Manifold pressure/vacuum

[ld50]

Whilst waiting for it to be sunny enough to finish stitching the syncro back up I’ve been fiddling with the fuelling on my mk2 16v gti which has a KR motor with ultra-basic K-Jet fuelling.

I noticed that if I lean the mixture out a bit it pulls much better in the lower parts of the range (e.g. 2.5-3k) but tails off *noticably* once you get above 5k rpm, especially in 5th.

If I richen the mixture the lower range performance suffers but it accellerates beautifully at high revs in 5th gear i.e. over about 5k -I’m afraid i can’t tell *exact* revs in that situation because I tend to be looking where I’m going but it’s definitely in the upper regions of the revs we’re talking about.

I’d like to richen the mixture at these high-rev/high gear situations and reckon I can do so by fiddling with the Warm-up-regulator (apparently some audis use that exact method for WOT enrichment).

I have a WUR from such an audi with the extra vacuum port for WOT enrichment but need to know where in the inlet tract i need to connect it…. I guess after the throttle-body but where exactly and why there? Could it go on the connector whcih also feeds the brake server and vacuum system for instance? but if there then after or before the reducer/one-way valve?

In this situation (say 5k rpm, 5th gear, accellerating flat out) what’s the status of the manifold pressure likely to be? lots of vacuum? no vacuum? I reckon if I understand what the vac status is I’ll be able to figure out where to connect the audi WUR.

For reference the various types of WUR are detailed on Chapter 6, section 16 of Bosch Fuel Injection & engine management. the one I’ve got and am hoping to fit is in fig 5.3.

Thanks in advance

[no such user]

It wants to be connected before any one way valves so it is seeing the actual manifold pressure, at WOT there is very little vacuum

[ld50]

ok thanks – I wasn’t sure whetehr the vac related to the load or the rpm or both. I guess I can fit it and see what happens… suppose it’ll be pretty obvious if the power drops off.

[ld50]

a further thought occurred to me before I try this – does the K-jet have anything like a “limp home” mode? and if so how would I find out if it’s running in it?

As far as I recall there is an ecu in the usual place but quite what it controls I don’t fully understand (yet).

[no such user]

No, on k-jet the fueling is entirly mechanical, there is an ECU but it only deals with ignition timing, it relies on rpm and Manifold pressure but if it detects knock it can retard the ignition, bit better than a dizzy but there are gains to be had by switching to megajolt.

[ld50]

excellent. Thanks danny – so at least It’s driving more or less how it should be – that’s fine for me to crack on then

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