Sutphen,

Yup. As Feelgood stated... Injectors were in serious need of cleaning. So bad that two were essentially useless, one more so than the other. We were essentially running on 6-1/2 cylinders, and I suspect the remaining cylinders weren't all that healthy.

Smitty (ArcticFriends) did the injector work and posted initial testing video and some data from said test. His prediction that the boat would be night and day couldn't have been more accurate.

Thanks. Brad.
(937)545-8991

Feelgood,

What, exactly is going on with a vacuum leak causing a full ECM engine to hunt at idle? Genuine question.

What about the MAP sensor? I had a Plymouth Horizon years ago that, when the MAP sensor went out, it wouldn't idle worth a crap. To the point I'd have to take it out of gear and keep my foot on the pedal, keeping it slightly above idle, for it to keep running.

I did notice during my escapades under the engine hatch that the vacuum lines seemed pretty hard; twenty years old and all. That might be my next improvement.

Thanks. Brad.
(937)545-8991

Vacuum leak is unmetered air. My guess is that there's multiple factors involved in the hunting idle, including the IAC trying to stabilize it, and varying manifold pressure as read by the MAP sensor leading to mixture adjustments.

A scan tool (Techmate, Diacom) would let you see what the MAP sensor is seeing / reporting. The MAP sensor voltage should be around 1V at idle, increase towards 5V as engine vacuum decreases, and boost builds (while load increases, typically). In your case, with a forced induction application, your MAP sensor will be different (3 bar?) from one on a naturally aspirated motor (1 bar) but still behave the same way at idle when under vacuum instead of boost.

Old school trick for identifying a vacuum leak is to use a propane torch (NOT LIT), to supply a stream of gas near the intake manifold, vacuum hoses, etc, to see if the engine RPM increases as a vacuum leak sucks in propane.

Here you go s30 and others that did not see the OP’s injectors being tested by arcticfriends. Post#130

Griff,

I've actually manipulated the throttle body on my engine, and I could peg the stick at WOT. It's set up pretty well in that regard. I don't know if there is any difference between 75-80% open at the butterfly and wide open, as far as reaction in RPM, but the mechanical connection has full range. I can tell you that I could hear a difference between 75% on the stick to WOT, prior to getting the injectors refreshed, but we just didn't get anything from it. I'm thinking (hoping) we will now.

I bought a 28P from a guy in upstate NY. We'll see how that goes. I'm optimistic. I know we could pull the 28 that was on the boat when we bought it, and, as I said, I'm fully of the opinion that this issue was already starting to develop at that time. I've been told by several people that the 280, with a 496HO should run in the 70MPH range without any power adders. I am planning on contacting BBlades and talking with them about their testing program.

Thanks. Brad.
(937)545-8991

SB,


https://cimg8.ibsrv.net/gimg/www.off...97069fb2f.jpeg
https://cimg9.ibsrv.net/gimg/www.off...10848095f.jpeg
Au contraire, mon frére…..

Thanks. Brad.
(937?545-8991

That is way old school we used to also use starting fluid but learn both of those are dangerous.

Use brake cleaner, not as flammable but if there is a vacuum leak you find out quick.

Wildman,

My plan is to replace all the vacuum lines I can and see if the behavior goes away. Vacuum hose is cheap, easy to replace and it can't hurt to have all new.

Thanks. Brad.
(937)545-8991

Definitely won't hurt. When was last time your throttle body and IAC port in the TB cleaned? 496's are notorious for ingesting belt dust and sending it to the IAC valve killing it. Your PC setup pulls air from a different location than stock so it might not apply. If you had a Techmate scanner you could monitor IAC operation while running to diagnose.

A 496 owner should have a scanner and learn how to use it. It will really prevent frustration and throwing darts.

Ryan,

I could be talked into inspecting the IAC port pretty easily. Couldn't hurt. And I've heard/read of many a costly recoveries that could have been minimized had a bad IAC been caught earlier.

THIS?

Thanks. Brad.
(937)545-8991

That's the Techmate. good little unit.

I really need to get me one of those.

It's an easy check. I keep a space IAC on boat at all times. JIC. They fail that often. Yes, running on a bad one will eventually burn up the IAC driver in the PCM. With a scan tool you can monitor your IAC operation while running and do an IAC test of the valve.

https://cimg0.ibsrv.net/gimg/www.off...6831aadcb5.jpg

Wildman,

I just ordered one. I know, I know... I shoulda done it a couple weeks ago. I'm not sure it would have helped, though. It does allow for a cylinder misfire sequence, but I'm not sure if it will do either/or ignition/injector deletes independently or not. I guess we'll find out when it comes in.

I'm hoping to not need to use this any time soon, but we all know what boat ownership entails, don't we?

Thanks. Brad.
(937)545-8991

Ryan, others....

What are the chances that that's exactly what is causing the idle hunting I'm seeing with my boat.....?

Thanks. Brad.
(937)545-8991

Yes, you can fire coils and injectors independently. I relocated my IAC input hose to pull filtered air from back of intake. Capped off port in throttle body.
https://cimg1.ibsrv.net/gimg/www.off...a0465e3c12.jpg

The IAC counts increase when you back off the throttle the IAC opens to keep a smooth transition air supply into the engine while the rpms come down and keep it from surging or stalling. When its back idling at 650 rpms the IAC counts go to 0 as its not needed and it waits for its next needed operation.

The short version is #7 injector was randomly stuck at about 20/30% flow and #4 was consistently 20 % or so low. Its a miracle that #4 didnt melt the piston and detonate itself to death being lean under boost! I extensively cleaned the injectors then cycled them for about 2 hours almost constantly on my machine on inductance test setting to make sure they didn't decay hot or act up again, then ran all my series of test, they were well within spec once cleaned, Smitty

Guys,

Gonna hopefully test the "new" Bravo 28P prop this weekend. In the event it's not enough (as I'm expecting), I am exploring options. There is currently a set of Hydromotive P5-X 26P props for sale in the Swap Shop. Price seems reasonable, and there's already somebody interested in the LH only, so we should be able to work something out if I can make use of the RH. I understand that Hydromotive props generally act like a Bravo of a couple inches more pitch, so this might be right in the sweet spot. Really looking for guidance on bow/stern lift characteristics re: single stepped hull. Yes, I know about the difference in slip and that effect on a stock B1 outdrive.

Refresher.... PowerQuest 280 (single stepped hull), advertised (by ProCharger) 615HP (zero manifold pressure @~3800-4000RPM). Buried the rev limiter with a Bravo26P well before burying the throttle.

Thoughts?

Thanks. Brad.
(937)545-8991

what's your current speed vs rpm? I owned one of these last year and I've either tuned on water or built, dynoed then tuned 4 others on water. Very sensitive to weight in the cabin and getting bow loose for speed but they run flat. We ran 77/78 gps sunday with last one with 26 pitch at 6 k, he had slot of weight in cabin, this week he ran 77/78 ,×with a 30 labbed at 5400 with 3 big guys in boat. Im.interested in what prop works for you.

Guys,

Prop search is over. Tested the Bravo28P this afternoon, and it is the prop we are going to run. It was slightly less lively than the 26P coming on plane, but loaded the engine at WOT just about perfectly. I could just get it to 5K RPM with the right amount of trim, and saw 75MPH at that point. The boat had a slight bit of slow chine walk that I was able to settle down with just a hint of tabs.

I plan to hang onto the Bravo26P for use when we’ve got a number of people with us or when we intend to pull a skier.


Thanks for all the help and advice in this thread. And hopefully, it can serve to guide others in rooting out similar problems.

Thanks. Brad.
(937)545-8991

Congrats on getting her dialed in with plenty of summer left!

Guys,

I am still only seeing about 52lbs of fuel pressure in boost condition. ProCharger manual indicates we should be at 62-65lbs. Assuming the pump is capable, the regulator is functioning properly and the gage is accurate, I should adjust the regulator to achieve that pressure?

I’ve also noticed that when I initially turn the key, when the fuel pump primes the system, the gage initially show that ~52lbs, then drops to the manifold vacuum condition pressure or 38lbs. Is that initial 52lb reading showing me the boost condition pressure? Or do I need to make an adjustment, make a hard run, make an adjustment, make a hard run, make an adjustment….. etc…. Until the boost fuel pressure is where we want it?

Thanks. Brad.
(937)545-8991

how much boost are you making?

Sutphen,

~3lbs @ 5K RPM.

Thanks. Brad.
(937)545-8991

with the way you have it set up,52psi is probably about right for your boost,as set up now.how are your afr's?

Sutphen,

AFRs….. Now you’re talkin’ Egyptian….

I do know what AFR is. I just don’t know how to get that data. I now have a Techmate Pro, if that helps.

Thanks. Brad.
(937)545-8991

air fuel ratio,,techmate doesn't do it

Need to add O2 sensors if you want to see AFR.

DrFeelgood,

Where do I add them where they won’t get eaten by the water in the exhaust? I have the stock Merc 496 manifolds.

Thanks. Brad.
(937)545-8991

They have to be added in a location prior to where water mixes with the exhaust gas. Something like this, for example:
https://affordable-fuel-injection.co...adapter-plate/

DrFeelgood,

Merc 496 Exhaust Assembly

So, where in this diagram would that unit go? I have an idea, but I’d like confirmation.

I’m assuming the water from the distribution tube goes into a jacket around the actual exhaust passage of the manifold, and is then introduced to the exhaust flow through the two hoses on either side of the base of the riser elbow….?

Also, since the 555 ECM doesn’t have provision for O2 data input, this addition would only be for test and tune purposes, then the sensor port would be plugged, right?

Assuming the additional height can be accounted for in the flexibility of the exhaust hose between the riser and the transom tubes….?

Also assuming it would be best to have these installed on both sides….?

Thanks. Brad.
(937)546-8991

You could permanently install a wideband O2 sensor with a gauge at the helm, if you wish to monitor on an ongoing basis. Doing both sides seems most logical but I'm sure there's some guys out there that arbitrarily just picked one side.

The stock manifold setup uses a wet joint at the manifold to riser joint. Most aftermarket setups eliminate that wet joint in favor of a jumper hose. In either event, there is no water in the exhaust gas stream at that point, it's just a matter of how cooling water gets from the outer cooling jacket of the manifold, to the outer cooling jacket of the riser.

DrFeelgood,

So it would go between the manifold and #15?

I wouldn’t be opposed to adding a couple O2 gages, just to monitor them, but I wouldn’t feel the need for them. I’m far more concerned with potential damage to those damned cast pistons if I’m running lean, but I also don’t want to be running overly rich, either. The transom soot is bad enough.

Thanks. Brad.
(937)545-8991

Based on that diagram, it looks like there's a dry joint with jumper hoses. Maybe Merc revised that with the 496, I don't know.

At any rate, 1 is the manifold and 7 is the riser. Ideally an O2 would go either in between those with an adapter plate, or in a bung welded into the riser.

496 exhaust is a dry joint from manifold to riser.
You could still use a plate between them or you could have a bunge welded in where the #7 is.

Guys,

Looking at IAC valves. Any reason not to buy the Sierra unit instead of the Quicksilver unit?

Thanks. Brad.
(937)545-8991

Get the ford motocraft one. Do a search, we have deciphered the part #.

Here is one such thread:
https://www.offshoreonly.com/forums/...iac-valve.html

SB,


https://cimg9.ibsrv.net/gimg/www.off...efba6309bd.png
Done did it. 😎

Thanks. Brad.
(937)545-8991

SB,

Finally got a chance to get the scan tool out and play with it a bit. I performed the IAC output test and got ZERO change in RPM from -100% to +100%. I'm assuming this is an indicator the IAC valve is bad. Since I already had the replacement part on hand, I swapped it out, but have not had the chance to get it wet again and fire it up for a final evaluation. Is it safe to assume the hunting idle will have gone away?

Thanks. Brad.
(937)545-8991