Buzzing Main Relay & Engine Does Not Start Once I Hit Vtec

[prelude_h22]

Hi All

Got an issue with the lude and it seems to be a starting issue which occurs after I hit vtec.

I got some gearbox work done by PAW last week however I am not implying in anyway that the gearbox work is related although the issue occurred after the work was done.

Anyways, it occurred yesterday after using the car for the second time in the evening.

I accelerated down the slip road and hit vtec – once that occurred the dials started to dance/bounce all over the place and engine light flickered for a split second. I cruised on the m25 and then came off due to the motorway being closed for works etc. Once we came off I hit vtec again leaving the roundabout and then the dials started to bounce abnormally again and all the lights flickered. The engine died and switched off.

I managed to pull to the side of the A41 and tried to restart the car but it refused to start. I then noticed that when pre ignition was selected the main relay made a buzzing squeal. The noise was definitely coming from the main relay. We waited for the RAC (2.5 hours) who also confirmed the noise was coming from the main relay. We then tried to start the car and it started ok, we turned it off and then it refused to start with the relay making the same noise. We left it for a few minutes and tried to start it which it did; I drove the car slowly home where we arrived safely.

I had a look at main relay this morning and after reading a few threads, I thought it could be the solder joints. I re worked the PCB of the main relay but the problem still persists.
This morning the car started fine when cold, took it for a drive and when I hit vtec the engine light and other lights flickered and the dials started bouncing then the engine died. I managed to restart the car and nursed it back home being just down the road.

I have taken a video of the relay noise when I turn the key to pre ignition repeatedly. The car refuses to start whenever you hear this noise on pre ignition.


[youtube]MXxNa6qhql8[/youtube]

My assumptions is the main relay needs replacing but I was wondering if you guys had any ideas or experienced this issue before?
Could it be ignition switch? Or dizzy? Perhaps ECU? The issue only occurs when the car has warmed up and I hit vtec.

What is the job of this main relay? Would it have an effect on the engine when it hits vtec?


Observations
- Starts ok from cold – if I don’t hit vtec the car drives perfectly
- When warmed up and I hit vtec all engine lights come on/dials flicker& bounce and engine dies
- When a restart is attempted the main relay buzzes as per video (engine does not start) – although sometimes or left for a while it can fire into life
- If started the car drives ok providing I don’t hit vtec

Attempted
- Re-worked/soldered main relay PCB
- Checked distributor cap and rotor arm – All seems ok.
- Ignition leads intact and ok
- All electrics are ok

Any help or ideas would be really appreciated – sorry for the long description

Thanks all 

[mercutio]

Main relay supplys power to the fuel and ignition circuits have you checked your earths it sounds electrical rather than anything else

[prelude_h22]

Hi mercutio

Yeah all earths seems be ok. gearbox earth is connected and all fuse box earths are intact.

Ahh - if the main relay provides power to the ignition/fuel would the relay fail if vtec is hit? additional current surge etc.
Thus causing the relay buzzing upon start up?

[mercutio]

vtec solenoid requires very little in the way of power as its oil pressure activated so i think it has nothing to do with that. I would suggest having a look at the ignition block/switch and work back from there

[prelude_h22]

Hi Guys

Its now sorted. Turned out to be a loose ground connection underneath the thermostat


It looked connected but the nut was loose and could be turned by hand.

Terminal cleaned and tighten


Thanks to mercutio and to Rich at PAW for helping diagnose the fault via email