TBMeech

Bit of a bizarre one this but you never know....

My car '99 STI Version 5 with a few 'light' mods has developed a strange feeling since I've taken the Link ECU out a few months back.

At approx 2800-3500 on very light throttle (i.e. constant throttle at 35mph for example) it seems to be 'surging' not a lot but you can deffo feel it, passengers notice it as well, on trailing throttle or anything over 10% fine and has no problems.

Anyone else got this? as its really starting to pi55 me off now.

I changed the MAF about a month ago as the idle went up the spout, tried using the std airbox for a bit, tried the std d/v but to no avail.

Any ideas?

Cheers

Edited for appauling spelling

[Edited by TBMeech - 6/24/2003 11:59:12 AM]

dnb

I take it you're using the standard ECU & map?

I wonder if the car is oscillating between "open" and "closed" loop modes, so is doing bizzare things with the fuelling? Sort of going rich to stoich. and back?

Just an idea - feel free to discuss!

TBMeech

dnb,

Yes mate, the car is heavily revised from it's previous incarnation so went back to the original ecu with a view to selling the car std, then have since added a few more bits back to it - tho it was doing it since the Link came out and before the new bits have been put on if that makes sense!!

When cruising the AFR is giving the same readings as I would expect like my old LambdaLink used to do, bounces from Rich to Stoich, WOT goes to rich.

mega_stream

Mine does this aswell sometimes, if it makes you feel any better

My UK99 used to do it aswell.

I keep meaning to get my deltadash software logging on it but still havnt got round to it, it still did it after changing the MAF on mine last year (I didn't change the MAF for this reason though, it actually fcuked)

TBMeech

Hi John - Long time no see matey

Problem is mine's doing it all the time, you think 60% of all driving is realistically in that rev range, especially when you're town driving, out in the country lanes its fine and I dont notice it.

john banks

Does it do it when warm? Most when cold hesitate a little because they go into closed loop early and hence run a bit lean for a cold engine which gives a little hesitation - a lot of cars do this to comply with cat light up time emissions regs. When warm it should go away.

Worth watching such events with Select Monitor, Deltadash etc if it does it when warm. You could be driving on the edge of open/closed loop control, and you would see this occuring when datalogging the car.

TBMeech

Hi John,

Yep it does it when warm, to be honest it's probably worse when it is warm than when it is cold.

I did an ecu reset on sunday with no avail.

TBMeech

Forgot to say I don't have access to Select or Delta Dash

TBMeech

bttt

mega_stream

You can have a go with my DD if you're ever down my way m8.
(I'm not getting in the car with you though )


Mine only sometimes does it and when it's cold, so probably JB's answer is what mines doing.

TBMeech

Thanks mate, I may have to force myself to come over to you then, would be good to find out whats going on!

Why you no want to get in the car with me? lol

I'll drop you an email.

Carlos-Fandango

My my00 does it too with the oringinal ecu and a tek2!

Carlos

Bob Rawle

I'll post here Toby and not mail you as I think its of interest to all.

What you are experienceing is definately the ecu running the car closed loop, the small surges and "hold backs" occur everytime the ecu adds and subtracts fuel to maintain stoich, anyone with uprated injectors and remapped using the EcuTek software will notice this sensation increases greatly due to the extra fuel that is then added and subtracted by the bigger injectors. There is no cure for as long as you use the factory ecu as there are no adjustments for it available to tuners. Some cars are more noticeable than others and those with uprated exhausts/induction/dumpvalves etc would probably feel it more as well.

Having said there is no cure I suppose if a steady state voltage of about 0.48v was fed to the ecu and the input impedance mimiced the hot lambda sesnor then the ecu would happily do nothing as it would decide that it was at stoich and therefore need not adjust.

Toby, as an experiment unplug your lambda sensor, you will eventually get a check engine but ignore that, if the car is running off the std map as it should normally do you will find this sensation disappears. Don't worry about driving it as the car should be running richer, the lambda sensor has no effect at any boost either so its ok to try it. Don't forget to plug it back in when experiment is over.

bob

TBMeech

Thanks Bob, I'll try that tonight and drop you an email.

First time i've run on a std map in over 2 years so the sensation is rather horrible to say the least.

dnb

It's nice to get close to the answer first time once in a while
(Even if it was badly explained on my part...)

Hope the lambda unplugging works for you!

Now you brought the subject up, I discovered that I can make my car do the same thing - annoying isn't it! Grrr. I should have never read this thread

BuRR

TBMeech... did you ever sort this in the end?

john banks

You can run all the time with the lambda disconnected IF your base fuel map is sensible but you need to check the AFRs to know. You will get the occasional CEL maybe once or twice a month but it clears when you restart the car.

The smoothest Subaru idles I've heard have all been open loop and a little richer than stoich.

snowcrash

my sti5 does this too (kangarooing at 3,000-3,200rpm), i've been wondering what the cause was (faulty maf or something) but Bob's answer sounds good and I might disconnect the lambda to test..

*Sonic*

Mine does this if I sit at dead on 3k rpm in 5th

I always put it down to closed/open loop, not a problem as car runs fine

TBMeech

Ok, as a follow up....

I unplugged the Lambda as Bob said, funnily enough it worked, to be honest, the car ran so much better without the Lambda plugged in, I presume it richens the mix up a little, the surging went, the only prob was as Bob / John mentioned the CEL comes on, this only happens after a very 'spirited' drive, i.e into 3 figures - I only noticed this when I was cruising on the motorway, at normal speeds & cruising it never came on.

Bizarrely tho, I took off my std centre and bb (STI) and the centre had a cat in (Should be just resonated), Put on my new Scoobysport (2 weeks ago), re-plugged the lambda back in, strangely enough there is no sign of the surging now, changed my exhaust again to my new ID Ti Hurricane (less restrictive than Scoobysport imo, more like my old Hiper), checking my AFR now, the mix is not as rich as say when I was running my TMIC (running HKS FMIC), but it never runs lean, I would safely say if you have an AFR check the readings, if its ok then unplug the Lambda, the car will be fine.

Am wondering if the full de-cat made a difference? (Had Scoobysport d/p on since day 1).

Imo this has been an interesting thread, i'd probably have never noticed this 'problem' if I had never had the car mapped in the first place, tbh, in hindsight i'd have kept my Link , the car does not feel nowhere as good as it did when it was on, even tho it's a cracking car, it just shows what a decent ECU and decent mapper can do

Wish I kept my Link now, some northern monkey is using it now lol

Scott.T

iTrader: (2)

Try another Lambda, that may correct it. I currently have a spare and one certainly causes it to run better then the other.

Also seems to run smoother after fitting a ScoobySport DP.