Front cylinder cutting out below 3,000 rpm. Need suggestions

[Dr. Joe]

I'm having a challenge with my 2010 SG Trike (SE air cleaner, cat-less header, slip-on mufflers, PCV tuner, TTS-100 cam, 60,000 miles on engine). The front cylinder will cut out when twisting the throttle wide open below 3,000 RPM ( like when trying to pass a vehicle) regardless of the gear I am in. However, it runs awesome when touring on flat roads, running at higher speeds, or banging through the gears just for the heck of it.

So here's what I have so far... The bike was doing this every now and then before I had the trike Dyno tuned and I figured it was either bad gas and/or in need of a tune (I was running the SE255 map on the TTS 100 cam until I had the time to get it Dyno tuned). After the tune it ran awesome! The Dyno really woke up the TTS cam!!!! However, the front cylinder was still cutting out from time to time (note: at this time I didn't know it was the front cylinder cutting out yet. We figured that out later)

I took it back to get it re-Dyno tuned and after a few runs without being able to duplicate it, the tech kicked it into 6th gear at a low RPM and rolled on the throttle and that would get the engine to run on just one cylinder every time. He double checked the air/fuel ratios and everything was coming up good so we were stumped as to what it might be. He then checked the fuel pump pressure and it was fine at all speeds, we disconnected the tuner and tried it with the stock ECM map and it did the same thing, he checked for any codes and the only one that showed up was one for an open purge valve (mine is a CA trike and I disconnected the purge system 55,000 miles ago). In a last resort effort he grabbed an old timing light and hooked it up to the front cylinder wire, ran the engine through it's paces, and whenever the engine cut out the timing light would not flash. We hooked it up to the rear wire and did the same test and the timing light flashed all the time, so we came to the conclusion that it was a bad front cylinder wire.

However, before I just go and replace the wires it still seems weird that the front cylinder wire cuts out ONLY when the engine is under a higher load (under 3,000 rpm... EXACTLY) and at 3/4 - full throttle. However, any kind of demands to the engine above 3,000RPM and it runs fine! It idles fine as well. About the only other issue I have with the engine is I think it kicks back too much when starting.

Is the solution really as simple as a bad wire, would a bad coil react this way under load, or could it be an even deeper issue? Any help would be greatly appreciated. Thanks

 

[PosseRider]

I'm having a challenge with my 2010 SG Trike (SE air cleaner, cat-less header, slip-on mufflers, PCV tuner, TTS-100 cam, 60,000 miles on engine). The front cylinder will cut out when twisting the throttle wide open below 3,000 RPM ( like when trying to pass a vehicle) regardless of the gear I am in. However, it runs awesome when touring on flat roads, running at higher speeds, or banging through the gears just for the heck of it.

So here's what I have so far... The bike was doing this every now and then before I had the trike Dyno tuned and I figured it was either bad gas and/or in need of a tune (I was running the SE255 map on the TTS 100 cam until I had the time to get it Dyno tuned). After the tune it ran awesome! The Dyno really woke up the TTS cam!!!! However, the front cylinder was still cutting out from time to time (note: at this time I didn't know it was the front cylinder cutting out yet. We figured that out later)

I took it back to get it re-Dyno tuned and after a few runs without being able to duplicate it, the tech kicked it into 6th gear at a low RPM and rolled on the throttle and that would get the engine to run on just one cylinder every time. He double checked the air/fuel ratios and everything was coming up good so we were stumped as to what it might be. He then checked the fuel pump pressure and it was fine at all speeds, we disconnected the tuner and tried it with the stock ECM map and it did the same thing, he checked for any codes and the only one that showed up was one for an open purge valve (mine is a CA trike and I disconnected the purge system 55,000 miles ago). In a last resort effort he grabbed an old timing light and hooked it up to the front cylinder wire, ran the engine through it's paces, and whenever the engine cut out the timing light would not flash. We hooked it up to the rear wire and did the same test and the timing light flashed all the time, so we came to the conclusion that it was a bad front cylinder wire.

However, before I just go and replace the wires it still seems weird that the front cylinder wire cuts out ONLY when the engine is under a higher load (under 3,000 rpm... EXACTLY) and at 3/4 - full throttle. However, any kind of demands to the engine above 3,000RPM and it runs fine! It idles fine as well. About the only other issue I have with the engine is I think it kicks back too much when starting.

Is the solution really as simple as a bad wire, would a bad coil react this way under load, or could it be an even deeper issue? Any help would be greatly appreciated. Thanks

Not sure if this helps, our car was doing exact thing.. Only under power, no prob on slow acceleration.... Weak coil was the culprit.

 

[rhino 2]

I'm having a challenge with my 2010 SG Trike (SE air cleaner, cat-less header, slip-on mufflers, PCV tuner, TTS-100 cam, 60,000 miles on engine). The front cylinder will cut out when twisting the throttle wide open below 3,000 RPM ( like when trying to pass a vehicle) regardless of the gear I am in. However, it runs awesome when touring on flat roads, running at higher speeds, or banging through the gears just for the heck of it.

So here's what I have so far... The bike was doing this every now and then before I had the trike Dyno tuned and I figured it was either bad gas and/or in need of a tune (I was running the SE255 map on the TTS 100 cam until I had the time to get it Dyno tuned). After the tune it ran awesome! The Dyno really woke up the TTS cam!!!! However, the front cylinder was still cutting out from time to time (note: at this time I didn't know it was the front cylinder cutting out yet. We figured that out later)

I took it back to get it re-Dyno tuned and after a few runs without being able to duplicate it, the tech kicked it into 6th gear at a low RPM and rolled on the throttle and that would get the engine to run on just one cylinder every time. He double checked the air/fuel ratios and everything was coming up good so we were stumped as to what it might be. He then checked the fuel pump pressure and it was fine at all speeds, we disconnected the tuner and tried it with the stock ECM map and it did the same thing, he checked for any codes and the only one that showed up was one for an open purge valve (mine is a CA trike and I disconnected the purge system 55,000 miles ago). In a last resort effort he grabbed an old timing light and hooked it up to the front cylinder wire, ran the engine through it's paces, and whenever the engine cut out the timing light would not flash. We hooked it up to the rear wire and did the same test and the timing light flashed all the time, so we came to the conclusion that it was a bad front cylinder wire.

However, before I just go and replace the wires it still seems weird that the front cylinder wire cuts out ONLY when the engine is under a higher load (under 3,000 rpm... EXACTLY) and at 3/4 - full throttle. However, any kind of demands to the engine above 3,000RPM and it runs fine! It idles fine as well. About the only other issue I have with the engine is I think it kicks back too much when starting.

Is the solution really as simple as a bad wire, would a bad coil react this way under load, or could it be an even deeper issue? Any help would be greatly appreciated. Thanks

Occams Razor........Change the wire...

 

[30glock]

Occams Razor........Change the wire...

Exactly where I would start.

 

[Dr. Joe]

Not sure if this helps, our car was doing exact thing.. Only under power, no prob on slow acceleration.... Weak coil was the culprit.

Thanks. I was going to change the coil as well anyways under the old: "As long as I'm..... might as well...." garage mechanic approach. And once I've had a bit more time to mull it over, it makes more sense to be a defective coil than just a wire because a weak wire would cut out all the time.

Thanks again

 

[Kaz]

Finally something I feel I can help with! New to Harleys, but from my old wrenching days in the '70s, we learned that the higher the loading, the more energy that is required to jump the gap on the plug. The highest loading comes in at lower RPMs and WOT. Whats happening is one of two things: Either the insulation on the spark plug wire is breaking down and leaking at the higher energy levels, or the coil is breaking down and cannot deliver the higher energy levels. So yes, I would replace both; but that is the reasoning behind the symptom you are seeing of it only happening below 3K and heavy throttle.

 

[Dr. Joe]

Finally something I feel I can help with! New to Harleys, but from my old wrenching days in the '70s, we learned that the higher the loading, the more energy that is required to jump the gap on the plug. The highest loading comes in at lower RPMs and WOT. Whats happening is one of two things: Either the insulation on the spark plug wire is breaking down and leaking at the higher energy levels, or the coil is breaking down and cannot deliver the higher energy levels. So yes, I would replace both; but that is the reasoning behind the symptom you are seeing of it only happening below 3K and heavy throttle.

Thanks a whole bunch! Great info!... which brings up a question... assuming the plugs and wires are ok... then if only the front cylinder cuts out then do I have a single fire coil? Otherwise, if it's a dual fire then wouldn't both cylinders be cutting out? Or would what's happening be indicative of the earlier stages of a failing coil?

.... ya can't ever know enough about ignition systems and what makes them tick... and un-tick :scooter:

Thanks

 

[Dr. Joe]

Well I decided to start at the plugs and work my way back to the coil so that I could determine the culprit. When I took out the front plug I noticed that the end of the plug that screws onto the post was loose and showed a bit of corrosion on the threads. So I cleaned the threads real well and reinstalled it and took the bike for a ride. It responded much better but the hotter the bike got the more I could get it to miss. It never got as bad as before but it still missed.

Next I installed a set of Champions I had laying around that I had taken out with only a few thousand miles on them so that I could try out this brand, and TA-DA!!!!! absolutely no missing at any rpm or load! :clapping: Don't ya just love it when it turns out to be an easy fix? And thanks again to KAX's explanation so that it made sense as to how the plug would only fail under load. Now if it ever happens to someone else I will be able to help out and maybe save someone a whole bunch of time.

So I'll still get new plugs, wires and coil due to the miles on the bike but any suggestions as to an upgrade or just stick with OEM stuff?

 

[Gorilla]

I would suggest OEM because the coil is designed for the resistance in the stock wires.

 

[Dr. Joe]

I would suggest OEM because the coil is designed for the resistance in the stock wires.

I also got a suggestion from a mechanic to go with silicone wires for the added durability as the wires on a Harley are subject to a lot of heat and movement. Not only do they touch the top of the engine in a few places but with the extreme heat they are subjected to, compared to an automobile, makes them prime candidates for an early demise.

Makes sense and the silicone wires aren't much more than OEM.

Whatcha think?

 

[PosseRider]

I also got a suggestion from a mechanic to go with silicone wires for the added durability as the wires on a Harley are subject to a lot of heat and movement. Not only do they touch the top of the engine in a few places but with the extreme heat they are subjected to, compared to an automobile, makes them prime candidates for an early demise.

Makes sense and the silicone wires aren't much more than OEM.

Whatcha think?

I never had a problem with HD wires. Ran over 100,000 miles on my 03 Ultra & never skipped a beat. Lots of those miles was in 100* desert heat. HD has always been air cooled till lately, I would stick with their wires. Not sure if the silicone wires would change resistance, but, what do I know. I ride a HD.

 

[Texan]

I was having somewhat the same problem on my Dyna....changed to a Accel dual fire coil and problem cured.

8~\o

 

[Dr. Joe]

With all the information (opinions) out there about what the best way to go (OEM or upgrade), the best products to use, resistance factors, etc, etc... I became more confused than ever so I called my buddy, Rick, who used to work for Chrysler as an electrical engineer and worked for 15 years in the R&D department of their ignition systems department. His job was to work directly with the manufacturers of coils, wires, and plugs - like Bosch, NGK, Champion, etc. to resolve any issues they had with their products and to develop reliable systems. Following in my "Cliff-Note" version of our discussion.

Firstly, many talk about wire resistance as being something akin to exhaust back-pressure, like it's needed in order to provide the best performance, and it just ain't so. Truth is, wire and plug resistance have nothing to do with whether or not the ignition system will function properly. Resistance for the wires and plugs was implemented as a way to reduce/eliminate radio frequency interference. Back in the old days, the ignition system would cause radio static and tv interference (which I remember so well when, back in the 50's, my brother would pull in with his hot rod and the tv picture would go berserk) so they developed wires and plug with resistance to solve this problem. Even today, if one were to go with a wire with no resistance or shielding, this could interfere with any number of electronic components and because we all now pilot a computer on three wheels, that something to consider when making any kind of electronic change.

However, according to Rick, all plugs manufactured today come with a built in resistor and most plug wires (I say most because you can buy plug wires for racing applications with little or no resistance/shielding) are made with RFI shielding. For example, I went to the Sumax site, who sell the silicone wires that I purchased, and this is what they say about their Street Thunder wires... "8mm Black Silicone and Synthetic Jacketing resist heat, oil, and abrasion. 500 ohm per foot resistance delivering greater spark energy, while improving power, idle, and fuel efficiency. A combination Kevlar Helically Spiral Wound Core conductor for greater strength and durability that suppresses Electro Magnetic (EMI) and Radio Frequency Interference (RFI)."

Electricity will take the path of least resistance. So the less resistance there is along the path, the better the spark at the other end. So in this case, if one were looking to get more output to their plugs, instead of installing a higher output coil, just change the wires and plugs to achieve the same (or great) affect, at a much reduced cost.

For example. I purchased the Sumax wires mentioned above from J&P Cycles for $20. They have an ohm resistance of 42ohms per inch vs OEM wires at 255ohms per inch. For a front wire at 32 inches long that means a resistance difference of 8160 ohms vs 1344 ohms. For the plugs, my old Champions have a resistance of 31.7 (with ohm meter set at 200k) and my new NGK iridium plugs ($20) read at 4.7. So for $40 I completely took away massive amounts of electrical resistance.

So my next question to Rick was "So what happens to all that extra ZAP! Does it affect anything negatively?" Again, my Cliff Note version of his response is to just pay a bit more attention to your plugs. They may burn our earlier than normal, say at 20,000 miles instead of 50,000 miles. So if you find your engine don't have as much "get-up-and-go" as it used to then check your plugs and/or change them. If you find that the tips are burning out too fast, get some new ones and play with the gap. A slightly wider gap will create more resistance = less burn.

Oh, and by the way, during this whole process I had to learn how to use my multi meter to measure ohms and so I checked my old plugs and wires and sure enough the plug was reading "0" and the front wire had no definite reading as it was jumping all over the place which means my front wire was on it's way out as well! I learned a bunch and am happy to pass this info along.

So I will be installing my new plugs and wires with the peace of mind knowing that I ain't gonna be doing anything that will screw up anything (contrary to what many bloggers say on some of the other HD sites), that my stock coil is more than adequate to do the job it was made to do (just needed to remove the "dam"), and that all my electronic equipment is safe from interference. The only "negative" I can come up with at the moment is that I MAY have to replace my plugs earlier than what is stated on the box... and I don't mind pulling a plug after every oil change to inspect it.

See ya on the road!..... Joe