496HO Down on power
 

Guys....

We've got a PowerQuest280 ('02) with a 496HO/M1ProCharger (supposedly a PQ factory build; boost and fuel pressure gage match the rest of the dash gages, including bezels) and a Whipple Stage 2 ECM tune (NOT factory) that is significantly down on power.

Info dump.... A little history and some details....

We bought the boat a year and a bit ago. It had ~143hrs on the Hobbs meter when we bought it, and an ECM scan confirmed that. It now has ~193. The tattle tale on the GPS says 71MPH, but we've never seen it. I'm sure that was with one person, vapors in the tank and a minimal load. We saw a solid 67-68 with a Bravo28P prop, four people, cooler and a half tank, and I figured the loss was due mostly to the load. All was good. We have since propped down, to 26P, trying to make it a bit more family/watersports friendly, which cost me about 2MPH. Still OK.

Beginning of this year, maybe even before the end of last year, I noticed a change. Transom soot is worse, and different. It's hard to explain, but went from a fairly uniform dark grey film to, just this weekend, a darker film that seems like a cleaner has left streaks in it. Previously perfectly polished exhast tips are now jet black, and cannot be cleaned without serious scrubbing and polishing compound. Top end is dropping off. It used to tach out at ~4600-4700RPM, and that 67MPH or so, but had dropped off to ~4200 at ~55MPH, and has now dropped off to ~4000 at WOT, and about ~50-52 MPH. I asked Dustin to set the rev limiter to 5250 (June of last year). I'm assuming he did so, but have no way of confirming. Boost is off as well. I never see anything more than ~1.5, MAYBE 2lbs of boost, where I was getting ~5lbs initially (Where the 496/M1 ProCharger kit is supposed to be). Fuel pressure seems good. As soon as the boost gage crosses into positive manifold pressure, fuel psi shifts from 40 lbs to 50 lbs. Something else that has sagged is the rev "wall" that the engine hits when taking off, until the hull starts to level off. It used to rev to about 3000-3200 at WOT at takeoff, but now it sticks at 2500 or so until the hull starts to level out, which takes significantly longer now than it did initially. I also see virtually no change in RPM, speed or engine sound from about 2/3 throttle position to full throttle position. I have religiously put at least REC90/alcohol-free gas in the tank. I usually put a 50/50 mix of 89 and 93 in it, since I can't seem to find any 91 anywhere near where we typically boat. We also seem to be going through a small amount of oil, which I monitor obsessively. I ran the serial number past the tech at Merc, and he confirmed the engine was built with the forged crank and rods, but still has those damned hypereutectic cast pistons.

I cannot point a specific "Uh-OH" moment, where something might have happened, strange noise, or anything that would lead me in a specific direction to start looking for something obvious, other than a certain drain plug incident, where we had a fair bit of water in the bilge, but not enough to the point of ingesting any water through the ProCharger intake. We also had a slight engine stutter immediately after start-up a couple weeks ago, where, afterwards, I noticed the radio had gone back to factory resets, including losing the two remote commanders, but that all reset itself to all custom settings, including regaining the remote commanders, after turning the radio off and back on again. Don't know if this would be related at all or not. I suppose it could have been an electrical "event" that got to the ECM, but the degrading behavior had started before that. I might be able to say the digression has gotten worse since then, but I'm not really sure. We went boating with some friends over the weekend. They were trailing us and he told me he could "seriously smell" our exhaust; raw gas. This makes sense, since everything in my limited understanding leads me to a think we are running a VERY rich mixture. I'm sure the ECM tune is expecting more boost than we are getting, so that would make sense, as well. I have not had a chance to read the plugs, but I will soon. I did notice a slight "worn" stripe on the non-working side of the ProCharger belt, but cannot find anything or anywhere it might be rubbing. I also cannot imagine that belt would slip for very long without completely letting go. The working side seems fine. There could be a leak in the intake tract, between the ProCharger and the intake plenum, but I don't know how to verify or rule this out.

I'm beyond thinking something has changed. It's more like something is changing. And I tend to think that's worse.

Any help would be appreciated. I'm hoping some of you engine gurus will recognize some of these symptoms, individually or in concert, and have some insight as to where to look. I'm willing to tow the boat to someone, hopefully relatively close, that could assess the symptoms more thoroughly and knowledgably, but don't personally know anybody willing to looking at it. I think I have a local option for a compression test of the cylinders, but have not pursued that yet. We are located just south of Dayton, OH, so advice on where to take it would be great.

Thanks. Brad.
(937)545-8991

Start with the basics. Plugs, wires, fuel filters and a compression test. Verify that all cylinders are firing with a spark tester and report back

Compression test and fuel psi test always first. And ^^^^

Change the belt for the pro charger. I had similar happen on my 525sc. I used to have to replace my SC belt every other year because it would start slipping and be down on boost

SB,

Working on the compression test. I know how to do it, even if only on an academic level, but I am not properly equipped. Trying to source either the hardware or the labor, or both.

Thanks. Brad.
(937)545-8991

Griff,

Is this a common thing with multi-V belts? I grew up on a blower motor boat, but it was a cog belt. We only had to change the belt a handful of times over the fifteen or so years we had it, and it was always the result of an incident; blown oil seal, severe backfire ripping the belt, etc... Just curious.

Looking and considering everything.

Thanks. Brad.
(937)545-8991

Griff,

Anything in specific to look for as an indicator the belt is bad?

Thanks. Brad.
(937)545-8991

I would check/ change the belt.

Is there a lot of belt dust on the front of the engine? It needs to be tight or it will slip. With your boost down, I would check that first.

Nothing specific that would make it definitive to the naked eye. Mine were 10 rib serp belts.
Belt would be fine on one trip and then a week later would go out and lost half my boost.

Guys,

Another question....

Looking through the ProCharger manual, it states that idle fuel pressure should be ~38lbs, and 62-65psi at full boost. I am reading ~40psi at idle, but only reading ~50psi at "boost" RPM. It seems appropriate to adjust the regulator to get proper WOT pressure, but the engine would appear to already be running rich, and increasing fuel pressure would obviously (I think) make it run even richer. Yes/No?

Thanks. Brad.
(937)545-8991

UnderPSI

I've got a new belt and tensioner arriving today. I'm hoping not to have to change the tensioner, because it's gonna be a PITA to change. I've got NO room to work with. The belt should be pretty easy. I've also acquired a compression gage. What's the best way to prevent the injectors or plugs from firing while cranking the engine? I've gotten a couple of suggestions from people. Just wondering what the experts say.....

Thanks. Brad.
(937)545-8991

Your down on boost, which will cause less fuel psi at that spot. More boost will cause more psi.

Cog belts can’t slip by design. Serpentine belts can snd will when worn some especially turning something that requires a handful of load to turn like a supercharger.

SB,

AHHH... I think I understand how that would work. So, you're saying the fuel pressure will increase when the boost is back up....? I'm only down about 1.5lbs of boost (I stated incorrectly previously.... It's only a 3lb system). Will the fuel pressure increase 12-15 lbs from just 1.5 lbs of boost? I get that liquid pressure is different than air pressure. Just want to make sure I understand the concepts.

Thanks. Brad.
(937)545-8991

ATI will have to let you know.
They use raising rate FMU’s. Some 6:1, some 7:1, some 10:1, and etc. Unlike standard regulators that are 1:1. Ie: 1 pound fuel psi is added from 1 pound fuel psi.

Here’s a more exact reply from me to a thresd in 2015.

​​​​​​​

Use a remote starter button on the slave solenoid to crank it over.
there’s no point at guessing what may or may not be wrong until you pull the plugs. Once you see the plugs it should be a lot easier to head in the right direction.

had a customer ask 100 questions and guess at everything else except what I told him to do first, check the plugs. 2 days later into his vacation he found he knocked 2 plug wires off while cleaning the bilge.

SB,

FMU... Fuel Metering Unit?

So, it's really starting to look like this is all stemming from the apparent loss of boost. I have closely inspected the intake tract between the blower and the throttle body, and can find nothing that would indicate a possible leak. The hoses are intact. The hose clamps are tight. I'm REALLY hoping its just a worn/stretched belt and/or a weak tensioner.

Thanks. Brad.
​​​​​​​(937)545-8991

Unlimited,

I can certainly check the plugs, and fully intend to do so. But.....

The only problem I see with this is that, according to the ProCharger manual and the interwebs, I should have run the boat hard and shut the engine off immediately, letting it coast to a stop (seems kinda scary to me), and pulled the plugs, which I didn't do. We idled into the ramp, dropped the wife off to retrieve the truck and trailer, and put it on the trailer, all while idling. Is this gonna muddy any useful data that can be had from the plugs?

Thanks. Brad.
(937)545-8991

Yes and no, a very successful "plug chop" would be done as instructed. Cruising along in the meat of the power curve the spark plugs are going to show a burn pattern for that range. By slowly cruising to the dock , loading the boat and such the last picture the plugs will show will be the burn pattern of how the engine is idling. Think of a plug chop as a picture of the last time the engine was running, do you want a picture of the engine running at cruising speed or at idle?

CarNuts,

Oh, I get it. It's just the prospects of turning the key at nearly full throttle, assumingly in gear and under load, scares the crap outta me. And it's definitely not the condition I have at the moment.

Thanks. Brad.
(937)545-8991

Unless you just changed your plugs i would buy a set to replace them. Put someone on watch and do a throttle chop in the middle of the lake and replace one or two easy to get to plugs with the new ones, if stuff turns sideways and your drifting on the rocks I would fire the boat up for a secondor two . Make sure you number where they came from , this will give you some insight even though its only 1/8th of the cylinders. If there is something major going on you'll have a better chance to see an abnormality when you replace them all, don't forget to number them.

I wouldnt go messing with fuel pressure unless you have an O2 sensor. A tweak here or there on one end is messing up the other end and you wont be able to wing it at a recommended 40 PSI and get excellent results. However, with the age and model, you might want to take the injectors off and have them flowed and cleaned. Some cool fuel units throw paint chips into the fuel rail.

Does your boat have the stock fuel pump and fuel regulator?
Were you ever able to attain the speeds the old owner got? Are you sure you got the same prop? When I got my boat it ran 73 on trial, upon arrival, 64 becasue the seller took the labbed props off and threw a used set of bravos on. Just sayin...

Change plugs Plugs, see what they look like.
Wires - stock wires on a 496 last to a long long time but you can change them

CarNuts,

Drifting is not what spooks me. I have an anchor It's the sudden thrust dump when I kill the engine at high throttle and what the boat will do. I've just never done that. I guess I can always try just a throttle dump and see what happens. I've just seen boats swerve pretty hard when the engine dies or whatever.

I also think a new set of plugs might be in order, just because I'm sure they are fouled after all the overly rich run time.

Thanks. Brad.
(937)545-8991

Keith,

I think we've worked out the fuel pressure for now. I'm hoping/expecting the fuel pressure to return to the recommended 62-65 psi when we get the boost back up to normal.

As I stated in the opening post, I'm fairly certain the 71MPH on the TattleTale is honest. We got a solid 67-68 out of it with 4-5 people and a half tank when we first got it, and I'm sure that 71MPH was with a minimally loaded boat. As for any midnight parts swaps, we did the sea trial, exchanged funds and rolled away with it. No chance for any shenanigans there.

To be honest, I don't know for sure whether it's a stock fuel pump and/or regulator or not. I guess, since the ProCharger was a factory build/install from PQ, and it's run as expected until now, I'd assumed that all the appropriate parts were installed when the ProCharger went in. I will get a closer look at it and get some pics if I'm not sure.

Thanks. Brad.
(937)545-8991

Just curious if anyone thinks new plugs will get the lost 3lbs of boost back?

UnderPsi,

Not sure if this was supposed to help, or where you're going with this, but, no... Nobody, including me, thinks changing plugs is supposed to recover the lost boost. I am in the process of installing a new blower belt and possible new idler tensioner. Trying to cover all bases, I am planning to install new plugs when I pull the old ones for reading burn patterns.

Thanks. Brad.
(937)545-8991

Guys,

I need a little help. With the ECM having been sent to Whipple for the stage 2 tune, I spoke with Dennis and he sent me their "Custom Calibration Test Results" form to fill out that will help them determine if any tweaks need to be made to the tune. Problem is, I'm a little confused as to how to fill it out. Obviously, I know what the RPM column is for, but the graph has me puzzled. I'm hoping some on here might be familiar with it, as I can't upload the PDF.

Any help would be appreciated.

Thanks. Brad.
(937)545-8991

If the boat ran fine before, then the ECM should not need to be touched and should not be recalibrated until the root of the problem is found.

FYI, Chopping the throttle back and turning off the engine is really no different than coming off plane normally.

Griff,

Completely agree on the ECM. My only interest is in the potential that I might have indicated a 5lb boost system to Whipple, on my tune request form, instead of the 3lb that the ProCharger kit I’ve got actually is, just as I did in my initial post. I can’t remember if I was thinking wrong then as I did here. I just wanted to be sure. In the meantime, I am, in fact, working to resolve the core issue.

I don’t think I’m going to have to change the idler pulley tensioner. I just tried changing the belt, and couldn’t get the tensioner off the belt enough to even come close to getting it off the pulley. That mother is STRONG. Now my only concern is the pulley itself. I’m wondering it it’s not what caused the wear groove on the non-working side of the belt. I’ve checked and rechecked. Nothing else is touching the non-grooved side of the belt. I need to get a longer breaker bar and enlist a second set of hands.

So…. No violent lurch, swerve or attempt to roll should be expected when/if I kill the key at throttle? I’m assuming the prop will free-spin with the oncoming water?

Thanks. Brad.
(937)545-8991

Guys,

Got the belt changed. Had to make a cheater bar for the breaker bar, and had my nephew hold the tensioner off the belt while I changed it. Only dropped the breaker bar into the bilge once. :rolleyes:

https://cimg5.ibsrv.net/gimg/www.off...02c6e815df.jpg
https://cimg7.ibsrv.net/gimg/www.off...e5856a349b.jpg

It certainly looks like something was rubbing on the outside of the belt, but I'm positive there wasn't. This doesn't mean there wasn't something rubbing on it in the past, before we bought the boat.

This doesn't look like a ton of wear on the belt, but I don't really know what to look for. There is some glazing in the valleys, at the bottom of the Vs, so that could be an indicator that the Vs themselves were worn to that point. The new belt was considerably tighter getting back on the pulleys. The old one came off with the tensioner still pulled back. Getting the new one on required relaxing the tensioner, getting the belt over the rims of the pulleys AND over the tensioner, then pushing the belt to the side, pulling the tensioner, working the belt around it, then releasing the tensioner while ensuring the belt was still between the rims of the pulleys.

Next comes the compression test. I picked up a remote starter switch. Now I gotta find the starter...... God, that's gonna be a PITFA......😡

Thanks. Brad.
(937)545-8991

Boat won't do anything squirrelly. I've accidently pulled the kill switch out before at speed. Another time we had a rotor come loose and a screw hit the inside of the cap so hard it moved the distributer and retarded the timing to where it killed the engine at speed.

Your engine doesn't have the remote starter solenoid ?
(#11) https://www.mercruiserparts.com/bam/.../31823/6708/30
Pic below

https://cimg3.ibsrv.net/gimg/www.off...3a3cb54f8e.png

Why is that belt so tight ? I can take my whipple belts off with a 1/2 ratchet..........I have 3 or 4 used marine BBC starters if your interested

Maybe someone was trying to remedy a belt slippage issue with more tension?

DrFeelgood,

I haven't touched it since we bought it. Part of the problem is the location and absolute absence of space to work. The tensioner has a 3/8" drive port. I was using a 12" long 1/2" breaker bar with a 1/2-3/8" reducer adapter, and had zero space to work in. Once I get the cheater bar in, it was pretty easy to release the belt.

Thanks. Brad.
(937)545-8991

SB,

Don't recall seeing one, but I wasn't looking for it, either. I'll crawl back up there and have a look see. Thanks for the head's up.

Thanks. Brad.
(937)545-8991

SB,

OK. So, I think I found that little unit. I'll have to pull the top cover off the engine to verify and obviously to use it. So.... How does one actually use it? Is it the actual starter solenoid? Or is it a bypass solenoid, in place simply for diagnostic purposes? I'm looking for wiring diagrams, and finding PLENTY of them, but none specific to Mercruiser, near as I can tell.

Thanks. Brad.
(937)545-8991

Just pull the kill switch lanyard and turn the key. Most kill switch lanyards don't cut power to the starter

Connecting the two big terminals should crank the starter. The run from the ignition key to starter is too long for proper voktage/amperage to move the starters solenoid, so a remote mount removes this issue. Plenty of diagrams fir Mercruiser's remote starter solenoid.

Griff,

That’s definitely worth a shot.

Thanks. Brad.
(937)545-8991