4722 replies to this topic

[Cookies220]

Nice one Nev Hope all goes well with the run in.

[yaaan]

That's awesome news I look forward to seeing the beast up and running when I'm next back.

[jules_s]

FairPlay Nev Hopefully you will be along for the meet and I seriously want a pax ride!!!

[edwards]

awesome news nev! enjoy

[Nev]

Crikey, I fiddled with the brake lights for 10 mins this evening and they seem to work now somehow ! This means I need to book Nipper in for an MOT, this is such a sudden system shock for me I am now concerned whether I can remember how to drive him. Can anyone tell me if they know that 13.0:1 AFR is too rich for pre boost revs (ie around 1500 to 2500 revs). I know thats running a bit rich but IMO that would be ok for a few hundred miles without causing any bore wash. I can always reduce the fuel pressure so its more like 13.5:1... but that also means it then runs lean at idle.

[alanoo]

it's absolutely OK

[Nev]

More woes from my garage...

Basically, the AFR has now gone mental (approx 17:1 to 20:1) since I tried re-seating the TB.

Edited by Nev, 08 April 2011 - 04:05 PM.

[Arno]

Basically, the AFR has now gone mental (approx 17:1 to 20:1) since I tried re-seating the TB.

It may not be your intake, but your exhaust/downpipe joints..

Remember.. A lambda sensor does nothing else than measure the free oxygen content in the exhaust gasses. It does not (and can not) measure the air-fuel ratio at all.

If you have an exhaust leak upstream of the sensor (eg. gasket not sealing, clamp not tigtened, etc.) then the exhaust gas flow will draw/suck in air from the outside. This will trigger the lambda sensor with an 'very high O2' content signal, which is translated by the controller to a 'very lean' result..

On an MOT emission machine this would show up as a car that has a (very) high CO content in the exhaust as the ECU also sees this free oxygen and tries to compensate for it by dumping in a lot of fuel. At the same time the measured O2 content will be high as it's being sucked into the exhaust *after* the engine, so any mixture adjustments will fail.

To test if it's an exhaust leak you can see if letting the engine idle and them using a rag to press the exhaust opening(s) closed gives more sane readings. 'Plugging' the exhaust will raise the pressure in the system, so after a little while it won't be able to draw air in through a leak/join and the measured A/F would stabilise/normalise.

Bye, Arno.

[Nev]

Yes Arno, you have explained some very interesting and quite possibly correct hypothesis. I know for a fact that my exhaust has a leak between the wastegate exit and downpipe (approx 1mm gap round the 44mm pipe circumferance). This is becuase of a poor fit. I had in fact thought about this issue that you had also identified aabout a couple of weeks ago, but at the time assumed that as the exhaust system has positive pressure in it that gas could only exit out of through this hole. However, considering the shape of the pipes, it may possibly be allowing atmospheric air to be drawn in because of the direction of the gas. I will get under the car this evening and try to reseat all the downpipe connections, and maybe put a gasket in temporarily. Your exhaust test using my hand over the tailpipe to raise the internal pressure is a great idea too. Thanks for your input

Edited by Nev, 11 April 2011 - 08:03 AM.

[Arno]

It's just something I ran into with my car with a (slip)joint on the exhaust which seemed perfectly fine (no blowing), but at MOT time the emissions were all over the place until I plugged the exhaust with a rag then it settled down to 'acceptable' values... I coated the whole joint with a 'quick repair' type exhaust putty to get it to pass.. Once it passed I took it apart it was clear that the pipe had ovalised a little and one side had a small gap in the join and it was drawing in outside air. New piece of pipe and a good clamp and it was spot on when I re-tested it just to check. In your case anything after the turbo, especially at idle, is very close (or even slightly under) the outside atmosferic pressure, but the exhaust flow and pulses 'pulls' in air from the outside like a spray-gun uses compresed air to suck in the paint. Between the cylinder head and the turbo you're probably always seeing some over-pressure as the turbine wheel is a big lump of metal restricting airflow At idle (or even revving at no-load) there's actually very little gasflow in the exhaust compared to when it's under load. At that time it would build up some gas pressure in the system and the ill-fitting seal would start to blow out super-hot exhaust gasses. Not something you want either though.. Bye, Arno.

[alanoo]

Firegum is always your best friend !

[Nev]

I think my downpipe needs some mods. Update here.

[steveboyslim]

Firegum is always your best friend !

Under no circumstance would I use any form of fire gum or paste on a v-band joint.
The v-band seal is one of the best form of sealing you can get, that is why GM and may other manufactures use it.
If the joint is leaking it will be a problem with the alignment, a flexible section in the 'screamer' pipe may be needed.
Very small mis-alignmet will seal as the pipe heats up and 'settles'.

Steve

[Nev]

Thanks steve, I have the car booked in on the 27th for the downpipe to be modified so it fits better.

[VXT Tim]

How are things going Nev? Downpipe sorted?

[Nev]

Yep downpipe is now fixed and sealing better. MOT is booked for next Friday *gulp* I do also have 2 oil leaks, which are more irritating than problematic. I think one is out of the sump and I have nipped up the sump bolts, but the other is probably from a leaky slave cylinder in the gearbox (a nightmare big job). Neither of these is a show stopper for getting it on the road really but might be a fire risk in the long run. If I feel brave, I may take the gearbox off and put a new slave clyinder in, but at the moment I dont want to take the car aparts as its working well and I would rather it gets through its MOT first.

Edited by Nev, 30 April 2011 - 01:39 PM.

[rob999]

Top stuff Nev, fingers crossed for next Friday

[VXT Tim]

So I take it's running/idling a lot better now the downpipe fits or is it still a bit rough on the old map?

[Nev]

I've swapped the petrol for some new stuff and that helped a lot (it also dropped the EGTs a hell of a lot). The rough idle is almost certainly the cams + map not adjusted, but the car is deffo drivable. The down pipe can let some oxygen in I think when its cold, but once its warmed up and expanded, the pipes mate much better.

Edited by Nev, 30 April 2011 - 04:18 PM.

[siztenboots]

what temperature numbers plugs are you planning to run, I want to give bkr8eix a try on mine, i use "6" in winter and normally 7 on track.