5.0 GXI intermittent severe misfire

[fisherman73]

Starting last season I have had an anomaly that I haven’t been able pinpoint. It didn’t occur for most of many trips this summer but happened multiple times yesterday. Either upon start up or sometimes when putting into reverse and making a quick stop the normally great running port fuel injected 5.0 suddenly starts running on what I am guessing is 4 cylinders, severe shake. It will almost always run normal if I shut it off and restart. Once running I’m forward gear it will literally run perfect all day but if I throw it in reverse it may occur or on a startup. No codes, I was able to pull injector connectors one at a time on the entire left bank with no change while it was happening, it started running normally before I got to the right side. I’m suspecting some kind of module issue, do these port fuel injected have any kind of limp mode?

 

[alldodge]

Could use a serial number?

Remove the fuel filter and pour contents into a clear jar to see if there is anything but clean gas.

Has the distributor cap and rotor been replaced? While this may not be the issue, the caps will fail without warning and loo fine

What is the fuel pressure? It should be 29 psi if GXI-A and 50-60 psi if B and higher

 

[fisherman73]

I will take a picture of the S/N tonight. I was thinking possible ignition issue as well. After it first occurred last year I found that one of the distributer cap screws had vibrated out. I replaced it and did not have any symptoms for months. Recently is began to reoccur. Seemed like too much of a coincidence that it went from happening every few start ups to not at all for hundreds of start ups after replacing that screw. Maybe the cap has an issue. I will check fuel pressure tonight as well and look at fuel quality but like I said this happens very intermittently and will happen like I flip a switch or go away the same way so Im thinking electrical. Do I need to find a marine specific cap and rotor or will automotive work just the same?

 

[fisherman73]

Engine 5.0 GXI-C S/N 4012082535
Drive SX-M 1.6 4202062839

 

[alldodge]

Thanks
You can use Auto cap

 

[fisherman73]

Do you ever see these ECM's fail? Do people really have to pay almost $3000 for one? That seems insane!

 

[alldodge]

Yes they do fail, but it doesn't happen that often.

 

[BRICH1260]

Do you have access to a Rhinda diagnosis unit? It could go along way to helping you resolve your problems.

 

[fisherman73]

Unfortunately no. I have pulled codes with an LED. Just got the steady 12. Definitely would like to see some more data. I have lots of automotive experience but limited boat experience. I'm hoping that I am wrong but I'm thinking module because of the key cycle changing things. I have done lots of tugging on wiring harnesses with no change although the harness thought was the only hypothesis I could come up with that would be associated with it happening when I put it in reverse with a quick stop. Thinking it would change the way the motor moves on its mounts vs a quick forward acceleration. Any other ideas about what could change when dropping it into reverse with a quick throttle bump vs just a change from forward to reverse at idle?

 

[alldodge]

If the IAC is operating at to high a count rate, then when the idle changes it may be on the edge of stalling. Same thing can happen if fuel pressure is low. Don't know without testing. If you could put a vacuum gauge on it to see

 

[fisherman73]

Definitely not a low idle issue. It wont smooth out under throttle. It is missing on approximately 4 cylinders and will kick back to normal like I flip a switch, at times or if I shut down and restart. Its such a violent miss that the whole motor will be rocking severely in its mounts. It will accelerate but of course with severe lack of power. Ill bring a can of carb cleaner and add some through the spark arrestor when it is happening next time to eliminate the possibility of a fuel issue next time it acts up.

 

[fisherman73]

Update: I started it this morning and it was acting up. Fuel pressure was 64 psi, fuel quality is perfect, adding fuel through the intake while the condition was occurring had no affect. Pulled injector connectors and misfire is definitely random. The symptom continued until I shut it off and restarted and then immediately ran good. I'm thinking primary ignition issue. Does anyone have any info as far as diagrams and testing on cam position and ignition module. Would these parts be the same as their automotive counter parts that are readily available? I'm thinking I will try a complete distributor and ignition module. I have a video of the symptom occurring then the restart and condition gone. Is there a way for me to share it?

 

[alldodge]

Its not the distributor
Could be CPS or bad connection. Take the connector off the CPS and see if it needs cleaning

If gauge is accurate the fuel pressure is a tad high bit it should not be causing the issues

 

[fisherman73]

Crank position sensor or cam position sensor? I'm leaning towards crank. I have not checked that connector yet. Cam connector looks perfect.

 

[alldodge]

Crank

 

[fisherman73]

Replaced crank sensor last night. Connector looked good. All good so far but this can be very intermittent so time will tell. Thanks for your help!

 

[QBhoy]

Still on the diz cap side of the fence...if not a poor battery or charging state. As we all know by now. These gxi and mpi are far too easily affected by either.