Running lean under boost

**Finn** · 13-11-12, 08:34

Went for a drive last friday with a pal and wanted to show how cool the car was. Car decided to have a bad day and it felt sluggish and ran quite lean under boost and there was some popping and sputtering in the exhaust. Saturday I checked quickly for leaks and cleaned the earths and changed the plugs (NGK BP6ES) and the same thing. Depressing the gaspedal slowly does help and the car accelerates better. But putting it flat down ends up almost 5 out of 10 times the same disappointing result.´

I'm not 100% if the fault was there before while I've been driving it a bit like a granny

The old and new plugs (after a short drive) were covered in white residue (old were NGK BP6ET). Tested the compression and it showed quite steady 11 bars (160psi) for all cylinders. Fuel pressure measured 3 bars (44psi).

I changed the ICV valve before the drive on friday. Car idles and drives well under partial load.

I have ordered a new fuel pump (Walbro 255lph) and new spark plugs (NGK B8EGV).

**mpampis_** · 13-11-12, 08:52

I'm using NGK B8EGV and I am very happy. Check the voltage of throttle pontiometer. As you know under WOT the ecu enrich the fuel mixture so maybe if the pontiometer has a fault the ecu don't recognize WOT so it doesn't enrich the fuel

**AlfaJack** · 13-11-12, 10:10

I have had similar - it was a hesitation at full boost and would not accelerate well past 100mph
I never diagnosed it but it seems a bit better these days. I could have been an air leak which I did not know I had. I have had B8EGV for some time too.

How much boost are you set at?
I want an AFR gauge as I think running lean for a time is how to melt a piston quickly.

**Finn** · 13-11-12, 10:40

I've been meaning to check the tps voltage for some time and will do it tonight. Startrek seems to indicate it is fine though.

@Jack: I read an old topic of your problems with the car and the symptoms certainly sounds similiar to mine. I have a squadra chip and although the boost gauge is quite erratic in its operation the base boost is 0.9 bar and it overboosts to 1.1 or 1.2.

I'd recommend an afr-gauge and like the Innovate MTX-L's fast response but it looks a bit "japanese" to me

But it's legible in the heat of the driving and like said lightning fast in response. Have to try the logging feature the next time I replicate the fault.

I think I'll have a go with a MBC, after I pour some injector cleaner in the tank and have tested with a new fuel pump and plugs.

**AlfaJack** · 13-11-12, 10:55

Reading back (4 years ago!!!) it looks like the plugs solved my problem then.
I rarely get to drive it absolutely flat out.
Let us know how you get on.

**Finn** · 17-11-12, 07:28

The old pump was tired and it ran out of puff under acceleration. With the new pump the fuel pressure shoots straight to four bars when accelerating. The old one produced only 3,2 bar. I left the old plugs in.

It seems that a newly replaced SKF front bearing is shot... oh joy!