1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

[ESekelsky]

Thank you in advance for any and all help in regards to helping me diagnose my 1998 5.0 TBI Searay 240DA. I purchased the boat in April of 2008 it has 200 hours on it.
I have a reasonable level of electrical and mechanical ability so don?t hold back with the tech talk. I am New to boating power plants and control systems but not new to V-8?s and ecm troubleshooting etc. Again thanks for your help in advance and here?s my boating problem.
I purchased the 240DA in say April of 2008 the boat seemed a little doggy, a neighboring sea ray owner with a 1986 350ci carbureted 240 DA (nice boat) confirmed my boat performance was a dog at best.
I performed a tune up, cap-rotor-wires-plugs-spin on fuel filter. I was told by the previous owners mechanic that the high volume fuel pump was replaced (maybe it?s not the right pump) and the boat WOKE UP from 32 mph to 42/43mph @ 4300rpm but....
From standing to top speed of 42/43 @ 4300 the boat pulls hard, boat goes fantastic, But when I open it up for a few miles I get a very pronounced "lean pop - small backfires - decrease in power" until I back it down to say 35mph 3200 rpm (all rpm?s are approximate as memory serves me from last season).
At the same time the tach reflects the same sort of anomaly, the tack jumps wildly it even seems to climb in rpm while the motor is lean popping. (Sort of like the tach is shorting out ??) or ignition is shorting out or rev limiter or neutral switch.
As the boat is one month away from hitting the water I wanted to get an early start on trouble shooting.
So far here is the list of items I am planning to test not necessarily in order. Please let me know which test if any could be performed while on land.
? Disconnect tach in case of internal shorting ? verify no other wires on motor are touching ground
? Batter terminal connections will be removed and cleaned and reinstalled and greased.
? Fuel Pressure (new spin on filter installed last year)
? Check for ecm codes
? Neutral or forward reverse switch jumper ?test? deep water test only not with anyone near prop
? Pull plugs test for compression and or water coming in via risers etc.
? Routing of plug wires
? Replace pickup coil
? Inspect fuel system including VENTS ? not to mention FRESH GAS.
? Verify correct gph fuel pump as this was replaced (should show up on fuel pressure test)
? I have the mercruiser manuals (thank you to whomever posted the links)
? Could I have a rev limiter problem? prop is the correct S.S. per Sea Ray web site
The boat was owned by a non mechanical person who seemed to take slow rides I don?t feel it saw allot of WOT.
Please feel free to cut and paste links which you feel may be of help as this might limit wasting your guy?s time. I am really open to any suggestions. Thanks again. Ed

 

[Lodgepole]

Re: 1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

Don't kmow about your Merc, but I had a 3.0 OMC problem that sounds somewhat similar. Tried everything, plugs, wires, carb, coil and turned out to be a flapper valve rotted/burned off and fell down partly blocking the exhaust into the drive.

 

[ESekelsky]

Re: 1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

Thank you for the reply, Silly question but how do you know ? How do you test for that.. pull the lower unit or pull a manifold and put a magnet down there ?

 

[Bondo]

Re: 1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

Ayuh,... Did you read #12 in the Adults Only section at the top of the forum,..??

 

[ESekelsky]

Re: 1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

Hi Bond-O thank you for the reply, I have a few things to mention. I did take your advice and look at #12 but I do achieve WOT 4800 (+ plus) I can hit 5200 if I want. If the shift interrupter switch does not fix it I will look harder. I will also be checking everything as a curse of pre-season visual check.
Scenario ?A? first run of the morning
Let me try to recap the issue in short... when the boat is warmed up for 15 -20 minutes at the dock and you clear the last buoy and open it up it will run WOT 4800 rpm for 5-10 miles but once the boat is up to operating temperature the motor will pop like a pack of lady fingers (minor popping but audible). @ the same time the tachometer will go up almost like its shorting out. Once you back the throttle down to approximately 3500 the popping will stop. (One note to mention the boat speed and vibration and bouncing up and down is minimized at the same time)
and you slow down and try a standing start ...
Scenario ?B? Warm after scenario above standing start out of the hole
(warm standing start after being run for 5-10 miles).. Out of the hole trim it down tabs up 4800 rrrrrrrrrrrrrrrrrrrrrrrrrrrrr on plane in maybe 50 ft .. not bad for a sea ray 24' pulls hard not a pop - peep sputter etc.
Boat goes for a mile or so at WOT the small popping from (air cleaner) pop, pop sort of like 1/2 lady fingers type sound until I get my foot out of it (pull back to say 3750 rpm. The boat will keep doing it over and over if you try to go WOT. The boat will achieve 4800 rpm but will be popping so we don?t want to damage the motor etc. so we slow down.
Scenario ?C? Warm after scenario above standing start out of the hole (same out of the hole every time)
Now if you come out of the hole again its great until the boat gets moving like 35 + mph then the popping from the E.F.I. carburetor come back until you slow.
So here is what I found please let me know if it sound like shift interrupter switch.
I did Ohm out the shift interrupter switch and got some VERY interesting readings. I disconnected the switch interrupter and placed a fluke multi-meter in the switch interrupter read anywhere from 1-15 ohms initially then went down to .43 ohms but..
If you so much as touch that plastic leaver (the shifter cable seesaw) for the sifting cables the meter goes up to infinite etc. Additionally it dawned on me that the problem may be related to W.O.T. vibration and bumping etc. I surmised that this is why the boat runs fine out of the hole and at moderate speeds (low g forces)
It seems like that when the boat is at wide open in 1-2-3 foot waves the cable that connects to the out drive bounces up down and sideways etc. I tapped and slapped the cable that goes down to the out drive and the ohmmeter goes crazy bouncing from infinite to 50 to 1-2 ohms.
I am going to replace at least the shift interrupter switch and or the plastic See saw piece that connects the two cables. The see saw piece is a little worn as the boat is a 1997.
My question is somewhat basic; do you think the shift interrupter switch could cause the W.O.T. popping kind of problem? Is it true that the shift interrupter switch sits in the ECM path sort of a serial data stream?
Thank you !
Ed

 

[boatguya1]

Re: 1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

Sounds like your on the right path with the interupter switch. If you were on the water I'd say plug the 2 wires the interupter switch plugs into together and test. This assumes it's the pushbutton style switch that is normally closed and opens when the button is pushed. If the problem goes away you're in the right area to fix it. Do this in open water without hazards around because boat won't want to shift out of gear. Then decide if it's the switch, adjustment, cam, or v spring behind the cam that's the problem. They have had some problems with these switches and they are fairly cheap to buy I might consider just slapping on a new one.

James

 

[ESekelsky]

Re: 1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

Thank you all. Shift interrupter switch was the problem. No more Wide open throttle misfires. The Cable running to the outdrive would bounce up and down when at W.O.T. due to the waves etc. That would flex the bracket and thus cause the shift interrupter switch to throw non linear resistance readings to the e.c.m. Basically the shift interrupter switch was acting like a rev limiter due to the boat moving and thus being dynamic. if anyone has this problem put an ohmmeter on the shift interrupter switch located on the motor. Tap on the outdrive control cable and flex and or move or push and tap on the engine speed control brackets. With the forward reverse control in neutral you should see the ohm meter go from low resistance to 400 ohms to 7000 ohms to infinite and jump all around as you probe and push and flex the brackets. Additionally you will notice that the switch has lost its linearity. In other words the 1/2 inch thro of the switch does not work correctly. A defective switch will change resistance readings within a millimeter or two. (Very touchy)
Re: Eddie

now onto the next problem same boat 1998 305 tbi efi alpha one gen 2 one manifold running hot.

 

[ricklaw67]

Re: 1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

Could this be the answer to my problem? My 93 searay 5.7L runs great on land but sputters and spits and conks out in sea. Have gone thru all the fuel componets, plugs, wires, cap and rotor. Still the same problem. Fire it up on the trailer and she purrs put it in the water and she runs good for about 5 or 1o minutes and bam conks out restart conk our sputters spits farts ect. Have to get towed in. Also when I get it started back up in the water (which takes a while) it runs great in neutral put it in gear and i have to putt putt along and it conks out again.

 

[Don S]

Re: 1998 Searay 240DA Mercruiser 5.0 TBI WOT misfire

Could this be the answer to my problem?

Instead of asking, why don't you check yours out.

Instead of asking a new question on an old thread start a new one OF YOUR OWN.