Chasing a runaway car - BEC, servo, ESC or RX?

[Yorkiebar]

No, not literally!

Been having issues for the last few months where at random times my XB4 will just sod off of it's own accord. It's getting so bad I'm always driving it on tenterhooks expecting it to happen at any time and not really progressing during racing as I'm tending to take it easy.

First - original setup:

Flysky GT3B TX/RX, Savox 1258TG, HW Quicrun 120A ESC, SP V3 7.5 sensored.

The Savox I got with the buggy so it stayed in almost throughout. Quickly realised that the GT3B was a bit parp and I wanted to change to sticks anyway, so I got an Sanwa Gemini II and converted it to 2.4 using the FrSky hack mod and bought a bunch of V8R4-II RXs.

Everything was gravy with the stick setup, until a few races passed and it started running away again. I even thought it may be my Fitbit interfering (Bluetooth and HR monitor) so tried taking that off, to no avail.

Made a glitch buster using a 16V 4500uF electrolytic, same problems

Changed motor to a Trackstar 8.5, and an LRP 7.5 and still have same issues.

Upgraded ESC to a Corally Cerix 160A which has a 5A BEC - still have same issues!

Ruling out some things - Cells are the same used in my truck and 2WD, no issues. TX same for truck and 2WD so rules that out. Same model RX in all 3 vehicles so possibly not issue unless RX in the XB4 is faulty.

Suspected it may be the Savox 1258 so swapped it for a 1256 which I had as a spare - was better but still had 2 runaways!

The failsafe is set correctly on the RX but it takes 2 seconds for it to drop inputs to zero, hence the runaway.

I used the servo tester on my Corally progbox and it shows a current draw of 4.9A in swing test with no load!

So that leaves me with one last thing to swap - the RX. I know many folk use the V8R4-II and have no issues in varying buggies, some with silly wind motors in and the others have no issues at all. I don't like the silly short antenna but one chap I know has removed it completely and has no issues, and some of the flying chaps get 2Km range out of them.

I'm loathed to add an external BEC as it's more hassle and limited to space to do a neat install in the XB4.

The only other spare servos I have are LP ones for my lad's Yoke, but other than ditch Savox altogether I'm running out of ideas - and to a point patience.

Any pointers from anyone who has chased a similar issue?

Cheers.