qsc 500 fuel lift pump?

[john]

So it looks like I am changing a lift pump for a 2006 qsc 500. I have not done the job before but know where it is. Some fine engineering there. Any tips on replacing it? I am not to proud to ask for some tips. 

Topic

[john]

So All these problems went away when the engine computors were swapped and the 12 v power supply pulled off when they were swapped. The wire was recrimped with a new eye and all the problems went away, amazing how those dam electrons work.

[john]

Well In my previous post I said the battery voltage was showing on the volt meter and I was going to replace the alternaor. I really wasn’t expecting much. I can’t really explain why but it is now starting properly. I was talking to a friend thats a cummins mechanic and he thinks the alternator might have been putting out ac voltage. messing with the ecm. That doesn’t make sense also as I swapped the imputs and the problem followed to the other engine. I really don’t see whats happening but I am really happy it is working as it should. I am  hoping the problem stays away. The owners are talking about taking it to socal so it might be someone elses problem. 

[Tony Athens]

IMO, you will eventually get tired of Mercury SmartCrap and figure out you’ll  never be able trust the wiring nightmare you have or inherited .. When you finally get to that point, Corey will help to go to one “thumb diameter” 12 wire harness from the engines ECM to the helm station.

[john]

So a little change since my last post. I have the engine running!!  Some help from Cory and I now have power in the start circuit. I think when the lift pump was going out i blew the fuse that sits in a fuse holder on the harness. That fuse powers up the whole start circuit. One problem down and one to go.

So now whats happening is when I release the start switch the engine dies. Just like fuel is cut off. I can advance the throttles (Glendinning controls)  on start up and I get a higher rpm with the start. I release the start switch and the engine stumbles and then runs fine and stays running at the higher rpm. it runs fine and normal even at idle. I all kinds of readings on the start circuit. looked at the fire suppression system and it seems to be closed the whole time while in the run position. only issue on the port non starting engine is the alternator is not working. The battery charger is on so that should not be a issue.  I also swap the ignition circuits and the problem follows to starboard engine, kinda driving me crazy at the moment.

[john]

So I am still trying to get the port engine to start. Pretty much went through the whole starting and engine wiring. The engine ecm gets power from a breaker in the engine room. The glendinning controls also get there power the same way. These are fed through the perko switches for each engine. The start circuit it seems is fed though a single black wire that goes into the cummins harness. I can jumper this to power and it starts but will not stay running when I release the start switch to the run position. Oddly when I advance the throttles it stays running and runs fine. I guess I need to order the wiring diagram that tony sells. has to be in there somewhere.

[john]

Yes the pump is mounted foreword with those hoses you see. that picture doesn’t really show the whole mess. foreword they looped up the excess for the engine harnesses. more wiring and a marine stereo box also.  Just a joy to work on.

Kinda getting somewhere it seems. The power for the start circuit comes from a breaker in the engine room. Two breakers for each engine. one circuit goes straight to the engine. The other goes to the start circuit. The start circuit has no continuity from that breaker up to wiring at the helm. most likely a break somewhere. now to find out there.

[Rob Schepis]

It appears there may be an autopilot pump hiding under there too.  Wow.

[john]

That wiring is from the boat builder. That is kinda what I thought when I pulled back the console as the helm area is on a hinge and pulled back. A bulk of that wire is from the pre build harness that was too long and they kinda coiled it up. Lots of hands in it since then also. I talked to the guy who just did new electronics and he did the best he could with what he had. To work with. His stuff looks good but all this mess is piled on top of it. 

[Tony Athens]

I am not sure how to respond to this picture.. Who can take credit for this?  

[john]

Kinda ripped the boat apart today. Went through most of the start circuit.  Seems power for the start circuit comes from the Glendinning control box. Today going to the boat it was totally dead with no power. I have open some dialogue with gendinning  and see where all this goes. A few pics. Sone stellar wiring to deal with. 

[john]

Tying this to this thread as it’s a not totally fixed yet. . Original problem was engine wouldn’t start. Lift pump was not coming on so replaced lift pump. Also serviced aftercooler as it has to be removed for access. Replaced starter solenoid also as it was broken off the mount.  Initial startup after all maintenance it started after a few tries. What happens is when you release the start switch it stops running. Like the fuel solenoid released. There have been a few times with normal start.  Pushing the port throttle foreword and starting and holding starter switch it eventually starts. And maintains the high rpm and runs fine. Acts like a relay is not staying latched.  It’s a two battery system with individual perko switches for each engine. Has a combiner on the dash with a Toggle switch. Boat is a 2006 luhrs. 

[john]

Well the aftercooler had to come off. It really needed servicing also so its a good thing. Ordering the oring kits today. 

[john]

I started it today. Got pulled way to do something else before I could even see it. Twin engine luhrs and laying over the engine and a hydraulic deck ram always in the way. Probably should do the aftercooler service also as it might get a little easier access with all of it removed. The beatings continue I guess

[Tony Athens]

No tricks–Cummins made it a challenge beyond any normal “thinker”.. 

[Author]

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