pluguglyinhere

Well so far no luck it is not the tank vent either. It is doing it again but I have been able to figure out a little more.

It only does it on hard acceleration, like gettting on plane. I can ease into it and get it on plane most of the time. It will sometimes dog, not cut out so that it takes a little bit but get there. I can run 1-4000 grand all I want but if I get into it hard it cut outs like it died but doesnt and pick back up.

If I dont let off the throttle it will see saw up and down. I was running at 3500 for a while no problem, hit it and it quit. The same at any other rpm

I will add that the diagnostic software showed no trouble codes.

What is the best way to drain and clean the tank?

Should I have more of an antisiphon, than a ball valve on top of the tank, to check?

scarabman

Have you checked your injectors to see if they are partially clogged/clogged?

pluguglyinhere

How do I check for a bad injector is there something like fuel in the oil or?

scarabman

I cant remember on the 502, are the injector harness connections accessible? If they are, at idle, or bumped up just a shade, pull each injector connection one at a time to see what, if any, effect it has on running quality. If a pulled injector has no effect on the idle quality you can start your focus at that cylinder.

If you cant get to the injector harness connections there is another trick.

pluguglyinhere

I have the 454 and can not seem to find a way to access the injectors without removing the intake (if that is what it is called for the MPI).

I am draining the remaining fuel and going to try anc check the pick up. It looks like my anti-siphon is nothing more than a ball valve. Does this seem correct?

I also foiund the yellow small lines between the mech fuel pump, throttle body and vst to be restricted. I had a hard time blowing or sucking through them. I am assuming these are the vacuum lines everyone is talking about? It took me forever to find these if that is the case I guess I did not see them as vacuum lines. Could this be causing the problem?

I will have the injectors looked at if these things create no change.

4bus

You seem to be turning back to that software and computer, don't forget to check the basics! The older EFI systems do not have a great diagnostic sample rate like the newer computers, meaning you rarely get codes for intermitten probs, just hard failures.

What about ignition? If you have an MEFI4 or 5 you can do an induced power balance test while under load, 1500 rpm is a good number. If no computer power balance is avail, do it the old fashioned way.


Run engine under load at 1500 rpm, on trailer is ok with rear straps secure
Wait for misfire to start, it will happenm give it some time.
With spark plug pliers remove wire one cly at a time, listening for no change in misfire pattern.


If you are down one, which is sound like you may be, removing another will cause the engine to fall on its face, removing the one from the dead hole will cause no change in rpm. The dead hole is where you want to focus your efforts. Check plug for fouling or dry white or very light brown. Dry plug is inj prob, wet plug is ign.

pluguglyinhere

Thanks 4bus I am trying to work throught the basics. I am a little inexperienced so trying to is the key.

The boat doesnt have a problem at 1500 rpm. So should I still do the test of pulling plug wires? My problem comes in at most any rpm that I get on it. It runs fine at all rpm until I get on it.

TWIN-SPINS

swap some of your relays around,,,just mark them so you know what was what??,,dosent cost a thing to try

pluguglyinhere

Well thanks all this has been a long journey that has taught me a lot. I love these forums, it was the first thing I did when even looking for a boat. I have had a forum for my cummins for years that has realy paid off.

It may be solved, i did as many of the basics as I could from everyones suggestions. Changed the fuel (for sale FYI 20 gallons), checked all connections, and new hoses between the mech fuel pump, throttle body, and vst. The water test was fine, ran great no problems. I did not have a lot of time but it went straight up on plane and allowed me to get into it a few times. It never quit so I am keeping my fingers crossed.

I still have a question, the hoses I replaced were yellow about 1/4 inch running as I said between the vst, throttle body and mech pump. Are these the vacuum lines?

Thanks again all hopefully I can put this to rest.

pluguglyinhere

well it ran flawlessy for two days of boating fun. Then coming in last night it did it again. It would stumble if I got on it, no problems if I eased into it.

I think it might be an alternator/power isssue. I did notice that, remember I am learning, the volt meter read like 13 volts the last couple of days. When it started again I noticed it was down to 10, even at 3000 rpm.

I have been checking the gauges more now for references as I learn. It seems if myu volts are up around 13 it runs fine, which it was and did for the last couple of days. If it ends up down it stumbles on hard acceleration.

The belt seems tight and not slipping but I need to check all those connections and such also.