Engine Ground

[Trini Jetboater]

HEy Guys, just finished rebuilding the top end of my Rotax 787, hope to go in the water tom....my question is how many grounds does this engine have? I see a ground running to the starter and one to the mpm. Is there supposed to be one running to the engine as well? And what would happen if this is left out? (reason being, i have a black heavy lead cable left over and I don't know where it goes?)

 

[Trini Jetboater]

New Problem, the boat starts easy but does not idle for more than 3-5mins before cutting off like if someone pulls the key. If i remove the key and restart it does the same idles for a few mins then suddenly dies.

 

[kustomkarl]

As for the ground cablefoll it to where it goes so you know what it might be for. The dess post might need a cleaning or replacement. That would cause it to just stop and shut off but when re-connected and start right up...use soapy water and leave it dry, no extra grease or anything on the post.

Karl

 

[Trini Jetboater]

As for the ground cablefoll it to where it goes so you know what it might be for. The dess post might need a cleaning or replacement. That would cause it to just stop and shut off but when re-connected and start right up...use soapy water and leave it dry, no extra grease or anything on the post.

Karl

Thanks Karl, cleaned post and same thing....Checked fuel and flowing freely. Carbs clean. Do you know if this engine needs an extra ground on the engine besides the one going to the starter?

 

[kustomkarl]

That is the only one...its possible that the cable end is corroded inside. You could cut it off and add a new end. I've seen that problem a bunch of times. The post still might be bad, on he lanyard...I've seen that problem before too.

Karl

 

[mudpie]

are you the orginal owner? if not maybe someone in the past has added a extra ground for some reason? the one to the starter can rot out
as for your shut down issue, what plugs are you running, i had a 787 engine that drove me nuts, would idle fine,but if i reved her up she would shut down like the key was pulled, turned out to be a set of dam champion spark plugs.
i think they were giving off interference. put some ngks in and problem solved
and yes, a bad dess post will do the same, they can just go bad, seemed to have problems with they around 1997 model years
and connections connections connections, check and inspect any and all electrical connections that you can get your hands on
good luck
mud

 

[Trini Jetboater]

Thanks Karl and mudpie.

I bought this earlier this year used. It has NGK plugs gapped correctly.
Is there a way to test the dess post and lanyard? Or do i just change it?

 

[mudpie]

i have not found a way to by pass dess post
nor to test it
i keep a known good one on hand for testing
mud

 

[kustomkarl]

Here is some info on the dess lanyard and some test to do;

I would start by cleaning the Post on the safety lanyard. It is beeping and saying it isn't connecting to the Mpem, (Multi Purpose Electronic Module) It needs to beep 2 times to let you know it is ready to start. Clean the post and cap with soapy water. Don't use any grease of lubricant on it as it needs a clean connection to make contact. Connect the lanyard to see if it is making a connection. 2 beeps and it's ready to fire up.

Engine start/stop switch verification;
Disconnect the Yellow/Red wire of the start/stop switch. Using an ohmmeter, connect test probes to the Yellow/Red wire and to ground. Measure resistance, it must be an open circuit (switch is normally open). Depress and hold switch, the ohmmeter should read close to “0” ohm.

Safety Lanyard Switch Verification;
If 2 short beeps are not heard when installing the safety lanyard, disconnect the switch wires.
Safety lanyard removed;
connect the test probes to switch Black and Black/Yellow wires. It’s an open circuit, there should be no continuity.
Connect one test probe to the White/Gray wire and the other test probe to the switch terminal. Measure resistance, it should be “0” ohm. Connect one test probe to the Black wire and the other test probe to the switch ring. Measure resistance, it must be close to “0” ohm.
Safety lanyard on switch; connect the probes to switch Black and Black /Yellow wires. Measure resistance, it must be “0” ohm.
Timer Verification;
The timer is integrated into the MPEM. Always confirm that the fuses are in good condition. To confirm operation of timer, remove the safety lanyard from switch. After 5 seconds delay, depress start/stop button once. The timer should stay on for 33 seconds (for example, the gauge(s) will be activated) and than turn off.

I hope this helps.

Karl

 

[Trini Jetboater]

Thanks again Mudpie & Karl, really appreciate the input.:cheers:

Ok, here's whats happening now, start the boat, runs sweet for a few mins then dies totally....no power at all to the 12v gauge i have hooked into the harness coming from the speedometer. I remove lanyard and put it back on and nothing....no power no beeps nothing. However the bilge still has power to it so there is power. I pull of lanyard and put it on again and nothing at all.....then after about ten mins put it back on and presto....runs for another 3 mins then dies totally again...remove and plug back the lanyard....nothing at all.

Will have to go get a proper multimeter tom to test the circuits Karl.....will keep you guys posted on the outcome.

 

[kustomkarl]

It's in the electrical...let us know how you do with the tests.

Karl

 

[Trini Jetboater]

Hey Guys, I just started again and the volt meter shot up to 16V then she just cut off again with no power at all. Does the mpem have a safety protection against high voltage?

 

[Trini Jetboater]

Hey Guys, sorry for the long delay....finally sorted out the problem late last year...the rectifier needed changing.....she's running like a dream now...thanks again for all the assistance...it is greatly appreciated!:cheers: