Hesitates from idle to slow accel, 2nd fuel pump needed?

[collawash]

I finally got my 99 Chap Sig 27 back to it's showroom performance after some previous issues. I've changed the cap, rotor, plugs, LOF, new fuel pump and filter, cleaned the spark arrester, checked timing, filled w/fresh fuel and new lower pitched props. The boat runs fabulous compared to it previous state. I've rechecked part numbers, looked for any air leaks and checked the throttle cables too. Everything checks out perfectly, but... <br /><br />It's not a big problem, but I now "NOTICE" a slight hesitation when I slowly accelerate from idle. It does not last more than a second and may be the fuel being pushed through the fuel rail, heck if I know. It may have been there before, but I just don't recall.[sigh] It may be that the boat's previous poor performance had me listening for other things. <br /><br />I spoke with 2 local marine mechanics and both mentioned a MCM service bulletin regarding the installation of another low pressure fuel pump to the existing HP pump. My engine number is OL335436. <br /><br />Is there someone who knows any real and accurate information on installing a secondary fuel pump? Do I need one? I know the high output 454 and 502 packages come with 2 pumps. Did MCM finally state the 7.4 MPI's now need one too? <br /><br />I can live with the issue, but thought since winter is around the corner, now is the time to make the repair if needed.<br /><br />As always, thanks to everyone for helping us less boat savvy mariners enjoy more time on the water. My pocketbook and my wife thank you.

 

[f_inscreenname]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

How fast is “slowly accelerate from idle.”? Dose it stumble in the same place every time? If you try to accelerate faster dose it get worse or stay the same? If you left the throttle where it starts to stumble at will it clean up by its self or the will the motor die or just continue to stumble? Is the little lever on the top front corner on the carb (if you have a manual it is called a accelerator pump lever) connected to the throttle lever have three holes in it? Working on a theory. I have never herd of the twin fuel pump thing.

 

[waterone1@aol.com]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

If the engine idles OK, and if it runs at wide open throttle OK, I don't think it is a fuel pressure problem. As the previous post described, it could be the accelerator pump, or it could be time for a carb rebuild. A check of the carb and intake for vacume leaks would also be in order.

 

[tommays]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

merc service bulletins for all years<br /><br /> http://www.boatfix.com/merc/Bullet/sbcover.pdf <br /><br />tommays

 

[Bondo]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

I don't know what the problem Is,<br />But, I'm Sure it's Not the Acc.Pump.......<br />He's got EFI...........

 

[Don S]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

You are about to find out that an MPI is not an easy sytem to trouble shoot without the proper tools. <br />If you were having a problem with high speed operation while under load, you might have a fuel pump problem, but not with just a slight hesitation.<br />Here is the basic outline for tests to find the problem. You will need Merc service manual #23 (PN 09-861326--1) to read all the details of the tests.<br />I would also suggest you don't just "Live with it" MPI problems only get worse and more expensive as the one problem can cause other problems.

 

[collawash]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

If I didn't say so, my engine is an MPI.<br /><br />If I move the throttle quickly (like pulling a skier/tube or just feel like burning fuel), the engine doesn't miss a beat. What I'm noticing is a just a slight hesitation just moving the throttle slowly from idle speed to a slow speed. The rpms dips ever so slightly before picking up and then there's no problem at all.<br /><br />I'm going out for a 2day cruise this weekend, hopefully the problem magically ceases to exist forever. If not, maybe I'll be able to better describe what it is. <br /><br />Don S.- I'll check and see if the bulletin can decipher the prob. Thanks to everyone.

 

[collawash]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

Yes, this occurs at the same time, place everytime.

 

[Don S]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

What I'm noticing is a just a slight hesitation just moving the throttle slowly from idle speed to a slow speed.

Are you talking about a hesitation, or possibly just the play in the throttle cable before it starts moving the engine linkage?

 

[f_inscreenname]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

I was thinking that too Don now that I found out it was EFI . You think the "shift cut out switch" may be hanging a little??

 

[Don S]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

Doesn't have a shift cutout switch with a Bravo drive, and the 7.4 MPI's didn't come with Alpha drives.

 

[waterone1@aol.com]

Re: Hesitates from idle to slow accel, 2nd fuel pump needed?

Sorry I missed that it is a efi engine. My first guess would be to look at the TPS. As Don said, you really need propper tools (scan tool, etc). Without being able to read the sensors inputs to the ECM, it's all a shot in the dark.