black smoke at 5000+ rpm

[ralliart-type-s]

:inquisiti Dunno if anyone can help but this problem is worrying me a bit. 1st I'll tell you the mods, then you may have a better idea.
I have fitted a forge twin spring BOV which was originally on a saph cosworth, got it free so had to say yes! Seems to hold boost fine but no gauge so cant really tell. Also a Blitz sus stainless filter and a stainless b/box. I havent fitted any fcd or boost control etc. the guy i bought the car from told me the boost had been increased but he also said the brakes and exhaust were brand new!! Which they clearly arent./pan He also told me he fitted denso iridium plugs, but I doubt it.:speechles

The problem occurs at over 5000 rpm and leaves a big trail ( not puff ) of black soot,:pimp2: if I back off back down to 4000 rpm it all goes quiet again. Now I know turbo 2 comes in at 4k. Is it fuel, which i hope it is. Or......is it turbo time??
Any light shed would be greatly appreciated. Thanx for reading.:inquisiti

[Kenneth]

:inquisiti Dunno if anyone can help but this problem is worrying me a bit. 1st I'll tell you the mods, then you may have a better idea.
I have fitted a forge twin spring BOV which was originally on a saph cosworth, got it free so had to say yes! Seems to hold boost fine but no gauge so cant really tell. Also a Blitz sus stainless filter and a stainless b/box. I havent fitted any fcd or boost control etc. the guy i bought the car from told me the boost had been increased but he also said the brakes and exhaust were brand new!! Which they clearly arent./pan He also told me he fitted denso iridium plugs, but I doubt it.:speechles

The problem occurs at over 5000 rpm and leaves a big trail ( not puff ) of black soot,:pimp2: if I back off back down to 4000 rpm it all goes quiet again. Now I know turbo 2 comes in at 4k. Is it fuel, which i hope it is. Or......is it turbo time??
Any light shed would be greatly appreciated. Thanx for reading.:inquisiti

Our turbos both work at the same time, one attached to each cylinder bank. This means that both turbos should be working at the same time, producing pressure from around 2500RPM.

Black smoke is usually a sign of too much fuel being burnt. How well does the car run? If it misfires, check the plugs.
If there is no misfire, I would try get hold of a standard air box and filter and try that.

After that, put in the standard compressor bypass valve (BOV) and see if that makes a difference. If the BOV is leaking air to the atmosphere, then you will over fuel.

[Kenneth]

Is it fuel, which i hope it is. Or......is it turbo time??

Oil usually gives off a blue smoke, so your turbos may be ok.

[calum]

Sounds like the boost may have been upped and the ECU is saying 'too much boost' and just maxing out the injectors to be on the safe side.

Take it it only does this on full throttle/ high load situations? That is, you don't get black smoke above 4k on part throttle?

Get a boost gauge and you'll be able to tell what's going on.

Cheers,

Calum

[White Lightning]

Agree that a boost gauge is a good idea to see what boost you are actually running.

Is the BOV a dump to atmosphere type ? If so, I would try replacing it with a standard one as, as others have said, it will be causing the engine to run too rich.

[ralliart-type-s]

:thinking: Thanx 4 that guys, it does seem to be since I fitted the bov. I also tried an HKS item from my pals s14a, but being a single piston job it just wasnt up to the task, I'll whip the forge one off and try the std one back on. I cd always leave the bung in the return pipe and still scare small children! I didnt know the turbos worked at the same time, skylines etc work simultaneously so I figured ours did too.:thinking:

[ralliart-type-s]

yeah calum, no smoke on light load, just at full bore.

[Kenneth]

Sounds like the boost may have been upped and the ECU is saying 'too much boost' and just maxing out the injectors to be on the safe side.

Take it it only does this on full throttle/ high load situations? That is, you don't get black smoke above 4k on part throttle?

Get a boost gauge and you'll be able to tell what's going on.

Cheers,

Calum

The VR-4 ECU does not do this... It looks at the air flow, and if it is within limits it gives the correct (it thinks) amount of fuel. If the air flow is outside limits, it just cuts the fuel totally.

If of course you have an air leak, then the ECU thinks more air is getting into the engine than what really is, and you over fuel.

[ralliart-type-s]

So my bov is opening slighly under full boost then?? Im sure stronger springs are available. When i got the bov i took it apart and cleaned and greased the shaft and stretched the spring a tiny bit just to try and compensate for the higher boost. Obviously not done the trick tho. So what valves duz the leggie prefer then?? Cos dey all too expensive for me. £200 etc.

[Kenneth]

So my bov is opening slighly under full boost then?? Im sure stronger springs are available. When i got the bov i took it apart and cleaned and greased the shaft and stretched the spring a tiny bit just to try and compensate for the higher boost. Obviously not done the trick tho. So what valves duz the leggie prefer then?? Cos dey all too expensive for me. £200 etc.

do you have the standard one still? Put that in for now. Because it is recirculating, even if it leaks you wont have fuel problems.
Best make sure its the BOV before you start spending money.

[ralliart-type-s]

Cheers kenneth, will do m8.

[ralliart-type-s]

:3d: As everyone suspected, it was the BOV. Took it off and used a screwdriver and a set of scales to measure spring strength against std one, it was slightly weaker.Dismantled forge one again, stretched BOTH springs and tested again. I snow slightly stronger than std. Back on car now and working gr8./toycar

:scholar: Thanx everyone for the help/advice, you are most kind.:iloveyou:

[Kenneth]

:3d: As everyone suspected, it was the BOV. Took it off and used a screwdriver and a set of scales to measure spring strength against std one, it was slightly weaker.Dismantled forge one again, stretched BOTH springs and tested again. I snow slightly stronger than std. Back on car now and working gr8./toycar

:scholar: Thanx everyone for the help/advice, you are most kind.:iloveyou:

Not a problem, glad you got it sorted.

I would go get some stronger springs though, those will settle over time and go back to what they were. You may be able to get replacement springs from your hardware store.

[ralliart-type-s]

I've seen replacement forge ones on flea-bay for around £10 PLUS P+P, Reckon i shd invest.

[White Lightning]

Glad you fixed it :thumbsup:

... at least temporarily ...