Logo
FULL SITE MENU

Mercruiser MEFI 3 Troll Mode Input

K

keithl

New member
"I have a 33' with twin 19

"I have a 33' with twin 1998 350 MPI 5.7L Horizon inboards. This year the port engine was not running well. After hiring a mechanic (which I usually do not do) I bought the Diacom software and looked into the EFI myself. The port engine has a marker saying that the 'Troll Mode Input" was on, the stbd engine 'Troll Mode Input' is off. I don't know how to clear this; can anyone help me out???"
 
"On some MEFI3 engines the Tro

"On some MEFI3 engines the Troll Mode Input is switched "ON", and others it is switched "OFF", but you can't clear it like a stored Trouble Code or switched Telltale. Either way, it won't cause any engine performance issues.

Maybe you could give some more details about your problem. Have you done a full tune-up? Checked compression?"
 
"I did a full tune up. I chan

"I did a full tune up. I changed the cap, rotor, plugs, wires, mag pick up in the distributor, oil transmission fluid, belts, fuel and oil filters, raw water pumps, fuel pump on the stbd engine, and cleaned the flame arrestors. I had a mechanic put it in base timing mode and set the timing. I also replaced the fly bridge over the winter; so I have all new gauges, throttle and clutch cables and operator handles. I dropped the boat in on 8/8 and it seemed to run fine. When I did an extended trip the port engine seemed to be limited on the power it was putting out; the RPM was limited to 2600 RPM. it also held the stbd engine back and I could not get the boat up to the 20 knots I was able to easily obtain last season. Note that the RPM gauges I replaced did not work so I was never sure last year what the RPM was; I bought the boat in Sept and only did a couple of rus with it. The mechanic said it may be the transmission slipping, but I cannot comprehend how that would hold back the max RPM I can get. After about half throttle I don't get anymore power or RPM. I had thought it was not reading a sensor to the ECM, that is why I bought the software and went on to see if I had any fault codes. As I did not have any codes in the ECM and everything appears to be operating well with no load I thought that maybe the troll mode input was affecting the power band and holding the engine back. any other thoughts?"
 
Have you recorded any data? I

Have you recorded any data? I have Diacom also and would like to look at your data files if you have any.
 
"you might try unpluging the o

"you might try unpluging the oil pressure switch,located near the oil filter. if the switch is bad you will be limited to around 2500 rpm. if the switch is bad , you should run out ok with it unpluged. you Diacom data page looks at the switch, you can check it there also.
hope this helps."
 
"I checked into it and Mercrui

"I checked into it and Mercruiser never used Troll Mode Input, so I don't think that's the problem. Also Mercruiser engines made between 1996 1/2 and 2001 do not have Engine Protection Mode enabled, so it's not the ECM restricting RPM due to some perceived hazardous condition, such as high coolant temp or low oil pressure. So I think it's unlikely that this issue is being caused by the engine control system.

Considering that you have lost a lot of power in that engine, I think it's possible it may have a mechanical problem. I would do a compression test next. If you can confirm good compression, then you can begin troubleshooting the fuel injection and ignition systems."
 
"Thanks for all the help. I f

"Thanks for all the help. I finally did a data log on the engines. The stbd engine MEFI would not maintain communications so I could not get data for that engine. I cannot post it as it is too large for this site, even after zip it is 114kB. A friend suggested that I check the fuel lines; I did and found no problems with restriction. Also found that when I run the boat I can get the engine up to 2600 RPM easily with same throttle position as port engine, but I have to go WOT to get 2800 with the port and the stdb can get to 3000 RPM with ease and not WOT. Someone else suggested that I may have an exhaust restriction, or possibly a fuel regulation problem. I am going to check the fuel rail pressure and the compression this weekend, but am a little wary about taking the exhaust riser apart. any other suggestions? thanks"
 
"am a little wary about ta

"am a little wary about taking the exhaust riser apart"

Don't take it apart yet. Pull the rubber off the top off the "y" downpipe and see if the shutter is closed or missing; broke and fell down into the pipe. If it looks OK then use a garder hose to try to fill the downpipe with water and see if it is blocked. One man found a mouse nest in the base of the pipe.
 
"Exhaust restriction is fairly

"Exhaust restriction is fairly common on sterndrives due to the shutter failure, but we are talking about inboard engines, so there are no shutters to fail. If the manifolds and elbows are original, then they could be restricted by rust buildup, but otherwise an exhaust restriction is not very likely.

As far as fuel problems, normally if you lose fuel pressure the engine will cut out when the throttle is advanced too far, it sounds like yours is not cutting out, just not developing full power. Correct?

Just a note about connection issues with Diacom, most of the time losing connection is due to high EMI/RFI generated by the ignition system, which can be due to worn spark plugs, excessive plug gaps, old plug wires, distributor cap or rotor. Always route the Diacom connection cable as far from the distributor as possible.

Could you email the Diacom data file (port engine) to me? newprtdave(at)aol.com"
 
"Again thanks to everyone for

"Again thanks to everyone for the help. I decided to take the risers off this past weekend, and there is not a restriction. so I still am at a loss for the cause of my problem. I was planning on checking the fuel pressure in the header and also the compression, but I forgot to bring my gauges with me. so I will be doing that this coming weekend. Dave I will email the file to you. any other thoughts and or ideas would be greatly appreciated."
 
"Hey Keith,
I took a look at

"Hey Keith,
I took a look at your data file. The very first thing I noticed was that you have a MAP Sensor Voltage Low (code 34) set. After some further reveiw I noticed that the engine MAP is too high (the engine is "running out" of vacuum at a low throttle position under load).

This suggests that the code 34 is active and the ECM is using a default (varies with RPM) MAP value rather than the actual MAP value, or the engine has mechanical problems. I hope it's the former, so getting to the bottom of why the code 34 is being set should be priority number one. Clear it and if it comes back right away, refer to the Merc factory service manual for troubleshooting procedure. Please keep me informed on your progress.
Dave"
 
Back
Top