merkruzer

I have a 97 502 efi that has made an extreamly loud hissing noise from day one. It is so loud you cannot hear the engine at idle speed and above with the hatch open. I recently re-powered (anther story all together) using the stock efi system, extrude honed intake remapped ecm etc. After having a tapping noise i returned the boat to the engine shop, and they said they never heard anything so loud. I thought since it did this from day one it was normal, but he thinks there is something wrong with the efi.
Problem is I have never been in another boat with the efi setup so I cannot compare sound level. Could anyone with the 454-502 efi let me know how there setup sounds?

As for the tapping neither I nor the shop can pinpoint where it is comming from. I used a long screwdriver as a scope and listened to all intake runners at the heads, and all exhaust ports and cannot determine th origin. It does however seem promenant when i listen with the scope on the top of the plenum. Any suggestions?

Also does anyone have experience with any of the aftermarket efi systems? My engine builder keeps suggesting a carb, but by the time I am done with purchasing the carb intake ignition, wiring harness, fuel pump, regulator etc. I will probably be close to the same price as the holley 950 efi system. which is 2600+-
Decisions decisions

audacity

your mods most likely reduced your idle vacuum...and increased your idle air demand...thus increasing the engine IAC (idle air control) demand....hence your hissing noise...i have build a lot of, reliable, hp from these engines....good luck bro!

ps...this is one of the things it could be,,,,again, i am not there personally diagnosing the issue(s) at hand...

merkruzer

Thanks for your replies.
Although the hissing was present from day 1 when I purchased the boat new with only a couple demo hours.
I aquired a new throttle body recently, so I may try that since it is complete with the IAC, etc. As far as the valves I dont know for sure bur 40# seems a little steep.
After about 3 hrs during break-in I had a poly-lock back off, so they went over the valve adjustment, everything seemed fine after that.
Audacity, with these efi setups what have you found to be the most power you can suck through these intakes?
Also what fuel pressure would you suggest?

audacity

a poly back off...you sure??...

you can get 525 no problem with some fluff. the most???...if ya want more than that start fresh,,,i'm into reliability.

i would not worry about the hissing. it's only at idle right? if not monitor the voltage of the IAC while running. also check timming with and with out a and b crossed. i think it's a and b...it's been some time...your engine builder shoud know ALL of this...

the fuel pressure?...every set-up varies...and NEEDS to be dialed in along with your EEC. good luck

merkruzer

Here is the setup, so to speak. 509", 9.3:1 brodix heads crane cam # 168731 / i 226 e 236 duration i .587 e .610 lift. matching roller lifters, crower steel roller rockers, stock crank/rods je pistons, extrude honed intake stock injectors, azs&m remapped ecm, lightning headers.
approx 40-45 lb fuel pressure. I thought for sure I would see 550 hp from all this. I am not sure of speed increase as I have not tried to run her open since the polylock incident. Which by the way was at about 10 hrs.
My plugs look brown- black so It seems I am not running too little pressure.

audacity

seems like 525-550 should be NO PROBLEM. the stock intake is a bit long in my opinion,,,,so we moed-it down...i take it this is a single...cam timing will play a VERY important role in how you boat performs. if they/you just bolted it in straight up then; you got lucky in a big way or your running way off the mark. so what did it make on the dyno?...what did all the curves look like?

10 hours??...let that thing have it!

415stinger

My twin 502s with Hirel MPFIs (AKA Holley) makes a loud hissing sound on cold startup as the IAC tries to raise the idle to the speed that has been programmed into the computer. After the engine warms up, the hissing goes away.

I think your idle screw needs to be adjusted to open the butterfly, so that the idle air uses more air from the butterfly than from the IAC.

Just my opinion.

Phil

audacity

using that screw will yield inconstant results. adjust the small orifice in the plate....take voltage readings off the IAC to calibrate the orifice size.

merkruzer

thanks again for your replies................but engine is comming out, turns out the tapping was a lifter issue and after removing the intake all the rollers on the lifters were galled and scratched as well as the cam. The engine had a slight water leak from the milled intake thal let water and obviously a little sand/mud (upper Chesapeake bottom crud) in to the lifter galley yet showed no signs of water in the oil (frothing etc.) Engine has had 4 oil changes since last August not a drop of water. I guess I better get that closed cooling system I planned on.


Anyone have a decent 502 for sale reasonable so I can stay on the water till this thing gets redone?
Steve

merkruzer

Were there any significant problems with the 525 sc mercs. I saw a pair with like 100 hrs for a decent price, but I thought I read somewhere they had problems