Can a cylinder head flow more than the exhaust can handle?

[steve briance]

I like that. It's not actually the original wire there now as that broke somewhere years ago and rather than trying to find the break hidden in the loom, I ran a new wire. Running a thick wire down the same route should be no bother and the one that's there now can be the signal.

[newsh]

Run the thick wire straight from the battery via a fuse.

If it was s lack of air then it would run rich.

[Bowie69]

Agreed, however if the MAF has run out of headroom, it may not be able to meter the extra air, therefore not adding enough fuel for it = lean.

I think the fuel pump is a very good shout though, good luck

[steve briance]

Fuel pump is on its way, I will sort out a relay and wiring at the same time.

I can see both arguments make sense so once fuel pump is in and relayed up, if it still runs weak, what are the options for 7A maf replacement? They don't seem to be available new any more (unlike the v6 ones) but if the signal of a new one runs out of headroom as suggested, then it would make no difference anyway...


Watch this space for updates!

[Airwolf]

Remember one dyno session we had with a 3series with s54b32. Made som New wiring to the fuelpump and had an increase of 30whp with nothing more to it.

on my s2 i have a 044 pump with 6mm2 wiring feed to it. No issues

[steve briance]

6mm2 cable is massive! 50amps and 600w capacity should be more than enough!
I think I'm going to measure flow out of the return line before I do anything then try again once new pump and relay is in, just to satisfy my curiosity...

[SA BOY]

Good idea just in case the return pipe is slightly blocked by corrosion or pinched somewhere. Also check fuel tank breather make sure thats ok.

[steve briance]

When you say breather do you mean the connection to carbon canister? It's funny you should mention that. I get the blue solenoid clicking but the black one doesn't that I've heard. I also don't get any vapour type smells coming out of it. Like many others out there, I do get a whooshing noise as I undo 6ue the filler cap. What would be the issue with pressurised tank / lack of breather?

[Bowie69]

Well, you get a vacuum in the tank, making the fuel pump have a much harder time - they are no good at sucking.

[Lago Blue]

Perhaps that's a question UrS4boy would likely be able to best answer, he did a detailed article here (but his attachments have mostly disappeared):

https://forums.quattroworld.com/s4s6/msgs/141611.phtml

Tank vent sys.png

Perhaps your N80 valve does not function? You could test it.

[steve briance]

Hmmm. It's something I shall look into but it cant be a vacuum if air rushes out of the filler cap? If it was a pump sucking out of a sealed tank I would see where the vacuum could happen but, It's also getting 2 litres a minute back into the tank down the return line.

I'm going to plug a test lead into the black solenoid wiring and see if it lights up while driving. It doesn't activate on idle. The. Blue solenoid next to it clicks like the clappers once the engine is hot.but it can't be feeding anything to the engine as it itself is fed from the back solenoid which I have never noticed open. It works with 12v to it so either the wiring is faulty or it just doesn't open very much at idle!

[Bowie69]

Point is, it still uses fuel, so on aggregate, there is less fuel in there after running = vacuum.

It can depend on weather, on hot days or maybe a long run, the fuel, and air in the tank will heat up, causing excess pressure.

But in todays weather, vacuum is more likely.

Run it with the cap loosened off for a test

[newsh]

The evap system on the S2 applies vacuum to the tank on overrun to draw off petrol fumes. That is when the revs are up and the throttle is closed ie. when decelerating. It stays closed at idle so as not to upset the mixture.

[SA BOY]

Check the entire fuel tank breather system front to back as vacuum or pressurized tank is not a good thing.

[Acki]

Measure the injector signal that you can see if the ECM isn’t increasing the timing or the injector don’t make more fuel into the chamber.