7.4LX Drivability Problem

[jguarniere]

My 1997 MerCruiser 7.4LX is currently experiencing a serious drivability problem. A few weeks ago, the boat started to lose power occasionally (once every 10-15 minutes), but only for less than a half second before recovering fully. This only occurred at high engine speeds. Last week, however, the problem became more frequent (once per minute), and more severe (loss for up to 1 second). It now occurs at lower engine speeds as well (down to 3000 rpm). Since the boat sat winterized/unused for two years (2000-2001), I replaced the fuel filter this weekend (no help). I also ran fuel injector cleaner through the engine a few weeks ago, after the problem started. The engine runs, but very erratically at this point. Any ideas regarding what I should check next?

 

[JB]

Re: 7.4LX Drivability Problem

Moving to I/O

 

[snapperbait]

Re: 7.4LX Drivability Problem

EFI does'nt like poor fuel quality... Fresh fuel and filters... Could be anything from a loose wire/bad connection to fouled up fuel injectors(my guess)...<br /><br />I'd get a code scanner and see if any trouble codes stored in the engines computer show up when you test it.. Or, just haul it down to a Mercruiser service dept. and let them do it.. Without a check for trouble codes, you'll just end up throwing parts at it...<br /><br /> CodeMate <br />EFI Code Reader Part #94008 <br /> http://216.230.203.183/marine/marine.htm

 

[Walt T]

Re: 7.4LX Drivability Problem

Check the number 8 plug wire. I may be hanging down by the knock sensor, causing it to retard the timing.

 

[jguarniere]

Re: 7.4LX Drivability Problem

Thanks for the suggestions so far; I should clarify the problem a little better. It seems that the engine actually shuts down for up to 1 second, as if the key were turned off. After the hesitation, everything is perfect again. Could clogged fuel injectors or a plug wire/knock sensor contact cause this brief problem?