MEP-806B running rough/ Actuator LED pulsing

[nholman]

Good morning everyone,

Been fighting this issue for a couple weeks now. I've got two gensets with an identical issue. Both generators are running rough and surging. The actuator LED on the Speed Control Unit is pulsing in time with the engine surges. So far I have replaced the batteries, removed and inspected all of the electrical connections in the box behind the control panel, replaced the MPU with a known good MPU, replaced the fuel with brand new fuel, replaced the air filter and replaced the fuel and oil filters. I also wired the fuel actuator straight to 12VDC to bypass the governor system and the engine runs normally in that case. I have all the applicable TM's and schematics available from LIW and here (thanks Guyfang) and cannot find anything in the literature mentioning why the actuator LED would be pulsing or a troubleshooting track to go down with it. One TS track does mention it and just says the speed control unit is bad, so I replaced it with a known good one and the same fault remains.

I looked through every thread here on the MEP-806b (and the 805b because, hey why not) and havent seen this issue mentioned yet. Any insight from the folks here would be much appreciated!

Thanks in advance!

 

[nholman]

This morning I also bypassed the muffler since the TM mentions exhaust blockage as a potential cause of the engine running erratically. As suspected, the engine continues to surge even with the exhaust coming straight from the manifold. As far as I can tell the only component I haven't replaced, that I can verify as serviceable through any other means, is the backplane. It's just odd that I've got two sets with the exact same symptoms. I also forgot to mention in my previous post that both sets have their injection pumps lined up with the timing marks correctly, though this was also verified when I ran the sets with the governor loop bypassed.

 

[nholman]

another update:

I got ahold of a backplane that was borrowed from a working genset. I swapped out it and the SCU onto one of the faulty gensets, and there was no change in the operation of it. Engine still surges, actuator light still blinks.

 

[uniquify]

Are the batteries fully charged?

I don't have anything larger than an 803 personally, but I've read where low batteries that can cause problems with the electronics in the 805B/806B.

 

[nholman]

Are the batteries fully charged?

I don't have anything larger than an 803 personally, but I've read where low batteries that can cause problems with the electronics in the 805B/806B.

Batteries are brand new in both sets. That's usually the first place I go with electrical issues, low voltage causes all sorts of gremlins.

 

[nextalcupfan]

We had a guy here a month or so ago having flickering lights issues on his 803a, turned out the CR1 diode had burned out and was giving him some odd electrical noise on the DC Charging side.
I honestly don't know if the 806b has a similar system but it might be worth a look to check the charging system for both sets.
I would even temporarily disable the alternator to see if that makes a difference.

 

[nholman]

Our inspector decided that we are just going to pass the generators up to our CSMS. I will update this thread if/when they figure out the issue. There is every possibility that the sets will be life cycled out of our hands anyways. I feel bad for whoever stumbles upon them at auction if that's the case! Thanks anyways guys!

 

[mciikurzroot]

Did you even try and set up the GAC speed board modual to be sure it was/is not adjusted correctly ? My experience sez this is the culprit...
mac/mc

 

[nholman]

Did you even try and set up the GAC speed board modual to be sure it was/is not adjusted correctly ? My experience sez this is the culprit...
mac/mc

Shoot i should've included that in my run-down of what I tried. Yes, I adjusted it per the TM and also tried making minor adjustments to see if it made any difference. It ran worse when adjusted to anything other than what the TM called for (this was expected) and at best it still surged bad. Our CSMS also tried to adjust them, and got the same results. At least they are struggling as much as I was. Again, I will post here if/when they get it figured out. Thanks for the suggestion though!

 

[nholman]

Finally got those generators returned to service (over a year later). Turns out if you continue to crank them for 3 seconds or so after the set starts, everything runs smooth. We were only cranking until it started and then letting off, ya know, like a normal piece of equipment would require. Oh well, the simple solution wins out again in the end. Just updating this thread in case anyone else runs across this issue.