Rich running 454/excessive carbon buildup on pistons
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Rich running 454/excessive carbon buildup on pistons

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    Off Road Badass Bonzen's Avatar
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    Default Rich running 454/excessive carbon buildup on pistons

    This is a motor question but also a jet boat question...for all intents and purposes, the motor is running great (BB 454), accelerates hard, idles nice, sounds good and starts...exactly what you want a boat to do lol. But changing the plugs yesterday they were very dark and smelled of gas or gas/oil mix. No buildup, clean but just dark and wet looking. Looking through the plug hole in the heads into the cylinder I can see the tops of the pistons and they have what I think is a lot of black, sooty looking carbon buildup on them. More so than the usual dark/blackish oil burn glaze that engines always have. Pistons are forged small dome, block is .030 over and has about 2 seasons on the rebuild(new pistons,rings,machining) Motor is TBI fuel injected, and TBI and injectors are new as well. Spray pattern in good. Fuel pressure reads around 28psi at the line in to the TBI. Base timing is around 2 degrees BTDC with the auto advance locked out, and then the computer auto advances it to whatever...don't remember off hand but I think it's like 12-15 at idle and 32-ish at WOT. Motor does not have a thermostat. Original motor that came with the boat didn't have one either. Temp runs around 125-145 idling and 110-125 at WOT. This is in SoCal/Arizona lakes and rivers. Plugs are standard ACdelco R34T with .035 gap. Engine compression is approx. 10:1. The main question here is, is this buildup common for a cool running BB 454? Should I be running a thermostat to bring up the temps for more heat inside the combustion chamber or should I switch to a hotter spark plug? Or advance the timing more to lean it out? Thanks!
    "I'd love to help you out wags, but there is larger issue concerning breast cup sizes on another thread that we have to work thru first. This subject suddenly became a non issue." - GN7

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    Senior Member Hass828's Avatar
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    Quote Originally Posted by Bonzen View Post
    This is a motor question but also a jet boat question...for all intents and purposes, the motor is running great (BB 454), accelerates hard, idles nice, sounds good and starts...exactly what you want a boat to do lol. But changing the plugs yesterday they were very dark and smelled of gas or gas/oil mix. No buildup, clean but just dark and wet looking. Looking through the plug hole in the heads into the cylinder I can see the tops of the pistons and they have what I think is a lot of black, sooty looking carbon buildup on them. More so than the usual dark/blackish oil burn glaze that engines always have. Pistons are forged small dome, block is .030 over and has about 2 seasons on the rebuild(new pistons,rings,machining) Motor is TBI fuel injected, and TBI and injectors are new as well. Spray pattern in good. Fuel pressure reads around 28psi at the line in to the TBI. Base timing is around 2 degrees BTDC with the auto advance locked out, and then the computer auto advances it to whatever...don't remember off hand but I think it's like 12-15 at idle and 32-ish at WOT. Motor does not have a thermostat. Original motor that came with the boat didn't have one either. Temp runs around 125-145 idling and 110-125 at WOT. This is in SoCal/Arizona lakes and rivers. Plugs are standard ACdelco R34T with .035 gap. Engine compression is approx. 10:1. The main question here is, is this buildup common for a cool running BB 454? Should I be running a thermostat to bring up the temps for more heat inside the combustion chamber or should I switch to a hotter spark plug? Or advance the timing more to lean it out? Thanks!
    Wont the ecu keep the engine rich because of the cold temp? Same as choke, the ecu thinks the engine is cold. I think you need to add the thermostat and get some temp in the engine.
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    Senior Member BGMAN's Avatar
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    Just remember, you can't just throw a thermostat into a open cooling system. You will need to run a bypass system like the one Rex Marine makes, part number 160100

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    Also just idle timing and total timing, not enough timing will cause the same thing, also agreed on the water temp. Too cold not good, mine runs 160 across the water and gets up 180 if I'm idling alot, and my plugs look perfect.

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    Off Road Badass Bonzen's Avatar
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    So the consensus is I need to make this thing run hotter...Obviously there is some oil blow-by due to the loose piston to wall tolerances but that should tighten up once it gets warm. But your saying it never gets warm enough to stop the blow by.


    Also the valve covers vent back into the air cleaner so IDK if it's getting oil into the cylinders that way too.

    What timing should I shoot for at full advance with the computer controlling it?


    Can someone post a picture of the t-stat setup and bypass. I have no clue how it works, thanks!
    "I'd love to help you out wags, but there is larger issue concerning breast cup sizes on another thread that we have to work thru first. This subject suddenly became a non issue." - GN7

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    Senior Member johnf's Avatar
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    Default thermostat kit

    CP has them even for FORDS!!!
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    Senior Member bp298's Avatar
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    Quote Originally Posted by Hass828 View Post
    Wont the ecu keep the engine rich because of the cold temp? Same as choke, the ecu thinks the engine is cold. I think you need to add the thermostat and get some temp in the engine.
    is it an open loop or closed loop system??? I wouldn't add a thermostat...

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    Off Road Badass Bonzen's Avatar
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    Not sure if it's open or closed loop system... here's a slightly older pic than current but the plumbing is exactly the same still. Like I said I never thought to run one because the original motor didn't have one. Plus I always thought it was a bad idea as sand could get in there and jam it.
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    "I'd love to help you out wags, but there is larger issue concerning breast cup sizes on another thread that we have to work thru first. This subject suddenly became a non issue." - GN7

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    Senior Member gregb's Avatar
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    Kind of hard to tell from the picture, but looks like someone adapted MEFI3 ? controller or maybe a 4 to run the TBI. Unless they had it reflashed, those are meant to run on a system with a thermostat. I'd add that setup, as others have stated it's probably always running in the "choke" mode. What temp do you see on the motor when it's running? If there's not O2 sensor (and I do not see one) it's an open loop setup.
    Last edited by gregb; 05-12-2015 at 08:25 AM.

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    Senior Member gregb's Avatar
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    Can you take a shot of the module? Maybe it's the MEFI 1 or 2, but still the same thing, never seen them attached to s system without a thermostat.
    Last edited by gregb; 05-12-2015 at 08:32 AM.

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    Off Road Badass Bonzen's Avatar
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    Yes it is a MEFI 1. Came with the OG motor. When it spun a few mains from what I determined to be a lack of oil, I rebuilt the whole engine and had the ECU re-flashed by Arizona Speed and Marine for the new camshaft specs and bumped up compression. Unfortunately after the fact I read a million horror stories about AZspeed & marine all over the internet on Offshoreonly forum...blown engines/bad tunes/no customer service, etc... but there was never any discussion about that MEFI system needing a T-stat. Now I'm wondering if the tune is just too rich at idle or across the RPM range. As far as temp, I see 110-125 at WOT and 125-150 idling.
    Last edited by Bonzen; 05-12-2015 at 11:26 AM.
    "I'd love to help you out wags, but there is larger issue concerning breast cup sizes on another thread that we have to work thru first. This subject suddenly became a non issue." - GN7

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    Senior Member gregb's Avatar
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    Did you tell them it was going in a jet with no temperature regulation? I think I might call me and ask about that. Else I might try the thermostat/bypass option anyway.

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    Off Road Badass Bonzen's Avatar
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    No that never came up. And it's not an option on their calibration/order form. Honestly I'm afraid to touch the damn ECU as it's currently "working", it's 20 years old, and I know that they don't even make MEFI 1 anymore lol. Would decreasing the fuel pressure a bit help it to run a little leaner at idle? I think that's where most of the issue is, at WOT I don't care if is slightly rich...I have an adjustable FPR and an inline gauge.
    "I'd love to help you out wags, but there is larger issue concerning breast cup sizes on another thread that we have to work thru first. This subject suddenly became a non issue." - GN7

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    Senior Member bp298's Avatar
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    Quote Originally Posted by Bonzen View Post
    No that never came up. And it's not an option on their calibration/order form. Honestly I'm afraid to touch the damn ECU as it's currently "working", it's 20 years old, and I know that they don't even make MEFI 1 anymore lol. Would decreasing the fuel pressure a bit help it to run a little leaner at idle? I think that's where most of the issue is, at WOT I don't care if is slightly rich...I have an adjustable FPR and an inline gauge.
    do you have any specs for this system? if there is a water temp sensor connected to the system that causes the system to increase fuel flow when temp is too low, what is that temp? 140? 150?

    28 already sounds low to me? I don't know, but don't think the injectors work all that well with lower and lower pressure? I would search for someone that really knows this system inside and out and can tune it correctly.

    I'm not a fan of idea of just dumping a thermostat in it and everything will be swell. it's a single pass cooling system, and just closing down on the cooling outlet can create other problems. your exhaust needs water flow through it at all times the engine is running. if you decide you need to add a t'stat to elevate water temp for the sensor, you need one that has a bypass to keep those exhaust hoses somewhat cool. and it would be nice to know exactly what temp the sensor needs to see for the system isn't adding excessive fuel.

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