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Been having running issues with my '04 RT since last summer's spline lube P.M. (See previous fuel pressure post)


After getting good advice from Dirt Rider, I disconnected both fuel injectors, and while spraying into a couple of glass graduated cylinders (thanks honey for standing out in the cold garage with me) I find that I have exactly 23cc's of dispensed fuel from each injector per 15 seconds of cranking the engine over.


Just wondering if that is in the range (flow rate)?


Current problem with the bike is a stalling issue at idle when fully warmed up.





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I don't have any idea about the volume, but I do know that the pressure needs to be at the specified level for the injectors to function properly.


Your post implies that it runs OK when cold. Is this the case?

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Danny caddyshack Noonan

Can't answer that directly but, if they're the same, a bad injector is ruled out.

1/10th of a cup in 15 seconds seems like a lot though.

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1/10th of a cup in 15 seconds seems like a lot though.


'A lot' is not a problem for RPG, his problem is with it stopping, not going.

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Evening RPG


Well if you can tell us how much air it took in during that same 15 second time frame we could give you some idea if the fuel flow is anywhere near close. Then if we knew the engine temperature, ambient air temperature, and cranking speed we could get it even closer.


Nice even injector output side to side is a VERY GOOD thing, 23cc per side in 15 seconds seems like plenty for starting and initial operation.


You need to see how much is flowing out of those injectors on each side just as it stalls but keep in mind that things like fuel pressure, 02 sensor, and TPS feedback to the fueling computer can effect the injected amount so you won’t really know if the injectors are the issue or if they are just reacting to a fueling computer command based on sensor input.


About all you can do at home is see if the injector flow on each side is even, a nice spray pattern, and enough to keep the engine running.


Seeing as you have GS-911 you can probably look at the 02 sensor cross counts at hot curb idle. If the spray at the injectors is not enough you will see no cross counts and a very lean 02 output (assuming the 02 is working correctly). If the 02 output is crossing center in a nice even wave form at hot curb idle obviously the injectors are providing enough fuel to toggle rich on a lean 02 input and get the 02 output back over center.


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Morning Rick




After thinking on your injector question a little more over a cup of coffee (actually 2 or 3 cups) this morning, lets look at this from a little different perspective.


-Your bike starts good cold therefore the injection process is working just peachy on cold start.


-Your bike idles good cold so again the injection process including the injector(s) is working as designed (cold)


-Your bike will sustain 90 mph for a couple of hours running so again that part of the injection process is working quite well.


-You haven’t mentioned any other ridability problems other than the warm engine occasional stall so if it runs OK other than stalling your injection process is more than likely working OK.


The above all points to the injectors performing as designed and up to par.


So what does the above tell us? It tells us the injectors are working OK at all operational modes except right at warm engine stall. What we don’t know is if the warm engine stall is even related to the injectors. Seeing as the injectors seem to be supplying enough fuel at all other RPM/load ranges there is no reason to believe they are not supplying enough fuel at hot curb idle.


What does this leave us with? The probability of the injectors not supplying “enough” fuel at engine stall is pretty darn low.


This doesn’t completely clear the injector(s) though. There is always the very slight possibility that an injector has a lazy or sticking pintle (hot engine) and is dripping a little extra fuel at low curb idle. This might not show up at other operational RPM/loads as a little rich in those areas wouldn’t even be noticed.

Your cold cranking test might not show that as the injector on time is pretty pronounced at cold engine cranking and injector bodies are cold.


As I mentioned above you should be able to see an over or under fueling problem at idle by watching the 02 sensor wave form. But this is also assuming that the problem (like sticking injector pintle) isn’t instantaneous and stalls the engine before the 02 has a chance to respond.


My educated guess based on years of working on fuel injection systems is your stalling problem “isn’t” a problematic injector.


If I remember correctly your stalling problems showed up after you had the bike apart- correct?

So we go back the old saying of --(what was the last thing done to the bike before the problem started). The bike was apart including ground and power wires connections, probably the Motronic connector, lots of connectors, grounds, apart, etc.


Top of (my) list for warm engine random stalling is 02 sensor, TPS, engine temp, HES inputs. Next would be fueling issues like plugged or blocked off fuel return (causes high fuel pressure).

Maybe even something causing the secondary spark plugs to quit working like loose primary wires at coil or partially inserted spark plug wires, etc. The secondary plugs are not really needed for decent down the road engine runability or even cold engine starting but without them operational you get a mighty low hot curb idle.


I guess if I were working on your stalling issue I would start with a quick verification of the secondary plugs getting/maintaining enough KV to operate just at hot engine stall. Either manually verify ALL is connected properly and has proper connection integrity or maybe use an induction timing light on one then the other secondary spark plug wire to see if the secondary’s have spark completely through the engine stall.


Probably run with the 02 disconnected for a while to take the 02 out of the equation. I know you installed a new 02 sensor without effecting the hot engine stalling but something like the 02 heater circuit not working could still be causing 02 operational issues at idle. If a disconnected 02 stops the stalling then verify the 02 heater circuit is functional, verify the 02 low (ground) is without resistance all the back to the Motronic.


Next we have the chassis grounds like bottom of L/H TB unit and other chassis grounding connections. Check them all for being tight and resistance free. Make sure you didn’t twist one when tightening therefore pulling a wire from a terminal.


Verify the TPS is ALWAYS returning to under .399 volts dc (choke off) at hot curb idle. Maybe do another TPS re-learn making sure the choke is (off) during the re-learn procedure.


Go back over the connectors including the Motronic connector and ground to make sure a terminal pin didn’t get partially displaced as the connector was pushed together. Especially verify 02 circuits, TPS circuits, engine temp circuits, HES circuits. Look at them all but the mentioned are the main players.


If you have the means rig up a fuel pressure tester to verify high/or/low fuel pressure just prior to and through the engine stall.


If you have access to a thermal temp gun take it with you and after every ride allow the engine to idle for a while (or if possible through engine stall). Look at exhaust pipe temps just as it leaves the cyl heads. Maybe you can catch one side cooling down more than the other just prior to engine stall.


Probably more but I am out of breath and need another cup of coffee.










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Peter Parts

Long ago and far away, Airheads used to have a really mysterious breakdown at high speeds. The spark was "amplified" by a little device the sits under the tank towards the front. If it got hot, it would self-limit (typically at high speeds on the highway) and then after a half a minute of poor firing, return to normal.


Seems the heat-transfer paste under the amp (really just a switch, eh, Dirtrider) dried out and the unit would get hot for a while, then cool.


No idea if this has any relevance to your problem but might be some inspiration.



glorious riding weather in Toronto, at last. 42F degrees and sunny

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RPG, Just an FYI as it sounds like your injectors are ok.

I have the same bike. 3 yrs ago I measured injector flow rates. I

got significantly different results.


---Each side flowed 1.5cc after 30 sec of cranking with the throttle closed.

---Each side flowed 2.2cc after 30 sec of cranking time with the throttle 1/3 open

---Each side flowed 4.3cc after 30 sec of cranking time with the throttle 2/3 open.

---Each side flowed 4.2cc after 30 sec of cranking time with the throttle wide open.



Based on your flow vs. mine you have a 10x increase.

I don't know if this helps you or not. My problem turned out not to be fuel related. It was a bad stickcoil.

Regards, Ron






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That is going to be difficult to figure a direct comparison between the tests.


A lot depends on both of your altitudes, engine temperatures, ambient air temps, as well a engine cranking RPM, battery voltage, etc


My tuning chart shows almost 14% difference in fuel delivery trim from just 0°c to 32°c, another 3% or so based on intake air temp with a couple of percent reduction based on moderate altitude change.


Now if you were both close to the same altitude and about the same ambient temp as well as close on engine temps and cranking about the same RPM at about the same battery voltage then the data is usable for comparison.




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All of which is why injectors are tested on specially designed flow benches where there is control over such factors as voltage, duty cycle, frequency, inlet pressure, etc. Just pissing in a bucket for 30 sec isn't going to tell you much.

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Pissing in a bucket, as you call it, for 30 sec did tell me one thing. Both sides pissed the same amount. Surely that is important.



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... Just pissing in a bucket for 30 sec isn't going to tell you much.


Well it does, it proves you can do it;-)

And that is better than nothing coming out, so it does prove something.

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Peter Parts

BMW specs their injectors plus-or-minus 10% or something like that. Would you tune your TBs plus-or-minus 10%?


Pretty crude for a boxer twin, I'd say. When a diesel shop tests 'em, their numbers give the impression of accuracy with a percent or two. That may be a bit of illusory number magic (where the actual measurements are far looser but the output report is written to six digits).


You can buy matched-pair from RC.



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No Ben I wouldn't, however if I were having running problems & I was trying to do some simple diagnosis, then seeing a nice cone shaped jet of fuel AND a maintained ability to do that, that would rule a good few things out. It's a bit like checking spark plugs, if you hold them close to the engine you see a spark and fairly healthy is a diagnostics tool, but unless you can really test them under compressive & thermal loads you never know for sure, but every little helps.


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Peter Parts

Andy - no intention on my part to disagree with you here (or ever). Just adding factoids to the discussion.



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