Vacuum sensing

[Tony Martyr]

Still working out how to fit 'direct to head' TBs.

The normal Rover inlet plenum has three vacuum sensing points or at least tappings into the plenum after the throttle and before the injectors.

The QED TBs have none.

Since the DTA ecu doesn't have a vacuum connection I don't apparently need the first, the second goes to the carbon canister which I can live without but the third IS needed by the fuel pressure valve.

I could put sensing points into the air-filter back plate (where the air temperature sensor is going to go) but that isn't the same as betwix throttle and cylinder is it.

I already have to machine the front TB to take the engine coolant to the header tank - no more holes surely?

[Mike Bees]

Just let the fuel pressure regulator reference to the atmosphere.

 

Mike

[Peter Carmichael]

The fuel pressure regulator is just using it to give a constant drop in pressure between the injector and the inlte tract. With 3D mapping you don't need this and you can run the pressure as high as your pump can maintain. 3.5 Bar is a good start, but check it with 14V+ supplied to the pump.

[Anna Rexia]

Try a Dyson!

[Petrolhead]

A Kirby will give that extra pressure Anna

 

 

[Tim Seipel]

Depending on the flow rate of your injectors, you may need to reference the fuel pressure regulator to manifold vacuum. Aim not to have the minimum pulsewidth at idle less than 1.5milliseconds or it will probably not control well at all. If you do what to put a pressure refence in for anything, don't just put it into just one tract if using individual throttles like yours. The pressure pulsation even at idle will give a bad signal and cause pressure measurement to oscillate up and down. As you also stated, it must be between throttle and head to get the vacuum.

[Roger King]

Tim's right about the pulsating signal if taken from only one tract. He also knows a lot more about this than I ever will. I have occasionally seen a similar problem on DCOE equipped cars where the owner has connected the distributor vacuum advance to a single tract. In this case the vacuum signal is being used for a completely different purpose, but the vacuum advance mechanism goes into a sort of spasm on small throttle angles. The solution is to join all four tracts together with a 'mini manifold' of a bore that is just sufficient to provide the signal.

[Mike Bees]

With my 3 bar pressure reg. referencing to atmos. and 311cc/min injectors (~30% bigger than the standard 1.6/1.8K jobbies) my engine likes a pulse width of 1.9ms at a warm 1200rpm idle.

 

I've just acquired some bigger injectors to allow me the luxurious and potentially short-lived option of using 9000+rpm. These are approx 380cc/min (from a Lotus Carlton!). Having scaled the map appropriately and popped them in it still idles quite happily although it seems to want a bit more fuel than before to idle nicely, maybe fuel wetting the ports or just inconsistent control of the injectors with a 1.5ms pulse width?

 

Mike