Another not reaching max rpm post.

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mklearl

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Apr 21, 2013
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Thanks again for the input. I'll post back in a couple weeks... just reading up on how to check the timing. Away for work for 2 weeks. Then hopefully I'll figure it out.
 
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mklearl

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Just checking back in on this one. Sorry for the delays. I finally ended up checking the timing and it was all ok. So I'm stumped again. The only thing I can think of now is that I'm overproped. I can't believe that this would be the case since these are the props that were always on it before I owned it. I can't really find anywhere that will tell me what props I should have on there. I.found one guide that states mph and rpms and specivic to engines but it doesn't take the weight of the vessel into consideration. I have a 28 foot master marine center console. Weight I believe is around 7500lbs. I have a 5.0gipbycce engine and a dpsm 1.95 out drive. I can get about 3600 rpms and a speed of about 30mph tops. I can't find anyone with a comparable setup. I saw one with a 225 outboard that maxed out at about 35 knots or 40+ mph so I'm thinking here is definately a problem. I currently have a set of D4 props on it.
The boat is hauled out for the winter so there isn't much I can do now. Just wondering if anyone has aNY additional suggestions or ideas that I can stew on for the winter.
Thanks again!
 
89retta

89retta

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I would do a compression check. You might have low or no compression in 1 or more cylinders
 
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ericga

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I still find it strange that compressing the regulator spring was "far from impossible". It is usually hard to keep everything together with the regulator on one hand and screw driver in the other. I have quite strong hands and always start with the longer screws.

I was first thinking someone may have installed a weaker spring or installed the diaphragm upside down but then you wouldn't get 30psi. Did you test the fuel pressure at different RPMs including WOT?
 
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ericga

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"The fuel filter had some sediment in it"

Have you check the anti-siphon valve? You may have debris preventing the valve from fully open.
 
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mklearl

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ericga said:
"The fuel filter had some sediment in it"

Have you check the anti-siphon valve? You may have debris preventing the valve from fully open.
Click to expand...

I have not checked the anti siphon valve but I have checked the fuel pressure at wot which was still 30psi. I have also run on an external tank with the same results.
 
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mklearl

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Did some more research tonight and I'm thinking of a couple of possibilities. Bad map sensor? I can't really say how my fuel economy was this season since I have nothing to compare it to but it might be something to consider. I've also read about a stretched timing chain causing a lack of power. I have no rattling noise though and the timing is good so I think I'm ruling that out.
Lastly, I've done pressure checks but I'm not familiar with how to run a vacuum test which by looking in the shop manual it gives symptoms and problems based on vacuum readings but I don't know the procedure... any step by step instructions on that?where to hook the vacuum gauge up?etc.
Thanks again for the input.
 
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ericga

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See your private messages I sent you a document.

PCV valve is a good vacuum source.
 
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mklearl

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Great info. Thank you ericga. I may try this before winterizing. I'm home next week for 2 weeks. That way I'm not sitting on it all winter.
Valve problem may make sense since the engine was frozen after the long sit. I thought that with the compression being good everything was fine. Aparantly not. I may just do a leak down test as well. Thanks for the input!
 
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ericga

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Another possibility I'm thinking of is the knock sensor. The sensor retard timing if engine knock is detected. The engine may have knock or the sensor became too sensitive or is wrong type.
 
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mklearl

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ericga said:
Another possibility I'm thinking of is the knock sensor. The sensor retard timing if engine knock is detected. The engine may have knock or the sensor became too sensitive or is wrong type.
Click to expand...

Is there any way to test the knock sensor as well as the map sensor without just replacing?
 
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ericga

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They are both difficult to test accurately.

Symptoms of a faulty map is an incorrect ful/air mixture ratio but not to a point of causing a 1k rpm penalty at WOT.
 
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mklearl

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ericga said:
They are both difficult to test accurately.

Symptoms of a faulty map is an incorrect ful/air mixture ratio but not to a point of causing a 1k rpm penalty at WOT.
Click to expand...

But a knock sensor would?
I'm going to start with a vacuum test first and go from there. Thanks again for pointing me in a direction.
 
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mklearl

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Apr 21, 2013
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Just reading on where the knock sensor is. When I started working on this I opened up all valves to drain any water. I thought the knock sensor was the temperature sensor. The fitting that it is "t" into was fI'll of corrosion and gunk. I cleaned all that out. But the sensor being electrical could very well be the culprit. Winterizing this week so I'll be pulling it out again. It may just be worth it to change that out.
Can you tell me what the part number for that knock sensor is? I look at the schematics on the volvo penta store website but I can't find the sensors or switches.
Thanks again
3850357?
 
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Senior B

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How is the "Hole Shot" on this boat? From what I read in the posts, it appears to me to be over propped and may also be a tach issue. This boat is a 28 footer at 7500 pounds with a single 5.0 pushing a 1.95 out drive with D4 props, Would expect D1 or D2s on this. 35 mph isn't bad for a boat of this size and weight on a single 5.0. If it's able to get up on plane and doesn't struggle, I would look at the back of your tach and see that it's set for a V-8. There's an adjustment screw to set for a 4 cyl, 6 cyl, then 8. Won't read correctly if it's not right. D4 to me is big prop for that boat and the 1.95 outdrive. Would seem more likely on the 2.30 DPS.
 
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