575 sci acting up
 

I have a low hours 575sci in my Scarab 26 and just recently it has started to cough when I throttle up, then when I return to idle it revs up and down a few times on its own and then dies. My mechanic is checking the fuel pressure but were not sure what it should be on the 575. Does anybody have any ideas as to what the problem is or what the fuel pressure is on these? Thanks for any help!!!

I believe it should be 35-38 pounds on idle.....check the pressure its extremely important on these motors or anything with a supercharger (I learned it the hard way)....I melted two pistons due to a bad pump and no fuel preesure guage....

They have 28 to 30 PSI @ Idle.
Have you checked the IAC?

35-38 is way too high. Don't forget these are still TBI units. That kind on fuel pressure will hold the injectors shut. I was told 26 psi at idle w/vac disconnected. Or 28-30 psi wot under load. Mine studdeded and misfired when my fuel pressure was spiking up at 33 psi wot. Good luck and keep up posted Mike

I say IAC

you could be right, I have to check with Lupe from Tnt again, him and my builder Steve from Progressive racing engines were in contact and maybe I heard wrong...........

checked today with my builder and yes 28-30 is correct......

It is easy to put a mechanical gauge in line to measure fuel pressure.
I'll bet it is the IAC. Set it @ 14-16 and it should run great.

Also doubt this is the cause - but DO check the timing as well.

575sci question
 

I'm having the same symptoms with my 575 in a 27 baja. Did you figure out what the problem was? I've had a fuel pressure gauge on my dash since I installed the used motor. It always reads 28 at idle and 26-28 at full throttle. My fuel pressure never changes when this problem occurs. I pulled the IAC motors and checked them with a ohm meter like the 575 service manual states. They both check out perfect. Any help would be appreciated. I just ordered a MAP sensor because it did not check out on both readings. One was fine 1.4Kohms, the other .50 ohms was reading 4.5mohms. I have a mercury scan tool and it shows no codes.

Thanks,

Dale

What is the IAC value @ idle from the scan tool?
Should be 15 or REAL close.

Had a similar problem this weekend and it was a loose spark plug wire... You can always dump your water seperator in a coffee can and see what you have there.

It sounds more like your loosing the head gaskets. The head gasket material between the cylinders gets very thin on the 575's and will burn out causing cross firing. Especially if they are original Mercury gaskets.

Be carefull, it could cost you alot of money.

Quiet storm is correct...if you have over a 100hrs change them to atleast felpros 17048 gaskets. I just had mine changed and they were pretty much toasted between the cylinders. While you have it apart I would send the blower out for a refresh also. Already been down that road also.

What about a possible vacuum leak?

575sci help
 

The head gaskets and heads were done @ 260hrs. I put felpro head gaskets on at that time. It has 395hrs on it now. The Iac reads 36 at idle. Injector on time is 2.4ms at idle. Doesn't the IAC only control idle? It runs rough at idle and at speed. It back fires through the throttle bodies when it back fires. I have replaced the following so far:
Distributer, module, wires, plugs, rotor, cap, solenoid.
Electric fuel pump. I took apart the mech. pump The diaphrams were fine. I even installed a temporary electric fuel pump to eliminate the mech. pump and a gas can to eliminate the tank and fuel line to the tank.
New MAP sensor.
Alternator (it actually was bad)
Fuel filter, fuel/water separator.
I have checked the vacuum line from the cool fuel regulator to the throttle body. I also checked the vacuum line from the map sensor to the intake. Is there some other vacuum line I'm missing? Any response or help would be appreciated.

Thanks again,

Try gapping the plugs down. Almost sounds like detonation to me.

They are at 35. What do you recoomend and what would this tell me?

Thanks

I would try 32 and see if that improves it. Cant really recommend a gap, but im familiar with issues like this on turbo applications.

575 Mef3 computer
 

Anybody ever heard or seen a Mef3 computer go bad? Who can test this? Jim @ Arizona speed said it would take about 2 weeks before they could get to it.

Thanks for all the ideas!!!

Get the IAC back down to 15 and try it. Betcha it will run properly.
575SCi's are picky about IAC setting.

If you had scan tool plugged in, why didn't you adjust it?
It is adjusted by what looks like idle screw on fron throttle body. Careful-you don't need to turn it too much. Let it settle - then blip throttle - let it settle and then check reading. Repeat as needed.

I can check it for you in one day, but, I dont think that is your problem. iac drivers can go bad but, the iac never moves when they do.
Mark
504-469-7463

If you don't think it is the computer do you have any other ideas or checks I can do? I looked at my iac at idle and was afraid to adjust it after the book says 0-40 counts and Jim at Arizona speed said my 34 was fine. Any thoughts on a wiring problem? I've tried to visual check all the wiring for shorts or melted wires. I just thought since my alternator burnt up one day then the boat started running bad the next might have something to do with each other.

Thanks for the advice

call me at shop on wednesday
mark 504-469-7463

My 575's would cough upon advancing the throttle w/ IAC set high.
Re-check the manual. It is supposed to be set @ 15.
The only thing that may be different - is yours single or dual IAC? Mine are single.

That's good to know.

One of mine will occasionally sneeze and die when
advancing the throttle off idle....only does it when
cold though....I'll have to check that.

Did you get your alarm problem figured out ?

Mine has 2 IAC's . 1 in each throttle body.

Then your IAC #'s will be different than mine. I am pretty certain your issue is fuel / air related.
I re-read the 1st post and it still sounds like IAC issues - especially the rev up & down.

I got the 575 package from Arizona speed and marine and they have worked great for the last year, great HP for the $

so what did you set the two IAC's up at?
thanks
brian

I have mine set at 10 running at idle. Works well