Am I crazy or what? MEP-002A AUX pump runs all the time

[Craig A Tull]

Well I drug home another MEP-002A and was looking over the schematic and noticed that it looks like if you select the AUX. pump selection the dang AUX. pump runs all the time and the tank switch only controls the fuel solenoid, sound outright crazy to me

 

[Triple Jim]

You're exactly correct. It's not so stupid though, because if you restrict the output of that type of pump, it slows way down. I've thought that maybe it was designed that way because the inductance and/or current consumption of the solenoid valve is not as high as that of the pump coil, so it's easier on the float switch. The MEP-003A is the same way.

 

[PeterD]

The MEP-003A is the same way.

The MEP-004 (and 005 and probably the 006) are the same as well. The pumps run full time and the solenoid controls the flow of fuel. The pump doesn't seem to suffer any ill effects from being deadheaded.

 

[Triple Jim]

If I remember the last time I had one apart correctly, a spring in the pump pushes the plunger to move fluid, and when it hits bottom the solenoid returns it. If it sealed perfectly, when the flow is stopped, it would quit running altogether, but they're made somewhat leaky, so they just slow down a lot.

 

[1800 Diesel]

The MEP-004 (and 005 and probably the 006) are the same as well. The pumps run full time and the solenoid controls the flow of fuel. The pump doesn't seem to suffer any ill effects from being deadheaded.

Hi Peter...wanted to ask about an MEP-004 that we have that decided to start running one of the fuel pumps whenever the batteries are connected, even with the run switch & battle short switch off. My son called me the other day when I was out of town and mentioned to me that he heard a pump running so I had him disconnect the battery wires. I haven't been able to get out to the shop yet with several other jobs ahead of this one--like fixing a hole in the roof from a falling limb....thanks for any info you could provide..will look at TM tonight to see if it has any relevant info.

Kevin

 

[PeterD]

Kevin, sounds like either a 'stuck' relay, or a short in the wiring, but I have no great ideas where to look other than hitting the manual and tracing back and seeing what's happening. Idea: pull the DC circuit breaker and see if the pump still runs. (BTW: most of us leave the main DC breaker open when the generator is not being used...)

 

[1800 Diesel]

Kevin, sounds like either a 'stuck' relay, or a short in the wiring, but I have no great ideas where to look other than hitting the manual and tracing back and seeing what's happening. Idea: pull the DC circuit breaker and see if the pump still runs. (BTW: most of us leave the main DC breaker open when the generator is not being used...)

Thanks--I'll steer towards a stuck relay. And once fixed, I'll make it SOP to pull the DC breaker too.

 

[steelypip]

Kevin, sounds like either a 'stuck' relay, or a short in the wiring, but I have no great ideas where to look other than hitting the manual and tracing back and seeing what's happening. Idea: pull the DC circuit breaker and see if the pump still runs. (BTW: most of us leave the main DC breaker open when the generator is not being used...)

I'm a big believer in battery disconnects. Because the small MEPs vibrate so much, I also like the idea of the batteries not being subjected to the continuous paint shaker when the set is running. Accordingly, I crimped up a set of 6' long battery cables out of a pair of jumper cables and have a battery disconnect switch on a terminal to isolate the battery from the genset when not in use. Result: the batteries don't move around unless I want them to and nothing going wrong in the sitting set (like my kid playing with the panel light switch) will cause the batteries to discharge. It's also a handy 'ignition lock' for the generator. Startup has one additional step: connect the battery cutoff switch before priming or preheating.

 

[1800 Diesel]

Peter,

I've looked through both the Op & Depot Maint TMs and can locate fuel solenoids but no relays specific to the fuel system. Are you using the term "relay" to mean "solenoid"?

Thanks

 

[1800 Diesel]

Kevin, sounds like either a 'stuck' relay, or a short in the wiring, but I have no great ideas where to look other than hitting the manual and tracing back and seeing what's happening. Idea: pull the DC circuit breaker and see if the pump still runs. (BTW: most of us leave the main DC breaker open when the generator is not being used...)

Peter,

I finally had a little time to check out the wiring to the pumps and took a look inside the unit. First a few pieces of basic info I gathered:

1. Voltage across batteries: 25.60 volts

2. With all switches off, voltage to radiator end pump (from connector near pump): 22.46v (The wire # to this pump is "P51R16".)

3. With all switches off, voltage to meter board end pump (from connector near pump): 22.45v (The wire # to this pump is "P51F16".)

4. Confirmed that both pumps are running with all switches off.

5. Again checked configuration & voltages on the battle short switch against an adjacent unit that is functioning properly.

6. Pumps quit running with DC breaker pulled.

With regard to voltage to the pumps, why is the voltage lower than battery voltage? Is this by design, a bad ground somewhere? a resistor?

Looking through the TM I see the following components that may or may not be relevant:

L1--Engine fuel solenoid
L2--Day Tank solenoid

K1--Stop/Run Relay
K8--Fuel Level Relay

FL1--Fuel level (float switch)
FL2--Fuel level (float switch)

CR6--Fuel pump diode

I'm leaning toward the stop/run relay (though I believe I already swapped this one out earlier) or fuel level relay or whatever fuel circuit is energized when the battle short switch is turned on. I thought about the fuel solenoids, but since both pumps are running it seems the solenoids are not the problem. Without fully understanding the wiring details and how all the components interact with each other I'm having trouble sorting out where to go. Also, besides the two relays inside the control cubicle (that I've already swapped out with known good ones), I haven't been able to locate any other relays.

I also haven't been able to locate any shorts after checking all visible wiring runs, though I'm not clear as to how a shorted positive wire leading to the pumps would cause then to run, vice make sparks or trip the DC breaker??? Also, since I confirmed that both pumps are running this would seem to point at something else, would it not? Would a short cause one of the relays to engage? Or is that what you meant to start with?

If anyone can help, please let me know.

 

[Munchies]

I am not going to chase circuits right now, but on my one running set here both only supply power to the aux pump in aux. otherwise it is 0.0V

 

[1800 Diesel]

I am not going to chase circuits right now, but on my one running set here both only supply power to the aux pump in aux. otherwise it is 0.0V

Yep, I figured they're supposed to be at zero voltage unless the unit is either running or if the battle short switch is on. Still can't figure out the electrical maze of what's malfunctioning to send the voltage to the pumps when it's not supposed to be there. Also this is a new problem on a unit that's had about 10 hours of testing on it since I got it in a year ago or so.

Tonight I ran a full power test on it for about 20 minutes and had to pull out the DC breaker when the normal shutoff switch didn't shut it down.

BTW, my dad worked at KAFB for 28 years. As a kid I spent alot of time over there whenever they had holiday picnics for Memorial Day, July 4th, Veterans Day & others. I remember the airmen would row us around Back Bay for a 30-minute boat ride for a quarter. Stayed at a Colonel's family on base many times on weekends--he was my dad's friend....good memories!

 

[Munchies]

It has changed a lot just since 2005/Katrina. Was here right before for a brief stint. Been here 2.5 yrs, 1.5 to go. I would look at the master switch first. Check wiring going to switch for abrasions and shorting to each other.

 

[1800 Diesel]

It has changed a lot just since 2005/Katrina. Was here right before for a brief stint. Been here 2.5 yrs, 1.5 to go. I would look at the master switch first. Check wiring going to switch for abrasions and shorting to each other.

I'll take another look at it tonight. Thought I already checked the master switch but will check it again and trace wires connected to the switch as well. What's confusing though, when you turn on the master switch the low oil indicator light comes on like it should. It seems like if the master switch was not "turning off", then the oil light would stay on all the time....?? The pumps running seem more like something amiss in the battle short switch, though I checked it against a known good one, but that was only to determine which terminals had 24v when the master switch was turned on. Maybe I should just swap out the master switch with another one.

BTW I also swapped out the K1 relay [again] yesterday with a known good one. (This is the stop/run relay.) Also swapped out the relay above that one (I think it's K6?) Maybe I should swap out the small circuit board the K1 & K6 mounts in, though that would be a pain, considering how many wire connections it has....still reading through the TM to see if anything jumps out....

 

[Munchies]

I was talking about my 002A. Sorry for the confusion. I dont have any 004/005/006's here to try at the moment

 

[1800 Diesel]

I was talking about my 002A. Sorry for the confusion. I dont have any 004/005/006's here to try at the moment

No prob Munchies--thanks for checking in. I'll keep slugging through the TM when I get the time. The stop/run switch (on the MEP4) could still be the culprit or maybe the battle short switch...These are quite more elaborate (in DC wiring) than the 002-003 units, so I'm still learning what I can....The air-cooled models are much easier to troubleshoot than these, IMHO.....dodging lightning bolts this morning...won't get out to the shop until later this afternoon. Thanks again!

 

[1800 Diesel]

START/STOP/RUN Switch checkout

Conducted a check of known-good working MEP004A switch against the unit that has the fuel pumps running. Found a difference in resistance at some of the terminals--comparing between the two switches. Results of test below:

The start/stop/run switch has two rows of terminals 4 each row, for a total of 8 terminals. I'll call the lower row the one closer to the hinge of the control cubicle door. For these two units, there was no difference in voltage readings but I'm posting the info in case someone else might need it in the future. References to left side means left side when facing the control cubicle. For those familiar with the MEP004A, this would be the same side as the hour meter. Edit for clarification: Now that I've pulled the switch out, I can report that the switch actually has 3 rows of 4 terminals, but the uppermost row has no lugs riveted so it was not visible looking inside the cubicle. Therefore the numbers used below do not match the numbers in the TM but are used relative to the positions described. If anyone needs the specific TM numbers for the terminals or a "cross-reference", let me know.

Voltage check (with DC breaker in) for both units 1 & unit 2:

Starting from left to right, "top row", the 1st, 3rd & 4th terminals all showed 24v. 2nd terminal no voltage.

For the bottom row, all 4 terminals showed no voltage. When the switch is set to run position, the 4th terminal from the left shows 24v. I did not determine which terminal engaged the starter.

To clarify--both units showed the same voltage readings at each respective terminal.

*********************************************************************

Resistance check (with DC breaker out): (individual terminal checks to ground only)

Working unit #2 "known good":

All 4 top terminals showing no continuity to ground.

Bottom terminals as follows: 1st from left showing 16.7 ohms, 2nd no continuity to ground, 3rd terminal 0.03 ohms & 4th terminal 2.56 ohms.

Unit #1 with fuel pump run issue:

Top terminals-- 1, 3 & 4 showing continuity to ground. Terminal 2 no continuity.

Bottom terminals-- 1 & 2 no continuity to ground, 3 showing continuity to ground & 4 showing a resistance of 2.78 ohms.

So at this point I don't know if the differences are caused by wiring issues or by a defective switch. The next step is to isolate the switch from the wiring and repeat the resistance tests on the switches first & then the wiring if necessary. I am hoping it's just a switch problem but if not, at least I can focus on the wiring numbers connected to the terminals showing the different readings.

If anyone has any thoughts or other ideas, send 'em over! Thanks!

Edit follow-up: Found in TM page 4-98 that provides terminal continuity/open info for S2 (Start/Stop/Run) switch terminals, but haven't sorted out terminal ID numbers as they relate to terminals on switch. Will check tonight for terminal labels on switch.

Yep--switch has engraved terminal numbers on the ends. Not all terminals are marked but I think I figured out the "code"....

Kevin

 

[1800 Diesel]

It has changed a lot just since 2005/Katrina. Was here right before for a brief stint. Been here 2.5 yrs, 1.5 to go. I would look at the master switch first. Check wiring going to switch for abrasions and shorting to each other.

OK, swapped out both start/run/stop switch and battle short switch--no change, pumps still running with DC breaker in & switches off...

Still looking for breaks in wiring but none found so far. Next check will be the diodes in the rectifier assembly.....fun, fun, fun.....

 

[Munchies]

I wish I had a 004/005/006 here so I could further help diagnose with you I get lost in the diagrams for them, I need a diagram plus visuals to make sense of anything. I did buy some 005's recently, so maybe if your still stuck in a few weeks I can help troubleshoot.

 

[1800 Diesel]

I wish I had a 004/005/006 here so I could further help diagnose with you I get lost in the diagrams for them, I need a diagram plus visuals to make sense of anything. I did buy some 005's recently, so maybe if your still stuck in a few weeks I can help troubleshoot.

Electrically those are similar, just 6 cyl big brother to the 198 in the MEP4 and of course more KW...are they close by? You got "some"?? If you need assist with pickup let me know...