5th gen runs rough and stalls when warm

I've had no problems until today. I go and fire the thing up and let her idle for a bit...I had just re-routed the circuit for the cooling fan and was testing it out to make sure it was working (previously the fan was just shorted to ground and on all the time)...before it even got to running temp it started running rough and stalled. I go and check things out...nothing obvious. FI light is on for the fuel injectors but it's been on since I built the buggy (I have not resolved to replace the injectors yet). I go to start it back up and she runs just fine for a minute...then rough and stalls. If she sits still for any length of time she starts right up and runs no problem, but only runs for a few minutes before stalling.

Fuel pressure sits at 39psi at idle and never dips before 35 running.
I changed the fuel filters.
I changed the oil (because I was down there and couldn't remember when I'd done it last)...no water in the oil or steam in the exhaust, anyway, so at least that rules out a blown head gasket, and never overheated
I cleaned the air filter and made sure the airbox was clean
I checked to make sure that all four cylinders were, in fact, firing (check)

What could I check next? I'd start taking those 12/13/14/15 error codes more seriously but the thing runs beautifully until it hits a certain point. I'm stumped.

 

I had something similar when I forgot to reconnect either the MAP sensor or it's hose. The bike started right up and idled OK, but ran ragged when I gave it any throttle. I believe the bike will start up in a standard default setting, then once the throttle is opened the ECU starts looking for the various sensors and gets upset if any are missing.

I'd suggest clearing the fault code memory, re-starting the engine and then see what fault codes it is throwing up. Running fine then not running fine sounds like an electrical issue to me.

 

How do you clear the fault codes? I'm sure it's easy to find by I'm mobile at the moment...I'd like to be able to jump right in it when I get home.

 

okay...so what happens after the engine warms up? What changes between warmup and cold? I'm convinced it has something to do with warmup.

 

There's a small black 2 pin female connector at the left rear on the standard loom. You stick a wire across the contacts and( from memory) turn the ignition on and off a couple of times. But that's just what I remember, better to check the manual.


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OK I was close but not exact. From the service manual:
1 Turn ignition off
2. Install the jumper wire
3. Turn ignition on
4. Pull the jumper out
5. The FI light comes on for about 5 seconds, while it is lit re-install the jumper wire.
6. The memory is erased if the light goes off, and then starts blinking.
7. If the light blinks 20 times the data has not been erased, try again.

Don't turn the ignition off during this process.

To answer your other question, the engine coolant temperature is monitored by the ECU and this is one of the things used to adjust injection volume. Also manifold air pressure, throttle position and inlet air temps are used to make adjustments to the injection volume. My guess is one of these sensors is not communicating with the ECU.

One other thing that could fail and give problems is the fuel pressure regulator, this keeps the pressure in the fuel rail constant compared to the manifold air pressure. It's basically a spring controlled regulator, plus a vacuum diaphragm which is connected to the inlet vacuum to reduce output fuel pressure as the inlet vacuum increases. I doubt this would change with the engine temp, but could certainly lead to rich running if the vacuum signal is lost due to a hose leak or a diaphragm rip.

The running good then going rough thing does sound like fuel starvation though doesn't it? You sure you don't have a blocked air vent into the tank? The fuel pressure numbers above look bang on but are these still happening when the engine conks out?

 

I will attempt this shortly. Thanks!

This is what I'm leaning most toward being the case...a temp sensor has been tampered with. I need to sort out where all the temp sensors are and make sure they're sound.

I thought it might possibly be vacuum locked and removed the cap just to be sure. This has never been an issue, though, and did not change my current symptoms. I originally thought fuel starvation and tried to address everything I could. New filters and lines, and I checked pressure immediately off the pump, off the high pressure filter, and off the fuel rail. Consistent all the way across, and no the pressure does not drop when it's trying to die.

 

I want to add that, once symptoms start, it affects everything. Engine revs are lethargic, lots of misfiring and backfiring, and dying.

 

Okay today I can say it's not even getting up to operating temps before acting up. Coolant hose on the pump side of the motor is cold, right side of the motor is hot. Nothing is flowing through the radiator.

Can anyone tell me where the block temp sensor is? I don't have a dash so I can't see what the ECU sees as far as temps go. I need to be able to get to it and put a standalone probe in place.

I would love to hear any other suggestions. Someone has suggested a vacuum leak or a clog. I will be going over my vac lines.

 

The engine coolant temperature sensor is plugged into the back of the front head down low in the v, left hand side. At 80C the resistance should be 2.1-2.6 kohms, at 120C 0.62-0.76 kohms. Resistance is measured between the bottom of 3 terminals and the casing.

 

Found it, thanks! I disconnected it and started the engine up again and...same problem. After 13 minutes of idling it started stumbling and dying...and died. The coolant had only just started flowing through the radiator.

So, I think that I can say it's not a matter of what the ECU is seeing from the sensor. It ran perfectly up to the point of stumbling...no fade. So I'm stuck looking for something else, I fear.

I'm going to pull off that sensor and put in an aftermarket temperature gauge and see if it's possibly overheating and my t-stat or waterpump are stuck.

 

Or not...because it seems to need some kind of special wrech/socked to get the damn sensor out. I really don't think that's my problem, anyway.

I need to find something else that can cause this.

 

Vacuum line crimped under tank, that would stop fuel flow once vacuum builds up? When it dies open gas tank. Get a "whoosh" of air? I don't think there would be backfiring from this issue though.

 

No the gas tank doesn't have a vac line under it and the cap is vented. It was my first idea.

 

I agree with the poster on the other forum: Re-examine all grounds.

 

I am currently making a loom that will will run grounds from the engine, light bar (since I moved it), radiator, and frame to the negative terminal. I don't think it can be grounds since I can ohm out the light bar, frame, engine, instrument cluster, etc and so on and they get zero resistance between them and ground.

 

My quick check for the thermostat function is to start the bike from cold and keep touching the radiator. If the tstat is doing its thing, it should hold the coolant in the pump/block area until it gets to operating temp (80C), then start to open to release hot coolant to the radiator. If the radiator starts heating slowly but as soon as the bike starts, the tstat is stuck open. If the radiator stays cold for a few minutes, then gets too hot to touch quickly, all is well. And if the radiator never gets hot, the tstat is stuck closed.

 

As an update....the FI light that was present from a clogged fuel line months ago was cleared. The ECU reads no other codes and that one has not come back.

 

I ran new grounds from the battery to the frame, radiator, engine, carriage, engine cradle, and I ran one from the only wire I could find from the ECU that I could see was a straight ground. No change.

 

Checked vacuum on a few peoples' advice...it pulses so it's hard to be really sure but it's pulling the needle past 20lbs at idle.