn't stutter, smoke or act odd other then feels like it's dragging a sea anchor.

The mechanic at the marina has claimed to have checked the fuel pump, carb, timing, etc. but can't figure it out. He was recently looking into swapping the sterndrive to see it was the problem.

I'm ready to just buy some tools and take a wack at it myself, or just sink the boat. The engine has had an issue every other year that's had to be repaired (broken water pump after 10 hours, burst hydraulic hose, gimbal joint failed, starter motor, etc...) and we don't run the boat hard. It would be nice if Honda or Toyota got into this field to kick quality into V-P like they did Ford/GM. But, I digress.

If anyone has a thought on where to look, I'd appreciate it. The marina is more interested in the 30+ footers. - Thx

 

[Bondo]

Re: Lost Top End - VP 4.3GL

Ayuh,..... Here ya Go,.... Courtesy of Don,.....

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation
• Remote control cables and linkage for proper travel to open throttle plates fully.

 

[Dakota47]

Re: Lost Top End - VP 4.3GL

Waterlogged boat maybe?? the foam under the floor gets soaked..

 

[dcg9381]

Re: Lost Top End - VP 4.3GL

The mechanic at the marina has claimed to have checked the fuel pump, carb, timing, etc. but can't figure it out. He was recently looking into swapping the sterndrive to see it was the problem.

It would be nice if Honda or Toyota got into this field to kick quality into V-P like they did Ford/GM. But, I digress.

I've seen a few Toyota V8s on comp ski boats. They're pretty rare.

The GM motors are fine -the 4.3, 305, 350, 454 - all of 'em - they're good solid motors and are well proven.

If your mechanic is thinking about swapping the out drive before running compression, run - don't walk - run away and get a new mechanic. He's playing the "throw parts at it" game and you don't want to be on the check writing side of that. When you're paying good money for a mechanic, you're paying for a systematic diagnosis of the problem - not just someone who is going to replace random parts until it's right.


The above list is a good list to go by. I'd start there.
A few ideas on my side:
1) Run compression. This will rule out a major cylinder/head issue.
2) Replace the plugs. Take the boat out and immediately run it WOT. Shut it down and have a look at the plugs. You're looking for a cylinder that looks different than the others.
3) I think the "water" idea is a good one - any chance that the boat is heavy, has taken on water, etc? Is it a trailered boat, would you notice if had taken on water?
4) Any damage to the prop? I don't think that a drive malfunction is likely.

 

[Maclin]

Re: Lost Top End - VP 4.3GL

If you want to sink it let me come and get it and sink it for you no charge...

The first two items from dcg9381 will eliminate a lot of guesswork.

Compression check is mandatory step in truly diagnosing this problem. If all is well with that then you know a LOT more about the condition of the engine than before, takes a lot of guessing out of it.

If compression is good then the plug read is a good next step, it will tell you a lot about the fuel delivery and metering from the carb during a WOT run.

When was the last time it had all new cap, rotor, sparkplugs and sparkplug wires? It could be crossfiring at the distributor cap, or between two wires somewhere along the way. Cross firing and other sparkplug wire/cap issues many times do not manifest themselves until under load at higher rpms.

It could still be a fuel delivery problem in the carb or fuel pump or filter or gasoline supply plumbing, but the spark plugs would probably tell the tale if any of these items are failing or sucking air, etc..

I suppose the outdrive could be the culprit, but I think it would be REALLY loud and not have lasted more than a couple of WOT runs if it was dragging that hard.

 

[simpsondb]

Re: Lost Top End - VP 4.3GL - update

Re: Lost Top End - VP 4.3GL - update

Thanks for the suggestions.

Just a quick progress update. The problem is still a work in progress, but I plan to post the solution once solved.

I've decided to work the problem through as suggested. Since the boat is on a lake and on an air lift when docked, there's no fouling problem. Also, no water in the bilge.

I was concerned that there could be a sterndive binding issue, but since we've been running the boat a few hours every week, it most likely would have shown up worse as suggested. As always, the boat starts instantantly, purrs at idle and slow speed, planes out slugishly to about 25/30 mph where it'll run all day, but only a bit higher at WOT. WOT is 3,600 rpm down from the original 4,600.

So, I've ordered the manuals and will begin working through the check points.

(I did try a quick check to see if the timing was advancing with a light I had. But, looking down into the engine offered no view of the marks. Got to remove the seat back to get to them at next effort.)

I'll post the success, or lack there of, as I work on it.

Regards.

 

[westwon]

Re: Lost Top End - VP 4.3GL

I had exactly the same problem on my Bayliner with a Volvo Penta 4.3 GL. The thing ran perfectly, but it simply wouldn't go past mid RPMs. It turned out to be water in my fuel. I changed the fuel filter (again) and it's run very well since.

 

[simpsondb]

Re: Lost Top End - VP 4.3GL

Well, I've been out of the country for a while, but have been able to put some work on the problem in the last month. Sadly, problem still exists but here's a rundown.

The boats clean as a whistle on an airlift so no drag. But, I thought I'd take the opportunity to give it a good tune up. New plugs, wires, distributor cap, fuel filter, etc. I didn't expect these steps to solve the problem (they didn't), but it's been a few years so was probably worth it.

Next I thought I'd check the timing which on this engine is a treat. You need a Volvo thing-a-ma-bob to plug into the distributor to disable the advance while checking the timing. Next challenge was to find the timing marks. Seems Volvo does a nice paint job on the engine so had to remove the back seat to get down to the marks to highlight them.

I found that the timing was 4 BTDC instead of the 1 BTDC spec. I adjusted the distributor making sure that the timing doesn't change when tightening the bolt on the distributor. It did change so I had to do about 2 ATDC then tighten the bolt which moved it back to 1 BTDC. Shades of my 64 VW.

Next step was to rebuild the carb. I didn't expect this to do much for the top end problem, but I was on a roll. Rebuilding carbs especially in your kitchen is a family favorite. I did find that the float and several other adjustments were off.

So now it'll start on a dime and runs smooth as can be. But, after 3800 rpms it still has no interest in going faster. I then looked at the prop and it was dinged a bit so it also became a candidate for work.

I noticed that the tabbed washer that holds the cotter pin and prop nut in place was missing. Even better, the prop nut was finger tight (thanks was not given to the marina who last worked on it). Anyhow, I decided to replace the prop myself and bought a Turning Point 13 1/4 x 21 (same as original). While no improvement in top end, it made a huge difference in vibration and getting on plane. (Oh, I did bother to take a torque wrench to it.)

So what's left. I haven't checked the fuel pressure yet to see if there's a fuel pump problem or restriction. Next weekend.

Oh, during all this I checked the bilge pump float switch while upside down under the engine. It didn't work and the bilge pump kind of crumbled when I tried to unhook it (Attwood V series). So, another project. I suggest you check your float switch to avoid a bad surprise.

I'll update again when this thing is solved. I've now become convinced the purpose of a boat is for a guy to pretend to be a mechanic with cool tools and manuals to work on a never ending series of "projects". Occasionally, it'll run around on the water as well. My wife of course completely understands.

Rgrds.