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,




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