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Surging Diagnosis 2006 BF200

P

Phaze

Member
Hey all,

Having heavy surging at idle out of gear. When cold starting she will jump up to almost 2000 rpm, come down to around 300 or less and shut off. After repeating this a few times she will steady out at ~650 to ~750, making me think the ECM is adjusting.

Once she steadies out, I can run her at WOT and get on plane fine, though I do get very slight surging as well and eventually will throw code 23 - knock sensor.

This all started after a waster hose popped off VST and I had to get the intake off and take VST out to get to it. Never opened the VST.

Any help would be appreciated! I can elaborate work done to this point in the comments to not muddy the post itself
 
William01 said:
Did you accidentally/inadvertently disturb a sensor in the vicinity of the VST during your repair?
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I followed the procedure according to the shop manual for disassembly and reassembly, plugged all sensors back in and routed hoses as they were. I have gone back through and checked and everything seems to be in place. Not saying I couldn’t have messed anything up though.

When the VST was out I did use a little cleaner and a brush to try and clean the outside of the tank up a bit, so it was getting turned around and upside down as I was cleaning. Possible that I messed up the float setting? HP fuel filter and cover O-ring, it was in bad shape.
 
Hard to determine. A surge on a cold startup is not unusual - up to maybe 1000 rpm. 2000 rpm seems excessive. Then dropping down to 300 rpm and stalling out is definitely not normal.

The first thing I would do is check whether or not the baffles on the IAB (Intake Air Bypass) are not stuck open.

Use needle-nosed pliers to grab the lever coming out of the IAB diaphragm (which sits over the top of the HP fuel filter cover) and pull on it as if the diaphragm was being activated. It should move until the spring arm engages (or nearly engages) the “stop” adjustment screw. Then let go and it should pop right back in place. If so, the IAB is operating as intended. If not, you will need to remove the IAB and lubricate the shaft that the baffles are attached to.

The other thing that comes to mind is that you may have disturbed some sediment in the VST when you removed it. Turn your key switch on briefly to pressurize the fuel system, then drain the VST per the owner's manual. If the drain screw is stuck, which many are, soak it in PB Blaster and put your properly fitting flat bade screwdriver in the drain screw slot, and tap it with a hammer a bunch of times.
 
You wrote: "HP fuel filter and cover O-ring, it was in bad shape.". Pull the fuel pressure regulator and clean it thoroughly.
 
chawk_man said:
You wrote: "HP fuel filter and cover O-ring, it was in bad shape.". Pull the fuel pressure regulator and clean it thoroughly.
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I meant to say that I “replaced HP…” sorry.

I’ll definitely follow those steps in your other reply as well, thank you. I also was going to run a fuel pressure test on the HP filter cover screw as my primer bulb does not get hard before turning the engine over so wondering if air is in the system as well.

What types of cleaner should I use? I don’t want to run anything like brake clean that would damage it
 
chawk_man said:
Hard to determine. A surge on a cold startup is not unusual - up to maybe 1000 rpm. 2000 rpm seems excessive. Then dropping down to 300 rpm and stalling out is definitely not normal.

The first thing I would do is check whether or not the baffles on the IAB (Intake Air Bypass) are not stuck open.

Use needle-nosed pliers to grab the lever coming out of the IAB diaphragm (which sits over the top of the HP fuel filter cover) and pull on it as if the diaphragm was being activated. It should move until the spring arm engages (or nearly engages) the “stop” adjustment screw. Then let go and it should pop right back in place. If so, the IAB is operating as intended. If not, you will need to remove the IAB and lubricate the shaft that the baffles are attached to.

The other thing that comes to mind is that you may have disturbed some sediment in the VST when you removed it. Turn your key switch on briefly to pressurize the fuel system, then drain the VST per the owner's manual. If the drain screw is stuck, which many are, soak it in PB Blaster and put your properly fitting flat bade screwdriver in the drain screw slot, and tap it with a hammer a bunch of times.
Click to expand...
So I got into it yesterday and caught a leak where the o-ring got pinched on the HP filter cover. Fixed that, took her out to test and once she worked the air out of the system the idle smoothed out to ~700. Took her out, ran at 5000 rpm for 15 minutes no issues. When I slowed down to turn around alarm went off, and I found that the float in the on-board fuel/water sep was stuck. Shook it up to get it loose, cleared ECM and no alarm getting back to the dock.

Think that float could cause a knock sensor to go off? I’m pretty sure that filter cover sucking air could cause the idle surge too but let me know what you think if you get the time. Thanks!
 
If the F/W separator was leaking air, that would definitely cause surging. I think that in turn, could activate the knock sensor. Not entirely sure of that.
 
chawk_man said:
If the F/W separator was leaking air, that would definitely cause surging. I think that in turn, could activate the knock sensor. Not entirely sure of that.
Click to expand...
Thanks Chawk,

The HP fuel filter cover was what was leaking, and it seemed that the float in the f/w separator was sticking. I’ll report back once I get a chance to run again.

Thank you for your continued help!
 
@chawk_man alright so just got back from taking her to the ramp.

I had fixed that leaking in the HP fuel filter cover. not leaking anymore, 100% confirmed. on first start she got up around 1000rpm and settled down to idle nicely. before I went to actually run her, I decided to ramp up the rpm to about 2500 on neutral throttle and see how she responded.

she got there fine but started dropping a little on her own and when I went back to neutral she died. couldnt get her to stay on when turning her over a few times so pumped primer bulb and she stayed on, but was surging. went up to 3500rpm, came down and died. then wouldnt stay on again.

At this point I think your hypothesis about disturbing sediment in the VST has become pretty evident and I'm thinking that one or more injectors are clogged. I think that's pretty plausible considering our discussion and my testing so far. I appreciate all your time and help. any thoughts on this hypothesis?
 
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