misfire that disappears when warm

[guzzimeister]

Hi

 

got a strange problem. My bike will start easily and idle OK warm or cold. But when cold under load it misfires badly, as if I've got a bad coil or not getting fuel. Today it nearly shuddered to a halt it was so bad. After 10 miles the problem disappears and the bike is fine.

 

If it was a coil, lead or plug, you would expect the problem to get worse. So my thoughts are:

 

- possible relay fault, loose or intermittent operation, don't know why it would disappear when warm but electrickery is funny stuff. I had fuse and relay problems before with loose and corroded terminals

- could be my PCIII Power Commander playing up

- could be the crank sensor furring up with iron dust (the bike has 47k miles on it)

- could be the oil temp sensor playing up, or the air temp sensor likewise

 

I have a diagnostic tool for Marelli ECU systems, but it showed no faults at all. With all of the above the temperature dependency of the fault is interesting, however it could be that 10 miles of white finger vibration improves connections and the problem disappears.

 

Anybody got any new ideas I can try?

 

Bye and safe riding

 

Guzzimeister

[docc]

Hi

 

got a strange problem. My bike will start easily and idle OK warm or cold. But when cold under load it misfires badly, as if I've got a bad coil or not getting fuel. Today it nearly shuddered to a halt it was so bad. After 10 miles the problem disappears and the bike is fine.

 

If it was a coil, lead or plug, you would expect the problem to get worse. So my thoughts are:

 

- possible relay fault, loose or intermittent operation, don't know why it would disappear when warm but electrickery is funny stuff. I had fuse and relay problems before with loose and corroded terminals

- could be my PCIII Power Commander playing up

- could be the crank sensor furring up with iron dust (the bike has 47k miles on it)

- could be the oil temp sensor playing up, or the air temp sensor likewise

 

I have a diagnostic tool for Marelli ECU systems, but it showed no faults at all. With all of the above the temperature dependency of the fault is interesting, however it could be that 10 miles of white finger vibration improves connections and the problem disappears.

 

Anybody got any new ideas I can try?

 

Bye and safe riding

 

Guzzimeister

 

About 89% of these problems have been solved with The Full Tune Up, including valve adjustment, TPS setting , and throttle body balance. !0% have been relay upgrades or battery replacement, and 1% would be whatever you'll come back and tell us if that doesn't work.

[guzzimeister]

About 89% of these problems have been solved with The Full Tune Up, including valve adjustment, TPS setting , and throttle body balance. !0% have been relay upgrades or battery replacement, and 1% would be whatever you'll come back and tell us if that doesn't work.

 

Hi Docc

 

like the precise statistics...lol. The bike is meticulously maintained if a bit scruffy and as you can see I'm approaching the 48K service interval. So I think I will go with your plan of action. I have checked the TPS position and did have to reset it 6k miles ago. I wouldn't have imagined that an out of tune bike would react so severely - to the point of nearly stopping in the road? Anyway I'll give it a go, and we'll see what happens. Thanks for your advice.

 

Cheers

 

Jon

[GuzziMoto]

It could be that the battery does not recover fast enough after starting the bike to allow for proper running. After 10 miles or so it has charged the battery back up and the bike runs fine. Your symptoms sound like voltage issues. I would check the battery before, during, and after starting to see what is going on electrically.

[guzzimeister]

It could be that the battery does not recover fast enough after starting the bike to allow for proper running. After 10 miles or so it has charged the battery back up and the bike runs fine. Your symptoms sound like voltage issues. I would check the battery before, during, and after starting to see what is going on electrically.

 

Hi

 

thanks for this. Don't think it's this as I have a voltmeter fitted to the bike and apart from the dip to 8v when it starts it recovers immediately to 13.5+v. The other clue to low batt voltage I found is the tacho stops working, and it's working OK at the moment. Gues how I found that out.....

 

I checked the crank sensor, it's clean, so now it's the TPS and a general tune up. I wiggled the realys and that didn't affect anything so none the wiser at the moment.

 

Cheers and thanks for your help

 

Guzzimeister

[savagehenry]

One thing that also seems to cause running issues related to temperature is the throttle body boots. They are rubber, and will cause running conditions to change as a hairline crack/ bad seal in one or both allow changes as they go through the warm up/cool down cycle. Try putting the little tube in the nozzle of a can of WD40 (to isolate the spray to a small area) and just aim little sprits at those rubber boots, bike running, both cold and when warm. Any draw down in the idle indicates the need for new ones. Not saying this is the reason, but it's easy to check, and will at least let you know they are still good, or need changing anyway. Good luck, S.H.

[Dan M]

Outside chance here but worth checking especially if it seems excessively rich when cold.

Check the resistance of your temp sensor when cold. There could be an open that occurs at cooler temps causing the ecu to dump excessive fuel. Once you warm past the problem area things return to normal.

[guzzimeister]

Outside chance here but worth checking especially if it seems excessively rich when cold.

Check the resistance of your temp sensor when cold. There could be an open that occurs at cooler temps causing the ecu to dump excessive fuel. Once you warm past the problem area things return to normal.

 

Hi Dan,

 

thanks for the advice. This weekend I serviced the bike fully, all oils and filters changed, TPS set, balnced , new plugs etc. Bike idled beautifully and ran fine on the stand. Toook it out on the road and it had all the symptoms of being lean, wouldn't pull past 1/4 throttle, no power at all. Pulled my Power Commander out and blipped the throttle to see if the fuel lights shifted and they stayed static. Thinking the PC was u/s, I disconnected that, and then had a bike with all the symptoms of being very rich. A plug chop confirmed this, so I put this on my diagnostic setup and found a TPS high voltage fault. Checked the TPS and found this reading 1812mv and not moving when I blipped the throttle. When servicing the bike I found that the idle "zero degree" trim had shifted to 287mv, so I should have suspected something then.

 

So have just bought a genuine Marelli PF3C TPS from Lamers for $400 (sob!), and will let you know if this fixes the problem. Does anyone have experience of the H-D Electra Glide PF4C TPS which is reckoned to be very similar? Apart from Lamers, no-one in Europe has any PF3Cs......and he had only 2.

 

Regarding the PC I suspect its calibration to the ECU dropped out when it saw rising inputs from all the other sensors, but nothing from the TPS. I'll be interested to see whether it restores itself with a new TPS or whether I will have to reprogramme it again. Any views?

 

Happy riding

 

Guzzimeister

[docc]

I replaced my TPS in November, 2008, with HD part # 27271-95 for about 45 USD.

[guzzimeister]

I replaced my TPS in November, 2008, with HD part # 27271-95 for about 45 USD.

 

Thanks Docc, after spending the big bucks on an PF3C, I bought one of these as a backup because despite received wisdom, a crank sensor is not the only EFI component which will leave you stranded. At last with this TPS I can install it, and set it so the engine will run well enough to get me home.

 

I replaced the TPS and the fault is cured. So I have now given some thought to a) how one would have diagnosed it, and ( what one could do without a diagnostic kit

 

Let's analyse the symptoms:

- misfired when cold, diappeared when warm

- did it have a spark? Yes so not the ignition system. Coils, plugs, leads get worse when warm so it couldn't be those

- why did it disappear initally when warm? Lean mixture on starting, no problem when warm

- why was it lean? Because the Power Commander was in the circuit. When the PC was removed it went rich. It could have gone either way depending on whether the TPS failed at low voltage or high voltage

- How could I tell if my TPS was working? With the PC it's easy, just look and see if the fuel lights move when you twist the throttle. If they don't, your TPS is shot

- If I don't have a PC how could I tell? Only way I could think of would be to start the bike, and at idle turn the TPS while keeping the throttle body at idle. Any raising or lowering of revs would be an indication. If you're not stuck at the side of the road use a voltmeter.

- It's running rich - check the TPS first, if OK almost certainly the oil temp sensor

- It's running lean when warm - must be the TPS

 

All the above assumes the bike is serviced. clean filters, plugs, no leaking rubbers etc. One thing I will say for EFI is when the fault is found the fix is absolute, and it stays fixed. On carbs, it's often not quite that simple. Hope it helps.

 

Guzz

[docc]

Guzz,

Glad you're back on the road!

 

When my TPS went bad, I found it by checking the resistance while it was gradually opened and closed. The progression of Ohms should be gradual with no 'jumps' or plateaus.

 

Mine would stick and jump. The replacement improved running notably. And the resistance check is really straight forward and easier than checking millivoltage.

 

I suppose I should be taking a VOM with me on the South'n Spine Raid.

[gstallons]

Don't look at it while you're riding !

[luhbo]

... And the resistance check is really straight forward and easier than checking millivoltage...

 

Don't check the resistance of a given TPS if you are in doubt whether it still works or not. It's a tricky thing. Stay to the signal. This can be done by every average noob. The signal rises from around zero to around 5V continuosly. If you still have one then take the old analog device for this purpose. It makes reading/interpreting the signal a bit easier.

 

Measuring the resistance is possible, of course, but with 400 USD/Euros in the back you should avoid any missreadings.

 

Hubert

[docc]

I may be the Average Noob of which you speak!

 

When struggling with a running condition a couple years ago, I did not see the jump in mV in the TPS signal, yet when checking it with the Ohm meter, it was obvious that the resistance would lag, then leap. Replacing the unit made a big improvement.

I thought it was pretty simple and safe test. Hubert, do you think there is a trouble in it?

 

BTW, Guzzimeister, what happens if you perform the resistance teat on you bad TPS, slowly opening and observing the milliOhms?

[gstallons]

You can simulate heat with a heat gun or hair dryer if it only does this during normaloperating temperature. Figure which terminals you want to hook your DVOM or analog meter to and set on ohm scale. Slowly open the throttle to wide open and back to idle. If you are going to see a glitch it will be in the normal throttle position (angle) at highway speed. This is because this is the position the wiper is in contact with the other portion of the (potentiometer) TPS.

The ohm scale reads from 0-999, then 1000 or 1k, then up to 999k, then 1,000,000 or 1 meg.

HTH

Gene