MPI Owners FYI!!!
 

I have been dealing with a lean poping conditions and poor fuel delivery for the last 6 months with my 97 sonics 502mpis. so to save the long story and get to the point of this thread i searched high and low for answers to my problems on here and found tons of info on the vst units issues. i have since removed them and replaced with high flow pumps at the tank. Still was having the same issues under load the motors would pop, ping, snort and cough. Sooooo i took to mercury and they did the computer thing and said no codes imagine that... tested all sensors and all good too. So whats wrong? WELL the fuel injectors on my motor have micron filters in the ends of them were the fuel enters from the rail. PLUGGED all of them, had over half the screen plugged with all kinds of crap. This would explain my motors idle fine but when a larger duty cycle is demanded to the injectors and more fuel is expected it would go lean due to the restriction in the inlet of the injectors. To fix i pulled the injectors all 16 and cleaned them with a chemical called B12 it disolves the crud in the mini filters of which you can pull out of the ends of the injectors. PROBLEM SOLVED..

I hope this helps anyone else out there that might be having the same problems.

Happy Boating:drink:

Thank's for posting that. I have the same engines. No problem now but you never know.

jerry.

One other thing to watch. I had some questionable looking burn patterns when I took my heads off. Checked all the injectors for ohms and they were all within specs but several were higher by 3-4 ohms than the rest. So I sent them to a place for cleaning and testing. Luckily this place did pulse testing, because the injectors all passed a flow test when held open. But when pulsed for 30 seconds the out of spec ones flowed 30% less fuel :eek::eek::eek: Due to the higher resistance they would open more slowly so it was starving those cylinders. Make sure to ohm test and change any that are more than 1 ohm off the rest.

yes your are correct i had mine flow tested after cleaning them, perfect. just had boat out today ran better than new. i might just suggest that once a year you clean these filters on the injectors exspecially with the quality of fuel out there now.

Install a good fuel filter (10 micron or so) and you can trap all the gunk there before it ever gets to the injectors

Yes injectors can cause some goofy chit to happen.. :) Jamie / Lakeside

You aint kidding. And there is already two filters before the injectors. The gunk looked like dried up gas or varnish, only can figure its from sitting long long winters.

injectors
 

Has anyone use B12 injector cleaner.

Yes, John did, read first post.

I do not want to pull the injectors. I want to put some in the fuel filter and then run through system. I wonder if I can do this.

It is a very easy off and on job. It only takes about an hour to complete per motor and thats with me and a six pack. 12 bolts three plugs and two vacume lines and the plenum is off. Way easy, then its 4 bolts and the rails off. Trust me anyone can do this. Then just pull the filters out the end of the injectors and spray out with b 12.

Brown mushy or flaky substance, depending on how wet it is, is exactly that....varnish.

varnish is what it was and random debree just like the stuff that plugs up the screen in the vst unit same type of filters in the injector ends.

johnlaskowski, Best post on this site!!!! :drink: (for me at least) I was having similar problems with my 496, eevn took it to my mechanic, and he checked all parts of the ignition, and proceeded to determine that it was springs or valves... Read this post, then called him and he said didn't seem likely, spent 6 bux on fuel injector cleaner and 45 minutes, and just like that it's all good, even poosted up here and was thinking valve job @ 16 hours!!!

http://www.offshoreonly.com/forums/g...exhaust-2.html

Thanks for sharing!!!!!!

THANK YOU :cool-smiley-011:

Its sad when a car mechanic fixes boats better than the supposed experts at the dealer. I guess from now on ill just do all my own repairs as I have more knowledge on these mpi systems then any dealer by me. :eek:

But heck its fixed and the boat runs goo so happy boating.