My boys and I picked up a BMS 800cc buggy (GK306) from Emrock ATV a couple of weeks ago. Given that I have a severely broken (and pinned) right arm and left collar bone, my 6 year old son helped with most of the assembly
Things went together pretty well, one major fit issue that I'll use the plasma cutter and mig to fix on the roll cage, but otherwise a decently built machine.
Engine fired right up the first time.
We've had her out for a couple of short trips (8 miles total) and had geared up today for a shake down run. Made it about 2 minutes from the house, was helping my son get his little 110cc buggy unstuck, the BMS was sitting idling (for about 60 seconds) and it died. When I restarted, it, well, woudn't hardly run. I turned it off and let it sit for a few minutes. The engine temp was barely warmed up (fans hadn't even kicked on yet). After a few minutes she started, and sort of ran, so I milked it home (all of 200 yards).
Once back at home I've checked: Fuel filter (clean, even bypassed it as a test), fuel pump (pumps when key turns on), all visible sensor connections (good), frayed wires (none I can find), etc. If I let her cool off, she'll run until about the time the fans kick on (call it about half on the temp gauge) and then you can hear it - sounds like fuel starvation or something - and she won't rev/dies/etc. This takes 2-3 minutes. Shut her off and wait a minute or two, and she'll run OK for 15-20 seconds.
I pulled the pressure regulator and checked the screen, drained and filtered the gas, checked the plugs (look perfect) and glanced at the dist cap (fine).
My only guess is the fuel pump is heating up and dropping off performance when hot? I didn't check fuel pressure (don't have the correct stuff here) but the pump does become warm to the touch (not hot) after a few minutes. I'd guess 125-130 degrees or so. I can hold my hand on the pump, but it is hotter than I would expect it to be.
not sure about the fuel pump, definitely a possibility... I dont have EFI on my buggy, my 800cc is carb but I know that most all EFI (and Bosch for sure) has a coolant temp sensor that the engine uses to adjust fuel enrichment using the coolant as a measure for the engines temp. when those go bad they often cause problems cause now your engines computer thinks its a way different temp than it really is so it adjusts the fueling incorrectly. its something you could try and test with a multimeter or just replace they are cheap usually less than $10. hope this helps or at least eliminates a possible cause. good luck _________________ 2006 Roketa 800cc - K&N + precharger, rejetted, manual carb secondary, Desertkart spark arrest muffler, limiting straps, & lots of repairs...
Well, all three temp sensors work fine (one for gauge, one is a fan switch, and the other variable data for the ecu)...
I can disconnect the sensor for the ecu and the condition persists. Same can be said for MAP sensor and MAF(IAT?) sensor on throttle body (for lack of a better term). Of course, disconnecting the TPS sensor does not allow the engine to run, as expected.
I can't imagine the ECU or any sensor would cause this, because it takes the better part of 7-10 minutes to warm up before the issue persists...wish there were more information online to how these systems work
Get a can of freeze spray from a local electronic parts store and take it with you on the next ride. When the problem starts, spray one electrical component or sensor at a time to see if conditions change. _________________ 08 Joyner SandViper 250
07 Joyner SandSpider 650
06 Tank Urban Touring 150SE
04 Yerf-Dog Spiderbox 4209 GX150 (SOLD)
04 Yerf-Dog Spiderbox 3206 GX150
81 Honda Passport C70B
I let it idle for about 15 minutes this evening, all the while monitoring voltage at the fuel pump with my trusty Fluke.
Guess what? It is generally 13.2-13.5 volts, but when this condition acts up, the voltage jumps to 13.75-85 volts! So, the ECU, for whatever reason, is bumping voltage and this causes the condition. It is sometimes associated (though not always) with the fans kicking on, which makes voltage drop, alternator kicks in, rpms drop, ecu bumps rpms up, etc.
The condition can be reset, but only for a few minutes, by disconnecting power to the ECU. Turn the main disconnect off for 10 seconds or so, and she'll start right up, with voltage back to 13.5 volts at the fuel pump, and run that way for anywhere from 1-5 minutes.
So now, the question is - ANYBODY KNOW WHY THE BOSCH ECU BUMPS FUEL PUMP VOLTAGE AT IDLE?
OK - had a little more time to check things out. Put an inline pressure gauge in place, and fired her up tonight (haven't started her for 2 days). Pressure gradually drops, once water temp is warm, down below 10 psi when it dies.
Therefore, I would have to guess the pump is junk. Good thing I picked up another, some limit straps, and well, some other goodies when I bought the gauge
The pump is fine, new pump and new filter doesn't change the issue I disassembled the entire fuel system and checked for clogs, etc.
The culprit? This thing is designed with a gravity feed fuel tank - single line that goes to a tee. The other lines go to A) fuel filter feeding fuel pump and B) return line from fuel rail.
The problem - somehow, this creates a fuel starvation problem. I'm no expert at fluid dynamics, so I can't say how, just that it does. I eliminated the T, as a test, and ran the fuel return line up into the top of the gas tank (cap removed). She ran fine for almost 40 minutes, no problems at all, fuel pump was nice and quiet, fuel pressure was stable.
So, there is a flaw in the factory design. The fix is relatively simple and I'll do it tomorrow. I'll drill and tap the tank for a return fitting, thereby eliminating whatever aeration or other problem the T is creating. I'm confident that there will be no further issues, at least with fuel supply, once this is complete.
For the record - BMS asked that I ship them the fuel pump and ECU so that they could determine if either were defective. I believe they're both fine, so will continue with my modification to improve the fuel system and report back here.
Also, for the record, plenty of hard black crap in the pressure regulator and elsewhere...
I resolved the problem, but BMS may want to address this themselves.
Turns out the issue is the fuel return to the tank. From the factory it has a 3 way, or Y fitting, that feeds fuel to the fuel filter/pump, connects to the tank (gravity feed) and connects to the fuel return from the fuel rail.
Somehow, this creates a vapor lock after running for a few minutes.
Solution? Drill and tap the end of the tank for the fuel return, and ditch the Y coupling altogether. Went for an hour long shake down and not a single issue...full review to come later.
Power? Needs more. Suspension? Too stiff...but I'll cover that in a review.
Thanks for the input here, this is a cool little site.
Just posted my solution to your problem on a different portion of this website. I'm new in this, so bear with me. I bought an 800cc BMS rig and outfitted it to drive on the street. First day out, it would die every time I rolled to a stop. Very hard to restart. The last time it died, I was close to my auto mechanic. He kept it for 2 weeks and reached the same conclusion you did. I took the tank to a weld shop close by, and they welded a 1/4" pad on the top of the tank, drilled and tapped it and I ran the new fuel bypass line to the top of the tank. I called BMS in California and they said they hadn't heard of any problems like this.!! Cart runs great on top end, but recently, fuel consumption is up from about 31mpg down to about 25 mpg. Cart still dies occasionally when I drive up to a stop sign. restarts quickly, but hesitates on low end accelleration. I occasionally smell fuel like its flooded. The mechanic oogling the cart at the local Wal-Mart said it sounded like a MAP sensor, and I asked him to show it to me. He looked and said it appeared to not have one. Now what? I again called BMS Tech Support in Calif. and the dude says to change the fuel filter! I thought he was reaching, but I did it anyway. its actually better! not cured, but better! Sounds like you have been much more professional in your troubleshooting than I'm capable of. Any help you could offer is appriciated. I think the cart has plenty of power for steet riding, but I wish I could add a fifth gear or change the 4th gear ratio. that would help my fuel milage. not interested in going faster, just with less fuel consumption! kart gets lots of compliments and questions!
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