Popping and misfiring

[Admin Jaap]

This topic has been about since the start of the forum, but now I'm experiencing it myself.

All the info is spread, maybe it's a good idea to have all possible culprits named here

 

With a hot engine the bike pops and misfires between 3000 and 4000 rpm:

 

I have checked the following w/o result:

 

- Throttle body rubbers for cracks

- Cleaned all injection related contacts with a good contact cleaning spray.

- Valves are set correctly

 

What could cause this? And more important, what could make this go away?

[fotoguzzi]

a Mistral x-over fixed my stumble around that rev range.

[luhbo]

The TPS is of cheap quality. Mine quit at around 50.000km, with the above mentioned effects. Get a new one from HD/Buell for about 40 Euros and try it out. If it's not the reason you could easily resell it here. To me for instance as I have another 70.000 on mine in the meantime.

 

Hubert

[gstallons]

This topic has been about since the start of the forum, but now I'm experiencing it myself.

All the info is spread, maybe it's a good idea to have all possible culprits named here

 

With a hot engine the bike pops and misfires between 3000 and 4000 rpm:

 

I have checked the following w/o result:

 

- Throttle body rubbers for cracks

- Cleaned all injection related contacts with a good contact cleaning spray.

- Valves are set correctly

 

What could cause this? And more important, what could make this go away?

 

Are you good using a DVOM ? Connect it to 2 terminals (of the TPS) and roll the throttle VERY slowly to watch a change in resistance. If nothing happens move one lead to the other terminal. Try this again. SLOWLY open the throttle and I mean slowly. This signal should be a linear increase or decrease in resistance. If you see a drop or open in the reading the tps is bad.

p.s. the ignition can or should be off. You can put the meter on a suitable scale to see a glitch on the screen.

[belfastguzzi]

Popping and mis-firing on over-run only, or in what conditions?

 

With the rev range that you give, I don't think this is what you're talking about, but as you mention throttle bodies: another common cause of popping is air getting into the exhaust side, through gaps or cracks in exhaust joints or pipes. At least that's easily fixed.

[gstallons]

This topic has been about since the start of the forum, but now I'm experiencing it myself.

All the info is spread, maybe it's a good idea to have all possible culprits named here

 

With a hot engine the bike pops and misfires between 3000 and 4000 rpm:

 

I have checked the following w/o result:

 

- Throttle body rubbers for cracks

- Cleaned all injection related contacts with a good contact cleaning spray.

- Valves are set correctly

 

What could cause this? And more important, what could make this go away?

 

 

How are you using a DVOM? If you have one and consider yourself good at it: connect it to two terminals of the tps sensor. Rol the throttle to see a change in resistance. If there is none, move one of the leads to the other terminal and try again. It should change resistance as the throttle is rotated.Now move the meter to a high scale, SLOWLY roll the throttle to watch a linear change in resistance. If you observe a glitch such as a drop or goes to infinity you have found your problem. the glitch will be at the same throttle position as the stumble.

p.s. you can do this with the key off as to not cause any damage.

[savagehenry]

I second the motion of our esteemed ambassador of Guzzidom from the Emerald Isle. With mine, it'a sure sign that my front exhaust cross over is leaking. Started popping here and there when hot just three days ago, and Yep! Damned thing is loose on the left side.

In terms of full disclosure, I do really need to do the full tune up procedeure, as mine has not caused me to feel the need for over 4 years now!

[Admin Jaap]

The popping/misfiring happens when I close throttle when braking and when riding at constant speed. I know I can ride higher revs but in the city that's not really comfortable.

Exhaust is leak free.

What I haven't checked yet: throttle body sync.

I have a DVOM (had to look that up: digital volt/ohm meter) and will check the TPS.

 

Thanks so far. I will let you know how I get on.

[gstallons]

I assume all this noise is coming from the exhaust since this is during decelleration? You probably have a lean condition causing this. I would check tps adjustment and throttle bodies for a good seal around the rubber mounts.

HTH......

[luhbo]

Should you really try to check the readings of your TPS (after having sorted all possible mechanical issues) you should:

 

- not use a digital unit. It's useless. You cannot interpret running digits, but you could at least hope to interpret a waving hand/pointer

- not measure resistance. The signal is voltage, and sticking to the correct signal eliminates other possible faults in your work

- not give too much on the results you achieve by "slowly turning the wrist". A worn TPS can give readings being only a few degrees behind the correct values, causing lean conditions. You can indentify a "dead" TPS this way, no problem, but normaly such fatal faults are well beyond "compromising the driveability".

 

Hubert

[Tom M]

Have you verified the TPS reading at idle yet Jaap? I look for 530 mV at 1100rpm (or 3.6 degrees if you can connect to the ECU). A significantly lower reading will cause a lean mixture leading to misfires & popping.

[vuzzi]

Here is another small check:

 

Since there was some oil leaking at the rpm and tdc sensor connection, I took it of and placed a new oil ring.

 

But before that I measured the air gap, which should be 0.7 - 0.9 mm according to the manual. But I already measured 0.4 mm without the gaskets, and there was 2 mm of gaskets installed. I know guzzi sometimes like to oversize things, but this seemed not right. So I took some gaskets off and reinstalled all, set to +/- 1 mm, still too much, but had no other gaskets (this was one of the easiest fixex of all).

 

The bike has hardly any misfires now. But I'm not sure if it's because of this fix, cause I also set the air bleed to 1 whole turn and did the whole tps thing and balancing.

 

And summer with temps of 30 deg C still has to come.

 

 

Anyways, it's a small check, so won't do any harm

[guzzimeister]

Here is another small check:

 

Since there was some oil leaking at the rpm and tdc sensor connection, I took it of and placed a new oil ring.

 

But before that I measured the air gap, which should be 0.7 - 0.9 mm according to the manual. But I already measured 0.4 mm without the gaskets, and there was 2 mm of gaskets installed. I know guzzi sometimes like to oversize things, but this seemed not right. So I took some gaskets off and reinstalled all, set to +/- 1 mm, still too much, but had no other gaskets (this was one of the easiest fixex of all).

 

The bike has hardly any misfires now. But I'm not sure if it's because of this fix, cause I also set the air bleed to 1 whole turn and did the whole tps thing and balancing.

 

And summer with temps of 30 deg C still has to come.

 

 

Anyways, it's a small check, so won't do any harm

 

Hi

 

as a last resort take throttle bodies off and check spindle seals. On some bikes these leak with age and give rise to these symptoms due to the weak mixture. Doesn't necessarily cause erratic idling either. I know 3 bikes with this problem. Hope it helps

 

Guzz

[gstallons]

Should you really try to check the readings of your TPS (after having sorted all possible mechanical issues) you should:

 

- not use a digital unit. It's useless. You cannot interpret running digits, but you could at least hope to interpret a waving hand/pointer

- not measure resistance. The signal is voltage, and sticking to the correct signal eliminates other possible faults in your work

- not give too much on the results you achieve by "slowly turning the wrist". A worn TPS can give readings being only a few degrees behind the correct values, causing lean conditions. You can indentify a "dead" TPS this way, no problem, but normaly such fatal faults are well beyond "compromising the driveability".

 

Hubert

 

 

I own a Fluke 88 DVOM and a Simpson 260 analog multi-meter. I use the DVOM to test the tps (potentiometer) on everything. I do not think I could catch a glitch with the analog meter. Slowly rotating the throttle barrel sweeps the tps sensor and asing the DVOM will show the resistance of the sensor from idle to full throttle. Most sensors fail in the position(s) or throttle angle they are usually in during riding.

[emry]

My vote is with guzzimeister for now. At 10k miles my shafts were worn enough that it would act up 3k~5k (missing) and I could change idle quality just by moving the shaft fore and aft.

 

Although every suggestion seems valid also.