Hi chaps have a tech thought for ya. When I ran a Sierra Cosworth I looked at the dump valves available at the time and the cost, and surmised that the ford fitted unit did exactly the same but vented back into the inlet. So I disconnected the return and blanked off the inlet and hey presto full sushh sound as Max Ford had intended. Later I uprated so much I fitted a dump valve with a kevlar diaphragm and so and so ...... but that another story.

 

Still with me? well decided to have a look at the same theory with my zed, after loads of puffing and grunting trying to remove the air box gave up and tackled it from below. Bloody under trays !!!! removed thr return and blanked the right hand bov in the manner as on my Cosworth started engine and awaited full nuke explosion (lol) engine ran ok but slight fluff on tick over, revved up ...little hesitant but revved ok. Checked at bov port that was now open to vent and could hear faint hiss. blocked off with my hand engine tick over came up a little and back to normal steady sound. Firstly I have put it all back to normal as it was upsetting the air mixture so all back to norm. However I remembered that as there is no map sensor like on the Cosworth any messing with air after the air mass meter will be a problem similar to that of the Escort RS Turbos had until improved dump valves were available (Baileys). Still here? hope so, I then got to thinking about the amount of people having hesitation problems, as my car has not any probs like that the bovs must have a little pass when on tick over and the vacuum high pulling on the bovs diafram, but if the pipe or clip or bov is faulty hesitation is exactly what you would get as I had seen and proved.As the little gits are tucked away so much it is doubtful any dealers would look here.... also it would be interesting to note if hesitation is more or only prevalent on cars with after market bovs ..or not or am I rattling on now?

Something to think about and check if your experiencing hesitation.

Jeez need a lie down now.

Jeff TT

Would also be interesting to see the O2 sensor voltage levels before and during the hesitation. Could be a fueling problem, leading to weak mixture.

Interesting Jeff me ode Technical bod.

If it helps, I have dump valves on my Zed and it never ever hesitates.

The driver of my Z on the other hand, tsk, incontinent old hesitator if ever there was one (unless there is a Scooby to snack on )

 

 

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Glen

Jeff/Glen,

 

you're right it's a fuelling problem..

 

And you're right, it's because the Z uses a MAF not a MAP sensor.. So basically, at idle (and overrun) there's a vacuum in the manifol, which is pulling the recirc valve open.. Fine when it's a sealed system, but not when it's open to air..

 

When its open to air, you've basically just added a second air intake that is *after* the MAF sensor..

 

So the ECU is sensing X volume of air entering the intake, but actually X+Y volume is going in.. The injectors will only be putting enough fuel in for X, so it'll be (possibly *very*) lean..

 

When you stamp the loud pedal, the revs will rise, vacuum will drop as boost increases and the recirc valve shut.. At this point, you're back to one air intake, which is being correctly sensed, so the A/F ratio goes back to normal (close to stoic.) and off you go..

 

 

Makes sense to me anyhow

 

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Az

De Maff...Aaiiiiiiiiii! ReZZpect! Boooo Selecta!

 

Timmy-G

;-)