Jacob375r
Hello all
I've got a 130kw model QT13068ANAC that would prefer to be in Rpm sense loss more than it would care to be ready to its job. The machine is maintained regularly and has a remote monitor on it.

A little history first,
The machine was activated on 7/10/12
mag pick-up replaced 12/10/14 (warranty)
no issues for @ 7 months
Nexus controller replaced 7/16/15 (warranty)
intermittent issues for the next 3 months
wire harness 10/16/15 (warranty)
no issues for @ 9 months
Replaced starter (0D5418), relay solenoid (056739), and 1 1/4" fuel regulator 7/15/16 (non-warranty)
No issues until 8/16/17

Sense then the machine has gone into rpm sense loss on almost a weekly basis both during exercise and when needed during a back-up situation. I've tuned the MPU as described by both Generac and Peddlers suggestion as well as setting the fuel pressure to 14" IWC. The machine has never duplicated the problem with a tech present weather starting the machine in manual or forcing it to exercise with a tech on site.

I've read every forum thread related to rpm sense loss and any starting issue before posting another RPM sense-loss thread.

Any help in direction that can point me to a fix would be appreciated.
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redman
Does it alarm on weekly exercise ? Or is it random ?
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redman
Does this Generator run a slow rpm weekly exercise ?
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Peddler
What is the ac voltage at the MPU while cranking. What is it running? I have had units where I have had to change the controller more than once to solve this problem. I contend, though Generac says no, that the hold off isn't long enough for the controller to pick up the signal from the MPU. If you were to disconnect the MPU and tried to start the unit I'll bet it doesn't turn over a quarter of a turn before it faults. I think if there is a drop of water or anything on the the tip of the MPU it faults before it has a chance to generate the signal.
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Jacob375r
redman:

No. The machine exercises at full speed - 3600 rpm. When it exercises.

Peddler:

I tuned it for @ 1 vac at crank. Can't remember what the running voltage is off hand right now but I will be going out to the machine tomorrow. I have tried to start the machine with the mpu unplugged in the past and it almost immediately goes into rpm sense loss. I usually do check to see if any metallic particles have attached themselves to the tip and have put a thin film of silicon lube on the tip to resist moisture build up.

Thanks
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MacL
About all that is left is cranking speed.

Make sure you have the correct size battery (probably group 24), but it is larger than the group 26 whatever it is. And that the battery connections on the inside where they meet the posts are shiny clean.

Perform a load test on the battery through the the cable ends. You can use the starter lug.

Also check starter connections on the red cable and the ground on the block.

Perform a load test clamping to the starter lug and block ground's bolt head.

Make sure the fuel enrichment solenoid is energizing by touching it with a screwdriver to verify it becomes magnetized. Open that connector and tighten the connections in there, they are often loose. A long crank time, or second crank time could drain the battery and cause a slow crank speed on attempt 2 but not attempt 1.

Check the time of the error and compare it with the set time of the exercise to determine whether it occurred instaneously, or several seconds in, or on a subsequent attempt.

example exercise set for 1200 Saturday.

Fault at 12:00:10 = Instantaneous
Fault at 12:00:16 = Detected at first then lost
Fault at 12:00:28 = Loss during second attempt

Turn gas off and simulate multiple crank attempts if you suspect that it may crank fast at first, fail to start for some other reason, then lose its crank speed on later attempts.
State your problem, not your diagnosis.
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Ziller Tech
I had almost the exact same unit with the same problems... Mine ended up being the fuel regulators internal to the unit were plugged with crap from a garbage install (pipe dope, plastic PE line shavings, etc...)

Check those out first. Mine would try to start, then stumble and fault on RPM loss because the PCB would track the initial RPM as a start and then stall... I chased that dumb thing for like 1 year before I finally heard it stumble and fault out... :mad:

As far as the Mag pickup goes, I set them all the same and have NEVER had a problem. It's also the method Generac used to use back in the day (maybe they still do) Bottom the sensor out on a peak of a tooth and back out 1.5 turns.
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78buckshot
Per MacL instructions, check the cold start solenoid wires, I have also found these loose.
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Jacob375r
I went out Yesterday and after resetting the controller and started it, it did exactly what Chris Flagg's unit he described did. It started, acted like it was going to run for a split second, stumbled and died then went into alarm.
On a side note, the engine revs up and down on start up for a few seconds before settling down at 3600rpm when it does fire up.

According to the alarm history the fault always occurs 5 seconds after start

I checked the voltage at the mpu. During crank .996 vac and running is 7.1 vac. i pulled it just to check and it had no debris on tip.

I verified fuel pressure at 13.9 iwc static and @ 12.5 iwc running. Gen has it's own 2 lb meter about 50' of pipe including 90's with 1 1/4" pipe feeding it with the regulator about 15 ft from machine. Reg has been replaced recently to eliminate it from being a issue

I also verified that the fuel enrichment solenoids are magnetizing and that both fuel solenoids are popping open.

So, maybe its safe to say that this machine has an issue with the internal fuel regs?

Thanks in advance for everyone's suggestions and help.

Edit: The battery is only 3 months old Interstate G27 that I swapped when the external reg was replaced

I load tested the batt at the starter lug and ground on block and found no difference in reading as opposed to testing at the terminals.
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Ziller Tech
I would do what I suggested and pull them apart and see if they are full of garbage... I fought that dumb thing for a while!
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Jacob375r
Hey guys, Thanks for everybody's suggestions and input. I did replace the demand regulators along with the solenoids and a couple months later, I can report that I haven't had any issues (knock on wood) I will report back to this thread if i come across this issue again.
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Ziller Tech
Did you pull the old ones apart to see what was in there? I always like to purge the line when they're off to make sure whatever was in there is totally out. ;)
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Jacob375r
I did, didn't find any trash just some corrosion that would be found on any aluminum part subjected to gulf coast weather. Anytime I have to do any service to the gas system, I purge the line for trash.
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Ziller Tech
Jacob375r;52167 wrote:
I did, didn't find any trash just some corrosion that would be found on any aluminum part subjected to gulf coast weather. Anytime I have to do any service to the gas system, I purge the line for trash.


Hmm, well hopefully this will solve the problems!
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Jacob375r
I hope so. A day after updating the thread the machine threw the fan belt and went in to " High Engine Temp" alarm. So at least for the time being its having other problems. But your suggestion on the demand regs being the issue was the one thing that hadn't been considered even by the manufacture.
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Jacob375r
Well...

This same machine is at it again.
Doing the same thing it always has.
Everything is the same.

Generator turns over, lights, stumbles then sometimes it will catch up and continue to run and sometimes it faults for RPM sense loss.
When it does catch and run, it will rev up and down for a couple of seconds then smooth out at 3600

Gas pres is set at 13.7 static
when its turning over and the FS's open gas will drop to @12.5
Gas will then drop to around 8-9" during the time the engine is stumbling
If it catches and runs, it will run at around 12"

I've had the gas company out here to verify supply, 2 lbs at test port.
1 1/4" 20 ft. pipe from meter to unit. machine is the only thing running off meter.

The only thing i can think of at this point is either the ign module or the cam and or crank sensors
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Peddler
I know this doesn't seem likely but I had a 80 KW with similar issues. In the end I had to enhance the fuel enrichment system. What I did was change the fittings and the hose to a larger size barb but the same thread but the bore through the brass adapter was bigger. This solved my problem maybe it will help your also. Good Luck
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