5th gen runs rough and stalls when warm

Well maybe that is good news that you no longer have a fault code showing, I presume that means that you can rule out a sensor as a fault.

So if the airflow is being properly managed does that leave fuel and sparks? I think (?) you've ruled out the fuel supply so maybe you have a coil that is faulty, or dodgy power supply to coil or plug? Both would be affected by heat.

 

First let me say I am unclear what vacuum you tested. Total vacuum? 20 lbs/square inch? I am unfamiliar with this test. That said, leading up to this problem did you change the starter valve settings? Here is the vacuum at each starter valves with the appropriate changes per the service manual. Note: This is in mm/Hg not pounds per square inch.

CYLINDER "Vacuum (relative)"
1 -10
2 0
3 -20
4 FIXED BASELINE

 

I tried to test the map sensor but the manual requires me to use a test harness. Can I just test the wires for the map sensor at the ECU or does this test harness do something more significant than just give me test points?

I have a very generic gauge so I can't get a particularly precise measurement. It was in psi. It's not something I think very likely but, when I run out of other things to check, I'll be coming back to it.

 

Yes, if you did not adjust the starter valves, then it is not the issue. I just wasn't sure if you had touched them leading up to the problem.

 

well then. I swapped in some new NGK plugs and she idled fine for 15 minutes. Still revved just fine at the end. I'm going to spend some time this afternoon putting her around and see how she handles.

 

Okay not resolved.

Went out to have another go. Exact same problem. I cleared the codes last night to get rid of the four clogged injector codes and then again this morning...after checking what I could of the MAP sensor it flagged a bad connection with it. No, once this problem starts, my FI lights on. It's comes on and off while running. But when I go to check for a code I get nothing. I tried driving around. Once it starts acting up I got no power, FI light is on, lots of bucking and backfiring and stalling. Couldn't even go up the slight slope of my driveway.

This is starting to really irk me.

What else can cause this?

 

So I'm still entertaining the idea of it being temperature related. I know that when the bike is cold it'll be running a "cold circuit". A little more fuel in the mix until temps rise. I know that after the engine is shut off for a moment, and fired back up, the ECM will be running on that cold circuit until it gets all it's information in.

If I disconnect the coolant temperature sensor, the ECM will just assume a cold engine and stay on the rich circuit, right? Or does it go straight to the hot circuit? Would I need to remove the sensor to test this theory?

I still can't help but think it's temperature related.

 

If it ran well for a while after tinkering with plugs does that suggest the plug wires or caps might be worth looking at closely?

 

caps, wires, and coils all check out per the fsrm.

 

Okay so I'm no longer convinced it's temperature related. I just went out to move the buggy and it was acting up almost immediately. Plus, it's 40*f out so if it were overheating I should have had more time than that.

It wasn't backfiring so much this time as it was just not idling, low power, and stalls. FI light was when it started struggling, but if I gassed it the light would go off. Still no codes.

 

This is a "buggy"? I cannot pull up enough history of your posts, so forgive me if you talked about this. This is an unconventional setup?

 

fifth gen powered minibuggy

 

Makenzie71, did you eventually resolve this issue? I ask because I've had similar problems for over a year and I'm at a stand still now. I've replaced the ECU and have had my 99 VFR 800 in the shop a multitude of times. I'm wondering about pieces like the ECT sensor, the fuel cut relay and the thermostat.

The FI light is often on solidly or it can vary according to my throttle. And the bike will stall out at speed, leaving me stranded wherever I am. The good news is that it starts reliably.

Anyway, I thought I'd see how your saga ended in case there's some light you can shed for me.

 

Yeah I did. It was shortly after a rather severe snow/freeze. Ice had gotten into the wiring harness and as the weather warmed up it let water short out a bunch of stuff. I ended up having to take teh full harness off, strip the whole thing, and re-wrap it to get the engine to run right again...but after I did it the thing ran better than it ever did.

 

Interesting, so you didn't have to buy a new harness.

Your FI light no longer illuminates either I suppose.

 

Nope didn't have to buy a new harness. My FI light was only on when the engine was misfiring. Once I cleaned the harness up and it wasn't misfiring anymore the light never came back.

 

Cool. This gives me hope. This problem has been dogging me for some time. I may have some more questions as I dig back into this in the coming months.

Thanks!

 

No problem. Feel free to hit me up any time. You can email me directly at makenzie71@gmail.com.

 

I'd be looking for an earth problem.


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Wow, a bad harness, this is good information for those that may be like the above. I can only imagine how much a PITA this is or was.. Good on you to finding the issue.