350 MAG MPI Injection question

Black_Diamond

Anyone know if the Mercury engine scan tool will read if an injector is not working correct or is clogged?

212rowboat

you've just described what happens when a MAP/MAF starts to fart, and before it poops.. it can fart a long time.

in short: your engines are likely not entering closed loop operations.. they are remaining in open loop, which draws fuel trims from set drafted tables on the PCM.... when an engine moves into closed loop, it has reached the bottom end of temperature range, it has sniffed air density and air flow, and if equipped, it has read and trusts air-fuel ratio as sniffed by an o2 sensor.... it needs those to close loop.. if it doesn't get those (bat thermostat, bad MAP/MAF, bad IAT), it doesn't close loop... it instead, dumps fuel and runs excessively rich... it does that because it is harder to ignite a wad of ingested air/fuel w/o spark (no predet) predet on a cold/cool engine is a death sentence.

TikiHut2

Fire off a PM to Drew or Al. They're probably hibernating..... Hope it's nothing major.

Wait a min. You're winterized too. Was it missing when you shut it down for the season or is this just something inquiring minds wonder about all winter?

212rowboat

the PCM will report IF there is an electrical fault, which is measured by ohms.. I don't know if the scan tool will read it, but I can't see why it wouldn't seeing as how it's pretty important.

the PCM doesn't know if there is a 'hung' injector whose mechanism has given up the ghost, so long as the injector motor is working (it could be a basket clog, or a gate fault in this condition).... at this point, and ONLY if the engine is monitored at the exhaust (o2 sensor) will it know if something is amiss.. it will either be lean or rich, and unless each bank of the motor is monitored, it won't know which cylinder..

redneck stethoscope that rascal... long screwdriver, handle side to ear, blade to injector.. you should hear and feel a slight but distinct click.. compare it to other injectors..

some scan tools can manage each individual injector- opening and closing at the behest of the scan tool operator.. these are best suited for pulling the rail with the injectors still attached, laying a towel under them, and exercising each of them.. some go as far as to place measured containers under them to value flow/volume..

I'll offer this, for what it's worth: these injectors are at least generation 4 injectors.. the bugs are gone, and these things will last most often the life of an engine.. what I see and hear about more often is clogged rails, clogged baskets, and abrasions on harnesses causing shorts...

if you must, and want to save a dime (and make sure it's done right, which is my motivation), get yourself an ultrasonic jewelry cleaner... use gasoline instead of acetone, and run them a while... replace the baskets, and for the love of all that's holy, use new o-rings anytime you pull one out... by the way, I've used all kinds of things from motor oil to dielectric grease, but the lube I use nowadays for reinserting injectors: freakin' KY jelly... You should see the look on folks faces when they see that in my tool kit.. :-)  I wonder what they say behind my back........ :-D

212rowboat

oh- one more thing:

I'll make this brief as I can... :-)

the blades/spades on the injector connector are pretty important.. I learned this the hard way and after likely 100 hours t/s'n an engine... no kidding..

injectors work in a specific and small electrical range.. if the blade/spade that electrically connects them to the harness has been damaged or not fully seating, you can have a wonky injector that is a bear to track down... ALWAYS take care when removing the connection, be it EV1 or EV6, as they are BOTH very sensitive to current, and need a precise pathway (the connection) providing very expected resistance to operate properly.  Look at the pins/blades, and then the female connector.. use a magnifying glass if you have to.. use dielectric grease on them to keep corrosion out, and make certain they are seated properly and fully.

Black_Diamond

Drew,

 

I'll have to wait until I'm back in the water to test some of this.  Thanks for the tips though.

My driver for asking all this comes from the other thread about peoples fuel usage last season.  My 2003 342 was a dog when I got it..4 adults and forget about getting on plane (yes that bad).  I repropped from 24P to 22P based on WOT numbers and it solved the performance problem of getting on plane.  What I'm randomly chasing now is what I see as poor mpg/gph with my twin 350MAG MPI's with BIII drives.  My mpg is in the 0.5 range / 32gph at cruise (total) and it seems others with the same or close set up are 2x the mpg.  I also get an odd rpm drop on the port engine while throttling up of ~1,000 rpm or more at times before it works it's way back up to match the other engine and have to make significant throttle adgustments to compensate.  Tachs are good by the way

 

Black_Diamond

Thanks! I'll chase those down. Know more in the spring!

212rowboat

I typed something... it entered the twilight zone, apparently... :-)

you're describing a failing MAF/MAP sensor... which isn't allowing the engine to enter closed loop operations.. it sounds like it's sticking in open loop, which is excessively rich, will cause a bog such as you describe, and is less than kind to economy...

an EFI MPI engine that is PCM controlled requires thermostat to gauge operational temperatures (which need to be close to the 'stats rating +/-20* or so), trust the Manifold absolute pressure or Mass Air Flow reading (which isn't to be trusted until temperature is reached), and the air intake temperature/mass- and if so equipped, it needs to be able to reconcile these readings off of an o2 sensor which sniffs the results of A:F ratio.... all of those sensors have to be operational for the PCM to 'pass' the engine into operation based on their readings... in addition to that, spark is controlled, too.. the PCM will retard spark closer to TDC in open loop... when loop closes and all sensors check out, it will start to advance it- and you'll see your power increase quite a bit, while your economy increases as well.. 

a cold/cool engine runs very rich, which is a bit counter-intuitive... a dense concentration of fuel in the air is harder to ignite than a lean mix.. a lean mix can detonate upon compression alone.. a rich wad of a:f ingested most often won't 'splode until struck with spark, which is why your engine won't advance spark timing until it KNOWS you're at operational temperature and your sensors check out... <- this was the bane of carb'd engines, who had issues with the choke getting stuck.... chokes disappeared with EFI MPI engines because that burden is transferred to a smarter piece of equipment, your PCM... the richness of open loop is for one purpose and one only: to keep the engine from pre-detonation, which will kill hard parts with a quickness, as well as blow gaskets under heads when excessive chamber pressures happen with a lean (read: violent) explosion... you want your fuel to burn, not explode... burn really fast, mind you, but not explode on the faces of pistons which bounce really hard off of rods, bearing caps, cranks, ect... 

I'd look at the weakest link in your primary sensor chain- the MAP/MAF... (I can't recall which technology merc uses)... they often operate at the bottom or top of the allowable parameter, but aren't doing what they are 'sposed to be doing... because the voltage doesn't fall out, there is no code to set... because a code isn't set, you go on down the lake not knowing you're wasting fuel and losing power because of it. 

jmoen438

Interesting Drew, is there a specific way to if if the MAF/MAP sensor has gone bad?

212rowboat

http://www.aa1car.com/library/map_sensors.htm

and if it is a MAF (mass air flow, which accomplishes the same fundamental task as a MAP):

http://www.aa1car.com/library/maf_sensors.htm

212rowboat

B_D:  use a can of ether and carefully spray around every port on the intake manifold, avoiding the throttle plates... while the engines are running.. if there is no increase in engine speed, start to move outboard following any hoses/lines that are under vacuum (there aren't many if any on a Marine engine)..

you're looking for a vacuum leak... ether is your friend.

if it's not a vacuum leak, then we're back to MAP/MAF.