mag mpi expert needed pls
 

have 502 mag mpi with bizzare injection problem. have scan tool and run diagnostics and am well versed in this type of injection but would really like to have a one on one dialog w/ someone that has done a LOT of these to maybe keep me from re inventing the wheel.

if that person is out there, please e mail me at [email protected]

Re: mag mpi expert needed pls
 

I have learned ALOT about 502 mag mpi and could possibly answer your question but the person who is a expert at it is Tyler Crockett-give him a call 810-324-2720,he is a great gut and will be able to help you,Smitty

Re: mag mpi expert needed pls
 

Could you give us an idea of what the symptoms are? Posting the problem and eventual solution may help some else with the same problem some day.

Dave

Re: mag mpi expert needed pls
 

true enough.... its long but here is the whole story

have 1996 502 mag mpi. they were takeouts w/ 125 hours on them. came absolutely complete and factory. after boat rebuilt to some significant degree, i installed the motors, fired them up and they ran absolutely perfectly. as documented elsewhere in this forum, went thru the trimming out process and learning curve ( am vastly experienced in other mechanical arena but no boat stuff) and had settled into nice top gun that would go 65 mph at 4900 rpm all day w/ good temps and pressures. it did this for 300 miles.

at 300 miles filled it w/ fuel ( also documented here ) and did analysis of performance/economy and all was wonderfull. on that same day AFTER fueling went to lunch...30 mile round trip more or less... as fast as the boat would go both ways just fine.

parked the boat... and weather turned lousy... so for about 25 days the boat stayed parked.

last sunday while the weather was STILL pretty bad, i decide to go out anyway... boat started and ran perfectly the 2 miles to get out to sea and i zapped it and all was wonderful except for the 4 ft seas... which meant that when i turned the corner at 15 miles the seas were going to be 6' .... so i said the hell with it and turned around and started home...

about 3 minutes later the port motor just went flat. temps and pressures good but would only idle ... any advance in throttle just gave a big nothing... starnord motor ran fine but not great...

i said to myself " hmmm throttle position sensor just fell off" so shut down port motor and went home on one just fine.

rain all day the next day... tuesday i go and start the motor and it sounds completely flat... tps still in place... i rattle all the connectors and screw around a bit looking for the easy fix but find nothing and the starboard motor doesn't sound particularly crisp and the weather is still lousy so i pack up and go home and order up a mercruiser scan tool. figure gonna need it anyway and will save time...

it arrives the next day...

so.... i check fuel pressure ok

i check all the sensor outputs and get some anomolies on the port motor but not so bad...

there is no water in the fuel that i can detect

i swap the throttle bodies around ... that gives me a good TPS and iac mtor and it makes a little diff but not much... i unplug the sensors one at a time to get them to default... no change...

its sitting idling flat and i rattle the coil wires... the lt inputs at the plug and WHAM the thing is clean on 8 and everything is great... i smile shove off get 1 mile and same thing blah flat ... and starboard motor STILL not great...

so... now i am absolutely convinced that somehow i now have 300 gallons of bad fuel.... no way it can be anything else... i cant see any water, filters are clean etc... but all was perefect bef fillup and now not... end of day 1

day 2 today.... 7 am i am at the dock w/ 2 5 gal cans of fresh fuel. i lash them into the engine compartment and hard plumb them to the fuel system completely isolating the boat tanks. i flush the fuel rails, filters and surge tanks...

i hit the switches and WHAM i am on a clean sharp 16 cylinders.... i shove off ( weather NICE today) get outside, nail the sticks and i am at 5100 rpm so fast i can't believe it... boat running better than ever and i see 67 mph 2 mph better than prev best....

WELL i say... that settles that... so i stop, throw out an anchor and switch the fuel system back to original... double blind test.... port motor goes flat immediatly ...starboard is ratty...

sounds simple ... except when i flush eveything and put it all back to the 5 gal containers, the starboard motor gets fine but the port stays flat. scanner says all the sensors are low voltage... which means cold which means wildly over rich which all adds up.... but now i have conflicting and coincidental problems which i don't believe....

go back on one motor which runs ok...

now... drain and barrel roughly 300 gals of fuel... cant SEE anything wrong but who knows at this point.... put in 50 gals fresh per side ( from dif source) and get rid of jerry cans before i blow myself up and put fuel sytem back to original,

starboard motor sounds MUCH better... port motor still flat... so i start to head back from fuel dock and after a bit there is this surge and suddenly everything is wonderful....

i head out to sea... 5100/67 mph instantly.... i smile... run a bit and turn and head back... and wham... port motor goes to idle with sticks at wot. i stop... it stalls. it takes me 10 mins to start it and when it does it blows unburned fuel out the exhaut for a full minute and is flat.... thing has gone full rich and washed the plugs instantly scanner says ALL the sensors are low voltage. starboard motor is perfect...

it starts to rain and i go home.

now ... ive been in this business for a long long time and im not a believer in coincidental problems.... but i believe there was a contamination problem w/ the fuel... i THINK somehow on the day i got fuel there was diesel contamination in the fuel i bought but SOMEHOW ( and i offer no rational explanation) the boat ran perfectly for that 30 mile rt so i got home fine. then the boat sat 25 days and whatever was there separated.. and screwed me up...space aliens maybe but bottom line is that fresh fuel made a big and repeatable dif.

but now i have this motor reading all the sensors at low volts... not possible and i don't believe it for a minute... what i BELIEVE is/was a bad harness ground... ... which i inspected and was perfect... and then it got dark and i went home.

tom im going to unplug the primary engine harness from the good motor and plug it into the " bad" if it STAYS bad then that suggests that it isn't a bad 12v feed to the ECU but does not address the injection harness itself... which looks perfect.

the problem now, very specifically, is that motor is wildly rich because all the sensors are telling the ecu that it is ice cold. the chances of a single sensor failure is reasonable... TWO at once is really unlikely and three is absolute zero. and combine that with , everyonce in a while when it feels like it , it runs perfect... i know i know... BAD connection somewhere.. my BOOKIE could have told me that... your job is to tell me " OH... they ALL do that... look here"

what i am looking for is someone that has worked on these specifically in a professional sense for so long that he is going to read this and say " oh there you go...another pin 24 problem in those gen 6 ecu's" or something like that...

and tommorow is another day. incidentally would be a buyer for a good serviceable late mag mpi harness and sensor array etc if anyone has one kicking around that they want to sell cheap. im far enough away from the real world out here that having a complete set of spares is something i would consider...

Re: mag mpi expert needed pls
 

Okay, just a thought. You say all the sensors read low voltage. Since it is a feedback system you need to have good reference voltage to each sensor to begin with. Someone will probably correct me if I'm wrong, but that should be 5 volts from the ECU to the sensor and then whatever the sensor sends back is what you read on the scanner. So first thing you need to find is iff you have 5 volts at each sensor. Now if you don't, you need to check all the + inputs to the ECU for good voltage. If the volts in are good ( I suspect they are not) and the volts out are bad then it is an ECU issue. Since you seem to be having the problem on both engines I suspect you are losing feed voltage in the boat and it is lowering reference voltage to the sensors, causing your rich condition.

Re: mag mpi expert needed pls
 

of course.

if ecu bad , then ref voltage would be wrong across the board if failed in that mode... but is intermittent. so implies harness /connection. also. NOT both motors now... only port. factory service manual covers all this and harness voltage checks at pin outs on my list of things to do for today. was simply hoping that this might have been a " common " problem that someone recognized

motors/electrics are complete stand alone. share absolutely NOTHING. except common ground and THAT only because everything has same ground... they both have seperate and ground WIRES actually multiple that return to each own battery as well as common grounding point... all fresh and been checked,

is not a systemic low voltage or high resistance but could easily be injection harness SPECIFIC low voltage or high resitance somewhere...

question is where.

Re: mag mpi expert needed pls
 

Another thought is the actual ECU ground-could be an issure. Sorry I haven't experienced the exact problem to tell you where to go-hope you let us know what you find. Definitely sounds like you're on the right track.

Re: mag mpi expert needed pls
 

I don't have the "magic bullet" you are looking for, but could you be more specific about your fuel pressure test(s)? Did you check the fuel pressure under load? Did you check the VST for float sticking, flooding, vapor pressure regulator failure or restricted high pressure pump intake screen?

When you say all the sensors are "low voltage meaning cold", I don't understand. There is only one sensor (ECT) that tells the ECM what the engine temp is. What temp is the ECM reporting? What are the voltages of the various sensors?

Are you aware that you engines have a "Power Reduction Mode"? Are you sure your engines are not linked by a data link harness, so when one engine goes into Power Reduction Mode, the other will too? All twin engine installations of that year were supposed to be linked.

Dave

Re: mag mpi expert needed pls
 

Another thing to add, as dave said if you have a vst system on the boat and the diapraghm's are going bad they will cause the motor to run rich, I had it happen to me where the bad diapraghm was causing the motor to run rich enough that it would not come up to temp, which caused the temp sensor to tell the motor to stay in "cold" or enrich mode which makes the problem worse.

The data link only purpose is so that you can hook up a scan tool connect it to one motor and be able to switch back and forth from motor to motor with the scan tool.

Also there should be a ground cable from motor to motor, it would seem to me that with it being intermittent, you have a bad ground somewhere.

Re: mag mpi expert needed pls
 

I had that problem before. Belive it or not it was the ICM on the distributor(delco-remi). Just swap them and give it a try just a 5 min swap. I wont go explaining why but its been a a problem I have encounter on few of my costumers boats. No bad codes, clean fuel{no water} everything test ok, but icm modules give that problem ,they mess up some ECM functions too, the engine just wont advance or acelerate.

Re: mag mpi expert needed pls
 

day three.... and a lot of " did all that "

good motor still started and ran perfect today... bad motor still bad... so no motor fairies overnight.

have no idea what a VST is...

fuel press measured w/ mechanical gage and fine under all conditions... all systems are independently and commonly and redundently grounded and there is absolutely no indication of low primary voltage.

all raw sensor voltages measure 5.25 volts ...both motors...

all sensor voltages running are w/in spec and essentially identical between the two motors regardless of what the codes say.. cleared the low voltage sensor codes and they haven't come back...

DO have one bad sensor for sure. inlet air temp reads high by about 40 deg but that would make it go leaner slightly and the number isn't really big... sort of just stays around 171 deg as opposed to 125 or so... and disconnecting it makes no dif nor does exchanging it w/ good motor...

exchanged ecus between motors... no change...

exhanged ignition modules, dist caps, and all sensors... same

so... much as i hated to do it, got in there like a snake and took out plugs... 4 perfect... 4 sort of blackish but not wet fouled.... no rhyme or reason as to which came from where i.e one bank or one riser etc... completely random. and yes... checked compression while i was there even tho i KNEW it was fine...and it was..

figured if fuel was REALLY bad maybe coated plugs w/ something and they just wouldn't clean... put in fresh set of plugs... now this is where it got interesting...

w/ new plugs no matter HOW rich or screwed up the injection is, it should still start and run on a clean 8 for at least as long as it takes to foul a plug... nope...

started on what sounded like six... essentially the same.

so at this point the entire sensor array is changed over including the ecu ... good motor still runs fine... bad motor still the same...

so i pull the intake plenum off to get to the fuel rail... pull out the injectors and start testing... 7 pulse and spray just fine... one is stone dead... no click no spray...

so i have at least one stone dead injector...

now i wuld have thought that that would make it go on a clean 7 ... and this seems a lot worse than that but the injection wiring is such that the ecu pulses them 4 at a time... and im wondering if that this injector is shorted to ground internally then what it would do to the voltage to the other 3 in the same string. which WOULD give me the symptom that i get... ordered 3 injectors and they will be here tuesday.. 3 because one to replace dead one, one in case i find another one that i don't like while im waiting for tuesday and one spare.

today the plan is to get some death injector cleaner and clean the injectors by pulsing the flow in both directions...

oh... another thing... the plenum was " loose" when i took it off... i.e it took virtually no effort at all to slacken the bolts that held it on and the gaskets underneith had a wet oil film across to where they should have been dry and sealed...

now i can't imagine there was much of a vacuum leak but maybe and im trying to reconcile what that unmetered air would do to the information the ecu was getting and what it all means... if anything... but either way it will be tight when it goes back on...

and i suppose i could just yank an injector out of the good motor and not wait until tuesday to get my answer...

but the truth is that im afraid to because if it DOESN'T fix it i am then at a complete loss...

but, weather permitting, i suspect thats what im going to do.

Re: mag mpi expert needed pls
 

I cant say that I have has this exact problem before, but I had similiar. Regarding your thoughts on the 1 shorted injector taking out the entire 4 on its bank. I was working on an '03 Ford 4.6 liter motor recently. It had been to the dealer, they sent it back out not finding he problem. I had a dead miss on #2 cylinder. No injector pulse was the culprit. Here is the strange part. It had injector pulse for about 15 seconds on every start up, then lost injector pulse, but had coil pulse. Make a long story short, the #2 coil would fire for a while, then short out, taking the injector pulse with it. So, in my opinion, yes what you are saying is very possible. I would say to check for injector pulse and power on that bank with the known bad injector plugged in and unplugged . See if there is a difference. That was my mistake. Not checking for injector pulse with the coil unplugged. It would have revealed the problem right away.

Good luck.

Re: mag mpi expert needed pls
 

weather here has turned bad so not exactly out working on it right now.

these motors have a single coil ...not the coil pak type ignition... but the injection/ecu wiring is explicit... two injector drivers driving 4 injectors each ...so i am hopeful that this bad one was killing the others and mind you i don't know that the others WERN'T working.... just that motor REALLY seemd to be flat as opposed to a cleanly dropped single cylinder...thats what sent me down the garden path all this time... the sense that it was systemic rather than a localized problem..

either way... if the weather clears up im going to take the injectors out of the good motor and put them in the " bad" motor and see if it works... can't imagine how it can't ....

if it doesn't, then we are down to the injection harness itself and the coil itself as the only two non mechanical components that haven't been changed over.

i am unwilling to believe it can possibly be anything mechanical... one minute its at 5100 perfect... the next instant its flat... and almost immediatly after that at 5100 again ... nothing hard mechanical is going to intermittent like that.... but if one injector goes to ground and kills a couple of others with it... and then comes alive again, then that would feel EXACTLY like that...

and thats my story and im sticking to it... for now anyway. will advise if weather clears.

Re: mag mpi expert needed pls
 

these motors have a single coil ...not the coil pak type ignition... but the injection/ecu wiring is explicit... two injector drivers driving 4 injectors each.

Yes I know that. I was merely suggesting that the likelyhood of your thinking is a strong possibility. I was agreeing with you about the shorted injector taking out the entire bank.

Keep us posted.

Re: mag mpi expert needed pls
 

ding ding ding............

pulled all injectors out of " good " motor... back flushed them to clean the screens and then flushed them 500 pulses with death cleaner in the correct direction .... put them in the bad motor and shazamm... instant sounds like it has 2000 hp motor. clean sharp instant throttle response... so that was it... one bad injector killing or severely wounding that circuit for the other three. also not convinced that the fuel i had was the best... but either way, thats the way it goes... motors are really nice to work on... manifold and injectors out in 10 minutes... reassemble after cleaning in 15 -20 ...piece of cake.

now if i can just find enough pieces to put the good motor back together again ill be happy.

thanks for input everyone...

Re: mag mpi expert needed pls
 

Great work.. :drink:

Re: mag mpi expert needed pls
 

Steve-did you ohm out the bad injector? Is it shorted or open?

Re: mag mpi expert needed pls
 

no... did not do that but good idea...is in the trash but not gone yet...will do that and report back. have got to believe shorted to ground.... if just bad solonoid or open do not believe it would have made the other three "bad". my best guess is shorted to ground and causing low voltage in rest of injector bank... as such either not opening at all or causing to open vastly reduced pulse width in other three....

but ill check the resistance and report back.

Re: mag mpi expert needed pls
 

Yeah, that's what I was thinking, that it drew off the whole pulse due to low resistance. Also just curious-how were you pulsing the injectors when you were cleaning them-what voltage and power source did you use?? And did you notice if they are Keihin injectors? I think mine are and I was thinking that finding them from another source might be more cost-effective than buying "MERCRUISER" parts at 4 times the cost :rolleyes:

Re: mag mpi expert needed pls
 

stevesxm,
Good job on your diagnosis. You mentioned that when you pulled the plugs there were four normal and four blackish plugs. Assuming they represent the two injector banks, which ones came from the failed bank, the four blackish ones or the four normal ones?

insptech,
Keihin injectors were used on 1993 to 1998 (MEFI 1) 502's (part #805225A1), GM injectors were used on 1999 and up (MEFI 3) 502's (part #861260T).

Dave

Re: mag mpi expert needed pls
 

the mercruiser scan tool has a built in injector testing circuit. you plug the harness into the injectoer and set the program for the " pulse " you want and hit the fire button and off it goes... options are single 400 msec pulse , 5 , 10, 20 or 50 400 msec pulses.

the dirty plugs were two each side... not on same anything... but then again, im not claiming that iknow for a fact that the 4 injectors that pulse simultaneously are on the same bank or for that matter , what the absolute truth of the effect that having a shorted injector did to ANY of the other circuitry. all i can say is that i know what a motor that has dropped one cylinder sounds like vs one that is just "flat" and that was the case here... it sounded like it had done exactly what the plugs suggest ...lost at least one cyl on each bank or more...

it just never dawned on me that it could have been a single injector... it was exactly when i had done full tanks so thinking horses not zebras i started looking at bad fuel...

as for the cleaning

i simply took the high pressure line from the pump and hose clamped a 3/8 line to it to a brass shut off that with another piece of 3/8 off the other end. the injector is such that either end will fit nicely into that hose and you hose clamp it tight. then just feed the pump with a separate line from a container with death injector cleaner and a little gas... turn the key on and off a few times to pressurize your rig and fire the injector into another container with the scan tool... takes only a couple mins each once you get organized. i flushed backwards to clean the screens a couple of 50 cycle pulses and then 10 -50 cycle pulses at pressure... the close the valve, disharge one last time to clear pressure from the hookup and do another one... easy and effective and building a bench rig would take about 15 mins.... but i did mine right in the engine bay.

my injectors are the first picture NOT the " A1 " ones and i may be wrong but i think they are delphi. did notice that they shoot a concentrated stream rather than a fan which surprised me as the fan pattern always worked a lot better on the race motors. i paid about 86 bucks from bam for them and felt that wasn't out of line. gotta say that of everyone ive dealt with since ive bought this boat, those guys are the absolute best for pricing and service. beat everyone by 10 or 20 % answer their phone and are polite, and ship instantly...

also pursuant to the knock down drag out fight we had here about extrude honeing and smooth finishes... i had to laugh when i took the plenum off and see the orange peel finish on the inside... i maintain that that is on purpose. not a cheap casting and i wouldn't think of changing it...

Re: mag mpi expert needed pls
 

I thought your engines were 1996. They must be 1999 or later since they are MEFI 3 (MEFI 1 would have the Keihin injectors and would not have the injector pulse test). My earlier comments about the VST (Vapor Seperator Tank) therefore do not apply. Sorry, my mistake.

Dave

Re: mag mpi expert needed pls
 

well... can't argue or dispute year... guy that sold them to me says 1996 ...motor number OLxxxxxx say 1996 but ecus are mfe3's for sure.... paid 5 k each absolutely complete to every last washer and was happy to do it.

was wondering.... am a real fan of roller rockers.... anyone have a direct replacement part number for the roller rockers that would go in these motors without bouncing the valves off the pistons ?

I know I am bringing back up an old thread, but I am having an issue that is very close to this. Except, all of my spark plugs are getting washed down, and I did in fact have bad fuel, that had water in it. A little back story, I have 502 mpi, cool fuel, full MSD ignition with 6M-2L box. Ugrades are a cam, lightening headers with 4 inch dry to the tip tails, and intake is modded with cut down runners and honed so looking around 540hp. Now motor just had bottom end done, and heads redone with new manley valves, springs, roller rockers, etc. First start up we noticed a miss, very slightly at idle, but apparent at about 2000-2500. We made a determination that it was ignition, boat had acdelco ignition, so replaced cap and rotor with no change. So I grabbed an MSD coil and did MSD 8.5mm plug wires. That seemed to knock out the miss, but just to cover basis we compression tested the motor at 160 on all 8, and went ahead and put a new billet MSD distributor in. Miss is gone, so we set timing (36 total timing) and took it for a test run. Boat planed out, and ran fine. cruised around to make sure it was as warm as it was going to get, also while taking it down to idle and bringing back up on plane. All seemed of so we did a pull up to about 4200 shut it down and checked plugs, plugs looked good, but noticed number 7 was a little lighter color, we just a put a brand new plug in that cylinder so thinking lets switch plugs on that cylinder and run again to see if it is running leaner. Did that buttoned it back up, cranked up and start idling. Then all of a sudden started to feel a rough idle, went to get up on plane it just felt lazy and started breaking up a little. Backed off thinking man did we leave a plug wire off, checked was all good. Cranked back up, idle still rough, and same symptoms. So we pull the boat out, and take off the fuel separator to dump in a jug to look at fuel. Fuel didn't look great, but not anything real alarming, so put a new fuel separator on, and it idled back to normal on the trailer. Dropped the boat back in the water and started heading out. Got about 100 yds and it seemed like it was idling rough again, try to get up on plane and same thing breaking up. Take it back in and park it. Take a look at that fuel again and it looks no good, pretty yellow, cloudy, and has a weak smell, so we decided ok fuel isn't good. I bought the boat in October I think, and the guy had filled the boat with 92 prior to parking it in July of last year, so we went ahead and pumped every oz of fuel/liquid out. We put some fuel pumped out early in a jug again, and sure enough there was some water in it as well. So pumped all 90ish gallons out, Then went and put little over 50 gallons of fresh 92 in it. Replaced the fuel separator again, and cranked it up. idled and revved great. Dropped it in the water started heading out, damn sure started idling rough again, tried to get up on plane and it went up on plane while feeling lazy, so i ran it for a minute to see if it just needed to get it out of the system, and it didn't, just seemed to get worse. While it was going it would spurt, like run lazy then lurch like it wanted to break out, but wouldn't. So put it back on the trailer, and put it away. Next morning pulled the 4 plugs on the port side of the motor and they were all dark and washed down with fuel. That afternoon when I got there I pulled the starboard side 4 and same thing, so all 8 plugs are dark and washed down with fuel. I can see one injector going bad and knocking out a batch of 4, but this would have to be an injector in each batch doing it to knock out all 8. These are also all brand new injectors, they are the new style 861260T injectors, now with a mefi 2 is there a chance the injectors aren't compatible considering the injectors were put out with the mefi3? We aren't thinking main harness, cause we aren't getting any electrical feedback in gauges, and its all been cleaned up cause we re rigged the boat. Now the ecu or injector harness I am not sure of.

ealeash, if you pulled 7, you probably swapped with 5. make sure those wires don't touch and are not crossed. they fire close in sequence.