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Car Forum / Driving, Maintenance, Tuning / RVs / March 20071996 Onan 6.5 gas NHE Generator runs great until it mysteriously shuts off
Sometimes this beast will run for 8 hours with the AC and TV etc on. Last August it ran the AC for 5 hours at 94 degrees with no problem.. The next day it ran for 10 minutes and died. Sometimes it will run for 15 minutes or so and then shut of.. It restarts but will then only run a very few minutes before it dies.. Seems to die quicker the more load that is on it, but running with just a fan or two on sometimes it still dies after just a few minutes.. Model 6.5NHEFA26100N Gen SN J9636003565 engine SN 5980U1G2Ra just 750 hours.. according to the hours meter.. This has been driving me nuts for 3 summers now.. I have the service manual and have always thought I was a capable trouble shooter. Prior M-Homes, appliances, Computers, HD TV, What ever breaks I fix it.. BUT this thing has me baffled . It has reduced me to a 'parts changer' ... After replacing fuel filter/plugs/plug wires and a few other tune up parts I still had the intermittent shut down issue.. Adjusted Rpm/frequency/voltage to spec with a Fluke etc.. flushed the carb with cleaner.. replaced the coils since it was out of spec and I thought it might be opening hot?? Then I found that the manual had a typo. <G>. Removed the brushes and inspected and cleaned the commutator.. resistance only changed a few ohm.. it was in spec before and after, but I was getting desperate.. Fuel pump was replaced temporarily by a little automotive unit I use as an occasional siphon.. same output as the Onan OE for pressure and volume.. no difference in gen set behavior, it ran an hour and then started shutting off.. Replaced the oil pressure sending unit since it controls the power to the fuel pump.. No difference in behavior.. Any ideas?? Heat sensitive component problem in the voltage regulator?? I hate to change yet another part that in static testing seems OK. Is there some known issue in the windings/armature that will show up only hot and then intermittently ( such wildly varialble time to failure??)? Sometimes seems like the generator engine pitch will lift its tone/ speed just an instant before the thing shuts off.. but then the next time I think I was imagining the momentary pitch change.. Rig comes out of storage next week and I probably don't need the generator to drive AC for a month up here in WI , but I am running out of ideas.. I hate the thought of taking it to Onan/Cummins N Power folks will charge me $100 an hour to go over the stuff I already worked on.. .. Any ideas for stuff I have missed?? Or a suggestion for a really good generator service center in the middle of Wisconsin?? On Thu, 22 Mar 2007 07:27:36 -0700, robert.gleason wrote: > Sometimes this beast will run for 8 hours with the AC and TV etc on. > Last August it ran the AC for 5 hours at 94 degrees with no problem.. [quoted text clipped - 41 lines] > .. Any ideas for stuff I have missed?? Or a suggestion for a really > good generator service center in the middle of Wisconsin?? Oil level?  SignatureFrank Tabor Q: Why don't lawyers go to the beach? A: The cats keep trying to bury them. Have tried running it a little lower oil level and just a hair higher and replaced the oil pressure sending unit and shorted the sending unit lead to ground just in case I really had low oil pressure.. that would eliminate the possibility of the sending unit having casued the shut down... None of these made any difference.. Thanks for trying <G> Bob Gleason > Oil level? > [quoted text clipped - 4 lines] > > - Show quoted text - I have had a pinhole in the fuel line that drove me crazy until I found it. SignatureJerryD(upstateNY) Last sumer I thought maybe a pinhole OR the fuel line was collapsing since unlike the in tank main pump, the generator fuel pump pulls/ sucks the fuel from the tank.. So I dropped the motorhome fuel tank and replaced the generator fuel line with a really high quality fuel line.. The generator ran maybe an hour that time before it crapped out.. <GRRRRR> Bob Gleason On Mar 22, 7:08 pm, "JerryD\(upstateNY\)" <jer...@wherever.com> wrote: > I have had a pinhole in the fuel line that drove me crazy until I found it. > > -- > JerryD(upstateNY) > Sometimes this beast will run for 8 hours with the AC and TV etc on. > Last August it ran the AC for 5 hours at 94 degrees with no problem.. [quoted text clipped - 42 lines] > worked on.. .. Any ideas for stuff I have missed?? Or a suggestion > for a really good generator service center in the middle of Wisconsin?? Just a few thoughts. (Area 1): Genset MUST be generating, must not have a stop signal from local or remote switch or associated wiring, and MUST have oil pressure to stay in run mode - otherwise it will shut down. (Area 2): Engine must have spark and fuel to stay running. You need to have some test instruments hooked up, and be looking at it/them RIGHT WHEN IT STARTS TO SHUT DOWN to get some idea of what's happening. Meter or test light hooked to coil positive will show if shutdown is caused by control or its associated signals (area 1). Then it's a case of checking the individual items/signals. If the meter or test light shows that it's not a 'commanded' shutdown, we're in area 2 - either the ignition trigger module is failing when hot, or there's a fuel supply problem. Checking voltage between coil negative and ground will show if the problem is the trigger module - if not, then problem is fuel supply. Went round and round with a genset on a telco truck last year that was doing similar semi-random shutdowns. Finally found that the gas tank vent line was clogged with rust/scale, would gradually create a vacuum in tank as genset was running until fuel pump couldn't draw any more fuel - the pump on the chassis engine was (of course) much more powerful, and didn't have any problem. How long it took the genset to die depended on how tight the gas tank cap was - if the cap was TIGHT, genset would reliably die after 16-18 minutes. Just average snug, might run 30 minutes or 3 hours. Not saying that's your problem - just throwing it out for consideration <g>. Alan If it has a low oil safety shut off you might try temporally by passing it Bypassed the low oil pressure switch two years ago and replaced it last year.. No difference. Runs anywhere from a few minutes to all day.. Frustration level is really high.. The rig is still stored.. Despite our beautiful weather and record high temps, I left it in storage building as I really don't want to deal with that generator.. I did get a couple new ideas to try over the winter, but am not my usual optomistic self.. <G> I'll post up the solution if I ever find it.. Bob Gleason > If it has a low oil safety shut off you might try temporally by passing > it Although you haven't given us so much as the remotest clue as to whether your problems are fuel or gas-related . . . Fuel problems, for the most part tend to be demonstrated by a prolonged cough-spit-gaspth scenario before finally going down; whereas electrical problems tend be a whole lot more sudden and immediate. On Mar 26, 9:22 pm, stan.bi...@hotmail.com wrote: > Although you haven't given us so much as the remotest clue as to > whether your problems are fuel or gas-related . . . [quoted text clipped - 3 lines] > whereas electrical problems tend be a whole lot more sudden and > immediate. My initial post does say that the generator runs perfectly right up to the moment that it shuts off.. I mention some of the items I have changed/cleaned/adjusted so that anyone suggesting a fix would be able to remove those items from the list of possibles.. I becoming convinced that the issue is either a bad(heat sensitive component buried in that pile of plastic?) regulator.. a problem with the ignition trigger module, or possibly a simple bad ground somewhere that I did not find.. I am hoping it's not the stator windings and because it is so very intemittent I am doubting that is the problem.. There are any number of possibilities for other items.. I will even check that fuel tank vent issue some one suggested, since it would sure be cheaper than a stator.. If it was not so amazingly variable in terms of run time, I think I would be happier to take it to Onan/Cummins.. But some days the darned thing runs 8 hours before it quits.. I have on several occasions decided that it was FIXED since I was running two AC and had no problems for many hours.. and then the next day the problem is back.. When I Google this issue I get lots and lots of folks with 'mysterious shut down' results etc.. especially on the NHE series.. From what I can see a lot of them are unresolved.. > I becoming >convinced that the issue is either a bad(heat sensitive component >buried in that pile of plastic?) regulator.. a problem with the >ignition trigger module, or possibly a simple bad ground somewhere >that I did not find.. You are indeed faced with a whole bunch of confusing and contradictory symptoms! :-( While you can run your A/Cs all day at 95 degrees without failing; and at other times in significanlty less-demanding situations for only ten minutes before shutdown; "heat" doesn't seem to be a significant factor. (Although this may not apply, genny failures in Fleetwood products due to inferior fuel lines are legendary. As might be expected of cracked fuel lines, the severity tends to vary with ambient conditions) So . . . best guess: A marginal connection in the wiring harness. Suggest a wiggle test. Next suspect would be a a marginal bridge rectifier that fails early an sporatically with any kind of load. Over the years, I've read many similar episodes. By ignition Trigger module, are you refering to the sending unit that is located on the end of the engine crankshaft?? I thought about changing that but it looked to me like it was going to require pulling the generator out of the coach?? I'll try clipping a meter between the coil positive and a ground and see if I can pay attention long enought to see if it is droppping out the instant before or an instant after the generator shuts down.. Too bad the old gen sets don't come with the 'trouble codes' and light box the newer generators have.. I talked to the guy that builds the Dinasaur boards a couple years ago about his developing an aftermarket box that would produce the error codes.. But not cost effective to add a $500 box to a 10 year old gen set.. I'll add your email to the stack of 'might be' ideas and let ya'll know when/if I get a fix.. Bob Gleason > <robert.glea...@gmail.com> wrote in message > [quoted text clipped - 81 lines] > > - Show quoted text - > By ignition Trigger module, are you refering to the sending unit that > is located on the end of the engine crankshaft?? The trigger itself is a nylon hub on the generator end of the crankshaft, with two arms that extend outwards and end in magnets. The module itself is a little metal box mounted on a plate that mounts to the generator adapter next to the engine, and holds the box in towards the crankshaft where the magnets in the end of the arms swing past it as the engine rotates. One magnet turns the module 'on', grounding the negative coil terminal and causing current to flow thru the coil primary. The other magnet turns the module 'off', stopping current flow thru the coil. This causes the field in the coil to collapse and induces a spark from the hi-voltage coil winding. (Turning the module on is like closing points and turning module off is like opening points on a 'conventional' ignition). > I thought about changing that but it looked to me like it was going to > require pulling the generator out of the coach?? Unless you are -very- lucky, you won't have enough clearance to do it with the genset in the coach. > I'll try clipping a meter between the coil positive and a ground and > see if I can pay attention long enought to see if it is droppping out > the instant before or an instant after the generator shuts down.. You've got it - the joy of troubleshooting intermittents. Unless you're looking in the right place at the right time, you wind up running around in circles.. > Too bad the old gen sets don't come with the 'trouble codes' and > light box the newer generators have.. I talked to the guy that builds > the Dinasaur boards a couple years ago about his developing an > aftermarket box that would produce the error codes.. But not cost > effective to add a $500 box to a 10 year old gen set.. The reason the newer sets have the trouble codes is that the 'control board' actually has a microprocessor with custom logic, rather than relay logic. Adding trouble codes just meant adding a little software code.. no additional hardware. > I'll add your email to the stack of 'might be' ideas and let ya'll > know when/if I get a fix.. If the frustration level gets too high, you might try hooking up a pc and a data logger such as http://www.apogeekits.com/data_logger.htm so you can go back after it dies and see what's happening when.. Alan |
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