Hesitation in 5.0L MPI

[Fedds]

2003 5.0L MPI in a 2003 Rinker RX1 boat. I have a hesitation that comes and goes under heavy load (like when coming out of the hole onto plane or at top end). Feels like a miss. I changed the fuel water seperator, and the plugs. Problem still exists. It comes and goes too. I hade the codes checked and there are none.

The only other issue I have is the tach is acting funny at times (reading can be a bit jumpy or just high). Tapping the gauge sometimes fixs the tach. The hesitation does NOT seem to coincide with the tach acting funny.

Where do I look next for the hesitation and how do I fix the tach?

 

[Don S]

Re: Hesitation in 5.0L MPI

Best thing I can say with an MPI engine is to get the proper OEM service manuals, special tools, and start following the systematic troubleshooting method. Or you will never find the problem and end up replacing a lot of very expensive good parts in the hopes of finding the problem.

 

[Fedds]

Re: Hesitation in 5.0L MPI

I guess I was under the impression that the MPI ECU (555ECM?) is as powerful as the vehicle one (I'm an EE and worked designing ECU's for Delphi/GM for 5 years). That said, this ECU should tell you which sensor is intermittent, out of range, and even what cylinder is misfiring. I looked online for a list of code that the ECM can set so that I can rule out what exactly "no codes set" means...does anyone have this list or know where I can find it?

Basically, I'm thinking that if there are no codes then it's not an ignition or sensor issue and I can start to look at fuel pressure and mechanicals.

I had the factory manuals for my carbed 3.7 motor and really, I didn't find them that much more informative as I grow up tinkering with boats and cars, but this MPI system is really pissing me off

 

[Don S]

Re: Hesitation in 5.0L MPI

You need Merc manual #36 for troubleshooting the 555 ECM.

 

[Reel Poor]

Re: Hesitation in 5.0L MPI

You will find the factory manual very helpful for diagnosing the fuel system and the ECU. If your familiar with electronic engine controls you may find "some" helpful information here.

 

[Fedds]

Re: Hesitation in 5.0L MPI

This turned out to be the distributor cap and button being corroded, as well as the screen vents in the bottom of the distributor being clogged causing condensation. Napa has the parts, have them search under ECH The part numbers for my motor (2002 Mercruiser 5.0L MPI 260 HP serail number OM618927) at Napa are RR207 for the distributor cap and RR256 for the Rotor).

Sorry to get back to the forum so late. It took 3ish years, but the issue just came back and it was time to do it again. Also see Service Bulletin 2003-06

 

[Don S]

Re: Hesitation in 5.0L MPI

I would start a single new thread with all the current information and what the problem is. With 2 very old threads at the same time, it very confusing.