Possible to Vapor-lock Fuel Tank? Bad Gas Cap? Comments Wanted.

[Ed Clark]

Am trying to diagnose an issue on a 2017 TRIXX in seemingly very good condition with 100 hours on the clock. Stated symptoms are:
Each new outing runs fine for awhile until it doesn't. Problem sequence starts with an unexpected engine "flame-out". Display still powered up. No check engine light or iBR problem or information message. Cantankerous about restarting. May run for a few seconds after each try then die again. Eventually, engine will run without dying but must baby the throttle and can only achieve low engine rpm's. Reported that if let setting for 10-20 minutes will restart and "run fine" for awhile.
I've run the machine "on the muffs" and can, of course, find no issues. I have exercised the iBR and trim systems. All good.
The only thing I can think of that seems to fit the described symptoms is fuel starvation. Something like the fuel tank is vapor locking due to a bad fuel cap, or the fuel pump is petering out after running for awhile. I am well aware that either of these two things would be rare on a fuel injected machine with fuel pump located in the fuel tank. However, it's my working theory right now because it's the only venue that adequately fits the symptoms in my playbook. I should say that the symptoms are, in my experience, exactly like what happens with an outboard if the fuel tank cap is not venting properly.
So, as soon as I have a test driver handy the plan is to run with a loose fuel cap to see if the problem reasserts itself. If it does, then next step, I'm thinking, is to remove the body, tap into the fuel pump-fuel rail line with a tee and install a fuel pump gauge on the handlebars to verify fuel pump pressure when and if the problem reasserts itself.
So, the purpose of this inquiry is to ask if others have encountered similar symptoms on an EFI-equipped machine such as this. If so, what was found? Also, does my plan of attack sound feasible or is there another diagnostic approach that is suggested? I do not have a BUDS diagnostic scanner but even if I did I'm not sure what I would learn from it with this type of symptoms. Perhaps "last minute" would reveal something but I doubt it. Remember, when it quits on the lake the main objective is to baby it to port which wipes out the "last minute" info immediately prior to engine shutdown.
Keep them cards and letters coming, guys. I'm fishing blind here.

 

[Ed Clark]

So, I'm very squeezed for time right now and it's the height of the ski season and my friend is really wanting to get her ski going. I despise replacing a part before positively diagnosing that it is bad. However . . . . Again, my working theory is that fuel starvation is the only root cause that would explain every single one of the symptoms that have been enumerated to me via "witness statements." I found the OEM replacement cost for a fuel pump and gas cap were north of $500 including tax, etc. On a lark, I was able to find a new, OEM gas cap and aftermarket fuel pump for less than $150 on ebay. Well, that's surely less than one diagnostic trip to the shop looking for a phantom problem that won't rear its head "on the muffs." So, I rolled the dice and ordered a new cap and fuel pump with the idea that it was going to be the cheapest and fastest way to eliminate (or not) fuel starvation as the culprit. Sometimes you just gotta do what you gotta do no matter how distasteful it is. Follow-up report will be forthcoming following a sea trial.

 

[Ed Clark]

Closing the loop on this one. As a diagnostic expedient, I installed an aftermarket fuel pump and new OEM gas cap. My friend has now put hours and hours on the machine with no issues. So, my conclusion is that fuel starvation was indeed the root cause and the noted replacements cured it.
My thinking was that there was a 90% probability that the fuel cap was the actual culprit. I decided to destroy it if necessary to see if I could find the malfunction. To my surprise I was able to disassemble it without damaging it. Upon examination I found two things. First, the vent system does not work like the manual says it does. Like all other caps that I've seen, there is a vacuum break valve, but not a high-pressure relief circuit as the manual stated. In my opinion, the vacuum break valve was simply designed, well made and I could find no defect. So, I must conclude that the OEM fuel pump was inexplicably losing muscle from time to time. Rare, I know. I realize there is a way to test fuel pump pressure, etc, etc. But go back to my original statement regarding "time being of the essence." Anyway, all's well that end's well says I.