I've been experiencing a wee bit of hesitation, and have decided to think about installing one of these do-it-yourself "knock smoothing kits" - courtesy of HobieGary in the USA. These kits have also been dissected on Ravensblade Impreza.

So, I'm a noob here, but how I understand it is that the preignition or "pinking" that the ECU "thinks" it hears is causing the hesitation. This kit nullifies this as far as I know.

SO, my big question is, will this knack my engine? Or should I just live with it and dream about all the upgrades that I can't afford?

Ok, welcome :D
First things first thou, what model and what year??
get that out of the way first ;)
Some scoobs are more seceptable to knock than others (pre-98's and Jap imports) as they prefer higher octane fuel (100 ron for the jap imports and always nice to run a uk car on sul ;))
Also, are you suffering from lack of power, hesitation thru the gears when the car is cold/hot??
The easiest way to reduce your chances of knock(or detination) is to fit a knock sensor and a link ecu to your car.
Ok its not cheap but det will naff your engine up, think of it like this, where normally your fuel is compressed then explodes, det explodes before its compressed, this does a couple of things, reduces your power and causes damage to the heads of your pistons.
As long as your car isnt suffering then you dont need to worry (uk cars are normally ok, its bad fuel on jap cars you need to watch out for).
Hope that helps but im not an expert on this :(

Tony

ok, thanks. My car is a MY99 5 door turbo. That idea's out of the window then :)

and the hesitation is mainly just after the temp gauge starts to climb after cold. The car seems to "surge" and hesitate whilst under light acceleration.

"they all do that sir" according to the dealers.

only cure I know of is a Link ECU from Bob Rawle.about £1500 but will give you big power gains.

It is a common problem on MY99/00 that you get hesitation :( fortunately mine doesnt (MY00) and as ive got a PPP fitted i have a spare ecu lying around (so if you want to try that to see if it stops it as my car never use to hesitate with it in) just give me a shout (cars in for a service on sat thou!)

Tony

My '00 used to do this a bit, but not since I started to run it on SUL (now Optimax).

I read some where that the ECU uses a different map when the engines' cold and sometimes this can cause this (= the aforementioned 'they all do that sir').

I'm sure even some PPP owners get hesitation under very light acceleration and it seems that once you have it you cannot get rid of it when using the standard ECU.after Bob Iles fitted a Link to his car it was gone.

NBW,

just seen your post,I run super but cannot get optimax up here and it still hesitates.

edit for spelling :o

[Edited by T-uk - 12/17/2001 10:59:49 PM]

Knock or Det happens when the mixture ignites before the spark is fired. The flame front that propagates hits the piston head before top-dead-center (TDC) of the stroke. When this happens, the piston head is subject to great shocks, and will eventually crack. Ideally, you want the flame front to hit the piston just after TDC for max power, and most tuners time the spark firing to achieve this.

I picture this as pushing a child on a swing. You want to push just at the end of the oscillation for max effect!

As for hesitation on light throttle, it's definitely not due to det. Turbo cars mostly only det at high boost, open throttle. If you're det'ting at light throttle, I'm sure your engine would be all over the road by now if you've given it any stick at all.

Hesitation could be due to contaminated MAF, questionable lambda sensor. I would try and check / change these 2 to start with. Hopefully, your mechanic has a spare lying around so you can do it without having to buy one.

The reason the Link stops scoobs hesitating is that it removes the MAF sensor (that orrible little bit of kit that dont like getting messed around) but also some ecu's just aint brilliant (there is one on here who replaced his with a MY99 ecu and his car now runs pretty good again :D)
Steve, ive got your mail! trouble is ive not got a number for you, but im contactable today on 01213459991 (til around 3pm)

Tony

(ps dont worry, this aint my phone ;))

I was experiencing some hesitation and loss of power at low rpm in top gear - I was loosing substantial power some times causing a drop off of 5-10 mph rapidly.

Took it to a dealer and they checked the knock sensor and found it mis aligned by a degree, it was adjusted and now the whole thing is a shed load better - feels like it did when I got it 2 years ago.

MY 99 - no mods.

T.