loss of power 454 need advice

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southern safaris
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loss of power 454 need advice

Post by southern safaris »

Well after bragging on how well this motor was spinning a new 74"ngq she has now had me chasing my tail a little , ...

Put the boat up a couple weeks ago running well, its a rebuilt 454dd on a 14x8 aluminum hull, it will ride out with 4 grown adults just fine in deep water , put her back in the water couple days ago wouldnt barely plane out and couldnt get the rpms over 2200 normally swings the 74" ngq 2800 no problem, so done the normal shakedown checking plugs vaccum leaks timing , fuel pressure ,etc .... Thought maybe tach messed up but then that doesnt explain her not planning out she just falls off after 2k , just for gigglez i pulled pitch out until i was down to the 1 mark ish and finally could get the rpms up but that was just to hear it spin up , not near enough push pitched that shallow , set her back on 2 to try and diagnose it but not having much luck, going to do a compression and leakdown next couple days but i guess my question would be what could cause an engine to spin up strong to that 2k then fall flat and not give me any other symptoms ... Runs smooth clean just lost my top end ? Motor has about 10hrs on it first 3-5 hrs she woke up little by little and i added pitch as needed thought this was normal but now has me wondering .....

454, aluminum intake ,demon 625cfm, hugger headers running mufflers, hei msd coil, rv cam , oil pressure temp all strong and steady
Anthony Hughes
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SWAMPHUNTER45
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Re: loss of power 454 need advice

Post by SWAMPHUNTER45 »

How is the oil pressure? Has it stayed the same, shot up or dropped?

Does it turn over easily at start up or struggle to crank up?

Can you pull oil filter and cut it open, see what it looks like inside.

A power loss at 10 hours could be a cam lobe or lifter failure among a whole host of other things.

flying fish
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Re: loss of power 454 need advice

Post by flying fish »

Cam going flat
Back barrels not opening on carb
Fuel to squirters
Detonation

Good luck-
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Re: loss of power 454 need advice

Post by flying fish »

:) oops. posted twice
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southern safaris
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Re: loss of power 454 need advice

Post by southern safaris »

Swamp.... Oil pressure hasnt budged stays right about 50psi
Busts right off just bumping the key didnt state before but total timing was set to 32*

Just now fired her up and thought let me see how its thumping and driver bank i can hold my hand over muff and doesnt burn or thump near as hard as pass bank so im ivestigating that and i have no exhaust leaks so somethings fishy here ... First glimmer of hope ive found yet ,

Flying fish i think ill be checking those valves and travel next ! Thanks for the replys so quick it does help very much
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SWAMPHUNTER45
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Re: loss of power 454 need advice

Post by SWAMPHUNTER45 »

OK so easy start, oil pressure stays the same and no noise pretty much rules out bearing fail. Think your onto it now with what Fish offered up and checking top end.

Lets hope it is just the throttle cable adjustment.

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Re: loss of power 454 need advice

Post by jeepinocala1111 »

flying fish wrote:Cam going flat
Back barrels not opening on carb
Fuel to squirters
Detonation

Good luck-
I have seen this same result while breaking in an engine they used synthetic oil and the cam lobes went flat in just a few days. But not saying that's the problem.

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southern safaris
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Re: loss of power 454 need advice

Post by southern safaris »

I broke it in with the oil the engine builder recommeded was a mineral type oil and a lucas break in additive burnished cam in per their ins.. Not saying i may not have screwed something up but ive broke in 8+ engines in the last few years and not had an issue but you can always have a bad day i guess ..... Compression test rendered lowest cyl 125 and highest 140 so i have a little spread there and those were on bank 1
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southern safaris
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Re: loss of power 454 need advice

Post by southern safaris »

Swamp , thats the funny part when she first didnt plane out i figured dang my throttle crimp slipped ,,, had that happen before on a differnt boat , ...... Why couldnt it be that simple! :banghead:
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Re: loss of power 454 need advice

Post by SWAMPHUNTER45 »

Lets hope it is not the cam / lifters but it is highly suspect.

Just curious what their break in instructions were?

Had you had the heads worked and springs replaced recently ?

In the Cadillac world we have seen cam failures rather frequently often because machine shops use a heavier spring thinking they are doing a high performance upgrade but in reality they create a spring pressure that eats the lobes off in a few hours. Just a discussion point as you explore cause and effect.

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southern safaris
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Re: loss of power 454 need advice

Post by southern safaris »

Never delt with these guys before and just ordered a long block dressed marine 4blt engine , they said all the right stuff and assured me it has a great warranty ...... So i bit hook line and sinker.. :fishing ....

As for break in and im going off memory cause im sure the ins are gone by now , it was after setting all timing and carb etc as close to perfect as you can before startup , prime motor with oil (drill type primer) additives were added fired up bring to 2000 rpm for x amount of minutes varying rpm between 1800 to 2200 ish i think , cool completely and do over varying rpm then after that seating ring procedure
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Rich Andrews
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Re: loss of power 454 need advice

Post by Rich Andrews »

i'm going with a carb issue, like no secondaries..
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southern safaris
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Re: loss of power 454 need advice

Post by southern safaris »

Going to go check that rich such a simple thing i havent checked yet , to verify that other than looking down carb which ill try the manifold pressure would need to be around what if thats how to check on guage?
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Re: loss of power 454 need advice

Post by Rich Andrews »

id first look without the engine running to see if the linkage is working right.
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southern safaris
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Re: loss of power 454 need advice

Post by southern safaris »

Linkage is working... under full throttle engine off secondary butterfly opens , fired up air valve goes full open almost immediatly when i rev it up..... Now im going to replace fuel filters for the heck of it and check again to see if maybe moisture if any did maybe build up in the tank when it sat in the barn for a couple weeks we have had some hot weather so maybe .... Yall think a little octane boost would be a bad idea ? Maybe a bad batch of gas?
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Re: loss of power 454 need advice

Post by Swampbuggy »

I would check the power valve in the carb - Is it vac secondary then take all the plugs out and be careful the motoer well move take your compression gage end and put it in set you air at 15 to 20 psi and plug it up the propis going to move so be careful that should tell you if there is bad cyd or cam

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Re: loss of power 454 need advice

Post by Swampbuggy »

It still sound like a bad power valve

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Re: loss of power 454 need advice

Post by Swampbuggy »

If you have a water sep filter check it real good I have had the close up

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Re: loss of power 454 need advice

Post by glades cat »

If you put it away running well and the next time it's lacking on the top end...???
I would suspect fuel starvation in the secondary circuit, possibly debris.
Just a suggestion. Have you tried squirting a little fuel while it's full throttle?
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southern safaris
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Re: loss of power 454 need advice

Post by southern safaris »

Glades .. No i havent but will try a little squirt and see real quick , and thats what bugs me about it i would think if it were internal it would have been showing symptoms not just night and day different from one trip to the next, i have an ol q jet on my other boat thats working well i just had her out yesterday ill swap carbs to rule that out if the test doesnt tell me anything and again thank you all for the help!
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Re: loss of power 454 need advice

Post by flying fish »

cranking cylinder pressure is low even @ 140#. Did you have the carb throttle plates open when cranking?

I would think on a direct drive piece 175# cranking cylinder pressure would be an absolute minimum. JMO-
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Re: loss of power 454 need advice

Post by glades cat »

flying fish wrote:cranking cylinder pressure is low even @ 140#. Did you have the carb throttle plates open when cranking?

I would think on a direct drive piece 175# cranking cylinder pressure would be an absolute minimum. JMO-
Something to consider...
If it has cam with considerable overlap...narrow lobe separation (110deg) and long duration, the static compression will be reduced. A wide lobe separation...114deg & conservative duration will produce higher static numbers.
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Re: loss of power 454 need advice

Post by CactusJack »

Just thinking.... is it possible the cam sprocket has jumped a tooth? Prolly unlikely, has it got a a hy-vo chain or double roller?

Does it have an adjustable cam sprocket? I have seen them loosen off enough to shift and retard the cam timing? Don't take much to upset the cam timing to make them run like a wet sponge :dontknow:

If it is under any sort of guarantee, I would be getting whoever built it to check it, so they don't make out you wrecked it fiddling with it?
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Re: loss of power 454 need advice

Post by barhopper »

Big vacuum port on the carb not plugged?

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Re: loss of power 454 need advice

Post by pax1ton »

flying fish wrote:cranking cylinder pressure is low even @ 140#. Did you have the carb throttle plates open when cranking?

I would think on a direct drive piece 175# cranking cylinder pressure would be an absolute minimum. JMO-
I'm with you on this one fish,
this sounds like a flat cam ,or bad valve springs, had a set of springs go south on an engine with 9 hrs on it once.
wonder what oil is being used and if any additives are being used.

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