stevesxm

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.

Vinny P

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.

stevesxm

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.

Vinny P

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.

stevesxm

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...

Vinny P

Great work..

Ted G

iTrader: (1)

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

stevesxm

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.

Ted G

iTrader: (1)

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

Dave_N

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