7.4 MPI WOT Limit

[GL2238]

I have 2001 26' Sea Ray Sundancer with 7.4 MPI B3 with 24P prop. Problem is WOT which during one run was 4K RPM at 35 MPH (GPS).<br /><br />All other times, since ownership, RPM seems limited to 3450 to 3550 at 31 MPH. Techs indicated there is some kind of safety limit built into the ECM when a problem is detected. All gauges read normal (Oil 50 lbs-confirmed) (Temp 165-170 F - confirmed) [fresh water cooled] . Engine is smooth running at all speeds. If I go down to idle from a wot test run and place in neutral and run up, RPM is not limited.<br /><br />Are there any connections I should check to the ECM that might be causing the auto RPM limitation. <br /><br />A technician plugged in a computer test unit and indications of "General Warning 1" and "General Warning 2" came up along with "Oil Pressure". He does not know what General Warnings mean? Also, am I to believe the indications clear/reset by themself when faulted conditions are no longer present, or must they be cleared by the tech?<br /><br />Two other identical boats with the same equipment have WOTs between 4200 and 4350.<br /><br /><br />Any help would sure be appreciated.

 

[LubeDude]

Re: 7.4 MPI WOT Limit

The rev limiter on the 454 FI the Boss has is 4,800.

 

[Don S]

Re: 7.4 MPI WOT Limit

The WOT Rpms should be between 4200 and 4600 rpm fro that engine.<br />I'm not sure what the "General Warnings" are either. The lowest trouble code number is 14. It may be called different things on different DDT's (Code readers)

 

[newport dave]

Re: 7.4 MPI WOT Limit

General Warnings are specific to MEFI3 and MEFI4 and are assignable/configurable by the OEM. I know that some late model Volvos have riser temperature sensors that, when overheated, will trigger a General Warning 1 or General Warning 2.<br /><br />I am very familar with the 7.4 MPI, and was not aware that the General Warnings were used with this engine. <br /><br />As far as trouble codes, once a condition that triggers a code no longer exists, the code will still show on the list of trouble codes, but it should not affect engine operation (rev limit) at all. <br /><br />The code will still be stored until cleared. Did you clear the codes to see if they come back?<br /><br />Dave

 

[GL2238]

Re: 7.4 MPI WOT Limit

Tnx Dave: As a matter of fact I questioned the tech about the General Warnings 1 and 2 and he said he found out they apply to automotive only. It was first time he ever saw them. I took out the boat last weekend but he is going on a test run with me tomorrow with the tester attached. He can also confirm what warnings, if any, happened last weekend. This problem has got a number of tech persons stumped. All sensors, including MAP, are normal. Compression is right on the money. This configuration should yield 4300 or so at 38 MPH. Actually I run mostly at 2800 which is confortable with good fuel efficiency.<br /><br />Jerry

 

[newport dave]

Re: 7.4 MPI WOT Limit

GL2238,<br />Has a diagnosis been made on your problem? I'm very curious to know what it is/was. Bad ECM?<br /><br />Dave

 

[waterone1@aol.com]

Re: 7.4 MPI WOT Limit

The general one and two codes are valid for the boat. The are assignable, as they are just contact closures. I don't have a chart handy, but on the MIE (inboard version) general two is used for transmission over-heat. I believe that is swapped to the gear lube tank on the outboard models.

 

[newport dave]

Re: 7.4 MPI WOT Limit

waterone1,<br />You are right about General Warnings 1 and 2 being assignable discrete switchs.<br /><br />You may be right that a Trans O/T or Gear Lube fault will throw a General Warning 1 or 2, the Merc service manual indicates no code (just audio warning) for these events. The manual shows no code for Oil Pressure either, but there it is.<br /><br /><br />The manual shows four discrete switchs, but only two (Gear Lube and Oil Pressure) in use for a sterndrive model, and three (Trans Overtemp, Oil Pressure, and Load Anticipation Mode) for an inboard model.<br /><br />What I don't get is how he could have an Oil Pressure code and both a General Warning 1 and General Warning 2 on a sterndrive model. That would seem to be one too many codes. <br /><br />Dave

 

[waterone1@aol.com]

Re: 7.4 MPI WOT Limit

Dave, you are jogging my memory. The load anticipation (for inboards) is only a switch closure on the trans linkage that opens the IAC to raise the idle when shifting into gear. It will not set a fault code. General one is used on both (inboard and I/O) as low oil pressure. The second warning (#2) is either trans overheat(inboard) or lube level(I/O). I agree having both codes would be rare for an actual failure, but I THINK(wish my manual was here) they share a common ground to the ECM. IF that is correct I would be looking for a wiring harness or multi-pin failure to the ECM( or these were stored at different times). If I have a chance later I'll get out the manuals and try to verify this. I do agree that a non-active code should not be affecting performance. As you and others have suggested, clear the codes and get the boat on the water and see if anything comes back.