fuel injector stuck open

[Haycack]

My motor is a 5.7 black scorpion s/n 1A091459

The issue started at the end of summer last year. It started as an intermittent problem. It would every once in awhile run rough. It got worse pretty quick though, until it would hardly want to run. I checked it with a scanner and had a fault 346 INJ7_outputFault. I pulled all the plugs and #7 was soaked so I pulled all the injectors and had them cleaned and tested. They all tested good before cleaning and a little better after. I put everything back together, fired it up and still had the same symptoms. So, just to triple check to make sure it isnt the #7 injector, I swapped it with #5. Still same symptoms. I did notice something interesting though. I took the plenum off and turned the key to the on position , looked into the intake ports and the #7 injector was dumping fuel. I then checked the resistance on each of the injector harness plugs. 1,3,5 measured about 1.4m ohms, #7 measured 11.9k ohms. I then unplugged the harness from the pcm and checked the plugs, they all had no continuity, so that cancels out the harness having a short.
Is there any other tests I can do or does the pcm have a short?
Also, I tried looking up a new pcm to get a price and I cant find one. Im not sure what i would do if the pcm is the problem. the part# on my pcm is 8M2100903

 

[alldodge]

I'm not finding that part number for the PCM, finding 8M0072021 and cost is 1627.38 at BAM



That said its not your injector, but the connection to it. The multiport injected motor fires 4 injectors, then 4 others at the same time for a given length on time. As speed increases of decreases the time open interval is changed. When intake valves open fuel and air are drawn in.



Injectors 2, 8, 3 and 5 go to pin 2
Injectors 1, 7, 4 and 6 go to pin 17

Don't worry about the pink/white wire, this is supplying power otherwise no injectors will fire. In order to fire the set of injectors the PCM supplies a ground to a given set of 4 injectors. Check the wiring for a bad connection to ground between splice 110 to injector 7 (letter h)

 

[Haycack]

Thanks for the reply.
I checked continuity to ground on all "green" wires (btw, on my harness they are not all green with a white or purple tracer). Non of them except #7 had continuity to ground. I then unplugged the harness from the pcm and rechecked continuity to ground. None of them had any. Correct me if I'm wrong but wouldnt that eliminate the harness from having a problem? Also, if all the "green/purple" wires were spliced together wouldn't it show continuity on all the "green/purple" wires?
thanks for your help!

 

[alldodge]

None of them except #7 had continuity to ground

You found your problem. So long as the injector has a ground, the injector will stay ON all the time. The wire should be connected so the PCM turns the ground ON and OFF.

My guess is somewhere in the harness the one wire coming from #7 is shorted to ground but is also disconnected from the other 3 injectors. You should be able to check continuity between 1,4,6,7 on the "green" wires and they should show they are connected together.

You could run another wire from 7 to 1,4 or 6 on the ground side and disconnect the wire going to 7, but think this will just cause another issue later. Need to get into the harness and trace the wire back to the internal splice.

While the Gr/Wht and Gr/Pur may be different colors from newer year motor changes, the wiring should the same

 

[Haycack]

But if #7 is only grounding out when the harness is plugged into the pcm, wouldnt that mean the short is in the pcm?

edit: nevermind... I guess it could be grounding out on another wire in the harness that has to be plugged in to the pcm to ground.

 

[Haycack]

Also, I checked continuity on all the other green wires and none of them are connected.

 

[alldodge]

Also, I checked continuity on all the other green wires an non of them are connected.

None of the injector green wires are connected to any of the other injector green wires?

If this the case I have no clue

 

[Haycack]

I dont think they are all connected on the PCM-09 controlled motors. I can find each injector wire going into the pcm plug.

 

[alldodge]

Guess its the PCM

 

[Fun Times]

Sounds like you may have an damaged Injector Driver within the PCM.
On your engine, are the colors of each injector wire slightly different in color heading to the PCM?....Some engine models were sequential driven via the injector firing order and black scorpions did do a few things slightly different vs other engine models too so wouldn't be to surprised.

What year is your boat?

Injector drivers failing within the PCM is sort of common. The problem may be that while some ECM's can be repaired depended upon PCM model, I'm not sure if the later models PCM such as the pcm-09 from mercruiser can be repaired by someone in the marine industry.

The company below does repair some ECM types and it looks as though they are expanding on the repair models given they now mention Command, Axius, Zeus, Steering Modules......Maybe you can talk them into at least taking a look at your ECM.:encouragement:

http://www.simonperformancetechnology.com/index.html

Or maybe try searching online pcm-09 repair as there seems to be a few auto type repair facilities that might be able to open it up and repair the injector driver.

 

[Haycack]

Thank you fun times! I will do some research on repairing the pcm.
The boat is an 09 but the motor has a nov 08 DOM. Yes, all the injector wires are green but with a different color tracer for each wire. Last night I checked continuity of the green/blk #7 wire with every pin in all 3 pcm plugs to try to find an internal short in the harness. Only had continuity to the pin with the green/blk wire. Also checked that #7 wire to ground, had nothing. Visually checked the harness, couldn't see anything. So I think its safe to cancel out the harness?

Also, if I have to buy a new pcm, would it have the correct programming for my motor/trans/vdrive? Or would i have to get it programmed?

 

[Fun Times]

Thanks for the info.
Yes it sounds like the harness is working okay.
As long as you didn't/don't have a Command Module typically mounted up under the helm area used for other smart craft accessories then a new ECM from the factory is generally plug and play with no additional programming needed so you should be okay in that regard.

As dumb as this sounds, you might want to try tapping a little bit on the ECM to see if it will stop the injector from leaking/change the ohms resistance reading to the others....You may get lucky but you might not too.

 

[alldodge]

Just a thought of concern.
With the injector staying on all the time the gas is washing out the oil off the cylinder. With no oil the rings will score the wall. It will also thin oil the oil in the crankcase

 

[Haycack]

Fun times,
I gave the ol' tap and test a shot, no luck. As for the command module, I haven't had a chance to check under the helm, but my boat has all smartcraft gauges and monitor with smart tow so I'm guessing it has it.

Alldodge,
Thanks for the concern! The injector was dumping so much fuel that it actually hydro-locked while cranking over. At that point I realized that it wasn't just running rich, it had a bigger problem. I haven't cranked it over since.

 

[Scott Danforth]

and these are the reasons I love my carbs