2010 Volvo penta 5.0 GXI-J 4400 rpm WOT knock and quick hesitation

Mansourman

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I have a 21' crownline lpx with a penta 5.0 gxi-j. It has a strange threshold where the engine will detonate at about 4400 to 4600 RPM. It hesitates for a fraction of a second and will continue to pop every few seconds with stable speed- (50MPH) with a very small hesitation on each knock. I checked compression- all good, took the fuel pump and regulator apart, no crap in either, changed the plugs and double checked gap- no change. I emptied the tank, fresh fuel same thing. I'm running a 21p prop also. I changed the distributor cap too. It just won't power past 4400 rpm. Everything else is smooth- starts up quick, idles fine, decent hole shot, but the damn thing starts knocking at 4400 to 4600 RPM and she won't power past...
 

Fun Times

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Hi again.:)

Have you had a chance to check both low and high fuel pressure during the event?
You've seemed to have ruled out some of the typical causes such as spark plugs & distributor cap plus hopefully rotor< ?

On your next trip out to the lake you'll want to try doing a cylinder drop test by putting the boat under heavy load and removing one plug wire at a time to see if you can hear and feel a change in the engines performance. You may have a bad plug wire and sometimes you can get lucky to see a light show if you run the engine at night. Listen for an electrical arc sound too.

Also using a timing light at speed, connect the light to the high tension coil wire and look for a consistent flash as you need one...Then do all 8 plug wires doing your best to time the flashes. although your inanition timing is non adjustable, ensure your timing is advancing too.

Does your tachometer meter bounce around any?

Next up on the list to do would be a cylinder leak-down test. http://www.bing.com/videos/search?q...ster&qpvt=cylinder+leak-down+tester&FORM=VDRE
 

Mansourman

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Ok. A little more info: we just did a test run and got the following info, low pump is 8psi, high pump is 40psi, computer says 30degrees timing- tach says 4500 rpm, computer says 5000 RPM- but judging by the "sound". Of the motor it doesn't sound like its at true WOT. The throttle seems to hav a linear response to the engine output up to about 75% then the rest of the throttle seems to get into that pre ignition limiting hesitation issue. It seems like the ecm is limiting WOT. When this all started we discovered a tulip per valve on the exhaust on one of the cylinders and we discovered a really burned plug on another one of the cylinders. Since we pulled the heads we did a full valve job, new head gasgets, new rotor, new plugs blew out injectors. It runs, idles and starts as expected but she just won't get to WOT with this knock issue- any of this give you any other ideas? I'll move forward with the plug wire testing...
 

Bondo

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When this all started we discovered a tulip per valve on the exhaust on one of the cylinders and we discovered a really burned plug on another one of the cylinders. Since we pulled the heads we did a full valve job, new head gasgets, new rotor, new plugs blew out injectors. It runs, idles and starts as expected but she just won't get to WOT with this knock issue- any of this give you any other ideas?

Ayuh,.... Welcome Aboard,... That's Destruction from Detonation,....

A Lean condition, or to advance timin' are the 2 leadin' causes of it,....
 

Mansourman

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Well, I'm wondering if the high pressure pump is low on pressure? I'm seeing 40 psi. I'm reading posts that it should be 50 to 60 PSI? Thoughts?
 

Bondo

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Well, I'm wondering if the high pressure pump is low on pressure? I'm seeing 40 psi. I'm reading posts that it should be 50 to 60 PSI? Thoughts?

Ayuh,... Sounds like a reasonable place to start,.....


How's the fuel, fuel tank, 'n it's plumbin',..??

A remote tank with fresh gas plumbed to the motor can by-pass the hull's tank, 'n plumbin' for testin' purposes,...
 

Mansourman

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Ok- one other thing that I'm just not buying- the computer tech was telling me that the computer was indicating 5000 rpm and that the pop occurred right at 5000 rpm and he thought it was due to the rev limiter. BUT THE TULIPED VALVE and the burnt plug have me dead on thinking this is a pre detonation issue - he also said the timing was 30? which is pretty compensating for something - I don't think the rev limiter would pop or knock- agreed?
 

Bondo

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Ayuh,.... 30? seems tame,.... Donno whether the rev-limiter would stumble the motor, nor how,...

But the evidence, along with poppin', 'n knockin' sure sounds like detonation, 'n nothin' but detonation,....

If timin' is at 30?, 'n the fuel pressure is low, the fuel system is the logical place to start lookin',....

Probably oughta fix or replace the tach too,.... 10% is a big error,...
 
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Mansourman

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Well the computer tech is saying that the popping was occurring at 5000 RPM according to the computer and the tach was reading 4400- and he thinks the rev limiter is kicking in but I don't buy it- I think the tulipped valve and the burned plug are pre detonation and the revi limiter wouldn't cause the pop- the high pressure pump is at 46 PSI...- agreed?
 

bruceb58

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You need to fix your tach. If you are actually running at 5000RPM, that's the reason you can't power past that.

Out of curiosity, how often do you run at that RPM?
 

Tail_Gunner

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You need to fix your tach. If you are actually running at 5000RPM, that's the reason you can't power past that.

Out of curiosity, how often do you run at that RPM?
Yes he's banging the rev limiter hard...boat tachs are little more than jewerlry cheap jewerly. You need to find a accurate tach and probably reprop

OP plz post your gearing on the outdrive...the speed of 50 mph is that gps or the boat speedo. The rev limiter cuts off the fuel supply creating a lean condition that could be the pop or knock your referring to and that engine has knock sensor's that would pick up the detonation far before you heard it and severely retard the timing to prevent knocking or detonation. A pic of the prop might help is it alum and in new condition or is it a bit worn from summer fun.
 
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Mansourman

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Well I do like to cruise WOT for a few minutes an outing. It's a 1.6 penta SX-A out drive with a 5.0 gxi 280HP. It's a crownline 21SS- 3800lb boat with 14.75 21P SS- seems like a 23p prop would be a little much for what I'm running?
 

Tail_Gunner

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21 pitch prop @5000rpm yields 60mph in theroy
50 mph with wisho meter gets 17% slip not good

Well is there a 23 pitch prop you can test or borrow that might be correct...it seems large but who know's. Thats a nice boat you have there i would find a accurate cheap tach and get a cheap gps and go collect some number's
 

Tail_Gunner

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Ok if that is gps your slipping badly do you have undergrowth or moss whatever on your boat???
What brand of prop do you have now any closeup pics.
Yes a 23 is a lot of prop for a 280hp boat 21' and 4k however that would put you at about 57 mph and that's not a strectch.

ESSENTIAL DATA REQUIRED
When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight


Your probably in need of a bigger prop.
 
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Mansourman

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Guys, thanks for all the time and the input. Tail Gunner- per your request:

No moss, waxed surface, F.A.S.T TAB 2010 Crownline Hull
GPS, into and with wind, 50 MPH

Several Prop, Prop ID and Lower Unit, Lower Unit Model Ratio numbers Closeups attached:

1. We are experiencing a pop- sounds a little like an empty metal paint can being struck with a wooden spoon- loud enough to hear at WOT, WOT by the computer says it is happening consistently at 5000 RPM. Throttle seems to have linear affect on engine up to about 75% throttle, after that it begins to pop- with small hesitation- but seems pretty constant speed. When this whole thing started we investigated and discovered a tuliped valve on one of the cylinders and a burnt plug on another cylinder. There was only one exhaust valve affected- we are concerned it is pre detonation that is the cause?? We want to avoid this issue again obviously- which is why we want to make damn sure the pop is the rev limiter and not due to a lean fuel issue. The low pressure was tested at 8 psi and the high pressure was at 46 psi. SLIP- how can that be improved- I wonder what "spec" might be? Is this really a prop issue? What size/type prop? I want to stick with stainless, decent hole shot, like to maintain a WOT in the high 4k rpm, with a 50+ mph, maintain efficiency and control- whose making the best prop for that?

2. Stainless, 21P 14.75 Volvo Penta OEM- model / ID in attached pic:

3. Attached pic:

4. Per the computer WOT is 5000, helm RPM is 4400- it doesn't sound like 5000 rpm but the computer is probably more accurate? I would bet 4300 lbs with the gear and myself, full tank

5. 2009 volvo penta 5.0 gxi-j pictures attached indicating exact lower unit, engine model, emission kit, EGC, "carter" fuel pump info, fuel tank info, hull info, two pages of specs data, system matrix info- pictures attached

6. 2010 crownline 21ss LPX, dry weight 3800


Thanks for taking a look...
 

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Tail_Gunner

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IT appears you need a new prop and its been cavitating a bit as to why that i do not know, Odd is that a spacer between your prop and drive or just the casting of the drive? Actually with the high slip your running its hard to pic a prop so to speak Do you have access to a loaner prop that is in better condition. Opps saw the second pic no spacer.
fetch

fetch
 
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Tail_Gunner

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http://boatpropellers.iboats.com/Vol...t_id=407268827 That's a safe bet.
http://boatpropellers.iboats.com/Vo...153-22_Propeller/544/22460/?cart_id=407268827 and then there's that and could get the best of all world's above 50mph for sure and great midrange
http://boatpropellers.iboats.com/Vol...t_id=407268827

And that may work as well however if you run with a load of people it will drag down the engine a bit. Its hard to be 100% certain here there is so much slip with that 21. But the advantage is a very fast prop.
 
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