WOT Power issue with 8.1

[villain style]

This seems strange that this issue was not noticed during a survey and sea trial? Was that done? I would also ask previous owner if they changed out the original cool fuel modules and had the fuel injectors cleaned? If this was first run of season also may be stale gas...

 

[Sous]

Thanks for all the suggestions. Plan on taking her out tomorrow with a replaced fuel filter. If problem persists, change the plugs n try again, still persists - swap plug wires - then try swapping the IAC. Paulswagelock, What is DTS ?

sounds like a good plan. Make sure you have ready access to plug wires as well when trying the plug swap. Depending on the condition you may end up trashing one or more when you try to remove them for the plug change... ask me how I know. Also depending on the last plug change you may well just want to change them anyway. 8.1s eat plugs anyhow so that is a relatively cheap preventative maintenance items so long as you use Rock Auto, Michigan Motorz, or other to get your plugs and wires much MUCH cheaper than going with the Merc parts.

Unless you had major re-power work done you don't have DTS that started in '08.

IAC is an easy fix but likely not the issue. Generally speaking that will keep you from being able to idle.

Other tips of checking fuel pressure and compression test are good ideas as well. Maybe try to wrangle the compression check when do the plugs to combine the efforts a bit, not sure if that is possible for you though.

 

[Korkie]

Thanks Mark and Sous. Definitely no DTS. And does idle fine. So rules out DTS and probably IAC. Didn't get her out this weekend. Way too windy here. Did drop in water and start both engines. The strb motor started ok but when I would advance the throttle other than really slow or even bump it up, the motor would stall but not shut down so long as I brought the throttle back down. Also, when taking it up (slowly) to around 1100 rpm it would not idle at 1100. It would speed up to 1200 then down to 1000 and do that kind of dieseling thing for a few minutes before staying in one place. Looks like weather going to cooperate this weekend and I will be able to do some decent trouble shooting. It did well on the sea trial and the maintenance records were supposed to be sent to me, but cannot seem to get the broker to follow through. Guess should have gotten them up front. Motors were compression tested back in October when it was taken in on trade, so I was told.
Anyways, guess i will do the plugs thing this weekend and go from there. Did find a marina about 15 minutes away that has a Merc mechanic that can help me out with the diagnosis if I get to the point nothing I am trying helps.

Have a Great Day ! Thanks, Korkie

 

[Henry Boyd]

It also might be the IAC sensor. That's a real easy fix. It's located on the back of the engine and looks almost exactly like a thermostat cover. It sits on the top back of the engine. You can swap with the other engine and see if the problem moves or not. Also it's a good idea to keep a spare IAC sensor on board.


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DO NOT DO THIS! Sorry for emphasis. Scott F tried this ( swapping IACs) a couple of years ago and toasted the ECM on both engines.

I also thought IAC issue was good running RPM, but engine shutdown at idle.

Henry


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[Sous]

I wouldn't swap an IAC from one engine to the other, unless it is certain the one being swapped is a good one. Or in other words, don't put a suspect IAC on a good engine, you could end up with two bad engines.

Henry beat me to it...

Excellent points. It would seem like the easy "does the problem follow the part" type troubleshooting but not worth the risk. IACs are cheap in boat bucks and it'll never hurt to have a spare anyway. Buy one (or two) and just replace it if that is a suspect item based on the symptoms.

 

[Kreole Kid]

Scott, I thought you swapped computers and got jammed up, not IAC


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[Bucit]

Not sure if this is the case on the 8.1's but on my 4.3's you can pull the back hose off the IAC and it will idle about 100 rpms higher but takes the bad IAC out of the equation. The motor will start fine, idle and run like normal.

 

[Scottzzzy]

I had a similar problem and it was plugs on my 8.1's.

 

[Korkie]

Good morning all. After some brief trouble shooting. Swapped plug wires between the two motors and the issue moved to the other motor. After swapping one cylinder at a time back, turned out to be the rear right plug wire had a bad connection between the plug clip and wire. Thanks for all the input, I certainly learned a lot of things that could be the cause the issue, but got lucky it was rather simple. Have a great season !

 

[Georgia SeaDawg]

Good deal!

 

[juggernaut1]

Good to see you got it sorted - and relatively cheaply - seems to be usually plug wires or plugs with these motors cause wot rpm issues.

 

[Georgia SeaDawg]

As a side note, since plugs were suggested, how often do 8.1L owners replace the plugs? Once every year, or every other year?

 

[Henry Boyd]

I usually change ours each year. Although since we only put 10 hours on the engine last year (GD family commitments) I am going to try to get a second season. I did pull them and check the condition and gap, basically brand new.

Henry


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[AFD]

^ I should hope so. 10hours isn't even a round trip to the cape.

 

[paulswagelock]

I have gone several years on a set.
Did you order plug wires yet? Merc is very proud of theirs and want $500 a set. You can order the Volvo equivalents for about $100.

 

[skibum]

You got that right, Paul. Merc plugs are outrageous. I found the proper plugs at the NAPA auto parts store for about $8 a piece a few years ago. They had a conversion manual that converted Merc number to the AC Delco number. They were visually identical. If they didn't have different brand markings on them, I wouldn't have been able to tell the difference.

 

[Henry Boyd]

You got that right, Paul. Merc plugs are outrageous. I found the proper plugs at the NAPA auto parts store for about $8 a piece a few years ago. They had a conversion manual that converted Merc number to the AC Delco number. They were visually identical. If they didn't have different brand markings on them, I wouldn't have been able to tell the difference.

I also have used the Ac plugs. The part number I used is AC 41-983

Henry

 

[dpmulvey]

I also have used the Ac plugs. The part number I used is AC 41-983

Henry

I have gone several years on a set.
Did you order plug wires yet? Merc is very proud of theirs and want $500 a set. You can order the Volvo equivalents for about $100.

You got that right, Paul. Merc plugs are outrageous. I found the proper plugs at the NAPA auto parts store for about $8 a piece a few years ago. They had a conversion manual that converted Merc number to the AC Delco number. They were visually identical. If they didn't have different brand markings on them, I wouldn't have been able to tell the difference.

So does Merc think we are as dumb as we look? :huh:

 

[juggernaut1]

You got that right, Paul. Merc plugs are outrageous. I found the proper plugs at the NAPA auto parts store for about $8 a piece a few years ago. They had a conversion manual that converted Merc number to the AC Delco number. They were visually identical. If they didn't have different brand markings on them, I wouldn't have been able to tell the difference.

I think Paul was referring to the cost of plug wires not plugs.

If you want plug wires here's a set of AC Delco's cheaper than the Volvo equivalent.

http://www.michiganmotorz.com/ignition-wire-delco-p-933.html

A month or so ago they were cheaper at circa $55.00 so I picked up a couple of sets for spares. They were identical to what I pulled of the motors.

 

[Sous]

I think Paul was referring to the cost of plug wires not plugs.

If you want plug wires here's a set of AC Delco's cheaper than the Volvo equivalent.

http://www.michiganmotorz.com/ignition-wire-delco-p-933.html

A month or so ago they were cheaper at circa $55.00 so I picked up a couple of sets for spares. They were identical to what I pulled of the motors.

Both plug and wires of the merc variety are outrageous. The plugs are in the $13 range and the wires as stated are 5+ bills. Crazy.